Alternating Voltage ?

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mgmelec

Member
Location
new jersey
I'm sure i've read about this problem before here on this forum. I went on a service call this morning, to an older home (waterfront property) problem is lights dimming ref, and a/c not working. Open panel, check all connections, check voltage with everything off and read 123v to gnd. on each phase 245v phase to phase, seems ok.

Turn on lights that are reportedly dimm and read 178v phase a to gnd. 69v phase b to gnd. Follow neutral back to p.o.a. there is a small amount of corrosion to the neutral, as it is an aluminum seu cable, in a salt air enviroment but not that bad, cable is 12 years old.

poco was at site night before and said not their problem. They preformed their test when nobody was home, therefore no load on service, home owner turned off main breaker. This is a summer home only used on weekends.

As a side note, house next door is vacant and being renovated , ec installed new service just this week. Could there be something wrong with neighbors new electrical work? as both homes are fed from same x former.

So far i've installed new bugs at p.o.a. and convinced h.o. to change over to copper service entrance cable which i'll do during the week. What else should i be looking for, prior to getting poco back to the house?

Thanks to all who reply. Mark
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
mgmelec said:
Turn on lights that are reportedly dimm and read 178v phase a to gnd. 69v phase b to gnd.
This can only be one thing: a high resistance in the neutral conductor somewhere between the panel and the utility transformer.
 

e57

Senior Member
mgmelec said:
Turn on lights that are reportedly dimm and read 178v phase a to gnd. 69v phase b to gnd. Follow neutral back to p.o.a. there is a small amount of corrosion to the neutral, as it is an aluminum seu cable, in a salt air enviroment but not that bad, cable is 12 years old.

Was this measurement taken at the panel when these subject lights were on, or elsewhere? If at the panel, I would agree with Larry.

The owner shutting off the main was the best thing he could do before this is corrected.

It just may be the corrosion you noticed, or some elsewhere between the point at which that voltage was measured.

First things first, I hope you did not allow these people to continue using this potential fire hazard - as it sounds as if the problem has not been corrected? YET? Did changing the bugs correct this problem?

The symptoms you describe are classic "Lost Neutral" (AKA "high/low voltage event") behavior and the voltages changing are due to changing the load across from phase to phase, as the grounded conductor is kind of floating in terms of it's reference to the other two voltages due to the other.

IMPO, testing this situation with the household loads is quite a bit of liability. It's best to shut off the (main, or sub) panels affected. Then either test the resistance across the neutral connections, or isolate it by using a disposable load and test for similar changes in voltages - like a high wattage light bulb if you don't see any resistance change across the neutrals. (moving back toward the main) Double check by by-passing the connection with a jumper - the voltage will stabilize. If finally found at the attachment - call the POCO, and do not allow these people to use this before the problem is corrected. Another method is to check amperage on the neutral before and after each neutral connection while under a dummy load.

FYI copper is not immune to this type of thing... But a better material for the environment, provided it is properly terminated.

And to the question of could the neighbors work be responsible - yes and no.... I have come across situations where the neutral connection was dependant on the water ground and neutral bonds of the neighbors house - are they responsible for that NO! But your problem could be anywhere inculding at the pole or transformer connection as it soulds like the area is fairly vacant it might not be noticed by summer renters who could care less.
 
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satcom

Senior Member
What was the condition of the meter socket, in the shore area where they used Al cable, the socket connections don't last long.
 

mgmelec

Member
Location
new jersey
voltage reading was done at the panel, changing bugs did not help the situation. H.O. is not spending the weekend down the shore as planned.

meter pan is in good shape the service was updated in 95 and passed inspection.

my plan for now is to replace al. seu with copper and re test with dissposable load as e57 suggested.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I wouldn't replace anything until I find the cause.

Test for voltage imbalance under load at every point the neutral is available (panel, meter load side, meter line side, service drop/lateral, utility transformer) until you find the point where the imbalance disappears.

Then, a redundant voltage test across this point (like an open fuse) should show the "missing" voltage.

The last time I found the same symptoms, the problem ended up being the neutral connection inside the pad-mounted utility transformer.
 

Joe R

Member
Does the panel in ? have a main breaker, that has gone bad, did u pull out the breakers and check for damage to buss bars sounds like u have a bad hot phase, was meter pulled and the meter jaws checked for corrosin.
 

mdshunk

Senior Member
Location
Right here.
Joe R said:
Does the panel in ? have a main breaker, that has gone bad, did u pull out the breakers and check for damage to buss bars sounds like u have a bad hot phase, was meter pulled and the meter jaws checked for corrosin.
That's the procedure for a low leg or legs, but he's measured higher than nominal voltage on one leg. That's only a neutral problem that can do that. The only thing a person needs to do is find out where.
 

