A new NEC is on top, with some of the most far-reaching changes ever made as we begin the next 100 years of the Code. Part 3 of a 4-part series.
This analysis of the changes represented in the 1996 edition of the National Electrical Code (NEC) covers only the most significant of the many changes were indeed major, including seven new articles, (with another article deleted), and others were for very minor editorial reasons. Major or minor, if you are involved with the particular subject matter, the most minor change can assume major proportions in unexpected ways . Every proposal was made for a reason, and this magazine article is no substitute for careful study of the Code itself. This month's issue covers from Art. 500 through the end chapter 5.
Sec. 500-2 (fourth paragraph). This is the former final paragraph relocated, and with a very important change. All threaded conduit joints must now be made up wrenchtight. The permission to use a bonding jumper across a loose joint has been deleted.
EC&M tip: Explosionproof unions are available if enclosures are oriented such that turning a conduit completely wrenchtight is impossible. Be sure the union is rated for the appropriate class and group. What happened: This paragraph used to refer to "minimiz(ing)" sparking if fault current moves over the conduit, and then gave permission to use a bonding jumper if the joint couldn't be made tight. Now, the word "minimize" has been replaced by "prevent," and the last sentence on bonding jumpers has been deleted. Note that not all conduit in these articles is threaded. There are places where heavy-wall threaded conduit isn't required, such as in Class I Div. 2 areas. Therefore, this paragraph now refers to "threaded" conduit.
Background: Fault current flowing over a conduit and approaching a loose joint (assume the old bonding jumper is in place) will divide between the conduit and the bonding jumper, with the current ratio dependent on the relative impedances. If enough current flows over the conduit (a likely possibility), there will be sparks thrown out of the loose joint even though perhaps a majority of the current passed over the bonding jumper. In a hazardous location such a shower of sparks is obviously a grave explosion hazard.
The other reason to make the joint tight is to ensure the explosionproof (or dust-ignitionproof) integrity of the system, particularly in cases where the seal is being used to, in effect, complete an explosionproof enclosure. Remember, Class I systems aren't designed to prevent explosions by excluding hazardous agents from the wiring system, which is assumed to be impossible. They are designed to contain explosions within the wiring system, which are assumed to be inevitable from time to time, so as to not ignite the surrounding atmosphere. A loose joint may not perform this function, and this paragraph now has an additional clause to that effect.
Sec. 500-3. "If Art. 505 is used, area classification, wiring, and equipment selection shall be under the supervision of a qualified Registered Professional Engineer."
Background: This is a new, additional paragraph to this section. Art. 505 is the zone concept, and particular care must be exercised over the installation. Remember, this system originated in Europe where the population densities are higher, the societies more highly regulated, and as a natural consequence of that culture, electrical installations are more intensively engineered and supervised than in this country.
There are many rules in the that relax requirements as a trade-off based on qualified maintenance and supervision in industrial occupancies. This requirement is an implicit recognition of a trade-off between more intensive and qualified supervision and the new system that relaxes some important requirements in the majority of what have historically been Class I Div. 1 locations.
In order for the concept to be valid, the assumptions must be valid. This provision calls for qualifications, and it calls for accountability. Both the professional qualifications, and the accountability to a professional board of registration of the individual in charge should be rigorously policed by the authority having jurisdiction.
Sec. 501 -4(a) Ex. 1. Rigid nonmetallic conduit can now be used below grade in Class I Div. 1 locations, provided it is encased in concrete.
EC&M tip: Don't forget that where steel conduit leaves concrete encasement below grade, UL has determined that severe corrosion is likely at the soil/concrete interface, at least for several inches each way. You must apply supplementary corrosion protection at that point, and UL has evaluated no such coatings. Therefore you will need to discuss with the AHJ what will be accepted locally. There are special asphalt paints and asphalt-impregnated wraps available for this purpose.
What happened: Rigid nonmetallic conduit can be run below grade in a Class I Div. 1 (but not Div. 2) location. The following restrictions apply:
* The conduit must be encased "in a concrete envelope" at least 2-in. thick and buried at least 24 in. There will be differences of interpretation over whether the 24-in. measurement is taken to the conduit or to the envelope. The literal text seems to refer to the envelope because the thickness rule and the burial depth rule are in the same clause, both modifying the words "concrete envelope." On the other hand, other burial tables in the Code, including Table 300-5, measure to the conduit. The likely intent was to measure to the conduit, but the AHJ will need to make the interpretation.
* You must make a transition to rigid or intermediate metal conduit at each end of the run, with the metal conduit not less than 24 in. in length between the end of the nonmetallic conduit and the point of emergence or to the "point of connection to the aboveground raceway." This means that even if the raceway enters a basement area, the same last 2-ft minimum must be in metal conduit, which will allow a seal fitting to be installed. This is important because customarily the Div. 1 location follows the conduit to its emergence, so a seal is required at the Div. 1 boundary. The steel conduit stem facilitates that installation.
* Since the nonmetallic conduit must be encased, the transition to the final 24-in. minimum metallic conduit stem must occur within the concrete. This, in turn, means that unless the concrete encasement extends all the way to the point of emergence from the soil, you will have to deal with the severely corrosive, soil/concrete interface problem as previously noted.
* Since this is rigid nonmetallic conduit, it has no inherent equipment grounding continuity and an equipment grounding conductor must be installed to provide continuity of the metal parts of the raceway system and for grounding noncurrent-carrying metal parts.
Background: This practice has been used in industry, particularly in large ductbanks. In addition, it is recognized without concrete encasement in gasoline stations (Sec. 514-8 Ex. 2), bulk storage plants, (Sec. 515-5), and new with this Code, service stations (Sec. 51 1-4 Ex.).
In general, areas below the grade surface in classified areas with heavier-than-air flammable liquids in particular are subject to concentrated vapors as a result of periodic spills. Although the wind rapidly dilutes the vapors above ground, they will accumulate below grade, and if a conduit passes thorough; they will invade the conduit over time. Although this change doesn't literally apply to Div. 2, that doesn't make a lot of practical difference because most of these areas below grade are classified as Div. 1 anyway.
Note that neither the new exception for service stations nor this exception has been correlated with Sec. 347-3(a). That section forbids the use of rigid nonmetallic conduit in hazardous (classified) locations, with specific approval for articles where it is recognized (including Sec. 514-8 and 515-5). Since provisions in Chapter 5 automatically supplement or modify the general rules in the first four chapters, the changes here take effect whether or not Sec. 347-3(a) is correlated. Presumably it will be in the next cycle, however.
Sec. 501-4(a) Ex. 2. A special type of metal-clad cable can now be used in Class I Div. 1 locations.
EC&M tip: This is not Type MC cable in the usual sense; it is MC cable that is specifically designed and listed for Class I Div. 1 locations. It has a gas/vapor-tight corrugated aluminum sheath, with an overall nonmetallic jacket and separate grounding conductor(s).
What happened: Type MC cable specifically listed for the application can now be used in Class I Div. 1 locations. This is a new Ex. 1 to the subsection. There are several conditions on this, all of which must be met:
* The location must be in an industrial facility with restricted public access.
* The conditions of maintenance and supervision must be that only qualified persons will service the installation.
* The termination fittings must be listed for the application, Note that Sec. 501-5(d)(1) provides specific requirements for sealing this cable; each individual conductor (after the jacket and any coverings are removed) must be surrounded by the sealing compound.
* In addition to the rules in this article, Sec. 334-3 and 334-4 on permitted uses and prohibited uses for Type MC cable, including the general language in Sec. 334-3 disallowing this cable where it is subject to physical damage, will apply to these installations, and a new FPN makes the appropriate references. Background: This cable has been used on offshore oil platforms for some time. Type MI cable tends to absorb too much moisture from the air unless the terminations are done with great care. Conduit systems breathe, with the result that moist, salt-laden air enters the system and corrodes even the coated varieties from the inside, where incipient failure cannot be readily detected.
Sec. 501-5(c). A new paragraph (6) requires that the cross-sectional area of the conductors in a seal fitting cannot exceed 25% of the cross-sectional area of a conduit of the some body size unless specifically approved for a higher percentage of fill.
EC&M tip: Pay close attention to the manufacturer's instructions, because there will be a maximum fill indicated on instruction sheets packed with each seal fitting. This is even more important now, because the new cross-sectional area tables in Appendix C have different cross-sectional areas depending on whether you are using rigid metal or intermediate metal conduit. Furthermore, the way this is set up, the directions will always take precedence over this code rule. If the directions call for a larger fill, this section says to use the directions. If the directions call for a smaller fill, then Sec. 110-3(b) says to use the directions.
Background: When the UL standards for seal fittings were overhauled in the late '60s, the 1968 NEC had set an upper limit of 25% wire fill (for most but not all conductors) in raceways for new work, and 40% for old work. Since a poured seal cannot be rewired, UL put the 25% fill into the standard. In 1971 the went to a straight 40%, but nothing happened on the fill requirements for seals. Meanwhile people who didn't know, which was most of the country, proceeded to attempt 40% fills in seal fittings that were only designed for a 25% fill.
This was exceedingly dangerous, because seals require a very high standard of workmanship or the compound won't surround each individual conductor, which is essential to obtain an appropriate seal. Remember, a poured seal cannot be inspected, so enforcement is difficult. For these reasons, UL modified the standard, and now requires manufacturers to include the detailed directions with each fitting.
There are now seals that accommodate a 40% fill by using the casting for a larger trade size fitting, but tapping it so the threads are those of a smaller trade size. Another approach is to take a standard explosionproof junction box, and put a seal cover on it. These are commonly available, but most have never actually been listed for this purpose so far. This latter approach, however, gives plenty of room, either to spread out a full 40% fill, or to open up a multiconductor cable to expose the individual conductors.
Sec. 501-5(d). A new paragraph covers the seals at the terminations of the new Type MC cable now allowed in Class I Div. 1 locations.
The subsection has been reorganized, with each paragraph numbered.
* The first paragraph (1) covers the new Type MC cable allowed in Sec. 501-4(a)(1) Ex. 2. Each individual conductor (after the jacket and any coverings are removed) must be surrounded by the sealing compound. In addition, the fitting must comply with the requirements for seals generally in subsection (c).This is new in the 1996 NEC.
* Paragraph (2) is the existing rule that requires a cable in a conduit that can transmit gases through its cable core to be sealed both to the jacket and to the individual conductors. The existing exception for just sealing to the cable wall and then using a special fitting at the cable termination in the enclosure to minimize the transmission of gas, follows this rule.
* The third paragraph (3) covers cables that can't transmit gas through their cores. There are no changes to the rules for this type of cable.
Sec. 505-5(d)(2) Ex. This exception now requires the "approved means" in the enclosure at the end of the cable to "minimize" (no longer "prevent") the entrance of gases or vapors and "prevent" the propagation of flame into the cable core. A new sentence says that on shielded and twisted pair cables, it is not required to separate the twisted pair or remove the shielding.
This exception (see discussion under "Paragraph 2" above) was new in the 1993 NEC, and now uses similar phrasing as Sec. 501-5 (FPN No. 1). No seal can completely prevent the migration of vapor or gas through it, especially under enough pressure. As of this writing, no products have been listed that comply with this exception. Any such product must include some mechanism to retain enough potting compound at the end of the cable within the enclosure so as to be sure that an explosion can't propagate into the cable core.
The new sentence appears to have been misplaced and improperly worded. It now only applies to the performance criteria for the device/compound that might be listed in the future under the exception. In this form, it overturns the reason this exception was introduced in the first place, namely, to allow sealing to individual conductors up in the enclosure. Here there was plenty of room and the shielding could be opened/pairs untwisted for a very short distance to allow sealing, and then retwisting and reshielded without loss of any continuity.
The new sentence would have to be a stand-alone second exception to the same rule to have its intended effect. Given the comparatively loose shielding on many multiconductor cables, some of which surrounds multiple cable pairs, interpreting the new second sentence as written as having the effect of a standalone exception would be almost tantamount to removing Sec. 501-5(d)(2) from the NEC. See the discussion under Sec. 5015(c)(6) for a better approach.
Sec. 501-11. New rules in the opening portions of this rule set generic standards for the use of flexible cord in hazardous locations, instead of requiring a case-by-case listing at the end of the section.
