NEC 422.10(A) & 422.11(E)(3)

[erickench]

Okay, I see a potential conflict in these two sections and I would like to have it clarified. In NEC 422.10(A) it state's:

Individual Circuits. ...The branch circuit rating for an appliance that is a continuous load, other than a motor-operated appliance, shall not be less than 125 percent of the marked rating,...

By branch circuit rating I assume they mean the OCPD? Or perhaps the conductor sizes? In NEC 422.11(E)(3) it state's:

If the branch circuit supplies a single non-motor-operated appliance, the rating of overcurrent protection shall comply with the following:
(3) Not exceed 150 percent of the appliance rated current if the overcurrent protection rating is not marked and the appliance is rated over 13.3 amperes.

Now in both cases it seem's to apply to the same type of circuit and the same type of appliance. Question: How is the OCPD sized? In one case it's at 125% and in the other it's at 150%.

 

[augie47]

I believe you have a not less than 125% and not to exceed 150%.

 

[erickench]

I believe you have a not less than 125% and not to exceed 150%.

That could be it. Also, if the appliance were rated at less than 13.3 amps then NEC 422.10(A) would apply. The thing is that at the end of NEC 422.11(E)(3) it state's:

Where 150 percent of the appliance rating does not correspond to a standard overcurrent protection device ampere rating, the next higher standard rating shall be permitted.

So it can't be a maximum.

 

[david luchini]

I don't see a conflict.

One section tells you what the Minimum size of the OCPD must be, the other section tell you what the Maximum size of the OCPD can be. As long as your OCPD size is between the Min and Max, you would be fine.

 

[david luchini]

That could be it. Also, if the appliance were rated at less than 13.3 amps then NEC 422.10(A) would apply. The thing is that at the end of NEC 422.11(E)(3) it state's:

Where 150 percent of the appliance rating does not correspond to a standard overcurrent protection device ampere rating, the next higher standard rating shall be permitted.

So it can't be a maximum.

I don't follow you. 422.11(E)(3) says "Not to exceed..." To me that means they are specifying a maximum size.

If the appliance had a load current of 14.2 Amps, and was a continuous load, 422.10(A) would specify a minimum size of 20A, and 422.11(E)(3) would specify a maximum size of 25A. The appliance could be on either a 20A or 25A branch circuit.

 

[erickench]

Why would they allow you to use the next higher standard rating if the OCPD was meant to be somewhere between 125% and 150%? Take the example of motor branch circuits and feeders. In the case of a branch circuit you're allowed to size up to the next higher standard rating under certain conditions. But with a feeder you never size up. Always down.

 

[david luchini]

Why would they allow you to use the next higher standard rating if the OCPD was meant to be somewhere between 125% and 150%? Take the example of motor branch circuits and feeders. In the case of a branch circuit you're allowed to size up to the next higher standard rating under certain conditions. But with a feeder you never size up. Always down.

Why would they allow you to use the next higher standard size anywhere? On a 150HP, 200V motor, you'd be allowed a 1200A OCPD which is 290% of the 414 FLA.

With a motor feeder you size down because you have already sized up for the largest motor.

For instance, if you had a feeder for twp 200v motors, (1) 30HP, and (1) 1/2HP

The total full load current for on the feeder is 94.5A. The feeder OCPD is allowed to be 250A, because I round up for the largest motor - 92*2.5=230A => round up to 250A. Add the second motor to the 250: 250+2.5=252.5. Then I round down to 250. But I'm still a 260% of the feeder FLA.

 

[erickench]

If they meant 150% maximum OCPD for appliances then it would be an absolute maximum. Frankly I think both rules should be combined.

 

[david luchini]

If they meant 150% maximum OCPD for appliances then it would be an absolute maximum. Frankly I think both rules should be combined.

If they meant 250% maximum for motor branch circuits then it would be an absolute maximum, as well. In multiple locations where the code specifies a maximum OCPD, they realize that a maximum will not correspond to a standard OCPD size and permit the next standard higher size OCPD.