Bad Buss in residential panel

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  #1  
Old 11-17-05, 09:44 AM
spearodiver
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Question Bad Buss in residential panel

I have two buss bars in my residential panel. The main breaker has 100 amp going to each buss. I had power go out to one buss bar so I changed both 100amp breakers thinking it was a bad main breaker. This did not work, the original bad buss is still not working (all circuits connected to that buss have no power).
I read 120 volts on both poles going into the main breaker when the breaker is off. Only one pole reads 120 volts when I switch the main breaker to the on position. The one pole that reads 120 volts is connected to the "good" buss.
Any ideas on what could be wrong? I was thinking of switching to a 125 amp main; would this make a difference?
 
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  #2  
Old 11-17-05, 10:53 AM
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Originally Posted by spearodiver
I have two buss bars in my residential panel. The main breaker has 100 amp going to each buss. I had power go out to one buss bar so I changed both 100amp breakers thinking it was a bad main breaker. This did not work, the original bad buss is still not working (all circuits connected to that buss have no power).
I read 120 volts on both poles going into the main breaker when the breaker is off. Only one pole reads 120 volts when I switch the main breaker to the on position. The one pole that reads 120 volts is connected to the "good" buss.
Any ideas on what could be wrong?
This part of your post is a little confusing. The problem you describe is often caused by a bad main breaker, but a panel only has one main breaker, not two. What make/model is your breaker panel? Is it a split-bus panel?

Changing a main breaker is a very dangerous job usually best left to a professional. The only safe way to do it is to have the power company pull the meter.

I was thinking of switching to a 125 amp main; would this make a difference?
Absolutely do not do this. You cannot upsize the main breaker without evaluating the entire electrical service to verify it can handle 125A. I say 99% chance it cannot, otherwise they would have installed a 125A to begin with.
 
  #3  
Old 11-17-05, 10:55 AM
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Changing to a different main breaker would be a very bad idea. If it did solve your problem, not only would it prove that the breaker was bad, but it MIGHT create a fire hazard.

I do not follow your tests. Try your testing this way.

Turn off ALL circuit breakers in the panel. Take measurements feeding the main breaker and leaving the main breaker. Take these measurements between the two lines and from each line to ground/neutral. It is very important that all breakers in the panel be turned off.

Feeding the main breaker you should get 120 volts between each line and ground/neutral. You should get 240 volts between the two lines. Leaving the main breaker you should get nothing.

Now turn on only the main breaker and make the same tests. If the main breaker works, you should get the same results. Report back on what you do get, and we'll go from there.
 
  #4  
Old 11-17-05, 01:42 PM
spearodiver
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Thank you in advance for your help. Here’s what I did.
Turned off ALL circuit breakers in the panel. Took measurements feeding the main breaker and leaving the main breaker. Feeding the main breaker I measured 120 volts between each line and ground/neutral. I measured 240 volts between the two lines. Leaving the main breaker got nothing.

I turned on only the main breaker and made the same tests with the same result (120V feeding each line & 120V at each buss bar {past the breaker}).

I took it one step further and slowly began switching on each breaker, measuring the voltage at the buss bar and feeding the main. Once this completed (without a change voltage) everything worked fine for about ten minutes then the voltage to the “bad” buss bar dropped to “0” as well as the feeding line going into the breaker. The other feeder line and buss bar continue to measure 120V.
 
  #5  
Old 11-17-05, 01:46 PM
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What do you mean by "the feeding line going into the breaker"?
 
  #6  
Old 11-17-05, 02:02 PM
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If your not getting any power into a main breaker.

You should call the power company and have them check the lines from the pole to your main panel.
most will do it for free.
 
  #7  
Old 11-17-05, 02:03 PM
spearodiver
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I was trying to use the term you had previously used. This is the metal bar that comes from the meter into the main breaker. There are two, each measured 120 volts. Am I correct in my assumption?
 
  #8  
Old 11-17-05, 02:03 PM
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Your problem is neither with your breaker nor with your bus bars.

Your problem is that there is a weak connection somewhere 'upstream' of your main panel, eg. in the meter, weatherhead, or somewhere else in the feeder wires.

With absolutely no load connected (eg. with the main breaker off or with all of the branch breakers off), enough current leaks through to give you a voltage reading. This might be 'phantom voltage', or it might have a significant amount of current handling capability behind it, but whatever it is, as soon as you apply load the voltage either goes away immediately, or goes away after the bad connection has a chance to heat up.

Call your power company to fix this.

I feel that you should be soundly berated for changing the main breaker in your panel. You we messing with conductors that are energized and un-fused. The shock hazard isn't particularly more than what you see mucking with a lightbulb. But the available fault current is much higher. This means that in the event that you dropped one of the wires against the metal panel, you wouldn't see a small shower of sparks before the breaker tripped. Instead you would see a heavy arc that would continue until something failed, eg. the service conductors to your home literally _burning away_. Frankly the language that I want to use is entirely inappropriate for this forum.

-Jon
 
  #9  
Old 11-17-05, 02:17 PM
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Based on what you have stated, you have a problem with the incoming service. Call the power company NOW. This could be serious.
 
  #10  
Old 11-17-05, 03:10 PM
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Loose Connection ?

Isn't it possible that this is caused by a loose connection at the buss bar? IOW, a screw that isn't thightened down completely which might work when cold but will cut out once it warms up?
 
  #11  
Old 11-17-05, 03:13 PM
spearodiver
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Thank you all for your advice. I’ve called the power company
Jon, consider me Chastised.
 
  #12  
Old 11-17-05, 07:08 PM
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spear: good on the POCO.

Just to answer Joe: The sort of situation that you describe is exactly the sort of problem that I believe is occurring. The only reason that I don't believe the problem is on the bus bar itself, nor with the connection between the breaker and the bus bar, is the evidence that the voltage in the conductor 'upstream' of the circuit breaker went to zero when a load was applied. The break in the circuit is 'upstream' of the metering points where the voltage drops to zero.

-Jon
 
  #13  
Old 11-18-05, 09:45 AM
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Hi Jon,

I agree, but with the following caveat:

I'm unsure if this installation has just a single main service panel with all circuit breakers in it or a main service and a subpanel. If it has a separate subpanel, then the problem could well be where the hot feeds are attached to the buss bars at the subpanel or at the attachment to the Subpanel feeder breaker.

Otherwise I can't see how the described condition can even occur if in fact the main service breaker has been replaced (which as has been pointed out is _extremely_ dangerous ----- service wires are always HOT).

Ahhh!........

I just checked the final tests and quote:

"I took it one step further and slowly began switching on each breaker, measuring the voltage at the buss bar and feeding the main. Once this completed (without a change voltage) everything worked fine for about ten minutes then the voltage to the “bad” buss bar dropped to “0” as well as the feeding line going into the breaker. The other feeder line and buss bar continue to measure 120V."

From this I deduce that one of the main service feeders shows no power and as you mentioned, this indicates an upstream problem that the power company will have to deal with. (assuming of course that I'm reading this right.)
 
  #14  
Old 11-19-05, 04:54 PM
spearodiver
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thanks for the help guys,

it turned out to be a corroded connection up at the power pole. The power co. came and cleaned the connection. Everything works fine now.

Thank again
 
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