0

I am getting ready to hang drywall in my basement but before I do that, I need to run wire from the main panel upstairs to the future location of the central AC furnace through the basement ceiling joists. I do not know yet who will be installing my AC but I will probably outsource it. At this point I just need to know what the electrical requirements for AC are so that I can bring the cable and hang the drywall. The house has three bedrooms and two living rooms, 1800 sq ft, two floors.

What amperage/AWG am I looking at? The wire distance from the panel to the furnace is only about 20' +/- and then I plan to sit the condenser on the roof (it is a low pitched mod bit roof so I can do this, many of my neighbors with similar homes do) directly above the furnace, two floors above (so another 16-20' total). It also may be worth mentioning that I plan to use this for just AC and not heat -- I have already a radiator system in place and I love radiant heat.

4
  • What would the length of this wire be? It's important to know for the calculation.
    – longneck
    Nov 11, 2013 at 16:29
  • Company installed spilt unit on inside wall and the condensor outside atop a wall the man that installed unit requires a 30 amp line 208 1ph lime
    – user56654
    Jul 21, 2016 at 1:27
  • You need no extra wire to the furnace. The power will be needed outside at the compressor. Aug 31, 2019 at 15:36
  • Where is this house located? Jan 30 at 16:05

6 Answers 6

4

You should either sort out what the AC is going to be, so you can get specific power supply and cabling needs sorted out now, or line up your joist holes nicely and follow the excellent suggestion from @longneck to run conduit, leaving the wiring for later. Use flexible conduit, if needed to get it in place. Run at least two - there may well be low voltage control circuits that need to be run separated from the power supply. Alternatively, leave a section of the drywall open for now, allowing for both cabling and refrigeration tubing to be run before you close it up.

3

It's going to completely depend on the unit that's being installed, but commonly it'll be 30-60 amp with 10-4 AWG wire. You're probably looking at a 3.5 ton unit, so you'll be in the 30-40A (10-8 AWG) range. It might be worth it to get a few quotes from local HVAC companies, and see what they want to install. The companies may have a preferred breaker and wire size, so they may want to redo any work you do anyway.

Don't forget you'll also need high and low pressure tubing, and control wires between the indoor and the outdoor units.

7
  • 7
    An alternative to installing wiring now would be to install conduit instead.
    – longneck
    Nov 11, 2013 at 16:41
  • no, @longneck, it needs to go through ceiling joist holes
    – amphibient
    Nov 11, 2013 at 16:52
  • do the condenser and air handler run on the same or separate circuits?
    – amphibient
    Nov 11, 2013 at 19:20
  • @amphibient Usually the furnace is on a 120V circuit, and the condensing unit is on a separate 240V circuit.
    – Tester101
    Nov 11, 2013 at 22:12
  • 1
    @amphibient I'm not familiar with this type of installation, all my experience is with installations where the A/C is an add-on to an existing furnace. In which case the furnace and condensing unit are on separate circuits. I'm guessing the indoor and outdoor units will still be separate, but I'm not positive. The air handler will likely only require a 120V 15-20A circuit, whereas the condensing unit will require 240V 20-50A circuit. If you're running cable for both, you'll probably want to run one 12/2 to the indoor unit and one 10/2 cable to the outdoor unit.
    – Tester101
    Nov 11, 2013 at 22:33
3

Most likely you need 8-3 with ground thnn or thwn with 50 amp disconnect mounted within several feet from unit with a 50 amp circuit breaker in the main distribution panel. This is good for 50 amp rated unit. Use 10 awg for 30 amp unit or 6 awg for 60 amp unit. These rating are adequate for runs of up to appx 60 ft

0
1

First the wire size depends on the size and requirements of the unit itself. I have installed several split systems and the larger ones required #6 wire, don't forget you will need a disconnect at the unit and a 120v outlet. I use a combination 240v disconnect and. 120v GFCI outlet that is weather and tamper resistant similar to Eaton dpf222rgf20wtst this is good for up to 60 amps but most split systems don't require a disconnect this large. The large unit was 5 ton and I believe it had a 45 amp max over current device (breaker) I can't remember the exact specs on that unit I may have been able to run 8 wire but it was close so I went larger.

1

The ac should be installed prior to any finish work from what is being said here. A 240 line is needed for the condenser directly to breaker panel with a disconnect at outside unit. Breaker size depends on what is installed and length of wire.

0
0

I see you did not get a good firm answer. I see the date so you are done with your project by now I hope. All I have to say is you have to many variables. You can't give a precise answer with out the exact spects, so you have to pick the unit you are going to use you have to know this to calculate the wire gage after you calculate the unit amp's with the full wire run. I my self if you are getting close to the max amp's for your run of wire i go up 1 size in wire because if the wire is to small it may feel a little worm the one thing no one told you stay in the mid,of specs if you draw to many amp its hard on the compressorand fan and will shorten the unit life and most of all if you are running to close to it will increase your elect, cost. Because if the wires are to small you will use more elect'worm wire ohms resistance will increase and all the money you spent to have a hi efficient unit you threw out the window. I figure all my work after I have all my parts on hand .Dave I hope all worked out for you

1
  • 1
    Can you please edit to explain what "Because if the wires are to small you will use more elect'worm wire ohms resistance will increase" means?
    – FreeMan
    Jan 31 at 12:23

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.