AC condenser and circuit protection

[dmaffei (David Maffei)]

So the AC condenser has a max ampacity rating of 40amps. The service disconnect at the unit has two 40amp fuses installed. The service panel on the side of the house has a 50amp braker installed. True, I should probably call this out but is it really a problem?

Thanks,

Dave

[dandersen (David Andersen, TN HI# 40)]

Explain why to think this…

[dmaffei (David Maffei)]

I would expect the fuses in the service disconnect to blow should the unit draw too much current/ too many amps. But the concern is the breakers in the panel are next to useless.

[dandersen (David Andersen, TN HI# 40)]

I don’t understand. Why?

[gskeeters (George Skeeters, HI-3186)]

Me neither? Please expand your concern thinking.

[rmeier2 (Robert Meier)]

What is the conductor size?

[Jim_Port]

I don’t see why someone would think this is a problem.

[rmeier2 (Robert Meier)]

From a practical standpoint it shouldn’t be a problem as Jim stated but depending on how you apply the NEC rules it could be a violation.

Let’s say that the unit has an MCA of 30 amps and a MAxOCPD of 40 amps. The conductors are #10. So far so good but the conductors from the service panel to the fused disconnect are feeder conductors by the Article 100 definition so the 50 amp OCPD cannot be used to protect the #10 conductors. You could apply the tap rules and possibly still use the #10’s.

Now if we call the fuses supplementary equipment protection then IMO you can use a 40 amp OCPD at the service with the fuses at the disconnect but to use a 50 amp OCPD the tap rules would need to be followed.

However, all of this goes out the window if you use a 50 amp conductor.

Confusing?

[cbottger (Charley L. Bottger)]

@Robert_Meier

From a practical standpoint it shouldn’t be a problem as Jim stated but depending on how you apply the NEC rules it could be a violation.

Let’s say that the unit has an MCA of 30 amps and a MAxOCPD of 40 amps. The conductors are #10. So far so good but the conductors from the service panel to the fused disconnect are feeder conductors by the Article 100 definition so the 50 amp OCPD cannot be used to protect the #10 conductors. You could apply the tap rules and possibly still use the #10’s.

Now if we call the fuses supplementary equipment protection then IMO you can use a 40 amp OCPD at the service with the fuses at the disconnect but to use a 50 amp OCPD the tap rules would need to be followed.

However, all of this goes out the window if you use a 50 amp conductor.

Confusing?

Perfectly understandable:D