Ac unit called for max size breaker of 30 amps. The breaker in the panel is 40 amps. Wrong yes, but what are the consequences? Is it necessary to put in a 30amp breaker?
I call it out every time. Could void a warranty. But I also think the manufacture puts this on a data plate for a reason.
The way I look at it, is what if 2 years from now they sell the place and the next inspector calls it out. Do you think they would wonder why you didn’t call it out?
The consequences is the thing pulls more than 30 amps but not the 40 to trip the breaker and the insulation on the wires start to melt.
Could have been a bad initial install. But it’s likely replacement equipment with the circuit wires sized for the old unit nameplate/breaker. Newer equipment typically draws less current, so this is a common defect for replacement equipment.
The concern with an oversized breaker is typically possible damage to the equipment. What are the size of the wires feeding the unit and the “minimum circuit ampacity” from the nameplate?
Perhaps the question should be; Is the breaker the appropriate size to protect the conductors attached to it. If so, then you can move on to the question of if the breaker is sufficient to protect the equipment.
I think the installer may have been confused with the HACR required breaker, and the 125% rule, thus the 40amp breaker.
Here’s a discussion regarding HACR breakers… starts off a bit off topic, but get’s right to the point of this topic further down… http://forums.mikeholt.com/showthread.php/65007-HACR-Breakers
was the OCD in the panel the only means of disconnect or is there a disco at the condensing unit that is properly sized for the equipment in question
Looks more like a #6 AL wire … but either one would work (actually #12 CU or #10 AL with a 30A OCPD would work). My bet is it’s replacement equipment that draws less, and they didn’t bother to change the breaker … :roll:
Good question … most modern disconnects at the condenser are the pull-type. But there could be a breaker/fuse type disconnect at the unit with a 30A rating which would then be fine.
If it doesn’t have a 30A breaker/fuse disconnect, it’s still a pretty easy breaker swap out (Yes it needs to be changed, and No it doesnt need to be an HACR type) … 
Exterior disconnect is the pull type. The condenser was manufactured in 2002. The panel was upgraded a few years ago, after the AC unit was installed.
They may have just installed whatever was there before in terms of the breaker rating, or the old panel had a 30A breaker and they just installed a breaker to match the wire size. A #6 Al wire typically matches a 40A breaker so I can see that happening.
The breaker is only there for short circuit and ground fault protection and is not sized to protect the conductors from overloading. That is accomplished by the thermal overloads in the unit. With a MCA of 18.9 amps you could use #14 conductors on a 30 amp OCPD and be 2008 NEC compliant.
Most of the “breakers” that you see as disconnects are not overcurrent devices regardless of the amp rating that you see on the handle. Read the labels on them carefully and you will see that most say that they are not overcurrent devices.
A/C condensers are UL listed devices, simply follow the label. The conductor must meet minimum ampacity and the OCD must not exceed the listed rating (some also list a minimum). Just make sure that you refer to the true OCD.