Two phases to house - loss of neutral

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.

"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".

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

See last para on same page.

..... Phil

"kreed"

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

..... Phil

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.

Oh?? Really?!?!

**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

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

"*within* a premises". The neutral *is* "earthed" right outside the home, typically. The Code goes to great lengths telling you exactly *how* to earth the mains at the service entrance.

However, this ignores the fact that most residential wiring is grandfathered into "acceptance". Previously, homes *were* grounded through their "water main" (e.g., my parents home has ground at the water meter).

So, you can encounter all sorts of different situations here in the US (I've even worked on homes with knob & tube wiring!)

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)

Wow, why all the hostility? A "personal gripe"?

Can I suggest that if you don't want to see posts by a particular person, you simply add his/her name to your "kill file" (or whatever Microsoft Outlook Express 6.00.2900.2180 uses for that feature)?

Speaking solely for myself -- but, perhaps, reflecting the experiences of many "fellow countrymen" -- I think most Americans have very little exposure to "other cultures/societies/power distribution systems/etc :> " owing, perhaps, to the large size of our country and its relative homogeneity. I find it interesting to hear how things are done "elsewhere" and, especially, *why*.

("Driving on the PARKWAY and parking in the DRIVEWAY...") ;-)

l and earth

Rubbish. In most of Canada, it is manditory that the neutral be bonded to earth at only ONE point, the service entrance switch enclosure. From that point an earth conductor is connected to 2 ground rods and to any metallic piping system(s). Neutral failure is a not uncommon problem especially with overhead aluminum 'triplex' service drops. A seagull deficates on the bare aluminum neutral and it soon rots off leaving an open neutral condition. Ground rod to earth resistances of 5 ohms are not uncommon, so a 10A unbalance between 'phases' could give a 50V offset of the neutral.

Neil S.

mains

All new construction [last 30 years] around here uses iron mains with rubber sealed joints and plastic service pipe into all homes, so there is NO bond from the house to the main. The Gas main is plastic, as are the service drops. So, the only earth connection is the rather 'iffy' pair of 8' ground rods usually in the rain shadow of the roof overhang.

Neil S.

It would be across both sets, but......

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.

Trouble is, if Phil were to killfile everyone he abuses, he wouldn't actually see any posts.

Sylvia.

So I guess it's "nothing personal"! ;-)

Hi!

(speaking from a 110V perspective as I'm in the US where power is delivered as 2x110 volt hot leads with one neutral)

The voltage between the two fluctuates wildly, that's what. The more heavily loaded of the two will have a voltage drop while the lightly loaded one goes up.

CRT computer monitors get the jitters even when things are relatively normal. I don't know why this is. Damage can occur to devices when they get nailed with high voltage.

It won't be a huge issue up to a point for simple devices, or those with autoranging power supplies that may try to compensate. Everything else will suffer--motors, transformer type power supplies, etc...and your electrican

*should* know that. A fire could start depending upon how badly something reacts to the over or under voltage.

William (had it happen here some years ago - one TV and a few surge protectors got burnt. Curiously, the TV was not completely dead afterwards, just temperamental about turning on when warm.)

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.

Copper or the old cast iron pipes would provide an excellent Earth, and excellent soil electrical contact due to the enormous surface area of the water main in contact with the soil over distance

Mine is all copper, all the way back to the water main, so no problems here.

Yes, why??

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.