MOCP on an air conditioning condenser

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Timothy Kent

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Have a failed inspection because the inspector claims that the MOCP is the only size allowed. There is no Min breaker size listed on data plate but the breaker we installed is over the MCA but less than the max OCP. When I said ok we will put a 60 amp breaker on the #8 wire and he said no way the wire is not rated for 60 amps. I found in one of the newsletters good info about the fact you can put a breaker that is rated higher than the wire (as long as it is no more than the MOCP) but can not find in plain English anything that states the OCP can be smaller than the rated MOCP. Even sent him the below article by Micheal Johnston from the NECA but he says no go. Any other sources out there that any one knows of.

http://iaeimagazine.org/magazine/20...air-conditioning-and-refrigeration-equipment/

Thanks
 
Unfortunately this is a common issue that we hear about. The inspector does not understand that the overcurrent protective device is there only for short circuit and ground fault protection. The overloads in the a/c will protect the conductors
 
It's not really a hard concept to grasp, the unit has two ratings the minimum circuit ampacity (MCA) and the maximum OCPD (MaxOCPD) size. If you size the OCPD and conductors to the MCA the circuit is compliant because you have satisfied the MINIMUM circuit ampacity.

The inspector is incorrect so ask for a code reference.
 
I concur, this is one of the biggest misconceptions in the trade and I believe anyone who cannot grasp these concepts has no business inspecting. Any person that cannot understand this shows me they lack an understanding of basic electrical concepts.
 
Timothy Kent said:
Have a failed inspection because the inspector claims that the MOCP is the only size allowed. There is no Min breaker size listed on data plate but the breaker we installed is over the MCA but less than the max OCP. When I said ok we will put a 60 amp breaker on the #8 wire and he said no way the wire is not rated for 60 amps. I found in one of the newsletters good info about the fact you can put a breaker that is rated higher than the wire (as long as it is no more than the MOCP) but can not find in plain English anything that states the OCP can be smaller than the rated MOCP. Even sent him the below article by Micheal Johnston from the NECA but he says no go. Any other sources out there that any one knows of.

http://iaeimagazine.org/magazine/20...air-conditioning-and-refrigeration-equipment/

Thanks
Click to expand...

Do you run into this often?
 
Timothy Kent said:
.... I found in one of the newsletters good info about the fact you can put a breaker that is rated higher than the wire (as long as it is no more than the MOCP) but can not find in plain English anything that states the OCP can be smaller than the rated MOCP.
Click to expand...
You are correct there is no place that just says "Motors are Different". It takes a bit of effort but 240.4 (G) clearly says "Overcurrent protection shall be permitted to be provided as referenced in Table 240.4 (G), and the first thing on the list is air conditioning. Then you have to carefully read 440.6(A) Exception 1 which basically tells you the manufacturers have done all the math and all you have to do is follow the nameplate.

Some people just won't try and understand why it's OK to put a bigger breaker on smalier breaker for AC and other motor loads. There are many such unfortunates and they make it rough on the rest of us.
 
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