NEC 422.10(A) & 422.11(E)(1)

[erickench]

I have discovered what might be a peculiarity in the NEC. NEC 422.10(A) state's:

The rating of an individual branch circuit shall not be less than the marked rating of the appliance....

But NEC 422.11(E)(1) state's:

If the branch circuit supplies a single non-motor-operated appliance, the rating of the overcurrent protection shall comply with the following:

(1) Not exceed that marked on the appliance


From the above I would say that it would be impossible to have a marked continuous non-motor appliance on an individual circuit without violating the code.
Also, if the appliance were noncontinuous it could result in not being able to find an OCPD to match that on the marked rating because the marked rating would not be the same as a standard rating given in NEC 240.6. You would have to use an inverse time CB with a long time setting.

Does anyone care to comment on this?

 

[RB1]

I don't see the conflict. 422.10(A) establishes the minimum rating of the circuit necessary to carry the load. 422.11(E)(1) applies where the appliance is marked with the maximum overcurrent protection.

 

[Smart $]

I agree with RB1.

I can see where this 422.11(E)(1) can be misinterpretted. What is to be not exceeded is the marked [maximum] overcurrent protection rating... not a marked [load] current rating.

 

[erickench]

I don't see the conflict. 422.10(A) establishes the minimum rating of the circuit necessary to carry the load. 422.11(E)(1) applies where the appliance is marked with the maximum overcurrent protection.

But isn't the rating of the circuit the same as the rating of the OCPD for that circuit?

 

[Dennis Alwon]

But isn't the rating of the circuit the same as the rating of the OCPD for that circuit?

That is correct and I don't understand why. I can have #12 wire being fed with a 40 amp OCPD and the circuit would be considered a 40 amp circuit. Ignore this post

 

[david luchini]

But isn't the rating of the circuit the same as the rating of the OCPD for that circuit?

Not necessarily. If you had, for instance, an appliance with a marked rating of 13A (422.10(A)) and a marked protected device size of 20A, that was to be a continuous load. 422.10(A) tells you that you will need conductors with an ampacity of at least 16.25A.

Consider if the conductors for this appliance shared a conduit with other circuits such that you had 8 CCC's. You planned to use #12 THWN conductors, which have an adjusted ampacity of 17.5A. These conductors meet the minimum requirements of 422.10(A). The conductors are protected by a 20A c/b which meets the requirements of 422.10(E)(1) for the appliance OCDP and 240.4(B) for the conductor OCPD.

The rating of the circuit conductors is less than the circuits OCPD.

 

[Dennis Alwon]

I take back my statement above. I understood rthe cmp panel to say what I stated but I just read 210.3 which clearly states if the conductors are of a higher ampacity for any reason then the rating of the branch cicuit is based on the ocpd.

 

[erickench]

Not necessarily. If you had, for instance, an appliance with a marked rating of 13A (422.10(A)) and a marked protected device size of 20A, that was to be a continuous load. 422.10(A) tells you that you will need conductors with an ampacity of at least 16.25A.

What your saying is in violation of NEC 422.11(E)(1). The OCPD would exceed the marked rating for a continuous appliance. An individual branch circuit would seem to be the same as a single appliance on a branch circuit. I think we could safely say that it is not advisable to use a marked appliance on an individual branch circuit because of the resulting conflicts in the rules.

 

[Dennis Alwon]

Maybe the confusion is the OCPD. If the appliance is marked with max OCPD you cannot exceed that however if this is a continuous duty appliance I would bet the OCPD marked on the appliance has that built into the equation.

Do you have real life example?

 

[Dennis Alwon]

Not to get off track but here was my confusion. This is something I read from MH. The bold sentence alone is not true but I did not read the NEC text when I read it.

The size of the circuit breaker installed on a branch circuit, not the conductor size, determines the rating of the circuit. Therefore, if the conductor size is increased to accommodate for voltage drop or for ampacity adjustment or correction purposes, the rating of the circuit remains the same as the circuit breaker size supplying it [210.3].

