> [broken neutral] Where I drew the // lines in it (below). The
> 500W load might be other lights, whatever.

>>> 120VAC
>>> o-------x    <----------x
>>>         |               |
>>>    [100W bulb]          |
>>> N       |               |
>>> o--//---x              240VAC
>>>         |               |
>>>     [500W load]         |
>>>         |               |
>>> o-------x    <----------x
>>> 120VAC

I've seen this up close.  Thought the story might amuse you.

I live in southern California.  Four years ago, a storm blew
through with _major_ wind storm damage.  Electric utility people
were totally overwhelmed.

Our neighbor asked me if I knew what might be wrong with their
power.  Certain appliances would only work if they had "enough"
light fixtures turned on, etc.  Weird behavior through-out the
house.  I knew that residential wiring frequently puts one phase
on the light fixtures and the other phase on the wall outlets.
So I suspected the neutral right away.

Breaker panel seemed OK.  Then I looked up.

Electric feed is overhead with steel messenger cable twisted
with two insulated wires.  Each insulated wire is one phase
from the pole mounted transformer.  Steel messenger cable is
used to carry cable tension and for the neutral return.
(Roughly balanced phases, so neutral carries lower current,
so steel is "OK", and they save money on wire.)

Wind had broken the steel messenger cable; insulated phase
cables were still intact.  But things would work if loads
were reasonably well matched on both power phases.  Mismatch
loads on the two phases and things behaved erratically.

I did a temporary repair.  I used rope around the feed cable
bundle tied to the entrance pipe to take up the physical
strain on the cable.  Then I used a car jumper cable to
reconnect the ends of the broken steel messenger wire.
Problem solved.

It was that way for 3 days until the local electrical
utility repair crew could get to it.  Repair guy fixing
it appreciated the kludge.  And I did get my jumper
cable back.

                                                Lee Jones

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