With so many alternate (standby) power systems being installed in premises wiring systems today, it is appropriate to visit a few National Electrical Code requirements regarding signage for emergency systems, legally required standby systems and optional standby systems. While standby power sources are often generators, other power sources could be installed that conform to the specific rules in articles 700, 701 or 702.
The specific power sources required and permitted for either an emergency standby system or a legally required standby system are identified in Part III of articles 700 and 701. The power sources for an optional standby system (covered by Article 702) can be any power source (such as generators, batteries or others) as indicated in Section 702.1. The power source for an optional standby system must be permanently installed in its entirety.
Sections 700.7, 701.7 and 702.7 have important requirements for warning signage to address significant safety concerns. Subdivisions (A) and (B) in each section must be applied to each situation—it’s not an either/or option here. Let’s take a closer look at each of these rules and the safety-driven reasons behind them.
In accordance with 700.7(A), 701.7(A) and 702.7(A), the first required sign must indicate the type and location of each power source on the premises, other than the service. The sign must be placed at the service equipment, according to the exact rule, but that location is too broad. For the greatest effectiveness, the sign should be located at the service disconnecting means. The term service equipment, by definition, includes many types of equipment and locations on such equipment. (This is a great opportunity for a Code change, but that’s a subject for another day.)
It is best to locate this sign at the operating handle of the service disconnecting means to warn the operator that another standby power source is going to be present after the service disconnect is opened. This is essential for warning first responders and emergency personnel about other power source(s). Often the reason for operating the service disconnect in an emergency is to remove all power, thus reducing possibilities of electric shock and electrocution.
This sign might read: “WARNING: A standby power generator is connected to this premises wiring system and is located in the basement southeast.” It is important to clarify that this is just one example; the NEC does not indicate the exact text to be used, because many different scenarios must be covered by this universal requirement. Each specific facility and property will warrant unique language on the sign that accomplishes the performance objectives anticipated by this requirement.
In accordance with sections 700.7(B), 701.7(B) and 702.7(B), a second required warning sign must be installed at the normal power source equipment, which is often the service equipment, to address potential shock hazards directly related to the grounding electrode connection of the alternate power source. The warning sign is necessary where the removal of a grounding or bonding connection in the normal source equipment, such as at the grounding bus within the service equipment enclosure, also interrupts the grounding electrode connection for the standby power source.
The NEC requires this exact warning text to be used: “WARNING: Shock hazard exists if grounding electrode conductor or bonding jumper connection in this equipment is removed while the alternate source(s) is energized.”
This warning is necessary usually as a result of the type of transfer equipment used in the standby power system. If the transfer equipment includes a switching action in the grounded conductor (often the neutral) connected to the alternate power source, such as a generator, then the alternate power source should have its own grounding electrode that is connected with the transfer equipment in either normal or standby position. In this case, the generator or alternate power source is grounded as a separately derived system in accordance with Section 250.30(A).
If the transfer equipment does not include a switching action in the grounded conductor (often the neutral), then whether the transfer equipment is in the normal mode or standby mode, the grounded conductor (usually the neutral) connected to the alternate power source is depending on the grounding electrode connection in the normal source equipment, such as the service equipment. Therefore, a shock hazard exists for those performing work in the equipment during a power failure mode. The warning sign (label) must also meet the requirements in Section 110.21(B), which includes being permanently affixed to the source or service equipment and being durable for the environment where it is installed.