 

[erickench]

Maybe the confusion is the OCPD. If the appliance is marked with max OCPD you cannot exceed that however if this is a continuous duty appliance I would bet the OCPD marked on the appliance has that built into the equation.

Do you have real life example?

Then how would you calculate it? Are you saying that the continuous appliance has two different ratings? The higher one would be less than or equal to 125% of the lower rating?

 

[david luchini]

What your saying is in violation of NEC 422.11(E)(1). The OCPD would exceed the marked rating for a continuous appliance. An individual branch circuit would seem to be the same as a single appliance on a branch circuit. I think we could safely say that it is not advisable to use a marked appliance on an individual branch circuit because of the resulting conflicts in the rules.

No, it is not a violation. In my example the appliance is marked with a Protective Device Rating of 20A, and is protected with a 20A protective device. How is that a violation of 422.11(E)(1)? 20A does not exceed 20A.

I think you are confusing a marked "rating of the appliance" (see 422.10) and a marked "protective device rating" (see 422.11.)

 

[erickench]

No, it is not a violation. In my example the appliance is marked with a Protective Device Rating of 20A, and is protected with a 20A protective device. How is that a violation of 422.11(E)(1)? 20A does not exceed 20A.

I think you are confusing a marked "rating of the appliance" (see 422.10) and a marked "protective device rating" (see 422.11.)

NEC 422.11(A) state's "marked rating of the appliance" and NEC 422.11(E)(1) state's "marked on the appliance". What is the difference between the two?

 

[erickench]

IT'S PECULIAR!!!! The only time that you could have a marked appliance on an individual circuit is if the appliance is noncontinuous and the marked rating is equal to one of the standard OCPD ratings in article 240.:jawdrop:

 

[david luchini]

NEC 422.11(A) state's "marked rating of the appliance" and NEC 422.11(E)(1) state's "marked on the appliance". What is the difference between the two?

Read 422.11(E) again. It says:

If the branch circuit supplies a single non-motor-operated appliance, the rating of the overcurrent protection shall comply with the following:
(1) Not exceed that marked on the appliance.


442.11(E) is referring the the rating of the overcurrent protection marked on the appliance.

442.10(A) is referring to the rated current of the appliance ("marked rating of the appliance.") The rated current is used to determine proper branch circuit conductor size. The conductors must be sized at least as large as the rated current of the appliance, or 125% of the rated current for a continuous load appliance.

Note that 422.11(A) tells you that the conductors must also meet the protection requirements of 240.4. If you had a 13A rated, non-continuous appliance, with a marked overcurrent protection of 20A, you wouldn't be able to use #14AWG conductors, even though you would be complying with 422.10(A) and 422.10(E)(1).

IT'S PECULIAR!!!! The only time that you could have a marked appliance on an individual circuit is if the appliance is noncontinuous and the marked rating is equal to one of the standard OCPD ratings in article 240.

This is not correct. You could have an appliance with a marked rating of 13A (and no marked "protective device rating.") This appliance could be on an individual 20A OCPD with #12 circuit conductors and it would comply with 422.10(A), 422.11(E)(2) and 240.4.

 

[erickench]

Read 422.11(E) again. It says:

If the branch circuit supplies a single non-motor-operated appliance, the rating of the overcurrent protection shall comply with the following:
(1) Not exceed that marked on the appliance.


442.11(E) is referring the the rating of the overcurrent protection marked on the appliance.

442.10(A) is referring to the rated current of the appliance ("marked rating of the appliance.") The rated current is used to determine proper branch circuit conductor size. The conductors must be sized at least as large as the rated current of the appliance, or 125% of the rated current for a continuous load appliance.

Note that 422.11(A) tells you that the conductors must also meet the protection requirements of 240.4. If you had a 13A rated, non-continuous appliance, with a marked overcurrent protection of 20A, you wouldn't be able to use #14AWG conductors, even though you would be complying with 422.10(A) and 422.10(E)(1).

But 422.10(A) does not speak of conductor sizing. It clearly state's that:

The rating of an individual branch circuit shall not be less than the marked rating of the appliance....


