cooling unit outside compressor

[wire monk]

On a split system the outside a/c compressor name plate say's min. cir amps 25. Max fuse size 40. The heating contractor say's it should be wired in #8 and we are saying #10 who is right.

 

[iwire]

On a split system the outside a/c compressor name plate say's min. cir amps 25. Max fuse size 40. The heating contractor say's it should be wired in #8 and we are saying #10 who is right.

You could wire it with 12 AWG and the 40 amp breaker if you wanted to.

Unless it is a long run I would likely go with the 40 amp breaker, non-fused disconnect at the unit and 10 AWG the entire way.

 

[AE-29]

If i'm not mistaking, min ckt amps is 25, that refers to the rating of the load. Max fuse size 40a refers to the fusibe rating at 175%. This gives the fuse time to overcome a current surge. #12 awg THHN or THW would be ok depending that you don't have a long run, and you don't have 3 % volt drop or more than 3 hot conductors etc...

 

[MikeGee]

I am an electrician that works for a HVAC company and I face this all the time. In this situation I would run #10 copper with a 30amp breaker.

 

[iwire]

I am an electrician that works for a HVAC company and I face this all the time. In this situation I would run #10 copper with a 30amp breaker.

What reason would you not use the 40 amp breaker?

 

[Buck Parrish]

. The heating contractor say's it should be wired in #8 and we are saying #10 who is right.

He's a heating contractor not an electrician.

 

[Pierre C Belarge]

What reason would you not use the 40 amp breaker?

So many installers are hung up on 240.4(D). It has been ingrained on their brain and stamped into being.
They are unaware of 240.4(G) which refers them to Article 440 which in turn allows them to use the nameplate rating and overcurrent protection other than 240.4
With that said, they also do not understand the principles behind which they can increase the overcurrent protective device and still have not only a compliant installation, but one that works as well.

(that was my short answer :wink: )

 

[charlie]

You might also add that the short circuit and ground fault protection is provided by the overcurrent device in the panelboard. The overload protection is provided in the compressor unit. That is why the nameplate data is permitted to be used for sizing the circuit and overcurrent protective device size. :smile:

 

[Ed Carr]

I may be wrong on this but if the required protection says "fuse"
then isn't that what is used instead of a breaker?

 

[Cavie]

I may be wrong on this but if the required protection says "fuse"
then isn't that what is used instead of a breaker?

You are correct. If it says "fuse" and not "fuse/breaker", you must use a fuse as per manufature specs.

 

[Cow]

I agree Ed.

I would likely go with the 40 amp breaker, non-fused disconnect at the unit

Fused or non-fused Bob?

 

[Cavie]

I am an electrician that works for a HVAC company and I face this all the time. In this situation I would run #10 copper with a 30amp breaker.

And as an inspector in Florida, in your siuation, I would turn you down. Your 30amp breaker could cause nusince trips in one of our many rain/lightning storms in the summer. Many companies are to cheep to install time delays on the compressors.

 

[jimman]

Cavie,
What code reference would you use to turn this down?

 

[Cavie]

Cavie,
What code reference would you use to turn this down?

Don't have one. Discussion went around the meeting of 15 inspectors and it was decided by majority vote and the AHJ that the Max breaker size would be inforced. Nusince trip was the most previlent reason and i have yo admit I went along with the idea. You have to go thru a summer storm here to understand.

 

[LarryFine]

Discussion went around the meeting of 15 inspectors and it was decided by majority vote and the AHJ that the Max breaker size would be inforced.

"Enforcing the maximum breaker size" only means not allowing it to be exceeded.

In spite of the majority vote, you're still making up a rule, unless it's been legally passed.

 

[infinity]

Don't have one. Discussion went around the meeting of 15 inspectors and it was decided by majority vote and the AHJ that the Max breaker size would be inforced. Nusince trip was the most previlent reason and i have yo admit I went along with the idea. You have to go thru a summer storm here to understand.

Don't have one because there isn't one. The "what if" reason for enforcing an unwritten code article is a very slippery slope.

 

[Cavie]

When the man that signs the paycheck says jump, you ask how high. Then work gets slow and he lets you and 15 of you coworkers go.

 

[charlie]

First, the maximum overcurrent device size is spelled out on the nameplate. The AHJ should permit smaller sizes than the maximum size but the installer should install sizes that permit proper operation of the unit.

Second, the following is from the UL White Book in the section Electrical Heating and Cooling Equipment Marking Guide in the back of the book (in my opinion, it is the rest of the code book). :smile:

"The markings for short-circuit and ground-fault protection always include some indication of the type of protection device as well as the maximum current rating. This is significant since the various types of devices recognized by the NEC? to provide this protection do not necessarily provide the same level of protection for all units. Briefly, if the marking indicates:

1) Only ?Fuse,? then only fuses are to be used;
2) ?HACR Type Circuit Breaker? and ?Fuse,? then either fuses or circuit breakers marked ?HACR Type? may be used; or
3) ?Fuse or Circuit Breaker? or ?Overcurrent Protection,? then fuses or any type of circuit breaker (including ?HACR Type?) may be used.

In any case, the devices used should be covered by the NEC? to provide short-circuit and ground-fault protection."

 

[iwire]

Fused or non-fused Bob?

I had not noticed that the OP had said Max fuse size 40.

That being the case I would have to get a fuse in the circuit somewhere.

 

[infinity]

When the man that signs the paycheck says jump, you ask how high. Then work gets slow and he lets you and 15 of you coworkers go.

I hear where you're coming from but this issue is pretty cut and dry. The word "maximum" doesn't make it a requirement to install it.