In article ,
Sylvia Else wrote:

I have to phases of power supply to my house - so three power lines, two
phases plus neutral.

I've on occasion wondered what would happen if we lost the neutral line.
It seems to me that we'd then have the voltage between the two phases
across two sets of appliances, one set attached to one phase, and the
other set attached to the other phase, with the two sets in series as a
result of their common connection to the neutral wire. Since the two
sets are unlikely to represent equal loads, the net result would be a
large overvoltage on one set of appliances.

My electrician says it's not an issue, but I can't see why.

It's a huge issue.

It has happened twice, at my house. In both cases, a squirrel had
chewed through the neutral wire (they apparently like to sharpen /
exercise their teeth on the rubbery insulation).

The symptoms were much as you suggest. Voltage goes wonky, with the
voltage being fed to each phase being dependent on the various loads
connected to both phases. Voltages at the high-amperage appliances
can drop (and this can result in burned-out motors) while voltages on
the opposite phase can spike upwards (burning out incandescent lights,
damaging other appliances through over-voltage). Worst case would be
a heavy load on one phase, and only very light loads on the other
phase... the lightly loaded side could jump up to almost double
voltage.

The oddest symptom we noticed was that when a heavy load switched on
(e.g. refrigerator or microwave), room lights would suddenly
brighten... just the opposite of what would normally occur.

Both times this happened, we noticed the weirdness immediately, called
the electric company (PG&E), and they dispatched a service team on a
priority basis.

The dispatcher told me that they consider *any* sort of "high voltage,
low voltage" trouble report to justify an urgent response. She had
understood my use of the phrase "open neutral", and I infer that this
is a not-terribly-unusual situation for them.

After the second time this happened, the PG&E guys decided that our
existing pole-drop was not repairable (it had already been spliced at
least one). They installed a newer, higher-amperage-rated drop (which
might even have had some armoring). The problem hasn't recurred...
I'm keeping my fingers crossed.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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