I just read through the "Deciphering Schematics" article in HP123. With respect to wiring, I think it's great that someone is taking the initiative to bridge the gap that has existed between automotive and the rest of the electrical world. This has been a point of confusion for a lot of people for a long time. I would like to bring up one point for discussion. For DC systems, Home Power selected black as the positive (ungrounded) and white as the negative (grounded) wire color. I've been pondering this color-coding issue for some time and have started using red for the ungrounded conductor and white for the grounded conductor in the DC portion of the system. And here is my reasoning.
In the AC world, the NEC is quite clear on color coding for equipment - grounding conductors - bare or green in some form or combination. For grounded circuit conductors, white or gray in some form is used. With respect to the ungrounded conductors, though, I am not aware of anything in the NEC that specifies color coding so specifically, except that they cannot be green or white. Convention uses black as the ungrounded for 120 VAC, and black and red for the ungrounded for 120/240 VAC. I agree wholeheartedly with continuing the white for the grounded conductor, and bare or green for the grounding. The Code is very clear on those conductors, and this requirement should carry through to the DC world.
However, I prefer red (instead of black) for the DC ungrounded conductor. Red is the traditional automotive ungrounded color. If we switch to black for the ungrounded, we will then have DC systems where the black could represent either the grounded or the ungrounded. If red is kept as the ungrounded color, the only change is black to white for the grounded - less confusing. Also, 120 VAC wiring is going to have a black-white-green wire set. In AC systems, red does not appear until 240 V, in which case there are usually four conductors. So a DC red-white-green conductor set would then be differentiated from the 120 VAC set.
I have one additional point. The DC colors are tied to positive and negative in the article. To stay consistent with NEC, they should be identified with the ungrounded and grounded portions of the DC circuit. In the majority of the DC systems, the negative is the grounded side, but not always.
Jim Norman, ABS Alaska - Anchorage, Alaska
Instructor Carol Weis from Solar Energy International had similar comments in response to "Deciphering Schematics" in HP123, and both of you make some very good points. Referring to conductors as "grounded" or "ungrounded" rather than negative and positive is better usage since these terms are consistent with the NEC.
The only specific requirements that the NEC makes regarding wire color codes is the proper way to identify equipment - grounding conductors and grounded conductors, as you mention above. In terms of the NEC, ungrounded conductors can be any color. In the field, black and red are the most common ungrounded wire identification colors. We feel that either a black or red conductor color for the ungrounded DC conductor is appropriate. Electricians will readily recognize both as ungrounded conductors.
Joe Schwartz • Home Power