Two phases to house - loss of neutral
in [Repair]
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From: TonyS on 23 Nov 2009 20:44 D Yuniskis wrote: > Sylvia Else 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?). Note that if the water > meter was removed, your earth-through-plumbing would fail. > > > This is how GFCI breakers work -- they watch for current "leaking" > off to ground someplace other than in the "return" conductor. In this case the GFCI (or RCD in AU) will not trip as the current through the load is the same going in and out. I have RCDs on all 3 phases and none of them tripped. Tony
From: bob urz on 23 Nov 2009 20:53 Phil Allison wrote: > "Stupider than Anyone 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. > > > ** Loss of the neutral conductor in a 3 phase ( or 2 phase) AC supply system > can easily be a DISASTROUS event. > > For example: > > In the live entertainment productions - high powered lighting and sound > systems operate from 3 phase outlets via a hefty 5 pin plug and socket. If, > due to wear and tear or damage to the plug or socket, one of the phases > drops out - that is an annoyance but not a disaster. > > However, if the pin carrying the neutral fails to connect or as is often the > case *disconnects* during a show because of overheating - ALL HELL > BREAKS LOOSE !! > > Typically, some of the lamps will glow very brightly for a second or two and > fail, then other previously dim lamps will follow suit. The AC fuses in > amplifiers will pop instantly and some equipment will be seriously damaged > when the PSU sections are destroyed. It all happens in a few seconds, while > the operators stand there with their mouths open !!! > > > > > .... Phil > > > > I recently had such an event happen at a theater. It was county fair season and the vendor was scrapping the bottom of the barrel for gear. It was an old distro, with a Yamaha 3500 FOH, with an effects racks. About 2 hours before house, everything was working when i heard the system crackling. I looked over at FOH and the lights were flashing. Then smoke started coming out of the effects rack. I ran to the stage to shut off power amps and shut everything down. It was split phase going to FOH. Measured 220 between the hots, and nothing to neutral. Somewhere, the neutral was lost. Checked the connector on stage and changed the plugged slot on the distro. At that point, power came back the way it should. BUT, the effects rack was still smoking due to fried MOV's in the Furman plug strip. And all the Drawmer compressors were DOA. luckily, the Yamaha console was ok. Did the show with a few less toys. bob
From: Dave Platt on 23 Nov 2009 20:55 In article <0083b31e$0$1587$c3e8da3(a)news.astraweb.com>, 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. It's a huge issue. It has happened twice, at my house. In both cases, a squirrel had chewed through the neutral wire (they apparently like to sharpen / exercise their teeth on the rubbery insulation). The symptoms were much as you suggest. Voltage goes wonky, with the voltage being fed to each phase being dependent on the various loads connected to both phases. Voltages at the high-amperage appliances can drop (and this can result in burned-out motors) while voltages on the opposite phase can spike upwards (burning out incandescent lights, damaging other appliances through over-voltage). Worst case would be a heavy load on one phase, and only very light loads on the other phase... the lightly loaded side could jump up to almost double voltage. The oddest symptom we noticed was that when a heavy load switched on (e.g. refrigerator or microwave), room lights would suddenly brighten... just the opposite of what would normally occur. Both times this happened, we noticed the weirdness immediately, called the electric company (PG&E), and they dispatched a service team on a priority basis. The dispatcher told me that they consider *any* sort of "high voltage, low voltage" trouble report to justify an urgent response. She had understood my use of the phrase "open neutral", and I infer that this is a not-terribly-unusual situation for them. After the second time this happened, the PG&E guys decided that our existing pole-drop was not repairable (it had already been spliced at least one). They installed a newer, higher-amperage-rated drop (which might even have had some armoring). The problem hasn't recurred... I'm keeping my fingers crossed. -- Dave Platt <dplatt(a)radagast.org> AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads!
From: Jamie on 23 Nov 2009 21:21 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. Please don't go there, there are many experts that really don't know how a GFCI is suppose to work. They thieve on the idea that most units now sold have the arc detection in them and no longer label arc (AGFCI) detection as part of the unit,which does not require a ground path, along with it having the original ground fault system which does require grd path to fault. Those that have installed these units in outlets that have no ground in them, there by, allowing the unaware person to become the ground for it. They think it's ok because just sliding the plug in/out, which causes those nice little arc's to form, from the appliance load, will trip it. And it's obvious, if you don't have a working ground from the receptacle to the appliance, the GFCI isn't going to work very well when the appliance starts generating small little intermitting shorts that would normally trip the device if the ground on the appliance was present to unbalance the common mode device in the GFCI, with out taking out a human in the process. Devices like lamp cords, that normally do not have a grd terminal, are excepted because, the arc detection will actually trip, some times. They have to be rather large ones before they work, and other times, things like high powered radio's going by, will false trip them.. That's what you get for trying to accommodate those that don't want to do it correctly. This problem is also prevalent in AF-breakers and code allows variance to accommodate for life saving equipment and the like. I just love it when the building inspectors use their U-ground testers on GFCI's that have no working ground at the receptacle to find it not tripping when they hit that GF test. It brings a smile to my face.. Have a good day..
From: Phil Allison on 23 Nov 2009 21:08
"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. ...... Phil |