Sizing Overcurrent for A/C Condenser

[gsbagshaw]

We have an inspector demanding we put the following A/C on a 60 amp breaker and fuses, Nameplate reads:
Minimum Circuit Ampacity = 35 amps
Minimum overcurrent = 45 amps
Maximum overcurrent = 60 amps

Inspector (probably not an electrician) is citing 440.12 (pretty much whole article) and we fail to see where this applies to his argument. We believe that 440.22 applies..... using 175% we come up with a little over 48 amps and we are on a 50 amp breaker and 50 amp fused disconnect. Before you respond with just do it ..... homeowner has a federal pacific panel and so far has refused to let us upgrade it (at his cost, of course). We replaced furnace and a/c... my feeling is once we replace the breaker in the panel, we basically own the panel should problems arise. Any thoughts? or can anyone back up the inspectors argument? or any ideas on the ideas on liability if we replace a breaker in an FPE --- as a rule we don't work on FPE equipment other than replacement.

 

[Dennis Alwon]

The inspector is incorrect Although we prefer to use the max overcurrent protective device it is not necessary

 

[augie47]

A 50 would be acceptable here, or anything meeting nameplate criteria
Minimum Circuit Ampacity = 35 amps
Minimum overcurrent = 45 amps
Maximum overcurrent = 60 amps

per 110.3(B) and 440.22(C)

 

[jumper]

I agree with with the hippie and the old guy.

 

[iwire]

Minimum Circuit Ampacity = 35 amps
Minimum overcurrent = 45 amps
Maximum overcurrent = 60 amps

Something is wrong here, the minimum circuit size cannot be less than the minimum breaker size.

 

[dkidd]

Something is wrong here, the minimum circuit size cannot be less than the minimum breaker size.

Huh?

 

[iwire]

Huh?

Huh huh?

 

[peter d]

Something is wrong here, the minimum circuit size cannot be less than the minimum breaker size.

:huh:

The circuit ampacity is almost always less than the OCPD size.

 

[iwire]

:huh:

The circuit ampacity is almost always less than the OCPD size.

Yes, less than the max breaker but not less than the minimum breaker.

Am I having a senior moment?

 

[peter d]

Yes, less than the max breaker but not less than the minimum breaker.

Am I having a senior moment?

I'm thinking that the minimum OCPD would always be more than the MCA because of the multipliers needed to compensate for inrush.

 

[infinity]

A 50 would be acceptable here, or anything meeting nameplate criteria
Minimum Circuit Ampacity = 35 amps
Minimum overcurrent = 45 amps
Maximum overcurrent = 60 amps

per 110.3(B) and 440.22(C)

I agree if the nameplate is correct then you would need a 35 amp conductor and a minimum 45 amp OCPD. Given the information one thing is for sure you do not need to use a 60 amp OCPD.

 

[Dennis Alwon]

Something is wrong here, the minimum circuit size cannot be less than the minimum breaker size.

I believe that is often the way it is.

 

[iwire]

I believe that is often the way it is.

Not going to argue here, you may well be right.

I can not remember seeing all three of these:

• Minimum Circuit Ampacity
• Minimum overcurrent
• Maximum overcurrent

I can only recall seeing these

• Minimum Circuit Ampacity
• Maximum overcurrent

 

[peter d]

Not going to argue here, you may well be right.

I can not remember seeing all three of these:

• Minimum Circuit Ampacity
• Minimum overcurrent
• Maximum overcurrent

I can only recall seeing these

• Minimum Circuit Ampacity
• Maximum overcurrent

Some units have have the Min OCPD listed, but most don't in my experience. Not that anyone seems to follow it anyway, 99% of them are wired with the conductors sized to the maximum OCPD size. :roll:

 

[MNSparky]

Most new condensers I see have all three listed. The minimum circuit ampacity is almost always lower than the minimum OCPD. It doesn't matter a whole lot on smaller resi ACs now that the smaller wire sizes have strict OCPD rules. You used to be able to fuse #12s at 25amps, but now you'd have to run 10s for that same unit.

 

[infinity]

Most new condensers I see have all three listed. The minimum circuit ampacity is almost always lower than the minimum OCPD. It doesn't matter a whole lot on smaller resi ACs now that the smaller wire sizes have strict OCPD rules. You used to be able to fuse #12s at 25amps, but now you'd have to run 10s for that same unit.

You could still use #12 at 25 amps if it wasn't NM cable. For raceways or MC cable the 75° ampacity can still be used.

 

[MNSparky]

You could still use #12 at 25 amps if it wasn't NM cable. For raceways or MC cable the 75° ampacity can still be used.

Doesn't 240.4(D) (2014 NEC) say #12 CU is limited to 20amps? I looked in 440 but I didn't see anything that would provide an exception. Am I missing something?

 

[cowboyjwc]

Still gonna be #8

 

[texie]

Doesn't 240.4(D) (2014 NEC) say #12 CU is limited to 20amps? I looked in 440 but I didn't see anything that would provide an exception. Am I missing something?

The so called small conductor rule in 240.4(D) is not applicable here. See 240.4(G). Same concept as for Art. 430 motor circuits.

 

[infinity]

Doesn't 240.4(D) (2014 NEC) say #12 CU is limited to 20amps? I looked in 440 but I didn't see anything that would provide an exception. Am I missing something?

The so called small conductor rule in 240.4(D) is not applicable here. See 240.4(G). Same concept as for Art. 430 motor circuits.

Yes 240.4(G). For the OP if this were conduit and wire or MC cable you could use #10 AWG THHN conductors if your terminations were all listed for 75° C.