What happened: In addition to portable lighting and other portable utilization equipment, now flexible cord can be used for certain other purposes in these locations. This rewrite of the opening to Sec. 501-11 recognizes, in industrial occupancies with qualified maintenance and engineering supervision, the use of cord " for that portion of the circuit where the fixed wiring methods of Section 5014(a) cannot provide the necessary degree of movement for fixed and mobile electrical utilization equipment." The cord must be "continuous" and protected, by guards or by location, from damage. All previous restrictions, such as being rated for extra-hard usage, still apply.
Background: Although Sec. 501-11 applies to both Div. 1 and Div. 2 locations, flexible cord with even fewer restrictions is already permitted by Sec. 501-4(b) for Div. 2 locations. Therefore, the new wording actually only affects Div. 1 environments, as the cross reference indicates [Sec. 501-4(a) only applies to Div. 1 locations].
The new rules will allow flexible cord in areas where traditional Class I Div. 1 wiring simply doesn't have enough flexibility. Note that the usual industrial language about qualified maintenance and supervision has been changed to specifically require qualified engineering for these uses.
Article 505-class 1, Zone 0, 1, and 2 Locations EC&M Overview: What is the zone concept?
Under the traditional NEC rules, hazardous (classified) locations are divided into divisions depending on how frequent the hazardous atmosphere or dusts are expected to be present. If the hazardous material is merely in secure storage, that storage area gets a less severe classification than an area where people routinely work with it. Under the traditional rules, the former location is Division 2 and the latter is Division 1.
European standards organizations have gone one step further and divided what we call Division 1 locations into Zone 1 and Zone 0, the latter classification reserved for areas such as inside a vented tank where the hazardous agent exists on a routine basis. They then assign more stringent requirements to the Zone O locations. Areas like our Division 2 have a Zone 2 classification. They also tend to have a work environment that is much more intensively engineered and supervised than we do. Having made these distinctions, and thereby having excluded the worst case (Zone O) from Zone 1, and having greater engineering support, they allow products into Zone 1 locations that traditional code practices would exclude from Division 1, including nonexplosionproof lighting.
EC&M Overview: How, Where can you use this concept in your plant?
Art. 505 represents the Zone classification concept imported into the NEC, after a 25-year battle. First, everyone will now agree that you can apply the Zone classifications in a new facility coming out of the ground. The major questions will arise in trying to use the system in existing installations. Therefore, the most important single issue, or at least the one to be resolved first, is whether, and how, you can apply the new system in your plant.
The requirement in Sec. 500-2 (second paragraph) for each room, section or area to be classified independently, has led some to conclude that the zone system cannot coexist in the same facility as the traditional division system. Although that would be administratively convenient, there is actually no support for that in any of the literal text at present. Each time a classification boundary is reached, by definition one has also reached a point where a new classification applies.
Take, for example, a semi-open wet pit with volatile hydrocarbons and a mixer. That is a Zone O location. At some fairly minimal distance from the wet pit, however, you reach a zone boundary, to Zone 1. Nothing prevents a design engineer from marking the Zone 1 boundary, add making a new classification On the wet pit area of Class I Div. 1. That would allow Sec. 501-11 (flexible cord) to apply to a removable mixer in the wet pit (which would not he allowed in Zone 0), and then Zone 1 w ring outside the immediate area, including increased safety, nonexplosionproof lighting (which would not be allow d in Class I Div. 1).
Another example would be a new piece of process equipment, perhaps an extruder, made in Europe and evaluated to IEC standards as creating a Zone 1 area classification. If the equipment is moved into an existing clean room with other equipment previously wired to Class I Div. 1 rules, now what? Does it have to be rewired? Here the problem might be resolved by setting up a unified classification for the entire room, instead of maintaining boundaries.
What you would do now is to call in the PE responsible for classifications. A savvy PE might then say, "No problem. The entire room is now Zone 1" (assuming it meets the criteria, which is likely). If the AHJ happens to be standing by, that pronouncement may well be questioned, particularly in terms of the existing wiring. How can that all be Zone 1 all of a sudden? Simple. Sec.505-15(b) allows all Class I Div. 1 wiring methods, and Sec. 505-20(b) Ex. allows all equipment approved for Class I Div. 1, in a Zone 1 location.
Both examples violate the expressly stated views of the panel regarding mixing systems: "It is not the intent to mix the zone and division classification systems." The first example is questionable but may be safe; the second example is probably safe. Probably neither example violates the present Code, although the AHJ has to decide in his or her jurisdiction. Both examples present administrative headaches and the danger of confused and misapplied requirements. Be prepared for a lot of controversy as we gradually get accustomed to integrating the new system.
Sec. 505-2 and Ex. The general rules of the NEC apply to these locations, except as modified by Art. 505.
This is the usual statement, which merely reinforces Sec. 90-3.
Sec. 505-5. This section covers the IEC gas groupings. Since the groupings all start out with a "II", a FPN answers the obvious question, explaining that group I electric apparatus is far use in underground mines.
Those applications are excluded from the NEC per Sec. 902(b)(2). The groups are as follows:
* (a) Group IIC. Acetylene, hydrogen, or gases or vapors of equivalent hazard. A FPN says this grouping is equivalent to Class I, Groups A and B. This is controversial, since two of the traditional groups have been made into one. One major issue is the grouping of hydrogen (traditionally classified as Group B) with acetylene (Group A). There will be problems in some cases particularly where an arcing device requires an explosionproof (Europe: "flameproof" ) enclosure. For example, flat joints usually can't be used with acetylene, but they can with hydrogen.
* (b) Group JIB. Acetaldehyde, ethylene, or equivalent. A FPN says this is supposed to be equivalent to Group C.
* (c) Group IIA. Acetone, ammonia, ethyl alcohol, gasoline, methane, propane, or equivalent. The first FPN following explains that this is supposed to be equivalent to Group D.
Three more FPNs follow:
* (FPN No. 2). This note explains that the gas subdivisions are based on the maximum experimental safe gap (MESG) and minimum igniting current (MIC), per IEC 70-l A. This is comparable to Sec. 500-3(a)(FPN No. 2).
* (FPN No. 3). This note explains that the positioning of various gases and vapors into the gas groupings is based on their MESG and MIC, as described in IEC 79-12.
