The ballast compartment of a fluorescent fixture must meet the same rules as any other field-wired enclosure with respect to system separation.

We have received a series of questions from a broad spectrum of the industry, including installers, inspectors, and manufacturers, regarding fluorescent ballasts that have Class 2 control circuits, particularly for remote dimming controls. As energy conservation takes hold, these controls are in increasing demand, including daylighting controls that dim the lights automatically in response to sunlight in rooms with windows.

The common element to the questions is what degree of separation, if any, is required between these control conductors and the conductors that are part of the power circuit to the light, including the branch-circuit conductors?

The EC&M panel's response

We think that these conductors must meet the normal separation rules for field wiring. This has implications not only for field-wiring practices, but also for product standards as well. Although the wiring within the listed ballast itself isn't directly subject to the Code, there are many ballasts whose configurations make it very difficult to comply with the literal provisions of the Code requirements for field wiring.

The basic requirement has been relocated in the process of rewriting Article 725 for the 1996 NEC, and now appears in Sec. 725-54(a)(1):

(1) In Cables, Compartments, Cable Trays, Enclosures, Manholes, Outlet Boxes, Device Boxes, and Raceways. Conductors of Class 2 and Class 3 circuits shall not be placed in any cable, cable tray, compartment, enclosure, manhole, outlet box, device box, raceway, or similar fitting with conductors of electric light, power, Class 1, and nonpower-limited fire alarm circuits.

In general, therefore, conductor insulation alone, no matter what its voltage rating, cannot be relied upon to provide the required system separation. This is much different than the concept in Sec. 300-3(c)(1) for power circuits, where different systems (but never exceeding 600v) need not be separated if "all conductors ... have an insulation rating equal to at least the maximum circuit voltage applied to any conductor within the enclosure ..."

Class 2 control circuits are an example of a special condition addressed in Chapter 7 of the Code. The rules in Chapter 7 supplement and modify the general rules in the first four chapters of the Code, as provided in Sec. 90-3. Therefore, there is no conflict within the Code. The reason for the stricter requirements is the fact that the allowable wiring methods for Class 2 circuits, and the product standards governing the control devices to which they are connected, all assume that the energy available is strictly limited to the point that there will be no fire or electrocution hazard. To the extent the systems are divorced, that assumption is valid.

Nevertheless, there are occasions where Class 2 and power (or other nonpower-limited) circuits must be in close proximity. The dimmable fluorescent ballasts covered in this question are a good example. When this happens, the Code provides exceptions, all of which maintain the concept that conductor insulation alone is insufficient separation.

Now consider the usual work procedure in changing ballasts, particularly in quantity. After changing the ballast, you stuff the conductors and the twist-on wire connectors into the channel any way they'll fit. The job is done when you don't see anything hanging out over the edge of the ballast channel. Very few inspectors would be likely to accept the resulting compressed spider's web of intertwined Class 2 and power conductors as meeting the objectives of the Code.

The ballasts

The first problem, unfortunately, may be the ballast itself. We are aware of at least three ballast designs, and only one of them promotes adherence to these Code rules. As shown in the drawing (p. 84) one ballast design has the power and signaling conductors exiting from the same opening in the ballast case. Another has a terminal strip on the end of the ballast. This is better, but there isn't sufficient spacing to meet the air-space separation requirement (we'll cover that shortly.) The third design, which fits in well with other Code rules, has the signaling conductors exiting the ballast case at some distance, generally about 3/4 in. from the power conductor opening.

All three of these designs comply with the applicable product standard and are available as listed items. We think that UL (which is responsible for UL 935 and UL 1570, the product standards for fluorescent ballasts and fixtures, respectively) should review its standards, which now allow designs that are difficult to install in accordance with the Code in this respect. We have discussed this with some manufacturers, and we are concerned that comparative costs may tend to favor the most problematic design unless UL changes the playing field by revising its standards. We understand that as this is written, UL is now considering changes; but even if the standard changes, there will still be many listed ballasts available with this problem for a long time to come.

What can be done?

There are a total of five options, and which one(s) can be used with which ballast design(s) will call for a judgment on the part of the AHJ. The first option is to use a barrier as covered in Sec. 725-54(a)(1) Ex. 1:

Exception No. 1: Where the conductors of the electric light, power, Class 1, and nonpower-limited fire alarm circuits are separated by a barrier from the Class 2 and Class 3 circuits. In enclosures, Class 2 or Class 3 circuits shall be permitted to be installed in a raceway within the enclosure to separate them from Class 1, electric light, power, and nonpower-limited fire alarm circuits.

