I find this quite often and wondered if you are finding this also. On the air conditioning unit the data plate said recommended breaker size-40 amps. Maximum breaker size 40 amps. The breaker in the service panel is only 30 amps which is undersized. Many times I find units labeled for a 20 amp breaker on the data plate and 30 amp in the panel. I write it up every time. Anybody else see this or am I missing something?
Which of these concerns you (you asked about both)?
Max breaker (per data plate) of 40A and a 30A in the panel.
No issue here.
or
Max breaker (per data plate) of 20A and a 30A in the panel.
Write it up
There is a minimum circuit ampacity and a maximum allowable circuit breaker size.
The breaker size is not allowed to exceed the maximum capacity requirement, but it does not necessarily need to meet the max. size.
The minimum tells you what the minimum conductor size needs to be, even if the breaker is oversized for the conductor.
…
Thanks for the advice
David,
Just make sure the MCA is a conductor that can handle the MCA listed and make sure that on the MOP does not exceed the listing given.
MCA : 28A ( would install a 10 AWG )
MOP : 40A ( would install a 40A or less breaker/fuse if it will hold )
It would also be important to remind everyone that IF the AC Compressor says “Fuse Only” then fuses must be in the system. Either at the panel or a the units disconnect. This does not mean the disconnect at the AC Compressor is required to be fused at all as it can be non-fused ( simple pull out ) but let say the nameplate says “Fuse Only” and you have a circuit breaker in th electrical panel…how would you comply. Simply change the non-fused disconnect to a fused disconnect and it would be compliant.
Just a tidbit of additional information…in brief form.
Paul, on this topic, why can the conductor sizes for AC units vary from the common 14 AWG for 15 A breaker, etc?
I know the proper answer is “because the manufactiurer says so”, but why!? :mrgreen:
TIA
Start up if I remember right.
Rick, wire sizing for AC are sized based on Article 440. The OCP is to allow the compressor to be able to start without tripping the breaker. This is a short term event. The wire is sized for the running current of the unit which is less than what is used at startup.
Jim…is your name Paul…lol…just kidding fella…Answer Away
I’ll leave you the tough ones for the Guru site. 
lol…Aint no tough ones over there…