Editor’s note: Jim Dollard is our new Code FAQs columnist. While he has big shoes to fill after Charlie Trout’s retirement, he has an extensive background in codes and standards. He also has a new email address for you to send in your questions: firstname.lastname@example.org.
If you have a question about the National Electrical Code (NEC), Jim will help you solve it. Answers are based on the 2014 NEC.
Reliability of service
We are in the design phase for a commercial occupancy, and the customer is questioning the need for an alternate source of power for the fire pump. The building owner went to the township, and they agreed that the utility-supplied service is reliable. We have never been able to get the electric utility to go on record as reliable. How do we move forward in compliance with the NEC?
The general rule in 695.3 is for a reliable source of power. The NEC requirements for fire pumps are driven by NFPA 20, which has purview over the performance of the fire pump installation. Utilities will not typically go on the record as being a reliable source for fire pumps for many reasons, including weather, equipment failure or accidents that can create power outages. Annex A in NFPA 20 2013 provides valuable information for the installer and inspector on this issue and states, “The determination of the reliability of a service is left up to the discretion of the authority having jurisdiction.” The annex material also includes characteristics according to NFPA 20 of what constitutes a reliable supply:
• No shutdowns of four or more hours in the last year
• No routine outages
• Overhead conductors outside the protected facility do not supply the normal source of power.
• Disconnects for the reliable source installed in accordance with the NEC
The determination of reliability is the responsibility of the authority having jurisdiction (AHJ), not the electrical contractor. Discuss this at length with the electrical inspector. If the AHJ recognizes the service as reliable, have them put it in writing.
Lockable disconnect for transformer installation
I was just red-tagged by the electrical inspector for not providing a locking means for circuit breakers supplying transformers. This is a typical tenant space in a commercial building. The building has a bus duct riser on the north end to distribute power at 277/480 volts (V). We installed transformers on the north and south end of the floors to supply general power at 120/208V. The inspector said the transformers in the north electrical closets were compliant because the circuit breaker for the transformer primary was just a few feet away. However, he said the circuit breakers supplying the transformer primaries in the south closets had to be lockable on all eight floors. I have circuit breaker lockout devices that screw onto the breakers, but the panel doors will not close. What should I do?
The inspector is correct. This requirement was added to the NEC in 2011. The industry has always provided a disconnecting means for transformers, but prior to 2011, there was no requirement. Section 450.14 is clear that the required disconnect can be in sight of the transformer or in a remote location. The transformers in the north electrical closets are in compliance because the disconnects meet the Article 100 definition of “in sight from.” The transformers in the south electrical closets are remote from the disconnect supplying the primary, and the disconnect (circuit breaker, in this case) must be lockable in accordance with 110.25. Therefore, those circuit breakers must be capable of being locked in the open position, and the provisions for locking shall remain in place with or without the lock installed. The devices you mentioned are meant for lockout/tagout and are not intended to remain in place. All circuit breaker manufacturers have circuit breakers available with a permanent locking means and accessory devices that go onto other circuit breakers that will remain in place, provide a means to lock in the open position and allow the panel covers to close. While the inspector may not have told you, 450.14 also requires that, where the primary disconnect is remote from the transformer, the disconnect location must be marked on the transformer.
Working space and personnel doors
I am in the middle of a discussion with an owner and architect about personnel doors and the NEC. On this project, I have a 1,200-ampere (A), 120/208V feeder supplying a switchboard in an electrical room fed from the basement. There are multiple smaller panelboards in the electrical room. The working space required in 110.26(A)(1) for this switchboard is 3 feet. There is a double personnel door 16 feet from the working space that leads into a foyer-type area with access to the freight elevator and another personnel door. The second personnel door is 21 feet from the working space. I told them that both doors have to open in the direction of egress, but they claim that only the first door is required. Am I right?
You are correct. 110.26(C)(3) requires all personnel doors intended for entrance to and egress from the switchboard fed at 1,200A, within 25 feet of the nearest edge of the working space, to open in the direction of egress and to be equipped with listed panic hardware. This requirement is necessary to provide installer/maintenance technicians with the ability to quickly exit the area if an arc flash incident were to occur. The threshold for personnel doors has been reduced in the 2014 NEC to 800A. While the electrical contractor is not typically involved with the installation of personnel doors, it is imperative to inform the building owner or general contractor of the NEC requirements to prevent problems during the final electrical inspection.
Disconnects need labels?
I installed two 200A fused disconnects in an electrical closet on the first floor per the contract drawings to supply panelboards on the second and third floors. The inspector wrote me up for not labeling the two disconnects. We made labels right away, and the job was closed out, but I am still confused. We labeled the panelboards with the location of the supply as required in 408.4(B). I agree it is a good idea to label the disconnects and usually do, but where is the requirement to label the two disconnects on the first floor?
The labeling is a general requirement and is found in 110.22. All disconnecting means must be legibly marked to indicate its purpose, unless they are located and arranged so the purpose is evident. This means that, if there is a disconnect a few feet from an appliance or motor, the marking is not required because the equipment supplied is easily seen and understood. The marking is required to be sufficient and durable, but there is no further information or requirement for a label. This means that, in many cases, you can simply write on the disconnect with a Sharpie to identify the equipment supplied.
SER cable installed underground?
I am installing a new garage that will be a stand-alone structure behind my home. To get power to the garage, I will run PVC conduit underground, emerging just outside of the house and the garage. Can I use SER cable installed in the underground conduit? We use it on building exteriors, and it is rated for wet locations, so it just makes sense to use it in PVC conduit underground.
SER cable is not permitted underground with or without a raceway. See 338.12(A)(2) in the NEC. Type USE cable is listed for direct burial and can be installed underground in this installation. The jacket on Type SER cable is not designed for the stress of being installed underground; the jacket on USE is significantly stronger. Any cable installed in conduit underground will be subject to complete submersion for extended periods of time. SER cable contains an uninsulated aluminum concentric conductor. A tear in the jacket of the SER will cause the cable to fill with water and could cause the aluminum concentric conductor to fail.