Two phases to house - loss of neutral

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.

Reply to
Sylvia Else
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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.

Reply to
kreed

"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.

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

Reply to
Phil Allison

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.

Reply to
Sylvia Else

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

Reply to
bob urz

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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Reply to
Dave Platt

"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.

..... Phil

Reply to
Phil Allison

**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.

--
Trevor Wilson
www.rageaudio.com.au
Reply to
Trevor Wilson

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.

Reply to
Sylvia Else

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

Sylvia.

Reply to
Sylvia Else

**AFAIK, the US system is fundamentally different to ours.
--
Trevor Wilson
www.rageaudio.com.au
Reply to
Trevor Wilson

"Stupider than Anyone Else Alive "

** 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

Reply to
Phil Allison

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.

Reply to
kreed

"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".

formatting link

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

See last para on same page.

..... Phil

Reply to
Phil Allison

"kreed"

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

..... Phil

Reply to
Phil Allison

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.

Reply to
kreed

"kreed"

** 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

Reply to
Phil Allison

**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.
--
Trevor Wilson
www.rageaudio.com.au
Reply to
Trevor Wilson

Sylvia

Thought one. Get rid of the electrician.

In my experience with loss of neutrals it is the number one cause of electrical equipment/lighting failure.

Bob AZ

Reply to
Bob AZ

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)

Reply to
F Murtz

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