Two phases to house - loss of neutral
in [Repair]
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From: Jerry Peters on 24 Nov 2009 15:37 D Yuniskis <not.going.to.be(a)seen.com> wrote: > Sylvia Else wrote: >> Phil Allison wrote: >>> 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. > > Grounding the mains to "plumbing" *was* common in the US many > years ago. Now, I believe, you *must* ground to a metal > rod driven into the earth (8 ft?). Note that if the water > meter was removed, your earth-through-plumbing would fail. You're *supposed* to have a bypass around the meter for just this reason, or the ground connected before the meter. Jerry > >> 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. > > This is how GFCI breakers work -- they watch for current "leaking" > off to ground someplace other than in the "return" conductor.
From: D Yuniskis on 24 Nov 2009 16:59 Jerry Peters wrote: > D Yuniskis <not.going.to.be(a)seen.com> wrote: >> Sylvia Else wrote: >>> Phil Allison wrote: >>>> 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. >> Grounding the mains to "plumbing" *was* common in the US many >> years ago. Now, I believe, you *must* ground to a metal >> rod driven into the earth (8 ft?). Note that if the water >> meter was removed, your earth-through-plumbing would fail. > > You're *supposed* to have a bypass around the meter for just this > reason, or the ground connected before the meter. I haven't checked a *current* CodeBook but I think connections to water pipes have to be within a few feet of the pipe's entry to the building, etc. And the water pipe must have a certain length *in* the soil, etc. Buildings with metal structural members often have the building itself earthed. And, of course, rules change depending on the potential available on each conductor, etc. But, as I said, I think this is all deprecated as you can't *count* on having metal pipes to the water main, etc.
From: Baron on 24 Nov 2009 17:26 Phil Allison wrote: > > "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 Except where plastic is in use. Mine is all plastic and the safety earth is linked to the armouring on the incoming mains feed cable. -- Best Regards: Baron.
From: Baron on 24 Nov 2009 17:36 Meat Plow wrote: > On Tue, 24 Nov 2009 11:10:26 +1100, Sylvia Else > <sylvia(a)not.at.this.address>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. > > Removing the return leg isn't going to cause problems in a properly > wired US home. Don't know about the UK. The lights would go out ! Domestic properties usually have just a 240v single phase feed. Usually you would get a single phase running down one side of the street and another phase running down the other. -- Best Regards: Baron.
From: whit3rd on 24 Nov 2009 18:19
On Nov 23, 5:38 pm, D Yuniskis <not.going.to...(a)seen.com> wrote: > Grounding the mains to "plumbing" *was* common in the US many > years ago. Now, I believe, you *must* ground to a metal > rod driven into the earth (8 ft?). Just to be clear, my copy of the US National Electric Code clearly requires (section 250-80) plumbing to be bonded to the electrical service ground, it just doesn't allow the buried water piping to substitute for a ground rod or similar to-the-soil connection. The ground wire from the interior water pipe grounds the pipes, not the electric wiring. |