Equipment tripping GFCI

Is it permitted to omit GFCI protection for temporary power to equipment that just keeps tripping it? A general contractor asked us to do just that because the painting contractor’s spray equipment (which is old) keeps tripping a GFCI-protected 20A circuit breaker. We replaced the breaker, but it keeps tripping the GFCI. It worked just fine on a non-GFCI-protected circuit. Can we label those receptacle outlets and omit GFCI protection for the period of time they need to use that equipment?

No, the painting contractor’s equipment is defective and should be removed or repaired before use. There is obviously leakage current to ground in values above the threshold for a Class A GFCI device. That equipment use presents a serious potential for shock that may be more than the “let go” threshold. See Section 590.6, which contains requirements for ground-fault protection of personnel. No provisions would allow omitting GFCI protection at 120V, 20A. Additionally, Section 90.4 could not be applied in this case, as there is no alternative method available to ensure that equivalent objectives can be achieved by establishing and maintaining effective safety.

Number of services

Are we permitted to install multiple sets of service conductors to supply three 400A service disconnects in the same location? The engineer designed three parallel 600-kcmil copper service conductors into a wireway with 500-kcmil copper conductors tapped to supply three 400A service disconnects. Is it permissible to take three sets of 500-kcmil copper service conductors from the utility-owned transformer directly into each 400A service disconnecting means?

Yes, see 230.2, which permits (230.40 Exception No. 2) underground sets of conductors, 1/0 AWG and larger, running to the same location and connected together at their supply end, but not connected together at their load end, to be considered to be supplying one service. Section 230.71(B) permits up to six service disconnects, and in general, requires each service disconnecting means to be installed in completely separate enclosures as described in your question. See 230.72(A), which requires the two to six disconnects, permitted in 230.71, to be grouped. Each service disconnect must be marked to indicate the load served. Depending on the size of the disconnecting means (not referenced in your question), Section 110.26(C)(2) will likely apply. See 110.26(C)(2), which requires multiple service disconnecting means installed in accordance with 230.71(B), with a combined ampere rating of 1,200A or more and a combined width over 6 feet, have one entrance to and egress from the required working space at each end of the working space. See also 110.26(C)(2)(a) and (b) for permissive requirements allowing a single entrance to and egress from the required working space.

Support wires above ceiling

Why do we need additional support wires above a lay-in ceiling to support type MC cable? An inspector told us we needed to tie the support wires we installed to the ceiling. What is the difference? Do I need to install support wires for each lighting fixture as well?

The requirement you are referencing (300.11) addresses securing and supporting cable assemblies, raceways and more above suspended ceilings. It is important to note that the number and placement of support wires installed by the ceiling contractor are the minimum required to support only the ceiling, the luminaires and the lay-in tiles. Section 300.11(B) addresses wiring systems installed above suspended ceilings. This permits wires installed in addition to those that support the ceiling grid to be used as the sole support for cable assemblies. 

The use of independent support wires for a cable assembly must be secured at both ends—this is what the inspector was referring to when you were directed to attach the independent support wire to the ceiling grid. These additional wires are not there to support the ceiling; they are there only to support the cable assemblies. Securing them at both ends is required, because if they were not tied in some manner to the ceiling grid, they would just flop around, creating a hazard. Independent support wires are permitted as additional support for luminaires, but are not required. See Section 410.36(B), which requires the framing members of suspended ceiling systems (this is done by the ceiling installer) that will support luminaires be securely fastened to each other and be securely attached to the building structure at appropriate intervals. The NEC requirement for securing the luminaire to the ceiling grid mandates a mechanical means such as bolts, screws or rivets. Listed clips identified for use with the type of ceiling framing members and luminaires are permitted.

Barriers required?

Where a service-rated transfer switch is installed in a dwelling unit, are barriers required like the ones we see in panelboards?

Yes, the general rule in 230.62(A) requires all energized parts in service equipment be enclosed to prevent accidental contact. Any exposed energized conductors or circuit parts must be guarded, as required in 230.62(B), which mandates barriers in all service equipment. The barriers must be placed such that no uninsulated, ungrounded service busbar or service terminal is exposed to inadvertent contact by persons or maintenance equipment while servicing load terminations with the service disconnect in the open position. This requirement applies to all service equipment including, but not limited to, panelboards, circuit breaker enclosures, fused disconnects, service-rated transfer switches and more.

Commissioning and witness test of emergency system

What is required for an emergency system with respect to commissioning and testing the system? Is this something we can do in-house and just provide documentation to the owner?

See Section 700.3 for requirements on testing and maintaining the emergency system. The AHJ must be involved. The AHJ is required to conduct or witness the commissioning of the complete emergency system [700.3(A)] upon installation, and periodically afterward. Periodic testing requirements are typically local requirements and may vary based on the occupancy type. All emergency system equipment must be maintained in accordance with manufacturer instructions and industry standards [700.3(C)]. This requirement falls on the equipment’s owner. Testing the emergency lighting and power systems must be performed under maximum anticipated load conditions [700.3(D)], and a written record must be kept of all tests and maintenance.

Disconnecting means for phase converters

We installed a phase converter in a carpentry shop that was supplied at 240/120V, single-phase, for new three-phase woodworking equipment. The inspector failed us and required a disconnecting means right next to the phase converter. This was not a phase converter with a motor; it was a transformer type. Was the inspector correct?

Yes, the inspector was correct. You installed a phase converter, not a transformer. As defined in Article 100, a phase converter is a device that converts single-phase power to three-phase electric power. A static phase converter has no rotating parts and is sized for a given three-phase load to facilitate operation from a single-phase supply. See Section 455.8, which requires a disconnect to simultaneously open all ungrounded single-phase supply conductors to the phase converter. 

The disconnecting means required in 455.8 must be readily accessible and located in sight from the phase converter. Transformers also require a disconnecting means; see 450.14. However, there is a permissive requirement for transformers allowing the disconnecting means to be located either in sight of the transformer or in a remote location. Where located in a remote location, the disconnecting means must be lockable in the open position in accordance with 110.25, and its location must be field marked on the transformer. The disconnect requirement for phase converters does not permit the required disconnect to be located remotely. 

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