Phil Allison wrote:
"Stupider than Anyone Else"

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.


** Loss of the neutral conductor in a 3 phase ( or 2 phase) AC supply system
can easily be a DISASTROUS event.

For example:

In the live entertainment productions - high powered lighting and sound
systems operate from 3 phase outlets via a hefty 5 pin plug and socket. If,
due to wear and tear or damage to the plug or socket, one of the phases
drops out - that is an annoyance but not a disaster.

However, if the pin carrying the neutral fails to connect or as is often the
case *disconnects* during a show because of overheating - ALL HELL
BREAKS LOOSE !!

Typically, some of the lamps will glow very brightly for a second or two and
fail, then other previously dim lamps will follow suit. The AC fuses in
amplifiers will pop instantly and some equipment will be seriously damaged
when the PSU sections are destroyed. It all happens in a few seconds, while
the operators stand there with their mouths open !!!




.... Phil




I recently had such an event happen at a theater. It was county fair
season and the vendor was scrapping the bottom of the barrel for gear.
It was an old distro, with a Yamaha 3500 FOH, with an effects racks.

About 2 hours before house, everything was working when i heard the
system crackling. I looked over at FOH and the lights were flashing.
Then smoke started coming out of the effects rack. I ran to the stage
to shut off power amps and shut everything down.

It was split phase going to FOH. Measured 220 between the hots, and
nothing to neutral. Somewhere, the neutral was lost. Checked the
connector on stage and changed the plugged slot on the distro.

At that point, power came back the way it should. BUT, the effects rack
was still smoking due to fried MOV's in the Furman plug strip.
And all the Drawmer compressors were DOA. luckily, the Yamaha console
was ok. Did the show with a few less toys.

bob