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Old 01-22-2009, 07:36 PM   #1
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Bad main breaker?


Hi all.

I have a Square D QOC-20M load center. 100 amp. 30+ years old.

Over the last year or so there has been sporadic failures of select breakers.

Seems to be worse in extreme temperatures.

An electrician did a casual look at load center, all 'looked' ok, the hot strips in the back or whatever they are called..

Power co came and checked everything on the outside to the box.

Within the past several weeks, these same key breakers have went off and stayed off.
Additionally, dryer and range circuits have failed completely.

So, no 220/240 volt service at all.

There is no visible scoring, corrosion, etc in the box. So my question is could it be as simple as a bad main breaker?

Would a bad main breaker cause these type of problems?

I am unable to do a 200 amp total upgrade at this time. Nor change out the box itself, as that would require substanial renovation to the wall. I need a temporary fix bad; ie. new main breaker?

I have heard of replacement Square D main breakers of this vintage costing hundreds. Has anyone done a main breaker replacement with this box? Maybe new cheap load center and just use main from it?

Please, any help is appreciated.

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Old 01-22-2009, 07:56 PM   #2
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Bad main breaker?


The part number you posted is the for the cover of the box. But, from what I can find, if you have a 20 space QO 100 A panel that is 30 years old, you will pay dearly for a new main. What you need to do is get some voltage measurements, so we can tell if the main is in fact the culprit. For now, try operating the main several times, this may clear the contacts ad make a good connection again.

Then, if it is determined to be the main, and you can't replace the panel immediately, then you might have to back feed a breaker plugged into the bus temporarily.

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Old 01-23-2009, 04:32 AM   #3
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Bad main breaker?


As 277 stated you have supplied the catalog number for the panel cover. The panel is a QO20M100. Closer to 40 years old, they were replaced by a QO20MW100 in the mid-1970's.

Those main breakers are a Q1-2100TF, and do indeed cost a couple of hundred dollars if you can find one at a wholesale house.

I have several used ones in my shop that worked fine when we removed the old panels for service upgrades. PM me if you want to buy one.
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Old 01-23-2009, 12:28 PM   #4
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Bad main breaker?


Breakers trip for a reason. Before you start thinking you have a breaker problem you should look into what might be causing the breaker or breakers to trip. Will the breakers in question reset?
I would call a licensed electrician asap. You may have issues that will be out of your comfort zone.
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Old 01-23-2009, 12:41 PM   #5
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Bad main breaker?


Quote:
I am unable to do a 200 amp total upgrade at this time. Nor change out the box itself, as that would require substanial renovation to the wall

Not necessarily. The right electrician could leave the box intact and change out the guts in a few hours. Your main may be bad and/or the bus behind the main may be bad. The cost (materials) of a new panel would likely be less than a replacement main breaker if it is not being manufactured anymore.
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Old 01-23-2009, 12:46 PM   #6
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Bad main breaker?


Less than 30mV across closed breaker contacts at rated current means good contacts.
More than 100mV across closed breaker contacts at rated current or less means bad contacts.

Also, see if you can measure the CB housing temp. with your "digital probe". I don't think it should feel warm (>97 ℉, >36 ℃).
I know for a 20A breaker the thermal part of tripping is handled by a 2W resistive wire, and I don't believe that 2W dissipated in a case that big should noticeably heat it, plus some of the 2W is conducted away from the breaker through the copper connections.

Last edited by Yoyizit; 01-23-2009 at 12:54 PM.
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Old 01-24-2009, 11:50 AM   #7
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Bad main breaker?


Quote:
Originally Posted by J. V. View Post
Breakers trip for a reason. Before you start thinking you have a breaker problem you should look into what might be causing the breaker or breakers to trip. Will the breakers in question reset?
I would call a licensed electrician asap. You may have issues that will be out of your comfort zone.
None of the breakers have tripped, ever. Just certain circuits stop working, and the breaker(s) are not tripped.

Kbsparky, I would indeed be intrested in buying one of those from you. Do you know if those are even removable? I am attaching pic of the top of this box, do the ones you have look like this one?
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Old 01-24-2009, 11:59 AM   #8
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Bad main breaker?


Those breaker are removable, however there may be one or more retaining brackets mounted on the pan rails on either side of the breaker.

Sometimes it is easier to remove the entire buss bar assembly and then change the breaker.

Probably the safest way in either case is to have the incoming power disconnected at the source before attempting this repair.

I will leave a message on your profile page for my contact information.

-Ken
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Old 01-24-2009, 12:22 PM   #9
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Bad main breaker?


Very important to understand that I am not an electrician and may not know what I am talking about. Right before I upgraded my electrical panels last week to 200 amps I had a similar problem with certain breakers not working at all and no 220/240 volts service at all for my dryer. What I found was that before my old panel there was another box (main disconnect???) that contain two "large fuses". One of the fuses was bad which allow only one cable going to the main to carry power thus the loss of 120 volts. I replaced both "large fuses" and everything went back to normal. I still did the upgrade a week later though. Again my two cents which are probably not worth a penny.
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Old 01-24-2009, 12:32 PM   #10
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Bad main breaker?


Sounds like you may have a problem with the main disconnect or the wires feeding power to your panel.
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Old 01-24-2009, 02:00 PM   #11
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Bad main breaker?


The only other thing I can see is the meter base just on the other side of the wall outside.

The power co came and said everything was good up to the load center...so I don't know.

I would like to replace the guts of the box- the bars and main breaker, I just don't know if the parts will be available.. it's a really small box.
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Old 01-24-2009, 04:30 PM   #12
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Bad main breaker?


Just replace the entire box if you are going that far. You'll have to get the power cut off to replace the main anyway most likely. Remember main lugs need to be torqued with a torque wrench.. if you get the torque too far off it will cause a fire.
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Old 01-29-2013, 11:16 PM   #13
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Bad main breaker?


I am having the same issue with my 20 space 100A Square D box... I found this based on the part # you had put for the cover, however, your panel looks older than mine. I measured voltage between main neutral and each of the individual hot poles with the breaker removed. Some read right on at 120v and the breakers I was having problems with (same problems you were), read nothing. What did you end up doing? I'm assuming I'm going to have to replace the entire panel with something a little newer.
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Old 11-09-2013, 09:32 AM   #14
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Bad main breaker?


[QUOTE=kbsparky;217680]As 277 stated you have supplied the catalog number for the panel cover. The panel is a QO20M100. Closer to 40 years old, they were replaced by a QO20MW100 in the mid-1970's.

Those main breakers are a Q1-2100TF, and do indeed cost a couple of hundred dollars if you can find one at a wholesale house.

I have several used ones in my shop that worked fine when we removed the old panels for servinto the breaker tce upgrades. PM me if you want to buy one. [/QUOT



Kbsparky,
I am new to this site so please bare with me.....lol.
I have a panel just like this one and need a main breaker as well. Do you still have any available? I recorded amps with my meter for about 30 minutes and when it trips I'm Only seeing 8.5 amps. Only one leg is tripping. The toggle is not moving to the tripped position so you have to shut off and turn back on. that same leg has the main service conductor coming Into the breaker and has a lot of play with the terminal behind the breaker. Possibly a bad connection now to the bus bar. The lug is torqued down tight.
I have recorded amps on all branch cicuits in the panel and non are pushing limits on thier perspective breakers. Only the main breaker is cutting out. I'm not an electrician, but have a moderate amount of experience. Enough to be safe and know when its out of my league. Hopefully that's not the case here! If you still have one please let me know the price. Not sure how to PM on here yet....might need insructions on that as well. Thanks a bunch!!!

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