Code Forum

Jul 1, 1999 12:00 PM, By Fred Hartwell, Senior Editor

Portable Standby Systems

Be careful when wiring standby systems from non-permanent sources. They don't fall under Art. 702, and a key safety rule in Art. 230 just disappeared.

As we approach the millennium, many homeowners who are convinced the power grid will fail on Jan. 1, 2000 are busy buying standby generators. If we're lucky, they'll approach qualified persons to make safe arrangements to use them. We hope the inspection community finds enough threads in this article to allow it to make enforcement decisions accordingly.

The EC&M panel's advice. Note the word "advice." The NEC, inadvertently in our view, turned dangerously deficient in the area of mandatory rules we've assumed for generations would prevent hazards to utility line crews. Therefore, this column departs somewhat from its format over the last nine years, where we always told you what the Code required on various issues. This month, we'll tell you what you should do.

Cord-connected generators. Most owners want to be able to move these generators around as they need them for other projects, instead of permanently wiring them. First, review the load. These are optional systems, so the owner decides what loads he wants connected. Size the cord per Sec. 445-5 to either 100% or 115% of rated generator output, and be sure you have overcurrent protection in the house accordingly (if it isn't in the generator), as covered in Sec. 445-4.

Then, avoid the temptation to put a plug on the end of this cord. You have to use a receptacle body, and wire the house connection with a flanged inlet to meet the new requirement for deenergized plug blades in Sec. 410-56(g).

In the house, connect the wire from the flanged inlet to the standby side of a manual transfer switch. Be sure that the switch is suitable for use as service equipment, as covered in Sec. 225-36. If you need to position the transfer switch remote from the point of entry, you'll need a switch near the point of entry that meets the same requirement.

Next, supply the transfer switch with a normal feeder from the house panel, sized and protected per Sec. 215-2(a) and Sec. 215-3. Wire from the transfer switch to a panel containing the circuits the owner wants, and which, per Art. 220, won't impose an overload on the standby system.

This arrangement meets the owners needs, and you can complete the work at a modest cost. Most importantly, your owner won't kill utility line crew personnel by inadvertently backfeeding the service conductors. In addition, with normal power on, you won't end up with energized blades in the flanged inlet.

What about Sec. 702-6? This section doesn't apply for two reasons. First, it doesn't actually require transfer equipment, only that, if installed, it should prevent inadvertent supply interconnections. Second, the scope of Art. 702 excludes portable equipment from coverage!

With Art. 702 out of the picture, what about Art. 230? With no transfer switch per se, the existing line up of circuit breakers and the feed from the flanged inlet become, collectively, the transfer equipment. Former Sec. 230-83, which referred to "transfer equipment, including transfer switches" (clearly suggesting coverage of other equipment than transfer switches) prohibited any possible interconnection of sources. We think interconnection is not only possible, but likely if you only rely on panelboard warnings to untrained owners.

Forgetting about the wider application of that rule, CMP 4 deleted Sec. 230-83 in the 1999 NEC, believing it to govern only the performance of transfer switches, a subject fully addressed in product standards. The 2002 Code should either reinstate Sec. 230-83, or broaden the scope of Art. 702, or both. Until then, inspectors need to apply more general rules, such as Sec. 110-2 requiring approval of all equipment.