This wouldn't be too practical in terms of labor, particularly on large jobs with hundreds of ballast changes involved. In isolated cases, it might be useful in some ballast channels, however. You could take a scrap of EMT, clip it to the fixture base, and use it to run the Class 2 conductors into a remote part of the ballast cavity where they could connect to the remote Class 2 cabling. You could even run it to a handy ell within the ballast compartment and chase-nippled to the base of the fixture for a truly bombproof installation, allowing the Class 2 conductors to exit the fixture with complete separation beyond the ballast.

Note that this provision can be used even where the power circuits go on to other fixtures. The remaining four options are all conditioned on the nonpower-limited conductors that enter the ballast channel being "introduced solely to connect to the equipment connected to Class 2 or Class 3 circuits to which the other conductors are connected." Requiring a final termination of all nonpower-limited conductors within the enclosure reduces the exposure of the Class 2 conductors. Therefore, if you decide on any of the other four options, you must do any "daisy-chaining" in a separate box and come into the fixture with a single whip (or nipple).

The second option is to maintain 1/4 in. separation from the power conductors, as covered in Sec. 725-54(a)(1) Ex. 2a.:

a. The electric light, power, Class 1, and nonpower-limited fire alarm circuit conductors are routed to maintain a minimum of 0.25 in. (6.35 mm) separation from the conductors and cables of Class 2 and Class 3 circuits.

The inspector would need to be assured that this separation would be maintained, even while the act of replacing the ballast cover obstructed the installer's view. Presumably the conductors would need to be anchored in place such that, in the inspector's judgment, the ballast cover couldn't push the systems together as it went into position.

The third option, new in the 1996 NEC, allows limited use of cabling suitable for the higher-voltage Class 3 circuits (although the circuit retains its Class 2 designation). This is covered in Sec. 725-54(a)(1) Ex. 2b.1.:

1. The Class 2 and Class 3 circuits are installed using Types CL3, CL3R, or CL3P or permitted substitute cables, provided these Class 3 cable conductors extending beyond the jacket are separated by a minimum of 0.25 in. (6.35 mm) or by a nonconductive sleeve or nonconductive barrier from all other conductors.

Thus, the Class 3 cabling with an intact cable jacket can provide the required separation, and nonconductive sleeving can be used where the jacket has been stripped off. Be careful! Both this option and the next are only permitted, however, where the nonpower-limited conductors "operate at 150 volts or less to ground." You cannot use either this provision or the following one, Sec. 725-54(a)(1) Ex. 2b. 2., on 277V lighting circuits:

2. The Class 2 and Class 3 circuit conductors are installed as a Class 1 circuit in accordance with Section 725-21.

This fourth option, also new in the 1996 NEC, is to run the Class 2 conductors as if they were Class 1 conductors, which generally involves Chapter 3 wiring methods. It also involves using control devices that would be suitable for Class 1 circuits. The exception doesn't say "Class 1 conductors" or "Class 1 wiring;" it says "Class 1 circuit." A Class 1 circuit is a Class 1 circuit everywhere, including the devices that are connected to it. This would immediately disqualify this provision as an option on most dimmable ballast systems we are aware of. Again, this option can't be used on 277V lighting circuits either.

Note that not all of these control circuits are Class 2, although the less expensive wiring for Class 2 is driving the market in that direction. We are aware of one dimmable ballast that is in the process of being evaluated for Class 2 control acceptability right now. If, however, the wiring is indeed Class 1, then these separation rules don't apply. Class 1 wiring can be in the same enclosures as power wiring with which it is functionally associated.

The fifth and final option is to use the new Sec. 725-54(a)(1) Ex. 3, which provides in part:

... If the conductors must enter an enclosure that is provided with a single opening, they shall be permitted to enter through a single fitting (such as a tee) provided the conductors are separated from the conductors of the other circuits by a continuous and firmly fixed nonconductor, such as flexible tubing.

The words "provided with a single opening" will need to be interpreted as to whether the single opening was provided by the manufacturer or by the installer. In other words, if there is only a single knockout actually removed in the back of the fixture, does it qualify even though additional knockouts are provided? We believe that it would be questionable because the condition "must enter an enclosure" would be untrue; the conductors could easily enter at some other point. The panel statement spoke of allowing this new exception in the context of the nonconductive tubing being easily inspectable due to its short length, and the fact that it addressed conductors entering the enclosure, as opposed to conductor routing within the enclosure. The original proposal referred to certain energy management devices that only had a single knockout.

Therefore, we believe the only feasible alternative is to maintain the 1/4-in. separation within the ballast channel through some means acceptable to the inspector, and with any "daisy-chaining" of the power circuits done remotely. If the separation cannot be maintained, or if the "daisy-chaining" must be done within the fixture, then a barrier, which could be a raceway such as EMT, must be in place within the channel. We also want to reiterate that the manufacturers and the standards writers must, as quickly as possible, eliminate ballast constructions that effectively frustrate compliance with these requirements in the ballast vicinity.