Kevin Ricks wrote:

David Nebenzahl wrote:
Was called to look at an electrical problem. I looked at the panel that
seemed to be the culprit, determined it to be a 240 v. 3-phase
(probably) panel with a few breakers that were causing problems. One
side of one of the power lugs was completely burned off, and the breaker
on the other lug was making sizzling sounds. Turned it off pronto.

The panel has 3 big fat wires coming into it. Measured between all of
them: 240 volts between all 3, which makes me think it's 3-phase (3
legs, equal voltage).

But here's the weird thing: there are some 120-volt outlets apparently
attached to this panel that function correctly. When I turned some of
the breakers off, the outlets lost power, so I assume that they're
directly powered from this panel.

How can this be? How do you get 120 volts from 240? (No big fat
transformers visible anywhere.) What am I missing here?

In case anyone's wondering, no, I don't mess with 3-phase power or any
other kind of heavy-duty commercial/industrial stuff. My customer's
reaction was "I'll call a licensed electrician", which would have been
my advice. It appears the entire panel needs replaced.

I'm just curious about this situation.



Sounds like its standard 240V panel with an open neutral.
When the neutral is open you get full voltage readings on the neutral
from the other leg via any loads that are attached and turned on.
The loads may be turned on but not functioning. ie a filament of the
light will be dark. Since no, or very little, current is flowing then
100% of the voltage is passed through the filament when read with a volt
meter.

Remember there is no voltage drop through a resistor where there is no
current flowing... so with a meter you will measure the same voltage on
both ends of that resistor.

Open neutrals do strange things Some lights will be dim, others very
bright and other will appear to be off depending on what load are
attached to each leg.

Kevin

That's a possibility. The presence of any three pole breakers in the
panel would be a tip off that it's three phase. Either way, with
sizzling breakers and burned off lugs it needs serious attention and
likely replacement.