AC unit triping breaker

samfox · 08-30-2010, 09:13 PM

Have not seen anything on this topic, my system is a 3ton, build is 1994, now the unit is tripping the C/B at the service panel. The C/B is a 40amp and the wiring from the service panel to the outside disconnect is 10/2, the amp pull on start up is is 25.7 just above the minimum. My main question is with a 40amp circuit should the wiring from the service panel be 8/2?? OH BTW, the wire sometimes gets warm and the distance from panel to outside is 20ft or so.

Thanks in advance!!

nap · 08-30-2010, 09:34 PM

with an AC, there is NEC code that allows what would appear to be an undersized wire for a given breaker. It is to allow the AC unit to start and not trip the breaker. That added draw is only for a short time and should not cause any overheating of the conductors.

there are usually 2 ratings given on an AC; the minimum circuit ampacity and the max OCPD (breaker size). You can size the wire to the minimum ampacity as long as the OCPD is no larger than the stated max OCPD.

If your startup current is only 26 amps and the breaker is tripping, I would look to a bad breaker. If you are getting warm wires, I would check all connections to be sure there isn't a loose connection.

samfox · 08-31-2010, 06:35 AM

All connection points are tight, next step is to change the breaker, seems weird that the breaker started tripping after 10 years in the house.

Thanks!!

**beenthere** · 09-01-2010, 04:54 AM

10-2 is fine for a 3 ton unit, specially at only 20' of wire run.

The 40 amp breaker may have been installed because of starting problems in the past, or when they first installed it

Not uncommon for this to start happening after a unit has been in for 5, 10, or 15 years.

Does your compressor have a hard start kit on it? Might need one.

samfox · 09-01-2010, 06:54 AM

What is a hard start kit?? Getting quotes for a new Trane system, XL15i 3t and the works.

**beenthere** · 09-01-2010, 05:20 PM

It gives the compressor a boost when it starts.

The 15i is a good unit, one of Trane's better ones. Get the VS blower with it. Should be able to qualify for the tax credit then.

samfox · 09-01-2010, 06:39 PM

Oh, ok that makes sense!! VS is a must and part of the package.