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Code Quandaries

Apr 1, 2000 12:00 PM, By Mike Holt, NEC Consultant

Here are the latest short answers to Code questions posted on our Web site. In our discussion this month, we will cover topics from Secs. 110-3(b), 240-81, 250-6(a), 250-20(d) FPN No. 1, 250-30(a), and 380-3 of the National Electrical Code (NEC).

Three-part question. I am installing a permanent generator at my home for optional standby power. I'll be using a manual double-pole/double-throw switch with a solid neutral as my transfer switch. The feeder to the subpanel from the main and the generator is 4-wire (two hots, neutral, and ground). There is no neutral-to-ground connection in the subpanel.

Q1. Is my generator considered a separately derived system?

A1. No. The NEC requires a neutral-to-ground connection for a separately derived system, such as a generator, at the separately derived system or at the first disconnect after the separately derived system [Sec. 250-30(a)]. Fine Print Note (FPN) No. 1 to Sec. 250-20(d) warns the user that the NEC doesn't consider a separately derived system an alternate AC power source if the neutral from the generator solidly interconnects to a service system neutral.

Q2. Should I make a neutral-to-ground connection at the generator?

A2. No. Since the neutral is not opened in the transfer switch, the neutral from the generator solidly interconnects to a service system neutral. Under this condition, the NEC doesn't consider the generator a separately derived system. Therefore, you must not make a neutral-to-ground connection at the generator or at its disconnect.

If you make a neutral-to-ground connection at the generator, this creates a parallel path for neutral current to flow on the neutral conductor as well as objectionable (neutral) current to flow through the grounding path in violation of Sec. 250-6(a).

Q3. Must I ground the generator to the earth?

A3. No. Since the generator is not a separately derived system, the NEC doesn't require you to ground a generator to a grounding electrode (earth).

Q. Can I install a panelboard with the main breaker upside down, so the "up" position of the handle is the "off" position?

A. No. Secs. 240-81 and 380-3 require "circuit breakers that are operated vertically be installed with the 'up' position of the handle to be the 'on' position."

Q. Is it a Code violation to wrap a stranded No. 12 wire around the post of a wiring device screw?

A. No. The NEC doesn't directly cover this scenario, but Sec. 110-3(b) requires you to install all equipment in accordance with the manufacturer's instructions.

According to wiring device manufacturers, the screws on wiring devices are listed for the termination of either solid, or stranded No. 14 or No. 12 wire.