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Generator Grounding and Bonding
Michael J. Johnston
Generators are commonly installed for buildings or structures requiring emergency systems, legally required standby systems, or optional standby power systems. Often the generator is located within the building or structure it serves, although in many designs the generator is located outside the building or structure it supplies. These installations all require feeder conductors from the generators to supply the standby system for the building or structure. When they are located outside the building or structure, the requirements in NEC Article 225—specifically, 225.31 through 225.39—apply. This article reviews these and other basic grounding and bonding requirements for generators.
System Grounding Requirements
Generators are separate power sources and are often required to be grounded as separately derived systems. How the system grounding and bonding connections are made at a generator is determined by the type of transfer equipment specified in the design. There is an important informational note (FPN) following 250.20(D) that describes the relationship between the transfer switch and how the grounding connections should be made for the generator. First, if a transfer switch for a generator includes a switching action in the grounded (usually a neutral) conductor, the generator has to be grounded as a separately derived system in accordance with all applicable requirements in 250.30(A). The reason is because in the normal power mode, the grounded (neutral) conductor is connected to the service grounding electrode; in the standby mode, the grounded (neutral) conductor is switched over to the generator source, which is grounded as a separately derived system. The result is that in either position of the transfer switch, the electrical system remains grounded. If there is no switching action in the grounded (neutral) conductor through the transfer equipment, then the generator system also remains grounded with the transfer switch in either position; normal or standby. The equipment grounding and bonding connections in this case have to meet the requirements in 250.35(B) for permanently installed generators. Read Full Article
Michael Johnston is NECA's Executive Director of Standards and Safety. Mike served on NEC CMP-5 in the 2002, 2005, and 2008 cycles and is currently the chair of CMP-5, representing NECA for the 2011 NEC cycle. An active member of IAEI, the NFPA Electrical Section, Education Section, the UL Electrical Council, and National Safety Council, Mike is a member of the IBEW and has experience as an electrical journeyman wireman, foreman, and project superintendent. |
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Question:
In an electrical room where Section 110.26(C) of the NEC® generally applies, are lever handles on the exit doors considered to be "other devices that open under simple pressure"?
Answer:
The focus of your question is this portion of 110.26(C)(3), Personnel Doors: "Where the entrance has a personnel door(s), the door(s) shall open in the direction of egress and be equipped with panic bars, pressure plates, or other devices that are normally latched but open under simple pressure."This provision was first included in the 2002 edition of the NEC and had been proposed for several previous editions. The substantiation in the proposals and comments makes it abundantly clear that the purpose of the specified hardware is to allow people to open the door under adverse or emergency conditions simply by applying pressure to the hardware with the arms or hands or by leaning against the unlatching mechanism. Adverse conditions include darkness, a room full of smoke due to an arc flash incident, and injury or incapacitation to parts of the body as a result of electrical burns or shock. Panic bars and pressure plates undoubtedly provide the requisite ease of operation. The assessment for approval of "other devices that are normally latched but open under simple pressure" has to be measured against the two specific choices offered in the requirement. If the authority having jurisdiction is satisfied that a particular door unlatching mechanism provides an equivalent or increased level of safety to that offered by a panic bar or pressure plate, he or she has the prerogative assigned by Section 110.2 to approve these other devices.
The panic bars are only required when the equipment is rated 1200 amperes and above and when the door is closer than 25 feet from the nearest edge of the working space.
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