Showed up on an electrical service call at a multifamily dwelling where they told me that half of their electrical was out. Called Georgia Power after I discovered that there was 120V to ground on ea. buss of the panel but no 240V between them.
GA Power pulled the panel cover and discovered that voltage was right on the line side of the breaker but one leg was completely dead on the load side of the breaker.
Pulled the breaker and it was fried on one leg and the buss that it connected to was also charred.
Replaced breaker and tipped my hat to the customer…fully expecting that I would not be back.
Got 5 mins down the road (already salivating for a good dinner) and they call me and tell me that all of the power is off.
Upon my return I found the main that I had just replaced was kicked off. Tripped as if there was a short or an overload.
Kicked breaker back on and observed while renter cooked supper and urged their heat pump to return heat to their house. Twenty mins. later I was about to head back to my van when the main cut off again. Sheesh…I am ashamed I left them in the dark (they are college students and very flexible).
Here is how I anticipate troubleshooting. First I will reset the main and measure the amperage on each leg. If significantly different I will plan to check amperage on both Heat Pump as well as Stove.
I will also recheck whether my breaker was set in properly.
I would love annnny other ideas. This is acting more like an overcurrent than a short.
Look forward to the group wisdom!!
I look down my nose at people who dare to look down their nose at people.
Replies
Sounds like you're on track. How many amps is the main breaker? I think you might find a bad resistance coil on the furnace, whatever the problem is it's probably on the previously burned leg.
125a main.... thanks for the clue on the resistance coil
I look down my nose at people who dare to look down their nose at people.
The breaker trips. When you reset it and it immediately trips instantly in a split second - that indicates a short circuit somewhere. If it takes some time to trip, that is indicative of an overload. It sounds like you have an overload.
As for getting 120v from each bus [?] to neutral but no 220v between them, this is wierd. You would only have single phase delivered by Georgia Electric Co.
One of the first principles of trouble-shooting is to inquire as to what was recently added.
Here is an electrical forum which may provide more specialized info:
http://www.elec-toolbox.com/frames.html
=Peter
In beerum veritas.
It's not weird, it's probably just the "A" leg feeding around through a 240v appliance back into the dead "B" bussbar, or vice-versa
Ed
Edited 12/2/2002 11:22:21 PM ET by Ed
I was going to say the same thing, except that would only be true if there was no load on the open leg, or a whopper of a load like a shorted 220v resistance coil. If the furnace is a problem, then its breaker may be stuck "on". Thats why I wonder what the main breaker is rated at. This sounds like an overload, but only on one leg.
I think your right on that Ed.
Another thing to look for is damage to equipment caused by the leg being out. It usually won't hurt a new A/C unit but an older one can get mulched by trying to run on anything substantially less than 240v. Normally it is motor driven equipment that suffers the most but low voltage can cause harm to lighting ballasts as they, over time, repeatedly try to start.
Also look for carbon tracking and damaged busses. tracking is more common with higher voltages, including lightning damage. Buss connections are an any time event. Particularly with GE mains. Usually where they made the connections to the busses at the factory. Cutler Hammer does a better job backing up their factory installed breakers.
Yo Pete - Are you an electrician? You didn't mention a couple of things that jump out at me.......
1) what did you do about the scorched bussbar? Did you repair it somehow?
2) aluminum feeders or copper? Did you remove the damaged ends and re-strip the cable?
3) did you put an ammeter on anything to check the load?
4) After you replaced the breaker did you check the actual voltage with an accurate meter on each leg to ground and then between them while under load? A voltage imbalance or drop could be significant.
5) Hopefully you are doing these things with branch circuits first OFF then ON for comparison
Ed
Ed, Yes I am a State licensed electrician with 20 years experience.
I attempted to recondition the buss by scraping carbon residue off of it. It was scorched but it was not physically deteriorating.
Aluminum feeders. No need to restrip wires etc. since they were not damaged. I did rough up the wires and applied alumalox.
At the time of the initial repair I did not check amperage since it seemed that the only problem was a bad breaker. Checking that this morning is first on my agenda. Actually the very first thing I am going to do is to pull the disconnect on the HVAC and try to power up and see how long power stays on. If power stays on for 30 mins then the problem is in the HVAC. I will then inspect the electrical connections both in the disconnect and in the unit itself.
I will repeat the above exercise on the oven if I am not confident that the problem is in the HVAC. Altho I doubt the problem is there.
Will also check voltages on ea. leg.
To All....
Thanks for your help and consideration, I promise to let you know what the problem was!
I look down my nose at people who dare to look down their nose at people.
Hi Pete -
I've come across the following scenario a number of times:
Older residential service (20+ years), usually 100a, aluminum feeder fed directly into the main breaker, bad deterioration on one leg which can damage /destroy the breaker/ bussbar. When repaired and replaced, there is no more problem.
When this happens, I figure this: original connections were not done quite right or else it just wasn't adequate for a home w/an electric oven, water heater and dryer, etc. Either anti-oxidant wasn't properly used or more likely the lugs weren't properly torqued. So over time one connection deteriorates and starts arcing which also causes it to heat up. Until it blows.
I would recommend that you bring some emery cloth and clean the bussbar with it. Also to check the quality of that connection you can pull the meter, install the new main, switch it to ON position , then see if there is a resistance reading between the line-side of the lug and somewhere on the same-leg bussbar. This would be done with all other (branch-circuit) breakers switched off. If the connection is good there will be no measurable resistance.
Other than those suggestions, your plan sounds good to me.
Ed
Plugged or damaged or deteriorated heat pump expansion valve? Or just clogged filter or condensor?
Checking with HVAC off good idea.
scenario - HP comes on, pressure builds up past normal due to non-open ex valve or lack of airflow, motor overloads, breaker trips.
Edited 12/3/2002 9:58:43 AM ET by JUNKHOUND
OK I promised an update. It is now 4 days after I simply took feed wires off, scuffed them up and applied alumalox. I also dressed the buss bar again. Tightened all connections. It is no longer tripping! Wish I knew which one of the above was the fix. Kind of the smorgasbord approach to troubleshooting. Thanks for all the input
I look down my nose at people who dare to look down their nose at people.