Jim Dollard has an extensive background in codes and standards. Send questions about the National Electrical Code (NEC) to Jim at firstname.lastname@example.org. Answers are based on the 2020 NEC .
Bonding at the concert
Does Article 525 for carnivals apply to an outdoor festival and concert? Is bonding required between all of the portable structures for food and dining, etc., if there is more than one generator?
Yes. The scope of Article 525 includes portable wiring for carnivals, circuses, fairs and similar functions, including wiring in or on all structures. Generators installed to supply power for these venues are separately derived systems because they do not have a direct connection to a grounded conductor of a service in a manner that a permanently mounted standby generator may have in an emergency, legally required or optional standby system. Section 525.11 requires that where there are multiple services or separately derived systems (generators) that supply portable structures that are separated by less than 12 feet, the equipment grounding conductors of those sources must be bonded together at the portable structures. Where this is required, the bonding jumper installed must be based on the size of the largest overcurrent device supplying the portable structures but, in no case, is it permitted to be smaller than a size 6 AWG copper.
The drawings supplied for a commercial occupancy included multiple branch circuits for signs. They don't contain sign outlets at every entrance, but the plan reviewer is requiring them. Is this an NEC rule?
Yes. Section 600.5(A) requires that at least one outlet for a sign or outline lighting system be installed in an accessible location for each entrance to each tenant space. The required outlets must be supplied by a branch circuit rated at least 20 amps. Sign outlets are only required where pedestrians have access to enter tenant spaces in commercial buildings and occupancies. Where an entrance is not used by the general public but is intended for use by employees or service personnel for deliveries, etc., a sign outlet is not required.
Service equipment replacement
Based on the new rule in 230.71(B), panelboards are no longer permitted to contain two to six service disconnects. How will this rule apply to an existing installation? Several customers have two to four service disconnects with plans to add more as they expand or demand grows. Will the inspector permit adding a service disconnect as long as we don’t exceed six disconnects, based on this new rule for just one disconnect? Why the limitation to one disconnect?
The revision in Section 230.71(B) still permits two to six service disconnects. Panelboards are addressed in 230.71(B)(2) and a main service disconnecting means is now required in each panelboard enclosure. Unfortunately, the committee that developed this revised text did not anticipate additional service disconnects being added to equipment installed under the previous permissive requirement. This issue is not limited to just panelboards because it impacts all existing service supplied enclosures identified in 230.71(B).
Before we move on, we must look at the intent of the revised requirement. The stated purpose of the NEC is the practical safeguarding of people and property from hazards arising from the use of electricity. NFPA 70, the NEC , contains installation requirements and has a sister document that addresses electrically safe work practices, NFPA 70E. The limitation to a single main service disconnect in panelboards and other enclosures is safety-driven. This will allow the installer to open the single main service-disconnecting means, removing voltage from the rest of the panelboard or enclosure, leaving only the line-side terminals of the main disconnect energized.
Together with the expanded requirements for all service equipment to contain barriers to prevent inadvertent contact with uninsulated, ungrounded service busbar or service terminals, this revision enhances safety. It is practical, and the intent is to provide the installer with the capability to create safer working conditions to reduce the likelihood of shock or arc flash. This directly affects all people performing maintenance on the load side of the main disconnect. By removing voltage on the panelboard and providing barriers on the line side terminations, the likelihood of contact with energized conductors or circuit parts is significantly reduced.
There are many factors that contribute to an arc flash hazard. The amount of energy released can be simplified for discussion to just the available fault current and upstream overcurrent protective device (OCPD) clearing time. Service equipment, in any installation, contains the highest available fault current in the system and there is no clearing time and no upstream OCPD to consider. For example, an arc flash risk assessment in accordance with NFPA 70E, using the arc flash PPE category method, requires that the user estimate values of maximum available fault current and maximum OCPD clearing time to meet the provided parameters. Again, there is no clearing time for service-supplied terminals or busbar, and there is no upstream OCPD.
It would be difficult for the AHJ to exercise Section 90.4 and provide you with special permission to add additional service disconnects in existing service equipment. This is because special permission must be in writing, and the AHJ must document how the safety-driven requirement of 230.71(B) is maintained as you add additional service disconnects. This is a problem for both the AHJ and installer. I am aware of ongoing efforts to build a tentative interim amendment to correct this situation quickly. Additionally, all interested parties should be submitting public inputs to address existing service equipment installed under previous editions of the Code that contain two to six service disconnects.
Service drop and service mast
Why does the NEC prohibit the use of a coupling on a service mast when using rigid metal conduit? Many buildings are of such a size that a coupling is necessary to reach the required height for compliance with the clearances in Section 230.24.
The NEC does not prohibit the use of a coupling on rigid metal conduit where a service mast is used as a support. The Code does not permit a service drop or overhead service conductors to be attached to the service mast between a weather-head or the end of a conduit and a coupling where the coupling is located above the last point of securement to the building. The use of a coupling above a building or structure is prohibited. The intent of this requirement is to eliminate stress on a coupling applied by the connected service drop or overhead service conductors that could be significant. Where a coupling is required, it must be below the last point of securement.
UF cable not permitted?
During an electrical inspection for new feeders in a small industrial location, the electrical inspector noted that previously installed UF cable (sized at 1/0 AWG) is not permitted to be installed in a switchboard. While we did not install it, and there was nothing the inspector could do at that point, we wonder why that is a violation?
Section 408.19 requires all conductor insulation used in switchboards to be rated not less than the voltage applied or the voltage of conductors or busbar it may contact. Conductor insulation must also be listed and flame-retardant. See Table 310.4 for information on conductor insulation. Type UF cable is moisture- and heat-resistant but not flame-retardant. Additionally, Table 310.4 lists conductor types XHHW, THW, THHN, TW and many more as flame-retardant.
Service conductors in cinder fill
We need to install service conductors underground, and the engineer is concerned about the soil containing cinder fill. What is cinder fill? The options for wiring methods provided includes NUCC. Is that permitted? We have never used it.
Yes. Section 230.43 contains a list of permitted wiring methods for service entrance conductors rated 1,000V or less and includes nonmetallic underground conduit with conductors (NUCC). Section 354.10 permits NUCC to be installed in cinder fill. It must be noted that, in general, Section 354.12 prohibits NUCC from being installed in a building. An exception permits the conductor—or the cable portion of the assembly, where suitable—to extend within a building for termination purposes. I suggest that you discuss “suitability” with the AHJ before the installation of NUCC. Cinder fill is a byproduct of coal-burning furnaces used as backfill and will destroy metal raceways unless approved corrosion protection is provided.