* (FPN No. 4). This note points out that the different equipment markings and these Group II classifications must be carefully watched in order to avoid confusion with the traditional Class I, Div. 1, Groups A, B, C, and D markings.
Sec. 505-7. This section includes the actual zone classifications.
* (a) This subsection covers Zone 0.
This zone includes areas where ignitable concentrations of flammable gases or vapors are present continuously or for long periods of time. The word "long" isn't defined, but the first two FPNs refer to other standards and also provide a narrative of typical Zone 0 locations, including the interior of vented vessels with flammable liquids, and inside exhaust ducts used for flammable vapors in ignitable concentrations.
There are two more FPNs. The third suggests that good design is to keep wiring out of Zone 0, or to only use intrinsically safe systems if that is impossible. The last note leads into Zone 1 by detailing what a normal operation is, which is relevant because Zone 1 applies during normal operations. "Minor releases" are part of normal operations and merit a Zone 1, instead of a Zone O classification.
* (b) This subsection covers Zone 1.
This zone includes locations where hazardous vapor could exist under normal operating conditions, or as a frequent occurrence from maintenance, or where a breakdown could cause enough of a failure that the electrical system could be an ignition source. These first three items reflect the same considerations as in Sec. 500-5(a), which is the definition of a Class I Div. 1 location. That is no accident. Zone O plus Zone 1 equal the traditional Division 1. Conversely, Zone O is simply the most hazardous portion of a Div. 1 location, carved out and treated under different rules. In addition, the FPN that follows is very similar to the note following Class I, Div. 1 [Sec.500-5 (a)(FPN)]. The last item identifies a Zone 1 location as necessarily surrounding a Zone 0 location, unless positive pressure with safeguards against failure are provided. This is similar to a comparable provision for Div. 2 adjacent to Div. 1, in Sec.500-5(b).
* (c) This subsection covers Zone 2.
This zone is functionally identical to the traditional Div. 2, as reflected in the definition. The FPN that follows is similar to the first sentence of Sec. 500-5(b)(FPN No. 1), about hazardous concentrations only under accidents or unusual operating conditions. It stops there, however, and doesn't cover the other material in the notes to Sec.500-5(b).
Sec. 505-10. lilts section covers listing and marking of equipment.
* (a) This subsection, entitled "Listing," permits equipment that is listed for Zone 0 to be used in Zones 1 or 2 of the same gas group. If the equipment is listed "or otherwise acceptable" for Zone 1, then it can be used in Zone 2, also within the same gas group.
The "otherwise acceptable" could come from a Class I Div. 1 listing; see Sec.505-20(b) Ex.
* (b) This subsection covers marking requirements.
The equipment must show the class, zone, gas group, and temperature class referenced to a 40 [degrees] C ambient. The temperature classes are given in Table 505-10(b). Those markings (T1, T2, T3, T4, T5, T6) are exactly consistent with the markings in Table 500-3(d) as far as they go, but omit the intermediate classifications (T2A, T2B, T2C, T3A, etc.)
* An exception to these marking rules covers equipment operating at elevated temperatures. It must be marked with both the maximum ambient temperature and the operating temperature or temperature range at that ambient temperature.
The same exception was also included in Sec.500-3(d) as Ex. 5. You use the marking to be sure the equipment doesn't run above the ignition temperature of the gas. You can also judge the same equipment at a lower temperature ambient. For example if a piece of instrumentation has a 50 [degrees] C temperature rise, and is suitable for use in a 150 [degrees] C ambient, it should not be used around diethyl ether (autoignition temp. 160 [degrees] C) at that temperature. On the other hand, the same instrumentation could be used safely in a 40 [degrees] C ambient.
Sec. 505-15. This section covers wiring methods.
* (a) This subsection covers Zone 0. Intrinsically safe wiring or nonconductive optical fiber cable or systems with approved energy-limited supplies are permitted. In addition, for either intrinsically safe or nonincendive circuits, rigid metal conduit or intermediate metal conduit, or Type MI cable can be used. Power circuits are not permitted.
This is the key aspect of the change for those who believe this is a safer protocol; no power circuits in a Zone 0 environment. In addition, conduit must use tapered threads and be made up wrenchtight in accordance with all the rules in the last paragraph of Sec. 500-2. Note that this is an error and refers to the former location of this material, which has now been relocated as the fourth paragraph. The conduit must also be sealed in accordance with the normal Div. 1 sealing rules in Sec.501-5(a) (c) and (d). A FPN indicates that the references in those sections to Div. 1 are to be interpreted as Zone 0.
* (b) This subsection covers Zone 1. The wiring methods in Zone 1 can be any of those allowed for either Zone 0 or for Div. 1.
In addition, all requirements for making seals that would apply in Div. 1 must be adhered to in these Zone 1 locations. Note that the actual wording is that Class I Div. 1 wiring is permitted. Although unintended, the actual wording does not incorporate a clear requirement for seals.
* (c) This subsection covers Zone 2. The wiring methods in Zone 2 can be any of those permitted for Class I, Div. 1 or Div. 2 and Class I, Zone 0 or Zone 1 locations are permitted.
All requirements for sealing are carried over by reference, and also cables approved for Div. 2 hazardous locations, such as Type MC cable, are permitted.
Sec. 505-20. This section covers equipment.
* (a) This subsection covers Zone 0, and only equipment specifically listed and marked for this purpose can be used.
It will take time to put together all the product standards and start the listing process.
* (b) This subsection covers Zone 1, and only equipment specifically listed and marked as suitable for the location is permitted under the main rule. An exception, however, allows Class I Div. 1 (or Zone 0) equipment to substitute for Zone 1 equipment.
It must be of the same gas group, and with a similar temperature marking if possible. Note that the literal text of the exception precludes equipment marked "Class I Group B" (for hydrogen) from being substituted in a Group IIC environment, because that isn't the same gas group; only equipment rated for both Groups A and B could be used. As noted in the gas group discussion, this is a real problem for hydrogen atmospheres. In Europe there is a common marking "Group IIB plus Hydrogen" for just this reason, but that won't help products marked in the traditional way.
* (c) This subsection covers Zone 2, and only equipment specifically listed and marked as suitable for the location is permitted under the main rule. An exception, however, allows Class I, Div. 1 or Div. 2, (or Zone 0 or Zone 1) equipment to substitute for Zone 1 equipment.
