Air Cond split system

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electricmanscott

electricmanscott

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Location
Boston, MA
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Massachusetts Master Electrician, one man show.
Wiring an addition to a house that is going to have "split system" air conditioning. Ac condenser outside and two inside units that are wall mounted. The wall mounts have blower and controls built in. The hvac guy and the specs (no equip on site yet) call for 230 volt 20 amp line for the outdoor unit and 18-4 sj_ _ (don't remember last two letters) run from the outside unit to each indoor unit. Anyone have any experience with these? The ones I have done all plug in to a receptacle at the indoor unit and the outside is fed separately.
 
Re: Air Cond split system

I've never heard of a set up like that.
(2 Air Handlers for the 1 Compressor)
And the only SJ wire I know of is SJOW which is 300V rubber cord, SOOW is rated at 600V. But, I know you don't want to use either of them!
It sounds like the 18-4 is just control wiring, right? The units should all be on seperate circuits I would think.

Do the units also Heat?

Dave
 
Re: Air Cond split system

You as an EC should know that you can't use SJ or any other cord for this. Check the specs also for the number of conductors and size. They are usually the same size as the power supply up to 20 amps.

We do these all the time. Most times the indoor unit is mounted on an exterior wall and the AC contractor will run UF with the refrigerant lines through a 3" hole in the wall down to the condenser. This enters the condensing unit through a separate KO from the power. We provide the circuit and the disconnect and usually the sealtite and wire to the condenser since I found these guys often don't carry the right size on their truck. They connect everything after the disconnect including the UF.

If the indoor unit is located on an interior wall you could still use UF but probably better to use romex or whatever the building is wired with. In this case I would want to run this myself rather than them ty-rapping it to the refrigerant lines across a basement or attic. Give them a tail where their refrigerant lines go into the indoor unit and bring the other end into the back of the disconnect then THWN through the sealtite to the condenser.

-Hal
 
Re: Air Cond split system

Dave, they make these things with as many as three indoor units. Check out Sanyo, Mitubishi and others.

Good point about the heat. Any that I've seen are also heat pumps so that wouldn't affect the wiring to the indoor unit. It's not just control wiring by the way, there is a blower motor and a motor that moves the louver in the indoor unit.

-Hal
 
Re: Air Cond split system

If the unit is a Fujitsu run a 14-4 romex from the interior fan coil units to an exterior j-box, and then sealtight with 4-#14 thwn plus ground. Re identify the white conductors in the romex. For Sanyo units I believe you can use a 14-3 cable for the same use. In Hawaii it is not uncommon to have up to 6 or more of these split type systems installed at a residence depending on the size of the house.
 
Re: Air Cond split system

Left out a key point in last post. If a Mitsubushi unit is installed the power supply to the compressor and the indoor units are essentially seperate. You have the option of running a seperate circuit to supply the compressor and a seperate circuit to supply the fan coil. Mitsubushi fan coils are wired for 120 volts so if installed in a bedroom ark fault breakers must be used to supply the fan coil. Honolulu C+C inspectors want a switch installed on the fan coil circuit near the fan coil for a disconect means. For the smaller units there is a built in terminal block in the compressor side to allow you to branch off the feeder to supply the fan coil, however code restrictions to limit any one load on the circuit to 50% also must be looked at .
 
Re: Air Cond split system

Scott,

It is real similar to a walk-in refridgerator in a comm. kitchen,only it cools the house instead!

frank
 
Re: Air Cond split system

Here's the deal. Units are now in place. Outside condenser requires a 240 volt 15 amp circuit. Interior fan units are fed with 36 volts DC and draw .8 amps from the condenser unit. The manufacturer recommends 18-4 sjow for the wiring between the condenser and the fan units. Since flexible cord is not permitted to be used as permanent wiring why not 18-4 t stat cable?

[ June 15, 2005, 07:29 PM: Message edited by: electricmanscott ]
 
Re: Air Cond split system

Scott, what brand is used in your situation? I have amped out the fan coils in the brands that I mentioned above and they usually draw around 2 amps running. For me there is allways 14-3 on my truck so I go with that and protect at 15 amps.
 
Re: Air Cond split system

The sjow cord wiring method would be allowed if the units were back to back and the cord didn't pass through the building.

But, when the wiring has to pass through the building, you would have to use chapter 3 wiring methods per 725.25

shortcircuit2
 
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