Why did the house almost burn down? (Central Air wiring)

[BRG25]

A friend of mine had a (friend??) replace the wiring between the fuse panel and disconnect for the compressor and...it burned and almost caught the house on fire. The Air Conditioning was working for a little while.

The guy ran (about 20 feet) of 12/2 to a 20 amp breaker which initially I thought was too small but...

The specs for the compressor indicate:
220 Volt
10.5 Amps RLA
56 Amps LRA
Minimum Circuit Amps: 14.26
Max Fuse 20 Amps

Why the excessive current draw?
Why didn't the breaker trip?
I haven't looked very closely at it yet but could it be hooked up incorrectly with one 110V leg going to ground or something?
Maybe the compressor is bad?

When I saw the burned wire it scared the crap out of me. Anyone have any ideas?

 

[SS MAYFLOAT]

Re: Why did the house almost burn down? (Central Air wiring)

LRA = Locked Rotor Amps,,, if the compressor locked up,,,,theres the reason. If the wire lugs are not torqued properly, resistance will build and heat up the wire also.

Was those specs off just the compressor or the whole condenser unit? Did he have the wire fused/breakered at the main panel? Was it a 20 amp? If so it should have blown. All condenser units that I install, I go one size over on the wire guage. Maybe overkill, but resistance is electrical current that you pay for. I don't like paying for lost current in a conductor. Sorta like trying to jump a car with speaker wire,,,it can't handle the amp draw.

 

[Bigprairie1]

Re: Why did the house almost burn down? (Central Air wiring)

I'm not entirely sure but it looks like that compressor is supposed to be wired with a 3 conductor wire for 220V (two hots and a neutral) not a 12/2 (2 conductor..1 hot, 1 neutral) wire which would be for 120volts.
ie: wired up similar to the stove or dryer...same power at 220volts.
Had it been a 120volt compressor he may not have had too many problems.
Not being an electrician...thats my take on it.
BP

 

[BRG25]

Re: Why did the house almost burn down? (Central Air wiring)

I believe those specs were read off the condenser unit in the back yard. It says it's manufactored for Texas Furnace (probably by someone else). Yes it was connected to a 20 amp double pole breaker that didn't trip (which scares me). He used 12/2 with ground.

 

[bruceb58]

Re: Why did the house almost burn down? (Central Air wiring)

I'm not entirely sure but it looks like that compressor is supposed to be wired with a 3 conductor wire for 220V (two hots and a neutral) not a 12/2 (2 conductor..1 hot, 1 neutral) wire which would be for 120volts.
ie: wired up similar to the stove or dryer...same power at 220volts.
Had it been a 120volt compressor he may not have had too many problems.
Not being an electrician...thats my take on it.
BP

If the compresor is a 220 compressor, there is no need for a neutral.

 

[SS MAYFLOAT]

Re: Why did the house almost burn down? (Central Air wiring)

If the compresor is a 220 compressor, there is no need for a neutral.

True providing that there is not a control circuit dedicated to 120v which is rare in residential equipment. Most residential units only require (that is what I see when I service the equipment) two hots and a ground.

Have you spun the fan blade to see if the fan motor maybe have froze up? If the fan doesn't run, it will cause high head pressure on the compressor. This can cause a serious amp draw greater than the normal RLA. May want to have the breaker checked as it should have tripped before the wire melted.

My wiring is run thru EMT conduit. Lets me sleep at night a bit better. Epsecially after hearing about that incident. This is not the first I have heard/saw about this kinda thing happening.

 

[Mark42]

Re: Why did the house almost burn down? (Central Air wiring)

12-2 is the accepted wire for that compressor in residential application. If the wire burned, the problem is not that the compressor failed, but that the breaker did not do its job and trip. Check that it was connected properly, and more importantly, call around to electical supply houses and see if you can have it tested somewhere. If not, spend the $20 for a new pair of breakers.

And be sure that the two breakers are a matched pair, side by side in the pannel, and the wire was not connected to two breakers that are not a matched pair, otherwise, they may have been the same phase and then the 240 v doesn't work. The matched pair of breakers should have a bar connecting the breaker switches so when one trips, they both trip.

Its a real simple setup, but if the guy who connected the appliance did not know the basics of 240v applications, the wiring could have been done incorreclty.

 

[rwise]

Re: Why did the house almost burn down? (Central Air wiring)

12 awg may be acceptable, but I would have ran 10 awg on a 30 amp 2 pole breaker to the 20 amp fuses at the unit. This will let the compressor start faster and last longer run cheaper, etc. just my 2 cents,,,

 

[Mark42]

Re: Why did the house almost burn down? (Central Air wiring)

12 awg may be acceptable, but I would have ran 10 awg on a 30 amp 2 pole breaker to the 20 amp fuses at the unit. This will let the compressor start faster and last longer run cheaper, etc. just my 2 cents,,,

If I had done the wiring, I would have done it like you did too. For a few dollars more, a much heavier duty service.

 

[joed]

Re: Why did the house almost burn down? (Central Air wiring)

There may have been a problem with the compressor to cause the huge current draw. However there is definitely a problem with the breaker. It should have tripped before the wire burnt up.
What brand and where was it made. There have been recalls on counterfiet SquareD breakers from China.

http://www.diylife.com/2008/05/30/counterfeit-square-d-circuit-breakers-recalled-again/

http://www.mikeholt.com/newsletters.php?action=display&letterID=487

 

[BRG25]

Re: Why did the house almost burn down? (Central Air wiring)

Update: I checked over the wiring carefully last night and here is what I'm going to do. I just got back from the Electrical Supply place and bought 3 lengths of 10AWG THHN (25 feet) that I'm going to run through 1/2 PVC conduit between the A/C compressor disconnect and the fuse panel. I've also bought a new 20 amp double pole breaker just to be safe. When I'm done there will bo no exposed wire anywhere and the guy at the store assured me this would meet code. I'm also going to borrow a clamp-on ammeter from a friend and measure the actual current draw from each 110 leg and make sure it's within the specs on the compressor. If there is a problem, then I will have to get it serviced. I also found where there might have been a screw driven into the romex (which the dumbass ran behind the vinyl siding) which may have caused all of this. I'll let you guys know how I make out. Thanks for all the comments, they were very helpful.

 

[BRG25]

Re: Why did the house almost burn down? (Central Air wiring)

I ran the new wire through conduit last night and everthing works fine. Thanks!