NEC Article 440.22 code interpretation question: An existing rooftop equipment is being replaced and is currently protected by 200A circuit breaker. new equipment has mca of 130, mocp of 175. Can the 200A circuit breaker be left and protect the #1/0 wiring with a fusible disconnect (200/175/3) at the rooftop unit? The 200A circuit breaker is still within 175% of the mca, but the unit has to be fused at 175. I guess my question is: with the addition of the fusible disconnect, are the wires from the panel now considered feeders and is normal wire sizing for 200A c/b (#3/0) applicable?
Article 440 ?
- Thread starter DW98
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If you can post this article and any relevant definitions and applicable rules I will try to see if a 'yes' answer to your question is a logical conclusion.
This is about as complicated a logic question as can exist. It's a good test question.
This is about as complicated a logic question as can exist. It's a good test question.
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- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I don't see any problem with that install. Leave the 200 amp breaker and protect the a/c unit with 175 amp fuses.
davidr43229
Senior Member
- Location
- Columbus, Oh
What is the Class of the 175amp Fuses ?
What is the breaker, make, style ?
What is the available fault current ?
What is the SCCR rating of the New A/c Unit ?
What is the breaker, make, style ?
What is the available fault current ?
What is the SCCR rating of the New A/c Unit ?
- Location
- Massachusetts
No, you can not leave the 200 protecting the 1/0s if you have a fused disco at the unit.
I'm afraid you are going tlo end up in a local AHJ call situation.
First you should address the items david43229 noted, but in many jurisdictions you would not be asked to do so.
Secondly, Bob (Iwire) is right, IMHO,.... by CODE and using Code definitions, but the silly thing is, if that were a 175 amp breaker and a N/F disconnect (and allowed by the listing) , the 1/0 or even smaller would be legal. There are some inspectors that would consider the load and your fusible dsconnect as "supplemental" or just as a "disconnect" and allow the 200 to remain. You will just have to ask.
First you should address the items david43229 noted, but in many jurisdictions you would not be asked to do so.
Secondly, Bob (Iwire) is right, IMHO,.... by CODE and using Code definitions, but the silly thing is, if that were a 175 amp breaker and a N/F disconnect (and allowed by the listing) , the 1/0 or even smaller would be legal. There are some inspectors that would consider the load and your fusible dsconnect as "supplemental" or just as a "disconnect" and allow the 200 to remain. You will just have to ask.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I guess the overload protection in the unit must be only good to 175 amps??? I don't understand why we can go up to 250% if the unit has trouble starting. Why can't the 1/0 good for 150 amps be protected by the 175 amps and overload at the unit. I am confused on this-- any help.
- Location
- Massachusetts
I agree it is kind of strange but it is the way it works out.
Dennis, In my opinion, the "problem" is, by Code definition, since the fusible disconnect provides OCP the circuit from the disconnect to the unit is a "branch circuit". The wiring supplying the disconnect would be a "feeder". Art 440 discusses sizing the branch circuit and SCGF protection all of which is handled by the fusible disconnect.
What Code article allows you to protect a 1/0 conductor used as a feeder to a 200 amp OCP device ? Art 430 or 630 perhaps, but we are in a Art 440 application.
What Code article allows you to protect a 1/0 conductor used as a feeder to a 200 amp OCP device ? Art 430 or 630 perhaps, but we are in a Art 440 application.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
So it is one of those technicalities or code issues that make absolutely no sense. :grin: I really think the definition of branch circuit and feeder need a change. To me that should all be a branch circuit and the fused disconnect a supplemental protection. IMO, a feeder should be feeding more than one branch circuit otherwise it should be a branch cir.
Maybe I will write a change proposal. I think this will be hard to word. I see the same problem with a hot tub when the disco has the gfci it changes the definition from branch circuit to feeder and it doesn't make sense to me.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
I agree the circuit before the disconnect with OCP is a feeder, and I also agree that it ought to be able to be considered part of the BC, mainly because it's supplying a single load.
Suppose the unit's disco and protection was built into the unit itself. Would the circuit be a feeder or branch circuit then? I agree the entire cicruit is a BC, and the code should agree.
Ain't I agreeable today?
Suppose the unit's disco and protection was built into the unit itself. Would the circuit be a feeder or branch circuit then? I agree the entire cicruit is a BC, and the code should agree.
Ain't I agreeable today?
My take on this is the feeder breaker cannot be any larger than the branch breaker or fuse supplying the specific load unless the conductors are sized for the feeder breaker. This is based on article 440.3 and 430.62(A). It would be ok to have a 175 as the feeder and a 175 for the branch but not the 200.
430.62 Rating or Setting ? Motor Load.
(A) Specific Load. A feeder supplying a specific fixed motor load(s) and consisting of conductor sizes based on 430.24 shall be provided with a protective device having a rating or setting not greater than the largest rating or setting of the branch-circuit short-circuit and ground-fault protective device for any motor supplied by the feeder [based on the maximum permitted value for the specific type of a protective device in accordance with 430.52, or 440.22(A) for hermetic refrigerant motor-compressors], plus the sum of the full-load currents of the other motors of the group.
Rick
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