The concept of industrial construction encompasses many types of buildings, structures within buildings, areas within buildings, and areas between buildings. And it isn’t just new construction. It includes upgrades, retrofit work, and equipment moves; these projects are often done with the plant still up and running.
Production equipment moves or replacements are common in most industrial facilities. This work typically begins with limited demolition. The electricians disconnect everything before the mechanical (and sometimes civil) work. When that work’s done, the electricians come back to “wire it up.”
Raceway and box fill
Here’s what often happens. The power distribution system is laid out based on the original requirements. Circuits are identified, and conductors are sized for the specified loads. Raceway, boxes, etc., are sized correctly. Then, the Engineering Change Notices (ECNs) start flowing in — or, as is more often the case, verbal orders change.
Now, instead of the 12 conductors you were going to pull, you’ve got 18. But the ECN came in after you finished the raceway, complete with pullboxes.
Do you run another raceway or add the conductors to this one? Using extra lube will let you get those conductors in. But the raceway fill requirement isn’t about reducing wire pull tension so much as it is about allowing the conductors to handle heat (that’s why not all wires are counted as part of the fill).
Therefore, you’ll need to check box fill [314.16] and raceway fill NEC requirements. You calculate raceway fill based on the type of conductor and raceway, so see Chapter 9 and Annex C. Don’t forget de-rating for more than three conductors [Table 310.15(B)(3)(a)].
Fell short? Determine whether upsizing (in this case, also including ripping out what you just installed) or adding is the correct solution.
Unprotected metal conduit
Throughout the NEC, we repeatedly find the “protect from physical damage” requirement. A variation exists in the “Uses Not Permitted” (typically Section 12) requirements in the various Chapter 3 Articles. The particular wiring method can’t be used “where subject to physical damage.”
This limitation is notably absent from Art. 342 (Intermediate Metal Conduit) and Art. 344 (Rigid Metal Conduit). This does not imply that where the raceway is exposed to physical damage, you can just run IMC or RMC and call it a day.
For example, lift trucks will be operating regularly near the wall you plan to secure the conduit to. As strong as IMC and RMC are, they can be smashed by a lift truck counterweight. Route the raceway up and away from the possible strike zone, or add another layer of protection by installing a protective rail, bollards, or other barrier.
As many times as the NEC mentions “protect from damage” (including, arguably, applicable here, 110.27(B)], we can logically conclude that even IMC and RMC may need protection although neither Art. 342 nor Art. 344 has a Section 12.
Working spaces
For industrial construction, the working space issue has special implications. Maintenance people must deal with walls and switchgear cabinets already in place. Construction people can design out problems maintenance people otherwise must deal with. Don’t think in terms of “three feet” but in terms of what will be adequate for operating and servicing the equipment [110.26].
Transformer follies
A mistake sometimes made in design and construction is the assumption that, since the facility will have a maintenance department, said department automatically qualifies for the “where conditions of supervision and maintenance” clause that allows for less stringent rules (e.g., Table 450.3(A) and elsewhere in the Code).
Generally, this clause does not apply. Assuming it does can lead to serious failures. Apply this clause only if the conditions are actually met. Facilities with a high reliability mission typically satisfy the clause; however, verify rather than assume.
The typical industrial maintenance department doesn’t have qualified persons who monitor and service transformer installations. The maintenance department usually hires and trains to maintain the production equipment, not (in any depth) the infrastructure serving that equipment. Typically, that infrastructure gets serious attention only when maintenance calls in a contractor to address power problems or to conduct testing during a planned shutdown.
Industrial transformers are often poorly protected. A classic example is the transformer placed 6 ft from a loading dock. Lift trucks drive right past it. But if you don’t install bollards or similar protection, it’s inevitable that someone will hit the transformer.
The mechanical protection requirement of 450.8(A) isn’t specific or prescriptive, in the sense that it doesn’t tell you what protection to implement in what circumstances. To comply with the requirement, assess the potential hazards arising from the intended use of the space near the transformer, and then provide reasonably adequate protection against those hazards.
Transformer “grounding” is another area of confusion. The 2014 NEC moved the existing requirements [450.10] into Subsection B and added a new Subsection A just for dry-type transformers. It explicitly requires bonding the enclosure to the grounding/bonding terminal bar.
A few years back, power quality consultants would sometimes advise disconnecting the factory-supplied enclosure bonding connection under the false notion this would somehow solve power quality problems. All it did was put the enclosure at a different potential from the rest of the system and thus create multiple hazards. The notion also got into new construction specs, leaving new transformers in a dangerous condition.
This practice violated the existing 450.10 requirement to bond exposed non-current-carrying metal parts. Adding Subsection A makes it explicit to bond the enclosure to the grounding and bonding terminal bar (if provided). In some transformers, compliance is now assured by a plate that automatically makes this connection when the enclosure is in place.
Fastened too fast
Wiring methods must be securely fastened in place [300.11(A)]. A strange thing happens when production equipment is moved or upgraded. There seems to be an epidemic of fastening and support deficiencies for cables, boxes, and fittings. Poor support/fastening puts the raceway at risk for simply coming apart. That can leave conductors exposed or damage them.
A contributing factor is these projects must often meet unrealistic time or budget constraints. That leads to another contributing factor: These projects are often done ad-hoc without engineering drawings or even a bill of materials. You can reduce violations by developing a standard checklist that can be copied and used for each section of the equipment being moved or upgraded (e.g., “Robotic Welder Six Feed Section”).
Grounding on the load side
There’s no electrical purpose served by grounding on the load side of a service or separately derived source. Yet, many industrial construction projects feature ground rods driven through the floor and connected to equipment. This not only adds cost, but it also leads to outright omissions in applying the requirements of Art. 250, Part V.
Further confusion arises when a document says to “ground” such equipment as motors and control systems. A connection to earth (see Art. 100 definition of “ground”) does not do the job of bonding.
Sometimes, the people writing specifications get creative when they imagine the amount of pointless “grounding” needed. At a paper mill, the installation specification for a Distributed Control System (DCS) required driving a 50-ft ground rod assembly and isolating it from “the main ground.” Supposedly, this would protect the DCS from “noise.” It didn’t do that, but it did create dangerous differences of potential between the DCS and the equipment it controlled.
If it’s not a power source, you bond it instead of ground it. Grounding instead of bonding (on the load side) sets the facility up for power quality problems and possibly lethal differences of potential. If the construction documents conflict with Art. 250 Part V, send them back for revision.
Code compliance
Industrial managers and operators have an understandable focus on minimizing production interruptions. Consequently, the environment for industrial electrical work is often high pressure and sometimes chaotic. And work scheduled during normal production hours gives you yet another layer of complication.
Taking shortcuts that “game” Code compliance might speed up the completion of work tasks and make the plant manager happy in the short-term, but shortcuts can eventually create “small” problems like a transformer going supernova. If the two hours you saved when completing the project cost $8,000 in destroyed equipment plus a week of lost production, how much money was actually saved?
It’s never a bad thing to have a record of safe and reliable industrial installations. Don’t seek to be a hero in the short-term just to meet unrealistic demands. Be an unsung hero in the long-term by making sure your industrial projects meet NEC requirements.
Lamendola is an electrical consultant located in Merriam, Kan. He can be reached at [email protected].
