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Date:	Sun, 9 Mar 2003 22:18:53 PST8
From:	Steve Carter <scarter@vcnet.com >
Reply-To:	scoug-help@scoug.com
To:	scoug-help@scoug.com
Subject:	SCOUG-Help: Re: Help with UPS...?

Content Type: text/plain

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On 3/9/03, Peter Skye wrote, in part:

>> The standard color scheme for 12V DC is
>> red = positive
>> and
>> black = negative
>
>Is this a true standard or did you mean "typical"?

I don't believe there is anything like the National Electrical Code
(NEC) for AC electrical wiring that requires black and red, but
it is indeed a standard. Anyone _could_ deviate from a standard,
but is most uncommon to do so.

>> Negative ground systems are most common
>
>I'm not much of a car mechanic, but didn't they used to ground (to the
>chassis) the positive side of some cars' electrical systems? I seem to
>remember (from 40 years ago) being told never to jumpstart two cars
>while their bumpers were touching because some cars grounded one side
>and some grounded the other side and you were likely to make more than
>just the starters jump. I know this has no bearing on UPS systems but
>I'm curious. >- Peter

George Boyd is, of course, right!

It is British cars that had a positive ground while American cars
have been negative ground since before I was born (~WWII). But I think
HAD is the operative word here. I don't think they are still positive
ground today. I know someone who owns a modern Jaguar. I could
call him (in Sweden) and ask. ;-)

BTW. the phone company is still positive ground and will be forever.
That's why their voltage is called -48V. There are some very good
galvanic corrosion reasons (which I don't understand) for this choice.
It is not-at-all arbitrary or backwards on their part.

--Steve

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