We are seeing a lot of "mini split" AC units. As an example, let's say we have a mini split with an MCA of 11 amps, and a maximum fuse or circuit breaker of 25 amps per the nameplate. The wiring method is Romex. Wiring the unit with 14/2 would satisfy the MCA, however I believe it would violate 250.122 due to the 25 amp OCPD. To comply with 250.122, using Romex it seems we would need 10/2, no? Am I missing something?

You have to determine the OCP that you are installing to determine the EGC for the circuit.

Using the nameplate MAX of 25 OCP would require #12. This is based on 250.122 table in '11 NEC as I read it.

BigB...The first sentence of 250.122(A) says that in no case shall the EGC be required to be larger than the circuit conductors supplying the equipment...

I use the Minimum Circuit Ampacity to size my branch circuit conductors for an AC unit...

Please note that the 2014 edition will have changes to this requirement in air conditioning article.

Ah so I was missing something. The scary part is I am pretty sure I knew that at one time. Getting old is no fun.

Perhaps a little clearer....

BigB example is 14/2NM, but he said 25 amp OCP, using the nameplate max figure.

Using the max OCP, a #12 EGC would be required, so using NM he has to use 12/2.

Yes, the EGC does not have to be larger than the circuit conductors, 'oversize' EGC to my knowledge is not available.

IMHO, I believe that he did not read Table 250.122 where the amperage col. jumps from 20 amps for #12, and 60 amps for #10.

I agree with the getting old and memory loss...

short:
Ditto!!

I'm not sure I follow you Hotline...

When doing AC units the nameplate has all the info for sizing the branch circuit wiring...and sizing the overcurrent device.

For example...if the nameplate gives a MINIMUM BRANCH CIRCUIT AMPACITY of 30amps and a MAXIMUM BRANCH CIRCUIT OVERCURRENT DEVICE of 50amps...

I will wire the unit with 10-2 romex and connect it to a 50amp breaker.

Follow me?

shortcircuit

I don't follow you, the nameplate MCA gives us the permission to size the wire accordingly. Also, 250.122 says #12 EGC for an OCPD not exceeding 20 amps. 25 amps exceeds 20 amps, and puts us into #10, (which is good up to 60 amps) is the way I am reading it.

BigB, Hotline...Ok I understand what your getting at now. Sorry for being slow to pick up on the grounding issue. It appears that your interpretation of the EGC sizing is in line with article 250.122 in your situation. Good catch.

What specific changes are we looking at?

From the thread "Let the Diss-CUSS-ion Begin:"

"7) Certain uses of EMT outdoors will be required to have a ground wire. This gem is buried in Article 440."

I haven't seen the text, but I'll be sure to look closely at AC grounding when it comes out! Heaven alone knows what other grounding changes are buried in the text.

I've been with ECN for several code cycles, and every new edition seems proceeded by threads where our learned discussion is torn apart by new code changes a few months later. This might be just such a thread.

Sorry I am late on this but Short Circuit pointed out 250.122 says you do not need to exceed the circuit conductor size for the EGC, so if the circuit can be #14, the EGC can be #14.



I am not seeing anything that contradicts this and requires more than #14 if the circuit conductors are #14.
If there is a fault, why should the EGC need to be be any bigger than the circuit feeding the fault?

But I would not let them use type NM to wire a condenser (wet location). If it was UF it would be OK but that is still going to be in a raceway in my patch.

Finally some support on my interpretation...although this discussion has confused me on which is correct.

I referred to my Soares book on grounding and it supports that the EGC never has to be larger than the circuit conductors.

It is certainly logical. Why would the return path for a fault ever have to be bigger than the supply?

This all gets back to the difference between overload and overcurrent.

Per OP, 14 gauge wire and 25 amp breaker. I'd pull a ground every time required or not. My license, my butt, my problem and I sleep peacefully at night.

I agree with Greg on both accounts. 25 Amp breaker is motor class 101. To prevent neuscuence tripping on startup. And possibliy overload protection to in this case. The ground does not have to be any bigger than the grounded conductor if the circuit is sized right. The grounding conductor carries a fault for only a split second. It will get warm and carry more that enough current to trip the breaker in the event of a ground fault. You can run a 3/0 grounding conductor with 3/0 circuit if you want but if the breaker but in a ground fault where the breaker fails, that 3/0 will burn up too just like a #6 will so why install more then needed

I am in complete agreement with your interpretation, I did not mean to confuse the issue by contesting Hotline's selection of the EGC size (even though selection is not needed per your interpretation).

In the majority of the installations the NM is usually inside the building and only passes through the wall to the disco.