Breaker sizing when HVAC condenser is also protected by fuses.

[Phil.Barnes]

An inspector issued a correction notice to us for having to large a breaker. The HVAC condenser calls for overcurrent protection of 35 amps. The unit is protected by 35 amp rated fuses. At the main panel the circuit breaker feeding the HVAC condenser is a 40 amp breaker. I can not find it in the NEC 2011, but I was always lead to believe you could go up to the next size in breakers as long as the fuses were sized correctly to the equipment.

 

[Dennis Alwon]

Your install is fine if the wire going to the unit is properly sized for the 40 amp breaker. The wire should be protected at the source. Thus if you had a #10 wire under the 40 amp breaker as a feeder then IMO that would not be correct-- This is especially silly because if the disconnect did not have overcurrent protective device then the install would be okay.

In order to give a better answer I need to know wire type, size and cable type (wiring method)

 

[jumper]

35A is a standard size for breakers according to 240.6(A).

 

[infinity]

What is the ampacity of the conductors?

 

[jxofaltrds]

And he cited one of these. Not. What was the article he cited?

Have him show you in the following where you violated the code.

Overcurrent. Any current in excess of the rated current of
equipment or the ampacity of a conductor. It may result
from overload, short circuit, or ground fault.

III. Branch-Circuit Short-Circuit and Ground-Fault
Protection
440.21 General.

Overload. Operation of equipment in excess of normal,
full-load rating, or of a conductor in excess of rated ampacity
that, when it persists for a sufficient length of time,
would cause damage or dangerous overheating. A fault,
such as a short circuit or ground fault, is not an overload.

VI. Motor-Compressor and Branch-Circuit Overload
Protection
440.51 General.

 

[cadpoint]

Welcome to the Forum!

Since you said condenser, could it be that you need to consider that the unit needs consideration of
440.4(B) Multimotor and Combination-Load Equipment? I don't know...

You % multiplier is different in 440, frankly I think the inspector is wrong and that your undersized on the panel breaker.

 

[Phil.Barnes]

Breaker sizing when HVAC condenser is also protected by fuses.

Thank you all for your help. The conductor is stranded #8 copper and his a home run from the panel to the condenser disconnect. The ampacity of the condenser is 22.3 amps and the equipment rating plate indicates a max circuit of 35 amp. We did install 35 long delay fuses at the condenser disconnect but the breaker at the main panel is 40 amp. Of course we can purchase 35 amp breakers but our trucks are set up with even sized breakers to reduce the skew loads on our inventory system. We had never been cited for this before and it sounded slightly picky. I think everyone's comments helped. Thanks!

 

[Smart $]

... We had never been cited for this before and it sounded slightly picky. ...

Worse than slightly picky... it's outright wrong. 8AWG copper is good for at least 40A at 60?C, giving a +4A cushion for adjustment and correction if necessary (40A - 36A, with 35A being the next lower standard size).

 

[Little Bill]

Sounds like the inspector is just going by the "max" breaker size listed on the nameplate of the unit, and not taking into account that you have it fused at 35A.

Even if the nameplate said "fuses" and not "fuses or breakers" you're install is correct because of the fused disconnect that you have.

I believe I would have a talk with him and ask him to explain his reasoning behind his correction notice.

 

[texie]

Thank you all for your help. The conductor is stranded #8 copper and his a home run from the panel to the condenser disconnect. The ampacity of the condenser is 22.3 amps and the equipment rating plate indicates a max circuit of 35 amp. We did install 35 long delay fuses at the condenser disconnect but the breaker at the main panel is 40 amp. Of course we can purchase 35 amp breakers but our trucks are set up with even sized breakers to reduce the skew loads on our inventory system. We had never been cited for this before and it sounded slightly picky. I think everyone's comments helped. Thanks!

If the MCA as stated on the label is 22.3 and the Max fuse or breaker is 35 amp, based on your your description, the inspector is wrong and probably misinformed.

The #8 wire (even at 60 degree, as pointed out by others) is good for 40 amps, so the 40 amp breaker is compliant. At the disconnect you have 35 amp fuses to comply with the max overcurrent device. And with an MCA of 22.3 you could even use sealtite and #12 conductors from the fusible disconnect to the unit and be compliant (assuming the unit has 75 degree terminals which is likely).

