Two phases to house - loss of neutral
in [Repair]
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From: Jamie on 23 Nov 2009 21:29 Sylvia Else wrote: > D Yuniskis 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. >> >>> 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. > > > In the scenario I outlined, the currents in the live and neutral > conductors passing through the breakers would remain equal, so they > wouldn't trip. > > What I need is something to detect current through the link between > neutral and ground, which would then disconnect both phases. Of course, > it could trip as the result of a fault with the neigbour's neutral wire, > but I could live with that. > > Sylvia. You need to pass the live and neutral through a common mode transformer. when one leg gets shorted to ground, it unbalances. You wrap another winding in that coil which will then produce some current for you to trigger a protection device. The current will only be present when the common mode becomes unbalanced due to them canceling each other out under normal operation. This will accommodate for both legs. have a good day..
From: Trevor Wilson on 23 Nov 2009 21:15 Sylvia Else 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? **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
From: Sylvia Else on 23 Nov 2009 21:16 Phil Allison wrote: > "Dave Platt" >> Sylvia 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. >> 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. 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.
From: Sylvia Else on 23 Nov 2009 21:18 Trevor Wilson wrote: > Sylvia Else 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? > > **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.
From: Trevor Wilson on 23 Nov 2009 21:22
Sylvia Else wrote: > Trevor Wilson wrote: >> Sylvia Else 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? >> >> **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. **AFAIK, the US system is fundamentally different to ours. -- Trevor Wilson www.rageaudio.com.au |