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Two phases to house - loss of neutral

S

Sylvia Else

Jan 1, 1970
0
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.
 
P

Phil Allison

Jan 1, 1970
0
"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 !!!

The MEN system:

In Australia, AC power delivery uses a system called " Multiple Earth
Neutral " - which requires that the neutral conductors in a premises be
connected to the plumbing system at the distribution board (ie power box).
It also requires that an earth stake be installed for the same purpose, but
some older premises may not have this.

Because EVERY premises has MEN installed, the ground itself and underground
metal plumbing act as an alternative neutral, should the supply conductor
feeding a given premises fail. The disastrous event sometimes experienced in
live entertainment systems is hardly possible in domestic or commercial
premises.

So the sparky is right.



..... Phil
 
S

Sylvia Else

Jan 1, 1970
0
Phil said:
"Stupider than Anyone Else"



** 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 !!!

The MEN system:

In Australia, AC power delivery uses a system called " Multiple Earth
Neutral " - which requires that the neutral conductors in a premises be
connected to the plumbing system at the distribution board (ie power box).
It also requires that an earth stake be installed for the same purpose, but
some older premises may not have this.

If as you say, neutral has to be tied to Earth at the premises, then I
can indeed see that the situation might not be so bad.

On the face of it, having significant current flowing from neutral to
Earth would have to indicate a fault. It would be nice for the breakers
to trip in such a situation, but I can't see that they will.

Sylvia.
 
B

bob urz

Jan 1, 1970
0
Phil said:
"Stupider than Anyone Else"



** 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
 
P

Phil Allison

Jan 1, 1970
0
"Dave Platt"
Sylvia Else


It's a huge issue.


** Sylvia lives in Sydney, Australia and is a MASSIVE TROLL.

Nuts of her the post such a COUNTRY SPECIFIC message to a US newsgroup.




...... Phil
 
T

Trevor Wilson

Jan 1, 1970
0
Sylvia said:
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?

**Not an issue, due to the MEN system used in AUSTRALIA. Cross-posting to an
international group will guarantee a bunch of useless comments. Pay
attention to Australian posters only.

Your electrician is correct.
 
S

Sylvia Else

Jan 1, 1970
0
Phil said:
"Dave Platt"


** Sylvia lives in Sydney, Australia and is a MASSIVE TROLL.

Nuts of her the post such a COUNTRY SPECIFIC message to a US newsgroup.

Last time I checked, multiphase power supply was pretty universal, and
the principles to be applied in understanding the consequences of faults
would be the same. Or perhaps you want to argue that the different
voltage in Australia is the deciding factor.

Sylvia.
 
S

Sylvia Else

Jan 1, 1970
0
Trevor said:
**Not an issue, due to the MEN system used in AUSTRALIA. Cross-posting to an
international group will guarantee a bunch of useless comments. Pay
attention to Australian posters only.

Your electrician is correct.

From the replies, the same system applies in the US. But people have
still had problems.

Sylvia.
 
T

Trevor Wilson

Jan 1, 1970
0
Sylvia said:
From the replies, the same system applies in the US. But people have
still had problems.

**AFAIK, the US system is fundamentally different to ours.
 
P

Phil Allison

Jan 1, 1970
0
"Stupider than Anyone Else Alive "
Last time I checked, multiphase power supply was pretty universal, and the
principles to be applied in understanding the consequences of faults would
be the same.


** 100 % WRONG !!!

The question this insane bitch posted IS country SPECIFIC !!!

Cos it was about her house in * Sydney, Australia *.

See Trevor Wilson's reply.



..... Phil
 
P

Phil Allison

Jan 1, 1970
0
"Stupider than Anyone Else on Earth "
From the replies, the same system applies in the US.


** Wot INSANE FUCKING CRAPOLOGY !!

The only relevant reply from the US so far indicates the DIRECT OPPOSITE .

Piss off - TROLLING BITCH.



...... Phil
 
P

Phil Allison

Jan 1, 1970
0
"Trevor Wilson"
**AFAIK, the US system is fundamentally different to ours.


** In the US and Canada - it is NOT permitted to link neutral and earth
or plumbing within a premises.

See here under the heading "Regulations".

http://en.wikipedia.org/wiki/Earthing_system

The MEN system used here in Australia seems to be unique.

See last para on same page.


...... Phil
 
P

Phil Allison

Jan 1, 1970
0
"kreed"
From what I can gather, pretty much every home in the US has a 120v -
0 - 120v system where the 2x 120v's are 180 degrees out of phase.
Between the 2 phases 240v is available for stoves, air conditioners
etc.

In Australia, most separate homes have a straight single phase 240v
supply, its not common for there to be 2,3 separate phases to the
average house. Therefore the scenario Sylvia mentions is less likely
to occur, as not many people have this multi phase system.