Just for sport I would have him come back and show him that you changed to using #12 wire from the fusible disco and really get him going.

Please sign here Mr inspector and I'll go on my way or shall we go to class together?

 

[infinity]

If the MCA as stated on the label is 22.3 and the Max fuse or breaker is 35 amp, based on your your description, the inspector is wrong and probably misinformed.

The #8 wire (even at 60 degree, as pointed out by others) is good for 40 amps, so the 40 amp breaker is compliant. At the disconnect you have 35 amp fuses to comply with the max overcurrent device. And with an MCA of 22.3 you could even use sealtite and #12 conductors from the fusible disconnect to the unit and be compliant (assuming the unit has 75 degree terminals which is likely).

Just for sport I would have him come back and show him that you changed to using #12 wire from the fusible disco and really get him going.

Please sign here Mr inspector and I'll go on my way or shall we go to class together?

I agree, the inspector is incorrect based on the conductor size protected by the 40 amp OCPD.

Trouble maker. :roll:

 

[jap]

If the MCA as stated on the label is 22.3 and the Max fuse or breaker is 35 amp, based on your your description, the inspector is wrong and probably misinformed.

The #8 wire (even at 60 degree, as pointed out by others) is good for 40 amps, so the 40 amp breaker is compliant. At the disconnect you have 35 amp fuses to comply with the max overcurrent device. And with an MCA of 22.3 you could even use sealtite and #12 conductors from the fusible disconnect to the unit and be compliant (assuming the unit has 75 degree terminals which is likely).

Just for sport I would have him come back and show him that you changed to using #12 wire from the fusible disco and really get him going.

Please sign here Mr inspector and I'll go on my way or shall we go to class together?

Are you saying that if the Disconnect was non fused and the breaker in the indoor panel was reduced to 35 amps that he could run #12 all the way from the panel to the unit?

 

[infinity]

Are you saying that if the Disconnect was non fused and the breaker in the indoor panel was reduced to 35 amps that he could run #12 all the way from the panel to the unit?

Yup, #12 THHN for this application has an ampacity of 25 amps so it's larger enough for the MCA of 22.3 amps. 240.4(D) does not apply to this type of installation. Also the terminals would all need to be rated for 75? C.

 

[kwired]

Yup, #12 THHN for this application has an ampacity of 25 amps so it's larger enough for the MCA of 22.3 amps. 240.4(D) does not apply to this type of installation. Also the terminals would all need to be rated for 75? C.

jap - please note that you can run 12 AWG 75C conductors for the entire circuit. NM cable is only allowed to be used at 60C max and would have to be increased in size.

 

[squaredan]

Can someone tell me when you can use a nonfuse disco at the HVAC Condenser? I always thought you had to use fuse or breaker disco at the unit.. This topic has come up at work alot.. I was tought you must use fuse or breaker when nameplate says Max fuse or Max Ckt, that is the size you must use and the wires going from breaker at main panel to the HVAC disco, feeder conductors, has to be sized to the MAX fuse or Ckt on nameplate(440.21) . The wires from load side of disco, Branch circiut conductors, sized to " minimum circuit amps" on the nameplate(440.31).. The breaker is sized for Ground Fault protection and Overloads are built into the unit..

Now I am hearing you can use a nonfuse disco and put Max Ckt at the main panel, now its a branch circiut with a switch on it and size the wire to Minimum circiut amps and use for the whole run..
When can you use Nonfuse disco? All the nameplates on these units have Max fuse or Max Ckt

 

[curt swartz]

There has never been a requirement to install a fused disconnect at equipment. You are only required to have a disconnect. Some older equipment stated the maximum fuse size only. If that is the case it just means you have to have fuses somewhere in the circuit. If the units states maximum fuse or circuit breaker size that means it must be protected by a fuse or circuit breaker. Every unit I have connected in the past 25+ years has allowed fuses or circuit breakers for protection.

 

[GoldDigger]

Another thing to remember is that you may see a specification for *minimum* circuit ampacity or MCA. For this the wire size (ampacity) and the overcurrent protection must both be at least this large.
A second specification is *maximum* overcurrent protection. Even though the wires you install may be good enough for a higher ampacity, the fuse or breaker may not be larger than this.
Of course maximum and minimum are both abbreviated "M", so you need to be sensitive to the context.

Tapatalk!