dnoyeB wrote:


Breakers protect the conductor, the equipment and the user.


Wrong. Panel Breakers and fuses protect wiring. A Components internal
breakers protect its internal components (motors usually have thermal
breakers) GFCI is designed to protect the user.


Under the NEC for motor circuits, like this, the panel fuse/breaker
provides short circuit protection for the wires. Protection for the
motor is provided by an overload device that matches the current and
starting characteristics of the motor - which is a motor starter
'overload unit' or 'thermal protection' in the motor. Fuses/breakers
have to withstand the starting current of the motor, and have widely
spaced ratings (30, 40 Amp), and as a result don't trip on overloads
although as Dan Ackers said they MAY trip on repeated restarts by the
'thermal protector'. In general time delay fuses can be 175% of the
motor running amps. The fuses can be larger than the rating of the
supply wires and protect them from short circuit - overload protection
is provided by the motor overload device. The rules for motors are IMHO
rather arcane and should be applied by soomeone who understands them.
All of this agrees with dnoyeB. However the panel fuse/breaker also
provides some protection for the equipment, and motor starters and other
equipment are likely to have a maximum fuse/breaker size.

Ahh, but the rating of the equipment on the nameplate does not match
the rating of the breaker and that seems to be what the inspector is
tripping on. If the appliance is hardwired, you should change the
breaker, if it is plugged in, it's your call as long as the breaker is
same or smaller than the marking on the receptacle (nod to wire gague
as well).


hardwiring vs. plug makes no difference.


If equipment comes with a cord and plug it would be reasonable to expect
it could be plugged into a matching receptacle. Hardwired equipment has
to follow information on the nameplate (but that is also true for cord
connnected equipment).


If the nameplate says it uses 30A, a larger breaker is appropriate.
If the nameplate says "breaker size" 30A that is much clearer. It may
have both ratings or just the first (consumption) if that is the case,
40A is the right size.


I'm not aware of any nameplate terminology standards!?


Hardwired compressor units for central air are commonly nameplate marked
with "maximum fuse size" or "maximum breaker size". It is a code
violation not to follow these ratings and could void a warranty.
"Maximum fuse size" requires fuses.

In reality on an A/C unit, there are probably no faults that will trip
a 30A that wouldn't also trip a 40A breaker. The difference in trip
current probably wouldn't make much of a difference because any such
fault would likely be due to a dead short. (I suppose a frozen
compressor might take a few more seconds to trip it but its toast by
then anyway)


In reality, breakers are designed to protect against resistive shorts;
Hard shorts are easy. I agree that resistive shorts are rare.
Nevertheless, this is what they do.


But equipment, like motor starters, often have a maximum fuse/breaker
size which protects the equipment from damage.

bud--