NEC 210.3 state's:

Branch circuits recognized by this article shall be rated in accordance with the maximum permitted ampere rating or setting of the overcurrent device.

 

[david luchini]

But 422.10(A) does not speak of conductor sizing. It clearly state's that:

The rating of an individual branch circuit shall not be less than the marked rating of the appliance....


NEC 210.3 state's:

Branch circuits recognized by this article shall be rated in accordance with the maximum permitted ampere rating or setting of the overcurrent device.

I agree the section is poorly written, but read the first part of 422.10: "This section specifies the rating of branch circuits capable of carrying appliance current without overheating under the conditions specified."

Read also the definition of Branch Circuit "The circuit conductors between the final overcurrent device protecting the circuit and the outlets."

It is clear that 422.10 is referring to the minimum size of the circuit conductors to ensure that the conductors can carry the appliance load current without overheating.

422.10 is followed by 422.11 Overcurrent Protection. The overcurrent protection for the appliance is addressed in 422.11, not 422.10.

But even if you read 422.10(A) as meaning both the branch circuit conductors and OCPD, it would still allow a marked 13A rated appliance (with no marked overcurrent protection rating) to be installed on a 20A branch circuit.

 

[erickench]

Well you may choose to interpret the code this way but I say these two sections are muddled. If 422.10(A) was meant to apply to conductor sizing it would use words like "conductor ampacity" which it doesn't. I hope you're not regretting something that you did Dave.

 

[david luchini]

Well you may choose to interpret the code this way but I say these two sections are muddled. If 422.10(A) was meant to apply to conductor sizing it would use words like "conductor ampacity" which it doesn't. I hope you're not regretting something that you did Dave.

Yes, I agree the section is muddled. It uses a poor choice of words by saying "Branch-Circuit Rating" when it clearly means branch circuit ampacity.

Try this thought experiment. Lets say you had an appliance with a marked rating of 18A (and no marked overcurrent protection,) and it will be non-continuous load.

Now say you want to put it on a 20A branch circuit. You would meet 422.10(A), because the "Branch-Circuit Rating" is not less than the appliance rating. The OCPD would meet 422.11(E)(3) because 20A does not exceed 150% of the appliance rating. So we're good with 422.10(A) and 422.11(E).

Now lets say we use #12 THWN for the branch circuit conductors, and they are adjusted to 17.5A ampacity for 8 CCC's. The #12's are properly protected per 240.4(B), so we also comply with 422.11(A).

Would this installation be acceptable? We are putting an 18A appliance load on a conductor with 17.5A ampacity.

But we have a 20A branch circuit, complying with 422.10(A)
We have a 20A OCPD, complying with 422.11(E)(3).
And we are properly protecting the #12 circuit conductors with the 20A OCPD per 240.4.

 

[erickench]

Yes, I agree the section is muddled. It uses a poor choice of words by saying "Branch-Circuit Rating" when it clearly means branch circuit ampacity.

Try this thought experiment. Lets say you had an appliance with a marked rating of 18A (and no marked overcurrent protection,) and it will be non-continuous load.

Now say you want to put it on a 20A branch circuit. You would meet 422.10(A), because the "Branch-Circuit Rating" is not less than the appliance rating. The OCPD would meet 422.11(E)(3) because 20A does not exceed 150% of the appliance rating. So we're good with 422.10(A) and 422.11(E).

Now lets say we use #12 THWN for the branch circuit conductors, and they are adjusted to 17.5A ampacity for 8 CCC's. The #12's are properly protected per 240.4(B), so we also comply with 422.11(A).

Would this installation be acceptable? We are putting an 18A appliance load on a conductor with 17.5A ampacity.

But we have a 20A branch circuit, complying with 422.10(A)
We have a 20A OCPD, complying with 422.11(E)(3).
And we are properly protecting the #12 circuit conductors with the 20A OCPD per 240.4.

But NEC 422.11(E)(2)&(3) only applies to appliances that are not marked. If the appliance is marked it could be put on a circuit with two or more loads without any conflict.