The exception here could be blocks of flats, if the main neutral to
the building fails, and there isn't a good earth, the imbalance could
be a risk.


** There is always a good "earth" available - courtesy of the water mains
in the street being linked to neutral at every premises.


...... Phil
 
P

Phil Allison

Jan 1, 1970
0
"kreed"
The scenario you mention with live entertainment is particularly bad,
as when you think about it, unlike a fixed installation you can't bond
the earth and neutral in these portable 3 phase to 240v outlet mains
boxes. If you did, it would trip any earth leakage breakers upstream
- if these are fitted.


To make matters worse, in live entertainment, the major loads are
almost all amplifiers, and lighting. None of these are stable loads
(amplifiers are changing their load current draw constantly with the
music and lights are being dimmed, flashed often in large groups. )


Therefore if the neutral lead fails, there is no bonding to earth to
back it up, unlike a residence, and with the inherent instabilty of
the load balance, massive damage is guaranteed.


** Current good practice for professional lighting dimmers is to use 800
volt rated triacs (so over-voltage will not trigger them) and 400 volt
rated primary transformers on each phase with a circuit on the secondaries
that detects any voltage imbalance.

Soon as a significant voltage imbalance is detected, all drive to the triacs
is instantly cancelled and it locks on.

Power amplifiers with iron transformers pretty much protect themselves by
blowing the AC fuse.

SMPSs of all sizes are vulnerable to instant damage or even exploding
electros.


...... Phil
 
T

Trevor Wilson

Jan 1, 1970
0
Phil said:
"Trevor Wilson"



** In the US and Canada - it is NOT permitted to link neutral
and earth or plumbing within a premises.

See here under the heading "Regulations".

http://en.wikipedia.org/wiki/Earthing_system

The MEN system used here in Australia seems to be unique.

See last para on same page.

**Interesting. I'd have thunk that some places in Europe might employ a
similar system. Guess not. Ever since I ran across my first US audio product
with a high value resistor to chassis from (allegedly) Neutral, I realised
that the US system was highly flawed.
 
F

F Murtz

Jan 1, 1970
0
Sylvia said:
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.
not a neutral problem but.
I can remember an old lady complaining that every time she turned the
hot water tap the lights came on half brilliance.and sure enough they did.
she had three phase and an instantaneous three phase water heater.

one phase had gone and the heater caused the dead phase to be live in
series with element.(the water flow closes the heater circuit)
 
T

terryc

Jan 1, 1970
0
the net result would be a
large overvoltage on one set of appliances.

It would be across both sets, but......
My electrician says it's not an issue, but I can't see why.

The neutral is actually grounded to the earth for such a case; hence MEN
(Multiple Earth Neutral), so the neutral would actually travel through
the ground to your neighbours earth stake and back into the neutral phase
there.

If the USA Godzilla remake is to be believed, all your earth worms will
come to the surface as an indicator, (or is that only for correct DC
connections?).

If you are worried about such an event happening, dump a bucket of wter
on your earth stake quarterly and encourage your neighbours to do the
same.
 
J

Jasen Betts

Jan 1, 1970
0
If as you say, neutral has to be tied to Earth at the premises, then I
can indeed see that the situation might not be so bad.

On the face of it, having significant current flowing from neutral to
Earth would have to indicate a fault. It would be nice for the breakers
to trip in such a situation, but I can't see that they will.

Having the breakers trip because a faulty neutral in an neighbours
house (which would cause his neutral current to flow through his earth and
your earth (etc) to the common neutral) could be an annoyance.

bye.
 
T

Trevor Wilson

Jan 1, 1970
0
kreed said:
That is true in a lot of cases, however I have noticed with a lot of
newer houses, (in QLD anyway) they are using some kind of either black
or grey pvc or poly pipe for home water mains. To make it worse, it
looks to me to be "crimped" together at joins, sometimes with what
look like soft metal rings but not always.

**It's going to be a lot more popular too. The stuff is around half the
price of copper pipes, is very easy to handle and use.
 
D

David

Jan 1, 1970
0
Phil said:
The MEN system:

In Australia, AC power delivery uses a system called " Multiple Earth
Neutral " - which requires that the neutral conductors in a premises be
connected to the plumbing system at the distribution board (ie power box).
It also requires that an earth stake be installed for the same purpose, but
some older premises may not have this.

Actually, the Neutral conductors are *NOT* connected to the plumbing
system. The Neutral conductor is connected by the MEN link to the main
earthing conductor, which is connected to the appropriate earth
electrode. AS/NZS 3000 then requires that conductive pipe work be
equipotentially bonded to the main earth conductor or earth terminal or
bar (NOT to the neutral).

David
 
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