MOCP for Exhaust Fan NEC Violation or Not?

[jar546]

This is the label. When you do your inspection, you see #12awg THWN in EMT fed by a 20A OCPD. Would that be a violation of the NEC?

 

[wwhitney]

I'm unclear on whether the unit has an integral thermal protector or other integral overload device; I would think that the label would specify if so, and I don't see any language to that effect (although the right side of the label that you cut off may address that question.)

So if the motor is relying on the MOCP 15A label to use a 15A OCPD as its overload protection, certainly using a 20A OCPD is an NEC violation. But I also think that 15A would be too high for overload protect for a motor with a nameplate full load current of 5.6A, although I didn't confirm that.

Whereas if the unit has integral overload protection, so that the branch circuit OCPD is only providing short circuit and ground fault (SC/GF) protection, there's no violation of NEC Article 430. A 1/3 HP 120V motor has a full load current of 7.2A per NEC Table 430.248, and Article 430 specifies to use the Table FLC values for basically all purposes other than overload sizing. Then the maximum SC/GF protection is 250% of the FLC per Table 430.52, which gives us 2.5 * 7.2 = 18A; and 430.52 has an exception allowing rounding up to the next standard OCPD size, or 20A.

Of course, one could still argue that since it is labeled MOCP 15A, using the 20A OCPD allowed by Article 430 would be a 110.3(B) violation (unless the cut off text on the right has something to say to modify the MOCP 15A label).

Cheers, Wayne

 

[jar546]

I'm unclear on whether the unit has an integral thermal protector or other integral overload device;

Yes, I agree. We an only make decisions based on what we see and know, not what might be.

 

[wwhitney]

Yes, I agree. We an only make decisions based on what we see and know, not what might be.

So then I'd read the right half of the label before making a decision. : - )

Cheers, Wayne

 

[jar546]

So then I'd read the right half of the label before making a decision. : - )

Cheers, Wayne

I don't want you to make hasty decisions, so I went back on the roof today just for you.

 

[wwhitney]

I don't want you to make hasty decisions, so I went back on the roof today just for you.

Great. So the phrase of interest is "This ventilator should be installed with remote motor-overload protection when 3 phase or 2HP or larger single phase motors are required."

Does that mean that as the name plate indicates a 1/3 HP single phase motor, remote motor-overload protection is not required because the unit has integral overload protection? If so, seems to me that using a 20A branch circuit OCPD with 20A ampacity conductors, or even with 15A ampacity conductors, complies with Article 430. In which case the only NEC issue I see is whether the unit being labeled MOCP 15A would make that a 110.3(B) violation.

I perused UL 705, the listing standard on the label, and it seems to me that it does not call for the manufacturer to label this unit with MOCP. The labeled FLC is 5.6A, and the labeled MCA is 7A, which is 125% * 5.6A. So there is no room in that computation for another load, the motor must be the only load. While UL 705 says:

36.8 A ventilator having one motor with other loads or more than one motor with or without other loads shall be marked with one of hte following:
a) The minimum circuit size and maximum current rating of the overcurrent-protective device unless both are 15A or less; or
b) The rating of the largest motor in volts and amperes, and the rating of any other loads in volts and either amperes or watts.
Exception: The current value of a motor rated 1/8 horsepower (93W output) or less, or a nonmotor load 1 ampere or less may be omitted unless either load constitutes the principal load.

So assuming all the above is correct, if we conclude that the manufacturer has unnecessarily labeled the unit MOCP 15A, may we ignore that, or is it a 110.3(B) issue?

BTW, the manufacturer seems to have dropped the ball on these provisions of UL 705:

36.5 A ventilator that incorporates motor-overload protection shall be marked to indicate the presence of such protection.

36.6 A ventilator that does not incorporate motor-overload protection shall be marked:
a) To indicate that the ventilator should be installed with remote motor-overload protection; and
b) To provide such motor-rating data--voltage, frequency, horsepower, and full-load current per phase--so that proper protection may be determined.

I.e. if the ventilator has motor-overload protection, as I infer, then the requisite 36.5 marking is missing. Whereas if it doesn't, then the requisite 36.6(a) marking is missing, as the label references that only for 3 phase and 2HP or larger single phase motors, which this unit does not have.

Cheers, Wayne

 

[jar546]

I.e. if the ventilator has motor-overload protection, as I infer, then the requisite 36.5 marking is missing. Whereas if it doesn't, then the requisite 36.6(a) marking is missing, as the label references that only for 3 phase and 2HP or larger single phase motors, which this unit does not have.

Great. So in the real world when an electrical inspector has 24 inspections in 18 different locations and 8 hours to do them in, he or she will fail the inspection if the contractor does not have a 15A OCPD in place and instead uses a 20A, OR they won't care and will just pass it as this really does not make a difference in the grand scheme of things until there is a roof fire and an expert witness uses the label against the contractor and inspector for negligence.

 

[ICE]

It's a given that 99.99% of the inspectors out there are no where close to as knowledgeable as you guys... but nearly all of us can read. 110.3(B) it is.