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

[erickench]

Okay, lets take the case of a central heating furnace. NEC 422.12 requires that the furnace be supplied by an individual branch circuit. The NEC does not consider a furnace to be a continuous load. If it did then we would all be in trouble. If the furnace were marked at a rating corresponding to a standard OCPD rating as given in NEC 240.6 then we would use that OCPD rating. If it didn't correspond then we would have to use an inverse time circuit breaker with a long time setting and adjust the trip to the marked rating on the furnace.

 

[david luchini]

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.

This is where your confusion is...I tried to point it out in Post #12.

422.10 and 422.11 are referring to DIFFERENT markings.

422.10 is referring to the marked "Rating of the Appliance." In other words, this appliance is rated 13Amps. The load current is 13Amps.

422.11 is referring to a marked "Protective Device Rating." In other words, this appliance can be protected by a 20A circuit breaker. These are two DIFFERENT markings.

See 422.11(A): "IF a protective device rating is marked on an appliance..." (Note the protective device rating may or may not be marked.)

See also, 422.11(E): "the rating of the overcurrent protection shall comply with the following:
(1) Not exceed that marked on the appliance. (That is the marked protective device rating.)
(2) Not exceed 20A if the overcurrent protection rating is not marked and the appliance is rated 13.3A or less (The protective device rating is NOT marked, but the appliance rated current is, and must be 13.3A or less.)
(3) Not exceed 150% of the appliance rated current if the overcurrent protection rating is not marked and the appliance is rated over 13.3A. (The protective device rating is NOT marked, but the appliance rated current is greater than 13.3A.)

The "Marked Rating of the Appliance" mentioned in 422.10(A) is completely different from the "Overcurrent Protection Rating" which is either 'marked' or 'not marked' in 422.11(E).

How would I know if the appliance rated current for purposes of 422.11(E)(2) and (3) was greater of less than 13.3A, if this rating was not marked?

 

[david luchini]

Okay, lets take the case of a central heating furnace. NEC 422.12 requires that the furnace be supplied by an individual branch circuit. The NEC does not consider a furnace to be a continuous load. If it did then we would all be in trouble. If the furnace were marked at a rating corresponding to a standard OCPD rating as given in NEC 240.6 then we would use that OCPD rating. If it didn't correspond then we would have to use an inverse time circuit breaker with a long time setting and adjust the trip to the marked rating on the furnace.

Hopefully the last post helped you out with this, but this is again incorrect.

Lets say you had a furnace with a marked 20A rating, but no marked OCP. 422.11(E)(3) would allow an OCPD up to 30A. So the furnace could go on a 30A OCPD with #10 circuit conductors. It would comply with 422.11(E) and 422.10(A).

Now lets say the furnace was considered a continuous load. 422.11(E)(3) would still allow an OCPD up to 30A. So the furnace could still go on a 30A OCPD with #10 conductors. Itw would also comply with 422.11(E) and 422.10(A).

 

[erickench]

So what you're telling me Dave is that there are two different marked ratings on appliances. Have you ever seen these two different ratings on appliances? What do they say exactly?

 

[david luchini]

So what you're telling me Dave is that there are two different marked ratings on appliances. Have you ever seen these two different ratings on appliances? What do they say exactly?

No, I'm telling you that there may be two different markings. 422.11(A) and (E) makes this clear.

The first would be the rating (ie, load current) of the appliance. Say 13A. This appliance's load is 13A.

The second is the overcurrent protection rating. This appliance can be put on a 20A OCPD, or a 30A OCPD, etc.

If the overcurrent protection rating is marked, then the appliance's OCPD cannot exceed that marked overcurrent protection rating (see 422.11(A) and 422.11(E)(1).)

If the overcurrent protection rating is NOT marked, then the OCPD must comply with 422.11(B), (C), (D), (E)(2), (E)(3), (F) and (G).

 

[erickench]

Still don't see the difference between the rating of an individual branch circuit and the rating of the OCPD. But thanks for your help anyway. Do you do alot of work with furnaces and water heaters?

 

[renosteinke]

The 'branch circuit rating' refers to the wire size. The 'rating of the overcurrent protection' refers to the fuse (or breaker).

So, where's the problem? Of course you can have the wire 'bigger' than the fuse.

The 'non motor' part simply recognizes that with motors there are starting currents and other factors to consider, in addition to the full load amps. If anything, this is where the text errs, as there are other things (like welders) that require some additional thought.

 

[erickench]

The 'branch circuit rating' refers to the wire size.

The branch circuit rating cannot refer to the wire size. NEC 210.3 make's that clear. It's just a problem with the NEC. I've found lots of them. I made alot of proposals for the next cycle. Too bad I missed this one.

 

[david luchini]

Still don't see the difference between the rating of an individual branch circuit and the rating of the OCPD. But thanks for your help anyway. Do you do alot of work with furnaces and water heaters?

You're not comparing the difference between an individual branch circuit and the rating of the OCPD. You are comparing the Rating of the APPLIANCE to the rating of the OCPD.

422.10(A) says the branch circuit for the appliance cannot be LESS THAN the Rating of the APPLIANCE. If the Rating of the APPLIANCE is 6 Amps, 422.10(A) would allow you to put it on a 15A, 20A, 25A, 30A, 40A or 50A branch circuit, etc.

422.11(E)(2) would limit me to a 20A OCPD, so I'm then left with either a 15A or 20A branch circuit for the 6A rated appliance.

You are confusing appliance rating, marked appliance overcurrent protection device rating, and branch circuit rating.

 

[erickench]

Okay, I looked at NEC 210.3 again. The last sentence seems to imply that it may be possible for a conductor's ampacity to be designated as the rating of the circuit. I guess that would apply where NEC 240.4(B) is in effect, i.e. using an OCPD higher than the ampacity of the conductor.