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Old 06-13-2008, 11:58 AM   #1
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wiring for central air

I have a 'new' central air unit that needs wire to it so I can use it.
I have 12 ga. Thnn or 10ga. thnn.(would put that in plastic conduit of course!!)
Or I also have some 12-2 w/gr. I can use also.
here we dont have code where you HAVE to run all wires thru conduit,,,bigger town nearby does!!
Old house thru unfinished basement with ledge(chances of being EVER finished is NILL) About 25' run from electric box to unit
Small house,small unit,,,saw on outside unit, max size of breaker 20A,,, min. size15A

i bought a disconnect box with a GFCI in it and has an outlet in it to plug my diesel pickup into since it has to set outside in Nebraska brutal winters. chances are slim of Ac and pluged in pickup at same time,,,NONE!! could have like a weed trimmer plugged in tho,,so does that influence wire size??Or corded tools etc.(my ONLY exterior outlet!!)
Thanks for any advice!!-don-


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Old 06-13-2008, 12:59 PM   #2
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You will need to run 4 wires to make it work, 2 hots, a netural and a ground wire.
Wire size can be #12.
I have not looked at that type of disconnect, so it might need a seperate circuit for the outlet.


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Old 06-13-2008, 01:16 PM   #3
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What voltage is this unit?
If it is 240 volts, you will have to run two circuits on for the ac unit one for the GFCI 120 volts.
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Old 06-14-2008, 10:00 AM   #4
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Thanks for the replies

Thank you for helping me get this right. So IF I understand correctly maybe conduit with the thnn wire would be way to go?? Since I obviously need two circuits run. So if I run 10 for the a/c and 12 for the gfi circuit,that should keep it straight. How big of conduit do I need? (those thnn wires are pretty small,,,thinking 1/2 or 3/4 would be plenty big??)

This disconnect box on outside,is their a code for how close to outside water spigot it can be?? Sort of space challenged in this area. First the gas meter, then the gas furnace intake and exhaust pipes,then the a/c piping and unit ,then the water spigot all in about 4-5 ' of space.

I just had new vinyl siding so do I need to use a box out for the disconnect box?? Or directly mounted thru siding?? Any setback from pvc furnace intake and exhaust??
thx so much-don-
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Old 06-14-2008, 03:07 PM   #5
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Don't forget about the thermostat wires (cable) and thermostat.

Ps.....This cable cannot be in the same conduit as the power conductors feeding the AC.

Last edited by J. V.; 06-15-2008 at 09:46 AM.
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