main breaker in house blowing

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There are so many computers and air purifiers and television equipment hooked up It's surprising my breakers aren't blowing all the time but...
why would the main breaker blow? Seems like the individual breakers would go first. A new AC compressor was just installed and there is something weird because one of the other breakers for "lights" or something stops the AC when it is tripped. The actual AC breakers trip the AC too.
Tia, : -)
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AKA gray asphalt wrote:

It's quite possible the total load is now greater than the panel capacity even though no individual circuit is overloaded.
If the breaker that you mention that stops the AC does something other than the inside air handler, you definitely have a problem.
Sounds like time for an electrician for some diagnostics and maybe the AC guys back to figure out whether there's something amiss w/ the wiring there...
--
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When the new compressor was installed, who had their hands inside the breaker box? The HVAC contractor? "Handyman"? Your brother in law?
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wrote:

Is it possible that the *control* for the A/C is on a lighting branch circuit?
It is possible, especially if you have a lot of breakers, that if the A/C goes on it might be pulling only 30A on a 40A breaker but the cumulative load of everything in the house would be over 150A or whatever your main breaker is...
nate
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N8N wrote:

Hardly. Any central A/C would require 240 and 30A+ and I've never seen that kind of a lighting circuit in a residence. Unless, of course, some _real_ doofus mixed stuff all up and has multiple wires connected to a breaker or some other really, really weird stuff. But, even then, any lighting circuit would normally be only 15A or 20A max, not enough to keep from tripping...

That's certainly possible, and I'm guessing the new A/C was the straw that the camel wasn't happy to see...
I'm also guessing there's something else not right and OP needs a pro to evaluate what's what...
--
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Had a problem that was similar to yours. Took amp. all OK . Problem was a bad main Breaker. Never thought it could happen,but it did.
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Bad main breaker is what the guys who installed the compressor are saying. Is it a difficult or dangerous thing to change? The breaker has pigtails the need to be unscrewed and it isn't clear how to shut off power between the main breaker and the feed. It doesn't seem right that 'standing or a board' would take care of it, insulation wise, as one guy told me.
It seems like replacing the main breaker might be cheaper and have a good chance of success instead of calling an electrical expert out to test the lines.
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You don't need to test the lines, but an ammeter will tell you if the main is tripping prematurely. They do go bad, but it's certainly not the first thing I'd be looking at, and definitely not guessing at

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On Mon, 18 Jun 2007 14:04:24 -0700, AKA gray asphalt wrote:

You need an electrician.
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or a knowqledgable person with a clamp on ampmeter.
if the main breaker needs replaced someone must pull the meter to do it safely.....
no biggie if you know how,
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On Mon, 18 Jun 2007 22:47:27 +0000, snipped-for-privacy@aol.com wrote:

Knowledgeable person = electrician or equivalent.

Yes the electric service provider must be notified. Around here they frown upon breaking their seal. Probably holds true with most.

I agree. The OP doesn't know how, he needs to find someone with experience. I had a stint as a commercial A/C installer (electrical) some years back. I know what it takes to be successful and stay alive at the same time :)
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well I like working on electrcal but am not a electrician, but know how to safely pull a meter.
there are times it must be done, like a fuse breaking off in a fuse box. that happened to a friend, I pulled the meter and notified the power company on monday, fuse broke off saturday morning...
power company said they didnt care provided they were notified.
might be a bad main breaker or more likely a unbalanced load. my neighbor had that problem with christmas lights, he lit up the neighborhood, after a quick check we re balanced his legs and all was well:)
I fix office machines for a living but could of been a electrician, I wierdly enjoy the challenge of snaking lines and thru walls.
this reminds me I had some stuff fall over in the basement and destroy the plastic seal on the water meter. need to call them so they can reseal it......
occasionally do jobs for friends always for free, I like being useful:)
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On Tue, 19 Jun 2007 01:12:34 +0000, snipped-for-privacy@aol.com wrote:

Personally I think the OPs mains breaker is weak if it trips more than once which should be a vary rare occurrence if at all. I did some work with an electrician years ago in my late teens. Learned and retained a lot from that years worth of experience. He did new home installs only so I didn't get any renovation/troubleshooting skills, those came later on in life. Recently I upgraded my girl's service from 60 amp fuses to 100 amp breakers. I'll have to call a friend to do the room by room rewire, I'm getting too old for that crap :)
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The "lights" breaker shouldn't affect a central AC system, unless it's a main breaker for a sub section of your panel, and the AC breakers are located in that sub section. If your service is too small for the loads in it, the main will trip. you need to get someone with an ammeter and take readings while switching on the circuits

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May be an unbalanced load, one side is overloaded more than the other side of the line, tripping the breaker.

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That's just the sort of thing five minutes with an ammeter would determine

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Sounds like you guys kind of agree. It not apparent to me, though, why there is any case that the regular breakers would not trip before the main. Maybe it's beyond someone so ignorant of the way this kind of thing works.

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On Mon, 18 Jun 2007 23:38:39 -0700, "AKA gray asphalt"

If you have a 200amp main breaker, with 20 20-amp breakers and 15 amps flowing through each of the 20 circuits, that's 300 amps total.
Which breaker will trip?
You can assume everything is working well.
If one breaker is getting weak, it might trip no matter what other breakers do, and no matter what the current.
Why not turn off the AC for a couple days and see if anything trips. Probably not since the AC was just added. Then you will have an idea of where the additional current is being used. Probably the AC is the culprit, but it's probably not using more than it should.
Then you can turn off everythign but the AC and see if the AC by itself trips the main breaker. Probably not, especially since it doesn't trip the individual breaker. but these tests interest me. If you get results that I or the others don't expect, you'll have a big clue as to the problem.
Or you could just take their suggested advice. They have more experience than I and they're probably right.

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AKA gray asphalt wrote:

As a couple of people said, you can install loads that are all smaller than the breaker they are connected to. But when you add up all the loads it can be larger than the main breaker.
Your original post said "a new compressor was just installed" If that means A/C was just installed when there was none before, or a larger A/C was installed, the total electrical load may now exceed the main breaker. This is easy to do with smaller services like 100A or less. In that case you need to increase the service size (relatively costly) or don't run major loads at the same time as the A/C. Major loads include electric drier, electric stove, electric water heater. When an electrician adds a major load they should determine if the existing service is large enough and at least warn you if it is not (it is a code violation if the NEC covers your area).
Else what is "new compressor"?
The furnace normally includes the thermostat and control circuit for the A/C. As several people said, if the furnace is on the lightning circuit you talk about, turning it off will also kill the A/C.
-- bud--

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It would be unlikely that you are pulling enough load to pop your main breaker. I'll bet the breaker went bad. Get an electrician, changing it is not really a DIY job.
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