Phases and legs?


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Old 03-09-14, 06:13 AM
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Phases and legs?

Ok after the problems I have been having (see "do I need new service") I think The problem is one spot on the bus bar. The #3 spot seems to be bad. I do have an electrician coming back Mon or Tues, but I would like to understand. I switched #5 CB with #3CB and now the intermittent outage is on #5 in the #3 spot (3 on 5 is fine now). I have something in every room that will blink or shut off if the power is interrupted. I am trying to understand phases and legs. Would I be correct that the top row is A phase second row (across) B then A then B and so forth. So A is one leg/phase, B is the second leg/phase. So would it also be correct that if #3/5(when 3 and 5 are switched) is the bad spot, if it was the leg then #4 should also have the intermittent problem? If it is just a bad spot, how does that happen on just one spot? It is now known that I have no rust problem or water problem in my square D breaker panel. Thanks, I am just trying to make sense of what is happening so if it happens again I will know. Thanks for your time.
 
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Old 03-09-14, 06:31 AM
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A typical panel will alternate ABAB from top to bottom. There are two connection points on the bus, one left, one right. If only #3 is bad #4 can work just fine even though it is on the same leg of the panel.
 
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Old 03-09-14, 07:08 AM
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Ok yes, I understand that but if the leg was bad then 4 (or anything else on B) would also have the intermittent outage problem correct? I ask because my electrician thinks it could be a leg (or the weather head) and I am not seeing it, and I think it is a bad spot. Would a bad spot be caused by years of use and thus causing the connection tab to become misshapen ?
 
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Old 03-09-14, 07:38 AM
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Ok yes, I understand that but if the leg was bad then 4 (or anything else on B) would also have the intermittent outage problem correct?
That's correct. In your other thread you said you didn't have the intermittent problem on any other circuits regardless of the leg they were on. That is how I deduced the problem is at the one position, I think it was #3.

my electrician thinks it could be a leg (or the weather head) and I am not seeing it
By all means, have him check it out because he will be there and we cannot see what he sees. That being said, the B leg would have problems on all circuits it feeds if this is the case.
 
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Old 03-09-14, 07:48 AM
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Thanks for the reply, now I won't sound stupid when I am talking to him. I still don't understand how just one spot can go bad though.
 
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Old 03-09-14, 10:17 AM
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A loose connection can arc. Over an extended period it will get worse and can lead to bus and/or breaker damage.
 
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Old 03-09-14, 11:08 AM
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Thanks for all the help, now I understand.
 
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Old 03-09-14, 12:06 PM
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While you have the breaker unsnapped out of the bad slot, inspect the fin behind that slot and also the clip on the underside of the breaker. If either of these are burned or deformed, you won't be able to re-use them. A bad slot can be left empty and covered up from the outside.

Avoid snapping a breaker that was on a bad slot into a different slot particularly if the clip underneath is bad. It could over a short period of time damage the fin in the new slot due to arcing if it is loose.
 
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Old 03-09-14, 01:06 PM
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Thanks Allan good advice. It is a brand new square D breaker that I put in Tues. There is nothing on the tab part no rust, no burn marks nothing looks good just doesn't work right any more.
 
 

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