On Tue, 28 Feb 2006 02:48:34 GMT, Gunner
wrote:

Buddy of mine is a shop teacher over at the Pasadena school district.
He claims a number of his machine tools wont start..so I had him
checking the voltages on the 3 ph wiring.

two, measured to ground..are 240..the third is 25 volts. When measured
to each other..its 240

Delta I belive..but...25 volts???? He called in the schools
electrician..and he claims they installed new transformers during
Christmas break..wired delta and that 25 volt leg is normal.

110 I can see..but ....wtf???

Gunner

Cornerground Delta I could see, but that would read Zero to ground,
not 25V. And nobody I know of installs cornerground new anymore - too
many people don't realize what they are dealing with, /I'M/ not even
sure how to deal with it, and the potential for mayhem is high with a
leg that "tests dead to ground" but isn't.

The last time I hit cornerground was a 60 year old submersible well
service on a ranch. (If it works, leave it alone.)

There might be an accidental ground (possibly high-resistance) on an
ungrounded Delta that's causing the odd reading.

And that wouldn't cause the machines not to start unless they were
originally wired for a 120/240V Open Delta and has 120V controls from
one leg to neutral. If the controls are on the 'wild leg' line that
has the high-res ground on it... Get in there with an open mind and
a proper VOM - a Wiggy might send mixed messages.

Remember that it ran before the work, and doesn't now, so you need
to look at what they changed - that's a very important clue that you
sometimes don't get when you come in cold. You might have to call the
guys and find out what they did.

And Never discount anything as the cause, no matter how unlikely it
might seem at first - When I say "Nahh, they'd never do anything THAT
stupid!" that's my clue to the path I check first - because they
would, they could, they have, and they may well have again.

Don't discount that they may have screwed up somewhere along the
line and fried a fuse somewhere, and since they didn't test run the
equipment they don't know.

Or they /DO KNOW/ they opened the neutral momentarily or brushed the
wires together and sent a blast of 9,600V or 34.5KV down the 240V
secondary and fried something, but they're keeping their mouths shut -
because if they admit they screwed up, then they (or the company) will
have to pay to fix it.

In the immortal words of John Banner:
SergeantSchultz "I know Nothing, NO-THING!" /SergeantSchultz

-- Bruce --

--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545
Spamtrapped address: Remove the python and the invalid, and use a net.