It must be of the same gas group and with a similar temperature marking if possible.
Sec. 505-25. Grounding and bonding must comply with Art. 250 and the additional requirements in Sec. 501-16.
Sec. 51 1-4. A new exception allows rigid nonmetallic conduit to be used as a wiring method where buried at least 24 in. below grade in a hazardous [classified) location at a garage within the scope of this article.
The full wording matches similar wording in Sec. 514-8 Ex. 2 and Sec. 515-5(a). It must include an equipment grounding conductor, and the last 24 in. on each end must be threaded rigid or intermediate metal conduit. It does not require concrete encasement. Similar wording was added for Class I Div. 1 locations generally in Sec. 501-4(a) Ex. 1, which requires concrete encasement. That rule has not been correlated with this rule, or with the rules in Art. 514 and 515. The result is a conflict, because the general requirement for concrete encasement theoretically applies in any Class I Div. 1 area.
When a general rule and a specific rule are in conflict, you should consider allowing the specific rule to stand within its scope, unless there is some evidence that it was intended to abolish all specific rules when the general requirement was adopted. In this case the specific rule was added at the same time, by the same panel, as the general requirement.
The AHJ will have to decide, but it was intended that concrete
encasement be permitted to be omitted at these locations. The panel was concerned that under the general case there could be problems with poor backfill that would be less of a problem in the limited excavations involved in Art. 511 installations.
Sec. 517-13(a). A new exception (No.3) grants limited relief for wiring lighting in patients care areas.
EC&M tip: This new exception has not been correlated with Sec. 517-13(b); the other requirements still apply if the literal text is enforced. Check with the AHJ to see whether there will be any leeway possible on the other subsection (b).
What happened: Sec. 517-13(a) requires a No. 12 copper equipment grounding conductor minimum in all branch circuits serving patient care areas, to provide a secure equipment grounding return path from receptacles and metal surfaces. These circuits must be run in metal raceways. The new exception does only one thing: waive the requirement for an insulated equipment grounding conductor. This is in the form of a new Ex. 3, and it applies to "Light fixtures more than 7 1/2 ft above the floor."
What did not happen: This exception does not remove the metal raceway wiring method rule. Although Ex. 1 does relieve this requirement, two exceptions cannot be applied at the same time. This exception also does not change any of the wiring method requirements in Sec. 51 7-13(b), which apply "in addition to the requirements of Section 517-13(a)."
What was supposed to happen: This change was intended to allow a blanket waiver of all branch-circuit wiring method restrictions where a fixture over 7 1/2 ft above the floor was installed. The idea was that although this is a patient care area, patients wouldn't be coming into contact with ceiling fixtures. There really isn't anything wrong with that concept, but the present text is unfortunately far removed from the intent.
Sec. 517-18(c) Instead of installing "tamper resistant receptacles in pediatric areas, now you can use a restrictive cover.
What happened: A new exception now allows a cover that "by its construction, limits improper access to the energized parts of the receptacle."
Background: This is open to a little interpretation, as AHJs try to figure out just how much "limitation" this new exception requires. Certainly a lock with keys only in the possession of the medical staff is limiting, but what about latches? If the latch takes the same or more force as a child-resistant pill bottle to open, is that sufficiently limiting? The AHJ will need to be consulted on this.
Sec. 517-19(a) Critical care locations fed from two critical branch transfer switches need not be supplied by normal power.
What happened: A new additional exception (No. 2) allows all branch circuits in a critical care location to originate from the emergency system, provided two different transfer switches supply each such location.
Background: The reason for the normal power requirement is to make sure that there is some power available in the event of a failure in a transfer switch. If there are two independent transfer switches serving each patient bed area, the result is even higher reliability. This change allows for, but does not require, that possibility.
Sec. 517-19(b). At least one of the six required receptacles at patient bed locations in critical care areas must be connected to a normal system branch circuit.
This change clarifies that the normal circuit ordinarily required to supply critical care patient bed locations must supply at least one receptacle at each of those locations. Remember, a receptacle is a single contact point, and a duplex receptacle is, therefore, two receptacles.
This change has not been correlated with the change immediately preceding it, which means there may well not be a normal system branch circuit at the bed location. Since the actual wording is "the normal system branch circuit required in Section 517-19(a)" and since that subsection now includes the exception allowing two emergency system circuits from different transfer switches, it would be reasonable to apply that new exception to this provision as well.
Sec. 51 7-30(b). A standby generator used as the source of supply for a hospital emergency system, can now be permitted to supply other hospital loads not part of that system, provide they have their own transfer switch. Other restrictions apply.
EC&M tip: The literal text of this new provision includes a potentially dangerous blunder (see drawing). Be sure to discuss your options carefully with the AHJ before making use of this.
What happened: A new paragraph (5) was added to cover " loads served by the generating equipment not specifically named in Sections 517-33 and 517-34." These loads require their own transfer switch(es) and there must be provisions so the transfer won't take place if the generator will be overloaded, or the loads must be shed if the generator becomes overloaded.
The problem is that Sections 517-33 and 517-34 cover the critical branch and the equipment system, respectively. Sec. 517-32, on the life safety branch, was inadvertently omitted. It is now a literal requirement of the 1996 NEC to shed the life safety branch if the generator approaches overload from nonessential load! This, of course, is a direct conflict with Sec.700-5(b), and should never be allowed.
Background: Sec. 3-184.108.40.206 of NFPA 99 recognizes on-site generation as a source of power to both essential system and other loads, with conditions. If a single generator is used, it must be in such a way that the mean service interval between overhauls must not be reduced to less than three years. If multiple generators are used, the essential system must be capable of being supplied with the largest single generator out of service. Many facilities use their generating equipment for other loads. If done properly, there is no problem, and the NFPA 99 Committee has agreed to further amend Sec. 3-220.127.116.11 for the next edition in a way that is consistent with this NEC change, albeit without the life-safety branch problem.
Sec. 517-30(c)(3). Hospital emergency system wiring must now be in nonflexible metal raceways. Two new exceptions apply, for Type MI cable and for flexible connections for medical headwalls and equipment connections.
What happened: There are three important changes, as follows:
* Hospital emergency systems must be wired in metal raceways (previous code), and now those metal raceways must be nonflexible. This change was made in the main rule.
