Two phases to house - loss of neutral
in [Repair]
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From: Jasen Betts on 24 Nov 2009 04:21 On 2009-11-24, Sylvia Else <sylvia(a)not.at.this.address> wrote: > Phil Allison wrote: >> 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. 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.
From: Trevor Wilson on 24 Nov 2009 04:36 kreed wrote: > On Nov 24, 12:40 pm, "Phil Allison" <phi...(a)tpg.com.au> 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 > > > 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. -- Trevor Wilson www.rageaudio.com.au
From: David on 24 Nov 2009 08:13 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. 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
From: mike on 24 Nov 2009 09:05 William R. Walsh wrote: > Hi! > > > I've on occasion wondered what would happen if we lost the neutral line. > > (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.) I witnessed potentially expensive neutral problems twice, once while living in Hawaii, and once at my present location in North Carolina. In Hawaii the house I was staying in had to be fumigated and while the workers were tenting the house, they managed to break a partially corroded-thru neutral wire coming from the power pole, which no one noticed. Upon moving back into the house, the recently-new refrigerator died a quick death upon being plugged back in, upon which an electrician was called in, who quickly located the broken neutral. The second time was when I'd been living where I am now, and I'd recently bought a new fridge - after a few months having it working fine I noticed it was sounding like it was struggling to start and at the same time some of the lights would get brighter (I guess they were on the other half of the 240V supply). Not wanting to have to deal with a dead fridge again, I investigated the incoming power panel and found the neutral to be rather lose, so I coated it and the other 2 incoming wires with some Noalox (an anti-aluminum oxidation compound) and tightened 'em all goot-n-tite. That was about 7 years ago, no more problems so far. Mike
From: Jerry Peters on 24 Nov 2009 15:35
In sci.electronics.repair kreed <kenreed1999(a)gmail.com> wrote: > On Nov 24, 10:10 am, Sylvia Else <syl...(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. > > > 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. I actually had the neutral fail (break) a few years back during a winter wind-storm. No deleterious effects. The imbalance (neutral) current was carried by the ground, a copper water pipe that's probably at least 10 feet below gound level and 20 0r so feet long. Jerry |