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-   -   Central A/C trips MAIN on power-up (http://www.diychatroom.com/f17/central-c-trips-main-power-up-24454/)

billq 07-29-2008 08:55 PM

Central A/C trips MAIN on power-up
 
I have 200 Amp service, and just recently started running into this problem. The house has it's original 200 Amp breaker, and was built in '79.

When my wife is running both the clothes washer and electric dryer, and the central A/C kicks on, it trips the main. It has never tripped it's own 50 amp breaker.

When I turn off the A/C, I can have any number of electrical appliances and tools running without issue. I have a 30 amp 220 volt compressor that I can use while she has the washer and drier going without a problem.

The A/C unit is about 7 years old. The tag says it's made by Goodman - Model CK49-1B.

Ideas, anyone?

Thanks!

chris75 07-29-2008 10:52 PM

Quote:

Originally Posted by billq (Post 144194)
I have 200 Amp service, and just recently started running into this problem. The house has it's original 200 Amp breaker, and was built in '79.

When my wife is running both the clothes washer and electric dryer, and the central A/C kicks on, it trips the main. It has never tripped it's own 50 amp breaker.

When I turn off the A/C, I can have any number of electrical appliances and tools running without issue. I have a 30 amp 220 volt compressor that I can use while she has the washer and drier going without a problem.

The A/C unit is about 7 years old. The tag says it's made by Goodman - Model CK49-1B.

Ideas, anyone?

Thanks!

Sounds like its time for a new main breaker...

billq 07-30-2008 05:00 PM

but why just the A/C?
 
I'm not sure I understand why it's only the A/C unit that seems to trip the main. As I mentioned, I have a number of other motor circuits that can be in use simultaneously, but the A/C kicks on and - *bam* - lights out, Loretta.:(

Thanks again for any further thoughts... I'd like to keep replacing the main as a last resort.

-Bill

Yoyizit 07-30-2008 06:52 PM

Quote:

Originally Posted by billq (Post 144194)
I have 200 Amp service,
When my wife is running both the clothes washer and electric dryer, and the central A/C kicks on, it trips the main.
The total of these three things should not be 200A
It has never tripped it's own 50 amp breaker.
Kinda' says it's not the AC.
When I turn off the A/C, I can have any number of electrical appliances and tools running without issue.
I have a 30 amp 220 volt compressor that I can use while she has the washer and drier going without a problem.
They don't reach the 200A breaker's new threshold of less than 200A.
By trying different total loads you might be able to guess at the new threshold.

I can't see how it can be anything else but what Chris75 said.

You could borrow a clamp-on ammeter and check the breaker's new, lower threshold, but there is an arc-flash danger and shock danger when working with this kind of power.

chris75 07-30-2008 07:05 PM

Quote:

Originally Posted by billq (Post 144414)
I'm not sure I understand why it's only the A/C unit that seems to trip the main. As I mentioned, I have a number of other motor circuits that can be in use simultaneously, but the A/C kicks on and - *bam* - lights out, Loretta.:(

Thanks again for any further thoughts... I'd like to keep replacing the main as a last resort.

-Bill


The AC's startup current is enormous, and you main breaker is shot, thats all there is to it.... :)

Yoyizit 07-30-2008 08:07 PM

It may not be only the AC that trips it; if you turn on the AC first, it may now appear that the total current draw of other appliances causes the breaker to trip.

Being careful of the shock danger, you could check the voltage drop across the closed contacts of the main breaker.
More than 100 millivolts across current-carrying contacts = bad contacts, but even if the contacts are good, there might be other things wrong with the breaker. For instance, it's ability to withstand "The AC's startup current."

And I guess there is some remote chance that a loose connection to the main breaker is causing it to trip early by heating the breaker, but I don't have any experience with this happening.

Sorry, Mr. q.

Yoyizit 07-31-2008 01:36 PM

What I learned from this thread, whether I wanted to learn it or not.
 
If you want to give a customer $10 there's no argument.

If you want to charge a customer, you might need to fully explain and fully justify your methods, materials used, troubleshooting strategy, everything.

Knowing yourself that you are an expert doesn't count for much if the customer doesn't know you, which applies to almost everyone on this forum.
Maybe being licensed, bonded and insured doesn't count for that much, either, but it is supposed to count for something.