* Type MI cable can be used as a substitute for metal raceways. If it contains a branch circuit for a patient care area, then it must comply with Sec. 517-13(b). This is a new Ex.5.
* Flexible raceways and cables are permitted to be used in prefabricated medical headwalls, or "when necessary for flexible connection to equipment." This is a new Ex.6.
Background: There have been many cases of designers carefully studying Sec. 517-13(b), picking out an appropriate cable such as Type AC with a separate equipment grounding conductor, and then having the entire job turned down because the branch circuits were part of the hospital emergency system. The emergency system protection rules apply to branch circuits as well as feeders.
The rule and the new Ex. 6 combine to exclude flexible wiring methods from most home runs, only allowing them at the end of the run where necessary to make equipment connections that require flexibility, or in prefabricated medical headwalls. The other exception is for Type MI cable. This cable is OK as normally shipped for feeders and non-patient care area duties.
If it will be a branch circuit for a patient care area, then it will have to be configured with an additional conductor, which will provide a separate equipment grounding conductor as required by Sec. 517-13(a). In addition, only the copper variety is suitable, because the sheath must meet Sec. 517-13(b), and Sec. 250-91 (b)(7) and Sec. 330-22 disallow a steel sheath as a grounding return path.
Sec. 517-30(d). New provisions in this subsection clarify and dramatically change the requirements for sizing the elements of a hospital emergency standby system. The feeders are still calculated under Art. 220, but the generator need not be.
What happened: Although the feeders still calculate under Art. 220, the generator(s) need only be sized large enough so that there is "sufficient capacity and proper rating to meet the demand produced by trite load of the essential electrical system(s) at any one time." Demand calculations for this purpose can be based on;
* Demand factors and historical data, OR
* Connected load, OR
* Feeder loading as determined by Art. 220, OR
* Any combination of the above
Background: Some AHJs have been requiring generators to be sized based on all connected loads, and Art. 220 doesn't adequately address diversity in many industrial and commercial facilities. Generators have been sized at over twice the actual required capacity, which is detrimental to engine performance and not in accordance with the required testing protocols in NFPA 99. In addition, the NFPA 99 Committee is moving (in Sec. 3-18.104.22.168) in the. same direction as this NEC change.
Sec. 517-45. A new section covers the essential electrical system requirements for an ambulatory health care center.
What happened: Ambulatory health care centers must have sufficient capacity in their standby electrical systems so that within 10 sec. of an outage there is sufficient power, for at least 1 1/2 hr, to energize:
* Task illumination as required for life safety and the safe cessation of procedures in progress;
* Anesthesia and resuscitative equipment in areas where inhalation anesthesia is in use;
* Life support equipment, "where procedures are performed that require such equipment for the support of the patient's life. "
The standby power source can be a generator or integral, self-contained batteries with the equipment. If, however, there is a critical care area within the facility, then a full essential electrical system as would otherwise be required in hospitals shall be
Background: These facilities are very common, both for outpatient surgery and for kidney dialysis. Please refer to the discussion in Sec. 517-3 (definitions) for more information.
Sec. 518-4. A new exception (No. 3) allows electrical nonmetallic tubing and rigid nonmetallic conduit in limited places of assembly as long as the high-rise fire-finish concealment rule for ENT is observed.
What happened: Rigid nonmetallic conduit and electrical nonmetallic tubing are now permitted in restaurants, conference and meeting rooms of hotels or motels, dining facilities, and church chapels. This permission is restricted to the traditional locations for ENT in high-rise construction (concealed in walls with a 15-min finish rating or above suspended ceilings with a similar rating). This exception does not waive the restrictions in Sec. 300-22(c) that exclude these methods from air-handling ceilings.
Background: This is the first time nonmetallic wiring methods have made it into any normal places of assembly that have a fire rating. The idea is that if the fire-finish principle in Sec. 331-3(2) is valid for high-rise construction, it should be equally valid, if not more so, for comparatively low-impact places of assembly, usually close to ground level, with abundant means of egress.
Article 525--Carnivals, Circuses, Fairs, and Similar Events. A new article provides comprehensive NEC coverage for "carnivals, circuses, fairs, and similar events."
What happened: A new Art. 525 covers these attractions, and includes many important new requirements, as follows:
* Sec. 525-3. This article doesn't apply in permanent structures; Art. 518 and 520 apply instead. If other articles and Art. 525 differ, then Art. 525 applies only to the portable wiring and equipment.
* Sec. 525-6. Mechanical protection must be provided on rides and concessions for electric equipment and wiring as needed to prevent damage.
* Sec. 525-10 Power Sources. Power sources must comply with their applicable articles and the following additional requirements:
* Sec. 525-10(a) Services. If in locations accessible to unqualified persons, they must be lockable. They must be on solid backing and protected from weather (unless weatherproof).
* Sec. 525-10(b) Separately Derived Systems. Generators must comply with Art. 445, and transformers, in addition to complying with Art. 450, must comply "with applicable requirements of Sec. 240-3(a), (b), (c), (d) and Sec. 250-26." This presumably refers not to the transformers themselves but to the systems supplied by transformers, and covers separately derived system grounding requirements and conductor overcurrent protection rules, including the tap rules.
* Sec. 525-12. Overhead conductors must comply with Sec. 225-18 for vertical clearances, and at least 15 ft horizontally from all other amusement rides and attractions.
* Sec. 525-13. Normal wiring method rules generally apply. Open conductors are prohibited except as part of a listed assembly or in festoon lighting, installed per Art. 225. The wiring for one amusement ride must not be supported by another ride.
Flexible cords must be listed for extra-hard usage, wet locations, and sunlight resistance. They must be continuous, without splices or taps between boxes or fittings. Cord connectors must not be laid on the ground. Cords laid on the ground and accessible to the public must be covered with approved nonconductive mats, arranged so as not to be a tripping hazard. Single conductor cords are permitted in sizes No. 2 and larger.
* Sec. 525-14. Boxes or fittings required at outlets, junction points, etc.
