Hi Everyone,

I had an electrician out a couple months ago to install a new breaker box. Just recently, my air conditioner stopped working and I had an A/C guy out who diagnosed the issue as a burnt out compressor. He said that the compressor was supposed to only have 40 watts(?) and the fuse that it was connected to was delivering 50. Is this the electrician's responsibility for not checking that the fuse was compatible with my air conditioning unit?

Thanks for the advice,
Adam

Good Afternoon:
I can explain this briefly:
The manufacturers nameplate on the HVAC CU has a minimum and maximum amperage listed for that specific model.

The maximum overcurrent (fuse or circuit breaker) is not to be exceeded. Also note that some units specify 'fuses only'.

More than likely, when your panel was changed, the electrician installed new circuit breakers sized to match the existing ones in the old panel.

You mention 'fuse'; but do not mention the circuit breaker that feeds the circuit from the panel.

I was going to lock this thread, but I will leave it up for a while.

Oversized overcurrent doesn't burn out motors and overcurrent protection doesn't protect against overload. Overcurrent protection on a motor (or compressor) protects the wires if there is a failure on the circuit. The overcurrent will trip if the motor is locked but the motor has to be locked first.

I call bs on the oversized overcurrent burning out the motor. I say the locked compressor tripped the breaker. It's the A/C guy's fault.

The A/C was not working first. So that's when we called the A/C guy. We already had the A/C before the breaker box was installed. The A/C guy didn't do anything, he just ruled out all the other things and found a dead compressor.

That's quite a smart AC guy who knows what took out that compressor. He must have a BS degree. I had a guy BS my aunt that way once. He very eloquently defended his BS actions while he refunded her $$$.
Joe

The solution was to replace the compressor so the compressor must have been the only problem.

If the A/C guy had to replace something else and the compressor, there might be a chance a smaller breaker could have saved the compressor if the "something else" might have caused the compressor to stall. If the something else just caused the compressor to overload, its internal overload protection should have handled that. Breakers don't protect against overload.

The A/C guy said the reason the compressor failed is that the breaker was too big, I have to wonder what motivated that. I don't think that idea will fly.

Sometimes compressors fail.

Still the breaker should be properly sized to protect the conductors. You might be able to stick the electrician with that cost. He relied on the guy before him to properly size the breaker. Maybe you can get the original installer to pay for the breaker.

Oh, and about the title to the thread "new breaker box blew out my a/c", that sounds really ... uninformed. The "who pays?" part makes it sound wilful.

Hi there,
Did the A/C guy actually state HOW the compressor was faulty?
Usually, the guy would need to put a megohm meter on it to check the winding resistances to ground and the actual winding resistances themselves, did he provide you with any test results after coming to that conclusion?

It isn't unusual for compressors to fail because of a voltage spike, no CB or fuse will ever protect against something like that, I've seen this happen quite a few times
You didn't state how old the A/C unit was in your OP?

I would find it pretty tenuous to blame an A/C unit failing because of a panel upgrade.

The A/C tech has to blame someone, the compressor has overloads, the fuses or circuit breaker is just for short circuit protection.

The A/C was manufactured in 2006. It has a diagnostic module which I also thought should have protected against overload. We have a Home Warranty and the A/C guy said he had to report to the Home Warranty Company about the oversized fuse. How can I prove to them that it's not due to the oversized fuse?

Thanks,
Uninformed

Maybe the installing electrician and the guy who upgraded the panel will help.

At a certain point someone is going to tell you the compressor was already going bad and the larger breaker was not the problem. It may have allowed it to sit there are run at the overload temperature a little longer than it might because of the compressor problem but the breaker is to protect the wire, not the compressor. The compressor would not have sat at locked rotor and operated the overload if there was nothing wrong with it.

My bet, a bad capacitor. I just had that with mine and the AC tech (neighbor) showed up with one in his pocket.

Somewhere close to the A/C unit should be a disconnect.

It is usually not part of the electrician's job, as a part of the panel change out, to check what size fuses are in it, or determine the proper size fuses.

The new breaker box has nothing to do with the A/C condenser failure.

Home warranties will look for any excuse not to pay. I think he has found one that in no way caused the problem, but it is an excuse to cause them not to pay.
The 50 amp breaker is in no way the cause of the compressor failure.

External fuses and circuit breakers,like those in a house's panelboard, have never been intended to generally prevent equipment from failing. Of course there will be some situations where the branch circuit device also acts as the motor protection, but then different sizing rules come into play.

If branch circuit protective devices, were intended to keep compressors from failing, we would not have verbiage in the code like NEC 2005 440.2 which allows for "greater than the marked rated-load current'.

The maximum protective device value from an equipment manufacturer may not have been sized to prevent a failure. The equipment often contains a compressor and a fan or two, so the branch device must inherently be larger than one chosen just for any of the individual components.

Regardless, if the manufacturer's instructions were not followed, pursue a warranty claim may be difficult.

I would not expect an electrician to investigate the correctness of protective device sizing, if the contract was 'replacement of existing'. However, I would expect the owner to be notified of common code compliance issues such as 110.3, 110.9, 110.14, and 240.4(D) which may become apparent during any replacement.

OK, I still wonder what the nameplate on the CU says, and is/was there a fused disconnect.

I see oversize fuses in discos with correct cbs in the panel; I see oversized cbs, and correct fuses in the disco, and I see non-fused discos with the proper cb in the panel.

All of the above are compliant, as long as it matches the mfg label.

Exactly. And very few installers understand this. One more I will add is the disconnect directly tapped from the load side of the main service with with properly sized fuses at the disco, and a code compliant tap in the service panel. I recently had a home inspector tell a HO this was so dangerous it should be de-energized immediately because the #8 THWN's could start a fire (in the conduit) from getting 125 amps pushed thru them.

Remember who you are talking about: Home Inspectors.