Window AC conductor size

[W6SJK]

Have an old old A/C unit, 230/208V, 15.8A/16.5A with no max CB size listed since that was not a requirement when it was manufactured.

It is clear that the CB size must be 30A on my 208V circuit. But what wire size needs to be used? I have an existing circuit that is #12 that I would like to use. If it were a regular motor circuit #12's would be fine.

California Elec Code (1999 NEC) Art 440 Part D (Branch Circuit Conductors) section 440-33, ex 2 says that for conductor sizing Part 'G' applies.

Part G says that the appliance shall be treated as a single motor appliance where all of the following conditions are met: 1 - cord and plug connected , 2 - not over 40A 250V, 3- Total rated load is on nameplate, 4 - Branch circuit CB/Fuse does not exceed ampacity of the wiring.

What if the four conditions are _NOT_ met? I can't go back to 440-33 because it directs me to Part G. I'm going around in circles!

 

[electricman2]

Re: Window AC conductor size

Does it have a cord and plug? If so what is the plugs NEMA configuration? Supply a branch circuit the same size.

 

[iwire]

Re: Window AC conductor size

I was racking my brain trying to come up with an answer to this thinking of all different code sections and then John posts this.

Originally posted by electricman2:
Does it have a cord and plug? If so what is the plugs NEMA configuration? Supply a branch circuit the same size.

That is such a perfectly simple direct answer.

[ June 20, 2005, 04:31 PM: Message edited by: iwire ]

 

[kevinware]

Re: Window AC conductor size

Ok I am just an apprentice but I too am trying to find a good answer for this and also understand. Now I have a question. If this unit we are talking about is a room air conditioner and connected to a 208V circuit would that make it a rated three phase unit? And looking at the last paragraph of 440.60 which states "A room air conditioner that is rated three phase or rated over 250V shall be directly connected to a wiring method recognized in chapter 3 and provisions of part VII shall not apply." If that is correct would I default to 440.6 and 440.32 and use the 16.5Amp rating to get the wire size? Or would this unit be a rated 208V single phase unit?

16.5
x 1.25
---------
20.625 (21Amps)

Then go to Table 310.16 and use the 75 Degree colume and get a wire size of #12

Please correct me...............

 

[wirenut1980]

Re: Window AC conductor size

kevinware, it is possible to have 208 V single phase. 2 ungrounded (hot) conductors and an EGC.

 

[W6SJK]

Re: Window AC conductor size

Update: Yes, it has a 30A plug. I didn't look at the wire size but it is probably #10.

But that doesn't answer my question about interpreting the code requirements...

kevinware, it is a 208V single phase unit.

 

[celtic]

Re: Window AC conductor size

Originally posted by sparkie001:
Update: Yes, it has a 30A plug. I didn't look at the wire size but it is probably #10.

But that doesn't answer my question about interpreting the code requirements...

You answered your own question....

Part G says ...where all of the following conditions are met:
1 - cord and plug connected ,
2 - not over 40A 250V,
3- Total rated load is on nameplate,
4 - Branch circuit CB/Fuse does not exceed ampacity of the wiring.

1 - meets G
2 - meets G
3 - meets G
4 - see below
If the plug is the original one, the circuit would have to be a #10/30A . What you have in the wall is another story

 

[iwire]

Re: Window AC conductor size

Originally posted by sparkie001:
Update: Yes, it has a 30A plug. I didn't look at the wire size but it is probably #10.

But that doesn't answer my question about interpreting the code requirements...

Yes it makes it easy, a 30 amp outlet can not be protected by a breaker larger than 30 no mater what the load is.

 

[W6SJK]

Re: Window AC conductor size

iwire - I'm not trying to protect the 30A recept at over 30A. But the code (Art 440) seems unclear on the wire size. If it were a motor #12's would be OK.

[ June 22, 2005, 07:55 PM: Message edited by: sparkie001 ]

 

[W6SJK]

Re: Window AC conductor size

celtic - The code doesn't apply to the cord/plug of a UL listed appliance. So what is the code requirement in section 440 for the branch circuit wire size? Thanks to all for your opinions...