* Sec. 525-15. Portable distribution and termination boxes must be designed so no live parts are exposed to accidental contact, and if used outdoors, the box must be weatherproof and arranged at least 6 in. above the ground. Busbar ampacities must at least equal the feeder overcurrent device rating, and suitable busbar connectors must be provided as required for conductor terminations. Receptacles must have overcurrent protection within the box, set no higher than the ampere rating of the receptacle (or higher if allowed by Art. 430 for pure motor circuits.) Note that this disallows a 15A configured receptacle on a 20A circuit. Single pole connectors must comply with Sec. 530-22. Note that this rule does not, and probably should, reiterate Sec. 400-10 requiring strain relief for cord terminations.
* Sec. 525-16. Overcurrent protection to comply with the usual requirements.
* Sec. 525-17. Motors and associated equipment to comply with Art. 430.
* Sec. 525-18. GFCI requirements in Sec. 305-6 don't apply in this article. There are no such requirements; this waiver wasn't correlated with the final action on Sec. 305-6. See the discussion at Sec. 518-3 (b) Ex. 2 for more information.
* Sec. 525-20. Grounding to be in accordance with Art. 250.
* Sec. 525-21. Metal raceways, metal electric equipment enclosures, and metal frames and parts of rides, concessions, trailers, trucks, or other equipment that support or contain electrical equipment must be bonded. This could include, but would be very problematic to arrange, for festoon lighting passing through a tent frame.
* Sec. 525-22. Usual rules for equipment grounding conductors. Regrounding of the grounded circuit conductor is not permitted on the load side of the service or separately derived system disconnecting means.
* Sec. 525-30. Every ride and concession must have a fused disconnect switch or circuit breaker within sight and within 6 ft of the operator's station, and readily accessible to the operator even while the ride is in motion. If accessible to unqualified persons, the disconnect must be lockable. The disconnect may be remote from the operator if there is a shunt-trip mechanism to open the disconnect, provided the ride operator can open the disconnect by closing a switch in the ride console.
Art. 530, Part G. This new part recognizes a new 60/120V distribution system designed to eliminate the effects of electronic noise on audio and video production work,
What happened: The new system, as shown in the drawing, uses two ungrounded circuit conductors at a potential of 120V, and the system secondary is mid-point tapped,and grounded to hold the system to 60V to ground. It can be used to reduce electronic noise in audio/video production or "other sensitive electronic equipment locations" provided it is restricted to electronic equipment only. In addition, the following restrictions apply:
* Sec. 530-71(a). Standard panelboards, such as 120/240 single-phase panelboards are permitted, but the voltage system must be clearly marked on the panel face or door. Common-trip two-pole circuit breakers must be used for all circuits, and they must be identified for use at the system voltage. In general, circuit breakers work OK as long their voltage rating isn't exceeded, and that won't be a problem on this system. As shown in the drawings, all loads supplied by these systems will use two ungrounded circuit conductors.
* Sec. 530-71(b). Junction box covers shall be clearly marked to indicate the distribution panelboard and the system voltage.
* Sec. 530-71(c). Feeders and branch-circuit must be identified as belonging to this kind of system at all splices and terminations by color, tagging, or equally effective means. The means chosen must be marked on all panelboards, and on the building disconnect. This is intended to reduce the possibility of confusion during future alterations.
* Sec. 530-71(d). The voltage drop on any branch circuit must not exceed 1.5%, and the total drop including the feeder contribution must not exceed 2.5%. These circuits are operating with only one-half the voltage to ground, which means that in any ground fault, only one-half the fault current would flow across the same fault. The intent of the rule is to maximize the available voltage so overcurrent devices will trip open as quickly as possible in the event of a fault. This, along with new Sec. 695-8(e) on fire pumps, is the only place in the Code that a mandatory rule on voltage drop appears.
* Sec. 530-72. The system is a separately derived system and must be grounded accordingly, as shown in the drawing. The neutral connection at the center tap of the transformer has no circuit load function; its sole function is to stabilize the voltage to ground and to provide an equipment grounding return path. It supplies, on the downstream side of the main bonding jumper for the system, equipment grounding terminal bars. They must be marked "Technical Equipment Ground."
If there were a succession of panelboards and the system designer decided to isolate the return path from the enclosing raceways and panelboard enclosures for further noise reduction, this section allows the use of insulated grounding conductors and having the equipment grounding bars isolated from the enclosures. This is the same procedure allowed in Sec. 250-74 Ex. 4 and Sec. 384-20. Note, however, that such raceways and enclosures must still be grounded. This can happen using any of the recognized equipment grounding conductors in Sec. 250-91 (b).
Conversely, the exception allows for a raceway grounding return path without any additional grounding conductors, provided that the impedance of the grounding return path over the raceway does not exceed the impedance of a separate grounding conductor installed to meet these minimum requirements. Remember, if the circuit conductors have been increased to meet the voltage-drop requirement, then Sec. 250-95 requires a corresponding increase in the size of grounding conductors on the same circuit. In this case the raceway impedance must be compared with the lower impedance of the larger equipment grounding conductor that would otherwise have been substituted. The FPNs that follow reinforce this concept.
* Sec. 530-73 (a). Where receptacles are used to connect equipment, all of the following conditions shall be met:
* (1) All 15- and 20A receptacles shall be GFCI protected.
* (2) All outlet strips, adapters, receptacle covers, and face-plates shall be marked: "WARNING--TECHNICAL POWER"; "Do not connect to lighting equipment"; "For electronic equipment use only"; "60/120 Volts 10 AC"; "GFCI Protected."
* (3) A conventional 125V 10 15A or 20A receptacle must be located within 6 ft of all permanently-installed 15A or 20A 60/120V technical power system receptacles.
* (4) All 125V 10 receptacles used for 60/120V technical power shall be uniquely configured and identified for use with this class of system.
The reason for these requirements is to make as certain as possible that the receptacles aren't used for cord- and plug-connected loads designed for use on systems with only one ungrounded conductor. For example, if a floor lamp were connected, the screw shell would remain alive at 60V to ground, even with the switch off, assuming a single-pole lampholder.
Item (1) then adds an additional level of safety by requiring GFCI protection at or ahead of all receptacle outlets. Be careful if you are considering using a 2-pole GFCI for this purpose. Its electronic circuitry may not work on a system voltage of only 60V to ground. The best choice is the so-called "master" GFCI units that are, in effect, feed-through GFCI receptacles without the contact slots. They will work because they would see only their design voltage of 120V. Remember, using an actual GFCI receptacle would violate the configuration rule in (4).
