Two phases to house - loss of neutral
in [Repair]
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From: nesesu on 23 Nov 2009 23:13 On Nov 23, 6:40 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 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.
From: terryc on 23 Nov 2009 23:25 On Tue, 24 Nov 2009 11:10:26 +1100, Sylvia Else wrote: > the net result would be a > large overvoltage on one set of appliances. It would be across both sets, but...... > > My electrician says it's not an issue, but I can't see why. 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.
From: William R. Walsh on 23 Nov 2009 23:52 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.)
From: kreed on 24 Nov 2009 01:49 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. 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.
From: scarborofun on 24 Nov 2009 01:59
Allodoxaphobia wrote: > On Tue, 24 Nov 2009 09:28:48 +0800, TonyS 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? >> I had exactly this happening two years ago. >> My supply has 3 phases ... <-snip-> > > Oh?? Really?!?! Yes, why?? |