In sci.electronics.repair kreed wrote:
On Nov 24, 10:10 am, 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.

Any thoughts?

Sylvia.


You are both right and wrong as in the absence of Neutral line, a lot
of the neutral current (imbalance) would probably flow via your earth
stake back to the transformer neutral or to a neighbours neutral via
their earth stake and while its not a perfect situation, imbalance
probably would not be as bad as you might think ?

Of course, if there is a long run through earth (terra firma) back to
the nearest neutral, the soil is really dry, the earth stake is sub-
standard etc etc it might not work very well.





Years and years back I once saw the result of this at a 3 phase
installation at a carnival, we were called out to fix

They would have with them, and take from site to site portable fuse
boxes with a 3 phase plug, going to a box with breakers feeding rows
of power points going to each phase (like in a normal building
installation, but portable). They would plug in all their gear to
these sockets, and plug the 3 phase into the 3 phase sockets provided
at the venues.

Of course, a lot of the carnival workers would probably just plug
things in at random, and who knows what load would be on the end of
each lead. There could also be very large numbers of flashing lights
on one lead too, so the load would be less than perfect, and surely
not anywhere near balanced or stable

One case, the neutral lead broke off. On one phase there was a lot of
damage to computer gear / arcade games (same sort of thing -
switchmode power supplies) etc. Some was just blown fuses, some
worse.
Note, they didn't have the earth and neutral bonded inside the box,
and didn't have a separate earth stake, where in a home fuse box they
would.

2 phase situation like yours would be a similar result, unless the
load was really well balanced, and consisting of mostly NON-switchmode
power supply type devices. The phase with the lowest load would
suffer overvoltage.

This load imbalance and voltage difference would change all the time
as various appliances automatically switch off and on, like fridges,
air cons, electric HWS etc. Light bulbs may blow from overvoltage,
this would also change the balance



Try connecting 12v bulbs of different wattages in series across 24v
and see what happens. The voltage will not be the same across each.
Much the same thing.

I actually had the neutral fail (break) a few years back during a
winter wind-storm. No deleterious effects. The imbalance (neutral)
current was carried by the ground, a copper water pipe that's probably
at least 10 feet below gound level and 20 0r so feet long.

Jerry