At some point in your explanation you may have to say that the reason you are doing something is that your instincts tell you to do it. I wouldn't say this except if it's true and as a last resort.

You can also say that you feel it is "good practice" to do something in the way that you propose to do it. The customer will have to take your word for this.

Depending on the customer, I'd spend a max of ~1/2 hour doing this persuasion bit.

And, depending on the customer, if he/she later decides that I'm a good guy after all and calls me back, I may then decline to bid on the job.
If he/she asks me why, I say "instinct" or "I don't wish to say."

'Nuff said.

ToolManTimTaylor 08-01-2008 01:53 PM

To suplement A/C compressor startup I have used a "Hot Start" Kit. It is basicly a capacitor that has enough storage capacity that it suplements the startup charge needed to start compressor and fan and reduced the load on the home panel.
http://www.mobilehomerepair.com/medi...an/B13-543.jpg

They range from 16 bucks like this kit on Ebay http://cgi.ebay.com/A-C-or-Heat-Pump...6.c0.m14.l1318

To 50-60 bucks at a HVAC supply store like Johnstone

Yoyizit 08-01-2008 03:59 PM

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biggles 08-02-2008 09:18 PM

any compressors on AC units draw 10X their tagged amps if you look at te condenser tag it wil show RLA and LRA...this is locked rotor amps that is produced for a split second on compressor starting...your 200 amp breaker can't handle it even for a split second.you also need a service company come in an do a megger test on your windings on that compressor...if this is something new in tripping the breaker your compressor is working itself into burnout .a megger test will confirm that the windings within are breaking down if the service tech comes have him read that LRA with a digital amprobe on a start out at the compressor

billq 08-12-2008 11:35 PM

Thanks very much
 
I certainly appreciate all the help. I do most of the work on my house myself, and I guess I consider myself handier than most of my suburban neighbors (judging by the "handyman" trucks I see parked in the neighborhood:whistling2:)

I've never tackled swapping out a main, before, and will likely call in a pro for this one...

Thanks again for the info, and I'm looking forward to making this my favorite new forum...

-Bill

fw2007 08-14-2008 07:33 PM

Quote:

Originally Posted by chris75 (Post 144219)
Sounds like its time for a new main breaker...

Don't be so quick to blame the main breaker. Circuit breakers don't go bad very often, and don't usually just "wear out".
What I suspect is that you are so close to the 200Amp limit that starting the AC puts you over.
Note: The 200Amp main breaker will trip when either of the legs of your 220V service carry more than 200Amps. Perhaps you have too many 120V appliances on one leg. Moving some of those appliances to the other leg will balance out the current draw, and perhaps put you well below the 200Amps capacity when the AC turns on.

You need a clamp-on ammeter to mearure current in the service panel, and I recommend that you get an electrician to make these measurements for you, unless you are experienced with working on live electrical panels.

Can you list all of the electric appliances you have in the house?
It might be time to upgrade your service!

Also, you should post over in the electrical section. There are a lot of guys over there who are pro electricians.

FW

fw2007 08-14-2008 07:36 PM

Quote:

Originally Posted by Yoyizit (Post 144449)
I can't see how it can be anything else but what Chris75 said.

You could borrow a clamp-on ammeter and check the breaker's new, lower threshold, but there is an arc-flash danger and shock danger when working with this kind of power.

Might be safer to make the clamp-on measurements up at the service head, where you usually have each wire accessible to get the ammeter loop around. I recommend using a wood or fiberglass, not a metal ladder for such work.

FW

billq 08-16-2008 06:40 PM

...and more great info.

I looked a little closer at my breaker panel the other day - let's say I was more than a bit surprised to see a 100 AMP MAIN. :-(

Let's see, a woodshop with a 3 HP dust collector + various woodworking tools running concurrently, an electric dryer, central A/C unit, four servers, four desktop PCs, three tv's.... yeah, I'm thinking a service upgrade is called for.

This is really bad news because I understand the city is requiring service entrance relocation to the side of the house when a permit is pulled for service upgrades :-( :-(

So, what is 100' of 00 copper going for these days? :-(


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