conductor size for 240volt air conditioning unit

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Re: conductor size for 240volt air conditioning unit

Editted! Stupid computer!

Thanks for the clarification! I guess you can teach new dogs new tricks too... :D

[ February 03, 2005, 07:15 AM: Message edited by: georgestolz ]
 
Re: conductor size for 240volt air conditioning unit

Interesting point Don and Iwire. I have always used 35A wire with 35A MOCP. Now you have me thinking. My only caution is that at design time you never know for sure what brand HVAC units will be used. Mech engineer might design based on Trane but end up Carrier. No garantee that the MCA's will be the same. If you cut it too close on the wire size, you might have problem when the units come in.
 
Re: conductor size for 240volt air conditioning unit

We have been bitten hard by that same situation.For along time we used the marked KW rating on the duct work for electric heat air handlers ( residential ) 5 KW were wired in # 10/2 NM Then on one project come trim out the air handlers were set and the min ampacity listed was 35 amps . There were around 40 2 story townhomes affected at one time :eek: So as a rule of thumb we now wire all 8 KW a/h/u`s in # 6/2 nm we use #6 so our warehouse doesn`t have to have so many different sizes in stock and all 10KW a/h/u`s in #6 SE.Yeah it might cost a little more as per the individual house but we put it in the bid price and have saved alot of money by not having to retro larger wire after drywall.
 
Re: conductor size for 240volt air conditioning unit

Originally posted by sceepe:
Interesting point Don and Iwire. I have always used 35A wire with 35A MOCP. Now you have me thinking. My only caution is that at design time you never know for sure what brand HVAC units will be used. Mech engineer might design based on Trane but end up Carrier. No garantee that the MCA's will be the same. If you cut it too close on the wire size, you might have problem when the units come in.
Click to expand...
sceepe this subject comes up a lot and while I will point out we can wire for the minimum circuit ampacity then protect that with the maximum branch circuit short circuit and ground fault protection stated on the unit I can't say I see that done much.

All the engineers that design the jobs we work on size the conductors at least as large as the branch circuit short circuit and ground fault protection device. :cool:

Also the ratings on the unit do not take into account voltage drop if it is a longer circuit.

[ February 05, 2005, 03:00 PM: Message edited by: iwire ]
 
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