Air conditioning condensing unit has a minimum ampacity rating of 18 amps.

A maximum over current protection device rating of 30 amps.

A 60 amp rated non-fused diconnect is used and installed in a readily accessible location.

14 AWG wire is run to the disconnect, and then #14 THWN to the condensing unit.

A double-pole 30 amp circuit breaker is installed at the panel.

Is this an NEC compliant installation?

Absolutely Green Sticker time.

I need some clarification on this one.

How can you use a 30a breaker to protect 14g wire?

heck I guess I need to know how 14-2 supports 18a aswell.

[This message has been edited by Trick440 (edited 10-05-2006).]

I agree with George.

Trick first off 14 AWG is rated anywhere from 20 to 25 amps depending on the insulation and terminations.

On typical branch circuits 240.4(D) requires us to use a 15 amp over current device.

However for HVAC units 240.4(G) applies and we can use 14 AWG up to the rating in 310.16 and the short circuit and ground fault protection can be as allowed in 440.6

Can't wait to pull this one on my boss.. lol.

Thank you for the code refs. and explanation.

Trick, this is exactly why I posted this. I did an over/ under split-system A/C install today and was talking to the HVAC contractor. He saw me looking at the specs on both CU's and told me, "just run a 30 amp 10/2 wire."

So I said, "ok, but I could really just run 14 wire and it'd be ok by NEC standards."

He says, "I've never heard of that so don't so it."

^^
(this coming from the HVAC guy, not an electrician)

Of course, the better install is to run the maximum size wire and the maximum size OCPD, I'm sure most would agree. But the point is, it can be done and pass inspection, and damn it felt good to hold my own in this discussion.

Thanks ECN!

Ron:
Ya did good! Just keep watching the mfg nameplates. Only other consideration could possibly be voltage drop, dependent on the run. That's my opinion, when ya cut it close.

John

Thanks John!

Most of the mini split systems I have done will list the max fuse or circuit breaker, and the minimum ampacity of the wiring. What I've noticed is they tend to want to protect thier machines from overworking and usually exceed code a bit on the minimum ampacity labeling. Code says go with what is on the label.

iwire, what about 240.6? In order for this to be code compliant you would need a 25 ampere breaker to comply with 240.4(B). IMHO
thanks Joe

240.(B) is not being used in this application, we are using 240.6(G)

When you read 240.6(G) you find it says 'shall be permitted'

Take that along with the sections in 440 and you get to go much larger that the next standard size.

Here is the reason this is permitted and it is safe.

The HVAC unit contains internal overload protection, if say a motor seizes up the units own over current protection will open before the conductors area damaged assuming you followed the name plate data.

The break at the panel is not being used for over current protection, it's only function is short circuit and ground fault protection.

I understand that 440 allows you to use 14 awg for this installation, but I cannot find were the code allows you to protect 14 awg with a 30 ampere breaker when by table 310.16 shows maximum of 25 amperes. This is the part that is confusing me.

Thanks

Mountan, look at 430.52

In this case look at 440.6 for the nameplate use, 440.12 for the disconnect size, 440.22 for the OC device and 440.31 for the wire size,.

But the key is the last sentence of 440.21: "They" (short circuit and ground fault OC devices) "are in addition to or amendatory of the provisions of Article 240."

Code compliant maybe, cutting it close, adding too many variables to the picture like ambiant temp, derateing, voltage drop, starting current etc. But with most inspectors, it just wont fly when you have a 3 second eye-ball inspection, or a full blown engineering calculation to go through.

Either way, we are in the buisiness of selling wire right? the bigger the better....

Mark there are always two answers, the code minimum (which the inspector must accept) or beyond code minimums.

99% of the time we run conductors that match the breaker size.

I had my outside AC unit moved from the west side of my house to the north side of my house, Granted it was a freebie job, I had done an electrical favor fer the ac guyz sister, and in re-payment he moved my ac, cut and brazed the freon lines etc, but when he moved it, he went from a 45amp 230v dissconect to the unit w/ #12 awg, that was laying out side my shed. and told my roomate, that I needed to replace it (the #12) as soon as possible..............

Is the 60 amp disconnect correct for the overload though?

Village:
Welcome to ECN.
Any size disconnect is OK, provided that the MOCP is sized properly. IF you wanted, for whatever reason, to install a 600 amp disco, that also would be OK

John