Item (2) on marking is self-explanatory. Item (3) relieves the temptation to plug the proverbial floor lamp into the wrong receptacle, because an appropriate receptacle must be nearby.
Item (4) asks for a unique configuration, which has yet to be developed. An exception follows, allowing a conventionally configured receptacle in "machine rooms, control rooms, equipment rooms, equipment racks, and similar locations that are restricted to use by qualified personnel." This will undoubtedly prove essential, particularly during the transition period.
Background: These systems have proven extremely effective at reducing audio hum and video interference. The noise from the filtering circuits (see drawing) tends to cancel on this type of balanced system. The transformers with the center-tapped 120V secondaries are increasingly available as well. All that has been missing, until now, is some recognition in the NEC.
Sec. 547-8(b). The equipotential prone is now mandatory in agricultural buildings with livestock confinement areas.
What happened: Instead of merely allowing embedded conductive elements in a concrete floor to be used as an equipotential grid, now you must install such embedded elements, and you must bond them to the grounding electrode system of the building. This is a major change. In addition, you must protect the livestock against step potentials as they enter (or exit) the building through the use of a "voltage gradient at entrances and exits." A new FPN refers the reader to the American Society of Agricultural Engineers Standard EP473, Equipotential Planes in Animal Confinement Areas, as one way to do this.
Background: For some time it has been generally understood that livestock, particularly cattle, have a lower threshold for injury due to voltage differentials than people do. In some cases the premises power system will be responsible for small voltages between local ground where an animal is standing, and ground as reflected in the metal surfaces of electric equipment that are connected to the equipment grounding system for the building. In addition, voltage gradients can appear due to imbalances in the utility primary neutrals, especially where these use the same conductors as the secondary neutrals. The idea is that an equipotential plane will ameliorate these problems, in the same way as the required bonding grid at swimming pools helps shield swimmers from voltage gradients.
The proposal was extremely controversial, particularly in the State of Wisconsin, which had such a mandatory requirement for many years and just succeeded in repealing it. There have been questions raised as to its long-term effectiveness, particularly in the highly moist and corrosive conditions involved. Some have also questioned the practicability, particularly if precast concrete is used. Finally, there are questions as to whether this has crossed over into electrical design, since no person has ever been injured by these voltages. The panel answered that by noting that livestock is property, and protecting property is within the scope of the NEC. Note that the rule only applies where livestock is involved.
Sec. 551-71. There are major changes in the required receptacle provisions at RV parks.
What happened: First, 5% of the electrified sites must now have 50A 125/250V receptacles, with the 30A 125V sites reduced proportionately. Second, dedicated tent sites with 15A or 20A electric supply can now be excluded from the number of electrified sites to which the percentages apply.
Background: This is the first time a specific number of sites will need to be set aside for the larger RVs. In addition, the rule also recognizes that some RV parks reserve sites for tent camping. Although electrified, these sites do not affect the vehicle percentages at an RV park. Example: 150 sites, 25 for tent camping without power, 25 for tent camping with power, balance for RVs.
* Exclude the 25 nonpower sites; they were never counted.
* Exclude the 25 tent sites with power; they are now exempt.
* Balance of electrified, countable sites is 100; 5 must be 125/ 250V 50A; 70 sites must have 125V 30A; all 100 sites must have 125V 20A.
Sec. 551-71. This section has been editorially revised b separate the GFCI requirements from both paragraphs and insert them into new third paragraph.
The third paragraph simply says: "All 125-volt, single-phase, 15- and 20-ampere receptacles shall have listed ground-fault circuit-interrupter protection for personnel." Be careful with this new paragraph format. The old format tied the GFCI rule directly to the affected text. It was clear that the GFCI rules applied to RV site receptacles. The new third paragraph has no such ties. The new paragraph can easily be interpreted to protect every receptacle of the described current and voltage rating throughout the RV park. This wasn't intended; the change was supposed to be strictly an editorial matter.
Sec. 551-73(a). Tent sites [electrified) are going into the required demand calculations for the first time, at 600VA.
To be eligible for treatment as a tent site, the supply must be no higher than 20A, and the site must be dedicated for that purpose.
Article 552--ark Trailers Art. 552. A new article covers "Park Trailers."
What happened: A new article covers "park trailers," defined as "A unit that meets the following criteria: (a) built on a single chassis mounted on wheels, and (b) having a gross trailer area not exceeding 400 sq. ft. (37.2 sq. m.) in the set up mode."
Note that in the Art. 551 definitions, a "travel trailer" can be up to 320 sq. ft. This new article covers a larger version of that, and the sections that follow generally reiterate the rules for RVs. However, there are some significant differences. Part D material in Art. 551 on multiple power sources, and most information about generator power supply, have been omitted. Also, undoubtedly reflective of the increased size of these units, there is some material imported from Art. 550 on mobile homes. In addition, the material in Art. 551 covering 15A and 20A power supplies, cords, plugs, etc. has been omitted, since units this large would never come with such a small power feed. Finally, since these units are towed and not driven, material in Art. 551 about wiring in engine compartments and such items as the cigarette lighter receptacle rule [Sec. 551-10(h)] weren't brought over as well.
Background: Approximately 10,000 of these units are now being produced annually, and they must be being set up somewhere. The new article has no site provisions, so presumably these park trailers come under the Art. 551 rules (in Part G). There are, however, no demand provisions in Sec. 551-73 for hard-wired feeders of indefinite capacity. Sec. 550-22 has demand factors for mobile homes, but those may be problematic to integrate with Sec. 551-73. This will be particularly true if the particular sites for these trailers aren't dedicated in the RV park, and nothing in the Code forces them to be.
Sec. 555-1. This article now also covers boathouses and similar occupancies.
What happened: This article now has responsibility for boat-houses, including those at a dwelling. This brings receptacles at these locations within the rules of Sec. 555-3, which requires GFCI protection. Although Sec. 210-8(a) dropped residential boathouses from its GFCI provisions, there will be no gap in coverage due to their inclusion in this article of the Code.
EC&M tip: Note that the shore power and other requirements in Art. 555 now apply in these boathouses to the extent applicable, not just the GFCI rules.