# Neutral failure!

C

#### CLT

Jan 1, 1970
0
We have a 3 phase sistem with 380 V betwen phases and 220v phase to
neutral. An electrician was doing a repairation and he just disconect
a neutral wire from a cabinet and conect it a few minutes later and
in that time 3 computers were destroyed, even one of them started to
burn. After that we measure the volts and with tne neutral wire
connected we have 220v betwen phase and neutral and wen we disconect
the neutral we have 500v betwen the same phase and the neutral. Can
any one tell me wat is going on?
Chris.

T

#### Teddy Rubberford

Jan 1, 1970
0
CLT said:
We have a 3 phase sistem with 380 V betwen phases and 220v phase to
neutral. An electrician was doing a repairation and he just disconect
a neutral wire from a cabinet and conect it a few minutes later and
in that time 3 computers were destroyed, even one of them started to
burn. After that we measure the volts and with tne neutral wire
connected we have 220v betwen phase and neutral and wen we disconect
the neutral we have 500v betwen the same phase and the neutral. Can
any one tell me wat is going on?
Chris.

Fizzle

R

#### Roy Q.T.

Jan 1, 1970
0
Chris there is a earlier Ground to Neutral Post here about a diagram
that might shed some light on your query.

R

#### Roy Q.T.

Jan 1, 1970
0
The Post is in alt.eng.~>compliance

M

#### Mr Bungle

Jan 1, 1970
0
CLT said:
We have a 3 phase sistem with 380 V betwen phases and 220v phase to
neutral. An electrician was doing a repairation and he just disconect
a neutral wire from a cabinet and conect it a few minutes later and
in that time 3 computers were destroyed, even one of them started to
burn. After that we measure the volts and with tne neutral wire
connected we have 220v betwen phase and neutral and wen we disconect
the neutral we have 500v betwen the same phase and the neutral. Can
any one tell me wat is going on?
Chris.

Only a moron works on electricity without turning the computers off first.
If you don't know what is going on, hire a real electrician to do it.
ever hear of neutral current? is your 3 phase really balanced?

P

#### Palindrâ˜»me

Jan 1, 1970
0
CLT said:
We have a 3 phase sistem with 380 V betwen phases and 220v phase to
neutral. An electrician was doing a repairation and he just disconect
a neutral wire from a cabinet and conect it a few minutes later and
in that time 3 computers were destroyed, even one of them started to
burn. After that we measure the volts and with tne neutral wire
connected we have 220v betwen phase and neutral and wen we disconect
the neutral we have 500v betwen the same phase and the neutral. Can
any one tell me wat is going on?

That was no electrician - although some people should be grateful that
he wasn't calling himself a brain surgeon.

To illustrate the effect of what he did, take two dissimilar elastic
bands, join the ends together and bang a nail through the join into a
handy bit of wood. Now stretch and relax each band or combination of
them. Each acts independently, yes? So you can REALLY load, or pull on
one band, without affecting the other.

Now remove the nail. When you pull on one band, the join moves and the
thin band really stretches whilst the thick band hardly stretches at all.

He pulled the nail out. The join point moved and the voltage of the
lightly loaded bit (the thin band) went way up whilst the voltage across
the heavily loaded bit (the thick band) went way down. Unfortunately,
the computers were on the lightly loaded bit.

The analogy is far from exact, but you maybe get the idea.

Sue the company, report it to your standards authority, write letters to
your senator or whatever you do when you are really p**ed off in your
Country. Never mind blowing a few computers - the guy could easily have
burnt the place down and/or killed people.

N

#### nospam

Jan 1, 1970
0
CLT said:
We have a 3 phase sistem with 380 V betwen phases and 220v phase to
neutral. An electrician was doing a repairation and he just disconect
a neutral wire from a cabinet and conect it a few minutes later and
in that time 3 computers were destroyed, even one of them started to
burn. After that we measure the volts and with tne neutral wire
connected we have 220v betwen phase and neutral and wen we disconect
the neutral we have 500v betwen the same phase and the neutral. Can
any one tell me wat is going on?
Chris.

This stupid idiot could have got someone electrocuted.

P

#### Paul Hovnanian P.E.

Jan 1, 1970
0
| He pulled the nail out. The join point moved and the voltage of the
| lightly loaded bit (the thin band) went way up whilst the voltage across
| the heavily loaded bit (the thick band) went way down. Unfortunately,
| the computers were on the lightly loaded bit.

Worse. The computers are switching power supplies, most likely, and
these tend to be designed for the 100 to 240 volt range. That means
they are switching on for a shorter time at 220 volts. During the time
they are switched off, they are essentially zero load. If only computers
are on one phase, then they will get hit with between 330 and 381 volts,
depending on the balance of the other 2 phases.

Why he was getting 500 volts I don't know. But reactive loads could be
doing that.

Some capacitance in the power supplies' input circuitry may have
interacted with the system's source reactive impedance and resulted in
higher than normal voltages. Possibly at higher harmonics than the
system fundamental frequency as well. When you combine non-linear loads
with unusual RLC circuits, weird things can happen.

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