Jim Dollard has an extensive background in codes and standards. If you have a query about the National Electrical Code (NEC), Jim will help you solve it. Questions can be sent to email@example.com. Answers are based on the 2014 NEC.
Phase converters and fire-pump service
We are wiring a six-unit apartment building, and the service is single-phase, 120/240-volt (V). The electric fire pump is rated at three-phase, 208V. Is it permissible to use a phase converter to supply a fire pump?
No. Section 695.3(G) prohibits the use of phase converters for fire-pump service. This requirement is extracted from NFPA 20, the Standard for the Installation of Stationary Pumps for Fire Protection. Article 455 defines a phase converter as an electrical device that converts single-phase to three-phase. A feasible option would be to request that the utility supply an additional service to supply the fire pump in accordance with 230.2(A)(1).
Our company was recently given multiple violations for installing a utility disconnect with current-limiting fuses. The job involved a single structure that was separated by fire-rated walls. We were contracted to install a 600-ampere (A) service for a new tenant on the far end of the structure. The utility-owned transformer could not be located near the new tenant space due to the parking lot layout and neighboring buildings. The transformer was near the opposite end of the structure, more than 250 feet away from the tenant space. Our original plan was to run PVC conduit underground from the utility-owned transformer, take service conductors to the structure and then run 250 feet on the side of the structure to the tenant space. We decided to add a disconnect with current-limiting fuses 30 feet from the utility-owned transformer as an additional safety measure, which we call a utility disconnect. The utility metering was done inside the tenant space. The inspector told us that the “utility disconnect” was the “service disconnect,” and we had to develop a grounding electrode system. He also made us pull equipment grounding conductors from the fused disconnect to the tenant space. We think that 230.82(1) permits a “current limiting device,” which we believe could be a disconnect with current limiting fuses. Can you help?
The inspector is correct. The NEC does not use or recognize the term “utility disconnect.” The fused disconnect in your installation is the “service disconnecting means,” and all requirements of the NEC apply, including a grounding electrode system. Section 230.82(1) permits “cable limiters or other current limiting devices” to be installed ahead of the service disconnecting means. It is notable that 230.82(1) does not use the term “disconnect.” Cable limiters are installed in series with a single conductor and may be used in parallel installations to limit a potential failure to a single cable. These devices contain a fusible element but do not provide overload protection, and no disconnect is involved. The additional text, “or other current limiting devices,” permits a similar device that may not contain a fusible element but provides a degree of current limitation.
The conductors on the load side of the service disconnect are feeders, and an equipment grounding conductor sized in accordance with 250.122 is required. As you noted in your question, the service conductors could have been taken underground to the structure and then run along the outside of the structure to the tenant space served.
Busways and concrete curbs
All of the busway installations in the commercial facilities we work in are installed vertically through the building with switches on each floor. In each of these installations, the busway is supported on each floor where it penetrates, and there is always a concrete curb. Is there an NEC requirement for installing a concrete curb around an opening in the floor for busway? If so, why don’t we install a curb around vertical conduits?
The concrete curbs installed for vertical runs of busway are an NEC requirement. Busways are permitted to be run through walls and floors in accordance with 368.10(C). Where a vertical busway riser is installed in a commercial venue through two or more floors, a minimum 4-inch-high curb must be installed around and within 12 inches of the floor opening. The requirement is specifically to prevent liquid from getting on and running down the busway. There is no such requirement for conduit risers. The reason for the curbs around busway is that a vertical run through two or more floors will contain splice joints and switches. Any liquid getting on the busway could migrate into the splice joints and switches. This could potentially damage the busway installation and create a short circuit or ground fault. Installation of a curb is not required for a conduit riser. While it is possible that liquid running down a conduit riser could migrate into electrical equipment, it is not as likely to create a problem.
Fire alarm disconnecting means access
On a recent renovation project, we were given a violation from the electrical inspector for marking the circuit breaker supplying the fire alarm system. We listed it on the panel schedule, labeled the panelboard next to the circuit and put two red stickers on the circuit breaker. The inspector made us make a red label with the words “Fire Alarm Circuit” to place directly on the breaker. This was difficult to do for a single-pole, 125V, 20A device. Is that required?
No. The circuit disconnecting means for both nonpower-limited and power-limited fire alarm systems are required in sections 760.41 and 760.121(B) to have red identification, be accessible only to qualified people, and be identified as a “Fire Alarm Circuit.” The circuit breaker must “have red identification,” and the red stickers you applied met that requirement. The identification must not damage the circuit breaker or obscure the manufacturer’s markings. The required text/title is not required to be on the circuit breaker itself.
Bonding of modular steel structures
Our contractor was called to hook up a triple-wide modular classroom. Each section had a 150A, single-phase panel installed. We installed a 600A meter base with three 150A fused service disconnects on the exterior. The modular classroom is made of steel beams and has the 3-inch-wide metal straps that are welded to it on 5-foot centers. The steel floor beams were all tied together with steel cross-bracing. The modular classroom was tied down to the ground every 4 feet using 4-foot-long tie-down anchors. The manufacturer had installed a 6 AWG ground between each section to tie all the steel together. The 600A service conductors were parallel 350 kcmil copper. Per 250.66, the grounding electrode conductor is a 2/0 copper conductor. We installed a 2/0 from the meter base to the steel beams in each section and then a 6 AWG copper to two ground rods. The local inspector turned it down, saying this is not actually building steel. We had to remove the 2/0 copper conductors to each building section. The inspector only permitted the 6 AWG copper to two ground rods and prohibited us from bonding the building steel. I disagree. The modular classroom is 90 feet long. That leaves a lot of steel ungrounded if someone has to work on it. Was our installation correct?
Your installation was correct. It seems that the inspector correctly recognized that the modular building steel did not qualify as a permitted grounding electrode in Section 250.52(A)(2) because there were no structural members in contact with 10 feet of earth or hold-down bolts tied to a concrete-encased electrode. The two ground rods and 6 AWG copper grounding electrode conductor are all that is required for the grounding electrode system.
However, Section 250.104(C) requires bonding of exposed structural metal that is interconnected to form a building frame that is not intentionally grounded or bonded and is likely to become energized. The bonding jumpers from the service equipment enclosure must be sized in accordance with 250.66, and the 2/0 copper conductors you installed to each modular section met NEC requirements. The inspector understood the requirements for the grounding electrode system but missed the bonding requirements in 250.104.