I recently inspected a condensing unit installation where the nameplate indicates 15A MOCP. It is fed from a 20A circuit breaker in a panel and I noted it as being a deficiency. The installer pointed out that the fused disconnect within the unit's built-in control panel is equipped with 15A fuses, and the installation thereby complies with NEC. Is this allowable?
Condensing unit internal fuses meet OCPD requirements?
- Thread starter alehman
- Start date
- Location
- Connecticut
- Occupation
- Engineer
No. The branch circuit short-circuit and ground fault protective device needs to be sized per the MOCP
David, Thanks for the quick response and that would be my normal reaction as well.
However, according to the definitions in Article 430, the fuses at the unit disconnect (internal to the control panel) would be the motor branch circuit short circuit and ground fault protection. I don't see that Article 440 changes that. The circuit between the panelboard and the unit would be considered the motor feeder, right?
Since the circuit between the panelboard and the HVAC unit supplies only a single unit, the motor feeder overcurrent protection cannot exceed the branch-circuit short-circuit and ground-fault protection unless the conductors are sized corresponding to the feeder protection. In this case the motor feeder conductors are sized for 20A, so it seems like the installer's argument would stand.
However, according to the definitions in Article 430, the fuses at the unit disconnect (internal to the control panel) would be the motor branch circuit short circuit and ground fault protection. I don't see that Article 440 changes that. The circuit between the panelboard and the unit would be considered the motor feeder, right?
Since the circuit between the panelboard and the HVAC unit supplies only a single unit, the motor feeder overcurrent protection cannot exceed the branch-circuit short-circuit and ground-fault protection unless the conductors are sized corresponding to the feeder protection. In this case the motor feeder conductors are sized for 20A, so it seems like the installer's argument would stand.
hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
- Occupation
- EC
MOCP means the maximum allowable over current protection for circuit or feeder supplying power to the unit. What the manufacturer does internally has nothing to do with it. The electrician isn't going to open doors or look at wiring diagrams when the nameplate clearly indicates what the manufacturer requires, a 15A feeder with a 15A breaker.
-Hal
-Hal
440.28?
sorry 440.35
440.35 Multimotor and Combination-Load Equipment. The ampacity of the conductors supplying multimotor and combination-load equipment shall not be less than the minimum circuit ampacity marked on the equipment in accordance with 440.4(B).
mtnelect
HVAC & Electrical Contractor
- Location
- Southern California
- Occupation
- Contractor, C10 & C20 - Semi Retired
This might help to explain.
mtnelect
HVAC & Electrical Contractor
- Location
- Southern California
- Occupation
- Contractor, C10 & C20 - Semi Retired
This might help to explain, Part 2
qcroanoke
Sometimes I don't know if I'm the boxer or the bag
- Location
- Roanoke, VA.
- Occupation
- Sorta retired........
We have installed wall mount hvac's with a 35 amp max overcurrent protection required. We cannot get 35 amp breakers so we use 40 amp breakers feeding a 60 amp disconnect with 35 amp fuses installed. To me that is completely to code. I would never reject what you have installed there.
The conductors are sized correctly. I don't that that is in question.
qcroanoke
Sometimes I don't know if I'm the boxer or the bag
- Location
- Roanoke, VA.
- Occupation
- Sorta retired........
For the unit I would accept internal or external. Yes.
- Location
- Connecticut
- Occupation
- Engineer
The branch circuit is the conductors from the panelboard to the unit, in this example. The branch circuit short-circuit and ground-fault protection is therefore in the panelboard.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Well, there is a requirement for air-handlers that says internal OCPDs must be externally operable to qualify as the unit's disconnect. I imagine this would apply to internal fuses, too, such as using pull-outs.
Granted, we're discussing OCP here, not disconnects, but you need to know whether the rules you're discussing cover the branch circuit conductors or just the HVAC unit itself.
There is an externally operable disconnect with the fuses. Think externally operable fused disconnect built in to the unit's control panel.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
If externally accessible, I believe they should qualify as the required OCPD, rendering the supply a feeder.
- Location
- Connecticut
- Occupation
- Engineer
In my view, you are still looking at a branch circuit. The "outlet" is where the premises wiring conductors attach to the built-in disconnect.
Elect117
Senior Member
- Location
- California
- Occupation
- Engineer E.E. P.E.
From NEC 2020 Handbook, 440.21
Enhanced Content:
"If supplemental overcurrent protection is provided within the heating, air conditioning, and refrigeration (HACR) equipment control panel, the manufacturer will have marked the equipment with specific information on the type of branch-circuit overcurrent protective device that can be used on the line side of the HACR unit in order to provide the necessary level of short-circuit and ground-fault protection for the equipment and controls internal to the HACR unit."
If the equipment is marked with 15A MOCP that is most likely for the ground fault protection based on how the handbook words it.
Enhanced Content:
"If supplemental overcurrent protection is provided within the heating, air conditioning, and refrigeration (HACR) equipment control panel, the manufacturer will have marked the equipment with specific information on the type of branch-circuit overcurrent protective device that can be used on the line side of the HACR unit in order to provide the necessary level of short-circuit and ground-fault protection for the equipment and controls internal to the HACR unit."
If the equipment is marked with 15A MOCP that is most likely for the ground fault protection based on how the handbook words it.
mtnelect
HVAC & Electrical Contractor
- Location
- Southern California
- Occupation
- Contractor, C10 & C20 - Semi Retired
HVAC is a specialty and a much different "animal" from the standard motor requirements in NEC, that's why I posted the section from "Electrical Wiring - Residential" above. I read it all the time on this website on how it is misapplied.
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