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Old 06-24-2009, 08:12 PM   #16
 
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thanks, kbsparky
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Old 06-24-2009, 08:15 PM   #17
 
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last question:

if i don't see 240 coming in - is there any chance that the problem could be with the subpanels's main breaker? should i try replacing it before tackling the line between main and sub

i am asking because i am on my way to home depot to get the multimeter and want to know if i should also pick up a 100amp breaker.
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Old 06-24-2009, 08:19 PM   #18
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If you don't see the 240 into the sub, then the problem is the cable or the breaker inside the main.

This is a good reason to always run pipe instead of cable, imo of course!
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Old 06-24-2009, 09:06 PM   #19
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Most likely you have a bad underground cable.
Sorry Sparky but, unless you have inside information, you diagnosing too early.


Problem could be in several points.

Power comes from the main panel bus, thru the breaker, thru the wires, into the subs main breaker, into the subs bus.

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if i don't see 240 coming in - is there any chance that the problem could be with the subpanels's main breaker? should i try replacing it before tackling the line between main and sub
Follow the path backwards Grasshoppa. Hopefully it's just a bad breaker....but don't count on it.


First, try turning both mains on/off a few times (with the panel cover on please)

Last edited by 220/221; 06-24-2009 at 09:10 PM.
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Old 06-24-2009, 10:16 PM   #20
 
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thanks 220

i picked up an xtra breaker and will diagnose first thing tomorrow morning. i am hoping it's just the breaker!!!
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Old 06-25-2009, 06:54 AM   #21
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Quote:
Originally Posted by treejep View Post
thanks 220

i picked up an xtra breaker and will diagnose first thing tomorrow morning. i am hoping it's just the breaker!!!
Redo the connections at each end of the feeder wires first, as described earlier. Most likely, that is where the problem is.
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Old 06-25-2009, 10:26 AM   #22
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Another idea would be to measure the voltage at the main when the panel is loaded. As much as you can turn on. Sometimes the problem will not reveal itself until you make it do some work. Pull current that is.
Do not buy a new breaker yet. You do not know where the problem lies, yet.
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Old 06-25-2009, 11:01 AM   #23
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Quote:
Originally Posted by treejep View Post
is there any chance that the problem could be with the subpanels's main breaker?
Here's where I'd test, with all the branch circuit breakers at the sub panel in the OFF position (and main breaker ON):

1) Main lugs on the main panel.
2) Terminals of the breaker at the main panel which feeds the sub.
3) Feeder wires at the main panel (the wires themselves after they leave the breaker -- if there's enough stripped back to get a probe in there, of course).
3) Feeder wires at sub panel (the wires themselves just before they hit the lugs).
4) Main lugs at sub panel (touching the probes to the lugs themselves).
5) Bus bar or any connection point immediately after the sub panel breaker.
6) The bus bar, on the opposite end as the main breaker (if accessible).

If you haven't found the problem by then, you have an even weirder issue. But that would determine whether it's a bad breaker, wire, or severe corrosion on terminals.

BTW - Did you try turning the breaker at the main panel that feeds the sub and the sub panel main breaker off and then on? If the breaker is faulty, maybe one side tripped and the lever didn't really move..

Quote:
Originally Posted by J.V.
Another idea would be to measure the voltage at the main when the panel is loaded. As much as you can turn on. Sometimes the problem will not reveal itself until you make it do some work. Pull current that is.
J.V. - Would that not be dangerous if he's got an open ungrounded connection?

Last edited by ScottR; 06-25-2009 at 11:03 AM.
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Old 06-25-2009, 11:01 AM   #24
 
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Redo the connections at each end of the feeder wires first, as described earlier. Most likely, that is where the problem is.
hi househelper-- yes i plan on doing what you suggest after i take voltage readings...

forgot to thank you yesterday.
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Old 06-25-2009, 07:32 PM   #25
 
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1. It turned out that the breaker on the main panel which feeds the sub-panel was the problem. I replaced it with a new breaker, but put it on a different part of the bus because I was having trouble fitting it between the 2 existing breakers.

2. After removing the faulty breaker I noticed that there were burn marks on one of the slots that connects to the bus. Why would this be burned? It was connection to the bus that was going in and out and causing the problems. Why didn't the breaker trip?
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Old 06-25-2009, 07:35 PM   #26
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Never pulled enough current long enough to trip.
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Old 06-25-2009, 09:45 PM   #27
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Quote:
Why would this be burned? It
It is quite common. Big draw+weak connection = arcing which gets progressively worse over time.

The breaker only trips when it draws too much current.
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