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.


In case Bud's post isn't clear enough let me explain. There are two
ampacities listed on the nameplate of a motor/compressor unit's name
plate. One is the circuit selection ampacity. This minimum circuit
ampacity is the minimum the circuits conductors must be rated for in
table 310.16 of the US NEC. Section 240.4 which limits 14, 12, and 10
gage conductors to certain overcurrent protection values reads in part
"240.4 Protection of Conductors.
Conductors, other than flexible cords, flexible cables, and fixture
wires, shall be protected against overcurrent in accordance with their
ampacities specified in 310.15, unless otherwise permitted or required
in 240.4(A) through (G).
(D) Small Conductors. Unless specifically permitted in 240.4(E) through
(G), the overcurrent protection shall not exceed 15 amperes for 14 AWG,
20 amperes for 12 AWG, and 30 amperes for 10 AWG copper; or 15 amperes
for 12 AWG and 25 amperes for 10 AWG aluminum and copper-clad aluminum
after any correction factors for ambient temperature and number of
conductors have been applied.
(G) Overcurrent Protection for Specific Conductor Applications.
Overcurrent protection for the specific conductors shall be permitted to
be provided as referenced in Table 240.4(G).

Table 240.4(G) Specific Conductor Applications
Conductor Article Section
Air-conditioning and refrigeration 440,
equipment circuit conductors Parts III, VI

Capacitor circuit conductors 460 460.8(B)and 460.25(A)–(D)
Control and instrumentation 727 727.9
circuit conductors (Type ITC)

Electric welder circuit conductors 630 630.12 and 630.32
Fire alarm system 760 760.23, 760.24, circuit conductors
760.41, and
Chapter 9, Tables 12(A) and 12(B)
Motor-operated appliance 422, Part II
circuit conductors

Motor and motor-control 430, Parts III,
circuit conductors IV, V, VI, VII

Phase converter supply conductors 455 455.7

Remote-control, signaling, 725 725.23, 725.24,
and power- limited circuit conductors 725.41, and


Chapter 9, Tables
11(A) and 11(B)
Secondary tie conductors 450 450.6"

Notice that the first line of Table 240.4(G) covers Air-conditioning and
refrigeration equipment circuit conductors. The referenced parts of
article 440 provide for the selection of Over Current Protective Devices
(OCPD)for air conditioning equipment. Conductors used to supply such
equipment are sized by the table 310.16 values and not by the size of
the OCPD. The OCPD is sized to allow the compressor to start reliably
even under adverse conditions such as already pressurized refrigerant
gas piping. The overload protection for both the circuit conductors and
the motor itself is provided by overload relays mounted in the motor
itself.

The upshot of all of that is that if the conductors are sized so that
their table 310.16 ampacity equals or exceeds the minimum circuit
ampacity that is on the compressor unit name plate then they are
properly sized. Likewise if the supply circuit's OCPD does not exceed
the maximum circuit over current protective device value, and type if
any, that is shown on the compressor unit name plate it is also properly
sized.

This also means that home inspectors should not attempt to do electrical
inspections but should leave that work to Master Electricians and
certified electrical inspectors.

RANT MODE ON
IT ISN'T JUST COLOR TO COLOR PEOPLE! You cannot do safe, competent, nor
cost effective electrical work without taking the time to actually learn
the craft. IF YOU CANNOT OR WILL NOT TAKE THAT TIME THEN KEEP YOUR
HANDS OUT OF ELECTRICAL EQUIPMENT AND KEEP YOUR "THOUGHTS" ABOUT HOW IT
SHOULD BE DONE TO YOUR SELF! Incompetent advice is a bigger danger than
incompetent work because the bad advise can cause dozens of hazards in
multiple places instead of just one or two in one place. I have plenty
of experience suppressing and reporting fires of electrical origin,
injuries caused by electric shock, and deaths by electrocution. I AND
THE REST OF THE NATIONS FIRE AND RESCUE SERVICE DO NOT NEED OR DESIRE
ANY MORE!
rant mode off.
--
Tom Horne, Firefighter EMT

Well we aren't no thin blue heroes and yet we aren't no blackguards to.
We're just working men and woman most remarkable like you.