dnoyeB wrote:
asco wrote:
An inspection on our home (7years old) recently revealed that both our
air conditioning units have 40 amp circuit breakers instead of 30 amp
(the unit asks for 30 amps). How big of a deal is this? And if so, is
it an expensive thing to change?

Thanks in advance.


No point in changing. The breakers match the wiring as stated earlier.
Reducing the breaker size wont do anything, but cost you money. IMHO.

What? The unit MOP (Maximum Overcurrent Protection) cannot be
exceeded, period, no exceptions. In a motor circuit the CB provides
the short-circuit and ground-fault protection. The motor overloads are
what protect the wire in a motor/compressor circuit. The wire needs to
be no larger than the MCA (Minimum Circuit Ampacity). For example, on
a condensing unit that has an MCA of 35 amps and an MOP of 60 amps, the
wire size need only be a #8 and the maximum breaker can be up to, but
not exceeding, 60 amps, as permitted by NEC. As you can see, a 60 amp
breaker on a #8 wire is not going to protect against overcurrent.
Again, the compressor overloads are what protect the wire IN THE CASE
of motors and compressors. The only time that the CB provides
short-circuit, ground-fault protection AND overcurrent protection in a
motor/compressor circuit is when it is rated at no more than 125% of
the motor/compressor Full Load Amps.