Joe R

Member
mdshunk said:
That's the procedure for a low leg or legs, but he's measured higher than nominal voltage on one leg. That's only a neutral problem that can do that. The only thing a person needs to do is find out where.
If he has corrosion on the nuetral that would be the place to start, i forgot to add that to my posts. But I would still check all the items I listed along with the ones u listed and as u stated ,not replace anything until he has found the problem point.
 

busman

Senior Member
Location
Northern Virginia
Occupation
Master Electrician / Electrical Engineer
It's not safe to assume that the PoCo did not load test the service just because the main breaker was off. They have a tool called a beast (super-beast or mega-beast) that puts about a 40-60 amp load on the service with alligator clips on the meter socket and has voltmeters to measure the imbalance if the neutral is not well connected.

Mark
 

mdshunk

Senior Member
Location
Right here.
busman said:
They have a tool called a beast (super-beast or mega-beast) that puts about a 40-60 amp load on the service with alligator clips on the meter socket and has voltmeters to measure the imbalance if the neutral is not well connected.
Some electrical contractors own that tool too! :wink:

BestOfBurdentop.jpg


BeastOfBurdenrear.jpg
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
busman said:
It's not safe to assume that the PoCo did not load test the service just because the main breaker was off.
It's also not safe to assume they DO test for voltage under load. On the job I mentioned above, the POCO assured the homeowner that there was no problem, as their voltage readings showed proper voltages.

Naturally, they did this with the two 150a main breakers open. Only after I visited and tested with one of the panels energized, and finding both panels' line terminals affected, did they return and find the open neutral.
 

mdshunk

Senior Member
Location
Right here.
A quick and dirty method for an electrician troubleshooting a suspected loose neutral is to boil a cup of water in the owner's microwave. That will put a pretty decent load on one leg and generally cause the imbalance to declare itself more dramatically. A hair dryer does the trick too, but there's normally not a safe place to lay it and let it run while you do the checks. The Beast of Burden tool basically contains 4 hair dryer elements and a fan inside to load the leg under test.
 

e57

Senior Member
Super cheap - I use a 1000w (2 - 500's) halogen shop light with my "cheater" GFI outlet pigtail. On one phase, then the other. (The bulbs blow less on the high side... best for testing to keep it on the higher phase.) The super or muey macho beast will only test prior to the meter base (I think?????) - often this type of problem will exist in the premisis wiring, sometimes on branch wiring...

Boiling water in the micro lends to you possibly owning a new microwave that you'll never get the pleasure of using IMO.
 

e57

Senior Member
mgmelec said:
voltage reading was done at the panel, changing bugs did not help the situation. H.O. is not spending the weekend down the shore as planned.

meter pan is in good shape the service was updated in 95 and passed inspection.

my plan for now is to replace al. seu with copper and re test with disposable load as e57 suggested.

The meter pan being inspected twelve years ago means nothing but it passed an inspection twelve years ago.... Rot can happen in less than a quarter of that time on copper or Al. The SE being AL means nothing other than its AL... And I too will say not to replace anything unnecessarly, as the SE may not be the problem! Find the problem and correct it first before making any improvements out of solely the opinion of material. At this point you need to determine POCO side or yours, and if on your side, where?
 

mdshunk

Senior Member
Location
Right here.
e57 said:
The super or muey macho beast will only test prior to the meter base (I think?????) - often this type of problem will exist in the premisis wiring, sometimes on branch wiring...
No, it can plug into the meter base, but it comes with it's own "base" that will adapt it to alligator clips so you can use the clips anywhere in the system. Here is a pic of the adaptor base, by itself:

BeastOfBurdenbase.jpg
 

mgmelec

Member
Location
new jersey
the buss bars in panel are clean i did pull out some of the breakers and saw no evidence of over heating.

meter pan is also very clean which is suprising considering it's location.

i'm replacing the alum. wiring due to the corrosion. why leave wire that will eventually fail?
 

e57

Senior Member
Hope you understand what I'm trying to say - you might look a little silly if after replacing the AL there is still a problem - especially if you have to say replace the panel they go to and your new copper is now too short... Who knows? It's not unheard of for cables to fail mid-conductor, nor it so common enough to justify doing so on mearly suspicion. It could very well be the problem, but it doesn't sound as if you have isolated it yet? Otherwise it is what consumer advocates call 'unnecessary repair' - even if you consider it 'preventative'. Although there's nothing wrong with selling the HO on preventative stuff after the necessary stuff is out of the way IMProO.

This type of problem can be eleusive, and not totally dependant on corrosion... It could also be a loose lug in a perfectly clean panel, and show no visual evidence of heating at all.

I can remember one where it was a hidden screw holding a lug to the neutral bar was just plain missing. The only reason I found it was I tested voltage across the conductor/lug/bar path. The only reason I did that is because in another situation I have also found a neutral bar that failed mid-way. The material the bar was made of became resistive over time where the terminals were threaded in - why - small cracks that I couldn't see until I got the bar out.
 
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