Air Conditioning - Breaker Size below Max Fusemax fuse at 20 amp and min ampacity atp

[Bdritter]

Single phase residential AC unit tag lists max fuse at 25 amp and min circuit ampacity around 17.8. Electrician installed a 20 amp breaker and inspector failed it because (not sure I have this exactly as he stated it) 80% of 20 Amps (breaker size) is less than min of 17.8. Is he right? I thought wire had to be sized based on min ampacity but breaker could be anything below max rating on tag. At another location same inspector is telling us that manufacturer unit rage must be wrong because it lists max fuse of 20 and min ampacity at 17.1.

Also, looking to confirm 3’ clearance required in front of outdoor AC non-fused disconnect (ie unit can’t be placed in front of disconnect)

Education / guidance appreciated.

 

[infinity]

The inspector shouldn't be there reinventing the manufacturer's nameplate. The MCA is just that, the minimum circuit ampacity required for the unit. With an MCA of 17.8 a 20 amp OCPD is permitted, you are not required to use the MaxOCPD. Some new units do have a minimum OCPD that is greater than the MCA so that is required to be used.

Welcome to the Forum.

 

[retirede]

Inspector is wrong.

But in the old days, if the nameplate said “max fuse”, using a circuit breaker would not be compliant. Not sure if that’s still true?

 

[KnightPower]

Like the other two stated.. and as for the 36" clearance rule there is an interesting argument to be said about that one as well. As a disconnect can be de-energized but I don't have that code reference.

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[jumper]

But in the old days, if the nameplate said “max fuse”, using a circuit breaker would not be compliant. Not sure if that’s still true?

Yes, still true.

 

[infinity]

Electrician installed a 20 amp breaker and inspector failed it because (not sure I have this exactly as he stated it) 80% of 20 Amps (breaker size) is less than min of 17.8. Is he right?

He doesn't understand how the MCA is calculated hence the confusion. The MCA already has 125% added to the largest load (typically the compressor) as part of the MCA calculation. If the MCA were 20.0 amps you could still use a 20 amp OCPD because all of the 125% or 80% stuff has already been figured out by the manufacturer.

 

[peter d]

A few weeks ago I wired an system with an MCA of 27 and a MOCP of 40. I used #10 on a 40 amp breaker. Some people reading this might have a heart attack. :lol:

 

[texie]

Single phase residential AC unit tag lists max fuse at 25 amp and min circuit ampacity around 17.8. Electrician installed a 20 amp breaker and inspector failed it because (not sure I have this exactly as he stated it) 80% of 20 Amps (breaker size) is less than min of 17.8. Is he right? I thought wire had to be sized based on min ampacity but breaker could be anything below max rating on tag. At another location same inspector is telling us that manufacturer unit rage must be wrong because it lists max fuse of 20 and min ampacity at 17.1.

Also, looking to confirm 3’ clearance required in front of outdoor AC non-fused disconnect (ie unit can’t be placed in front of disconnect)

Education / guidance appreciated.

As others have said, the inspector is misinformed. He needs some training for sure. While code compliant, I would be leery of using the 20 amp breaker when the max is 25 as if it trips occasionally the A/C dealer and manufacturer are going to stick it back on you to change. Gets to be an expensive call back on a job with many units.
As for the disconnect, that might be a difficult battle in most jurisdictions.
Oh, does the label really say fuse? Or did you mean breaker. If fuse is the only OCPD stated it must be a fuse.

 

[infinity]

A few weeks ago I wired an system with an MCA of 27 and a MOCP of 40. I used #10 on a 40 amp breaker. Some people reading this might have a heart attack. :lol:

LOL. :lol: