Question on New HVAC Compressor & Electrical
 

I'm having all new HVAC installed. My old system is 1992 and I'm getting all new and moving the unit into the attic to free up the utility room inside the house.

This is a split system with the compressor outside. However, I am relocating the compressor to another area. To reduce my costs, I agreed to pour the pad for the new compressor and install a shut-off box with 220v wiring. This is a 4-ton system if that matters for wire gauge.

My question:
1) Do I need to get a shut-off box that has circuit breakers or just an on/off switch? The final destination will be to my regular fuse box that has dedicated circuit breaker for this line. I'm basically moving one 220v line to a new place. My old compressor does not have a shut-off box, just wired to the main electrical panel.

2) I will be putting in new wiring to the shutoff box since it is a longer run and the old line will not work. I'm confused on the specific Romex I should get (6-2 or 6-3)? I'm thinking I need the 6-3 which would be the left, right, neutral, plus ground.

Any advice would be appreciated.

Up here it only needs to be a disconnect, so power can be shut off when servicing. Check the install manual for the compressor but I don't think it will need the neutral, but does no harm having it there. Check the install manual for required amperage, that will determine your wire size and breaker and switch capacity.

I've been looking on the net for info and I found that I only need a disconnect. Also, it is suggesting 10-2 guage. I read that the 3 wire setup is more for appliances that have both 120 and 240 being used by the appliance (i.e., stove with 240 oven and 120 lights). So that saves a little money. I will probably use 8 gauge since it's a long run at 80'.

4Ton #10-2 does not sound correct. I think you are closer with the #6 wire

Make sure you do not need the neutral...sometimes the fans are 110V.

Disconnect within 50' and in plain view of the unit. Wire gauge is determined by the breaker size. The breaker size is determined by the amperage draw of the unit. Since this is the evaporator unit on 240v, normally a 30 amp breaker on #10 wire will handle it unless the run is longer than 50 feet. At that point you begin to get close.

Wire in conduit can be rated higher than NM-B cable. You may find some #8 NM-B if you need to go to 40A. Read the manual online.

So your #8 is a good call and will never get warm on 30 amps at 80'. Yes, 8/2 is all you need. You may be required to place a 120v outdoor receptacle within a certain distance from the unit.

Whats the model and specs of the pump? I run a large 80 gallon 2 stage compressor at the end of 100' 10/2 roll from Lowes. 30 amp circuit. No brown out voltage at the motor so, shrug, works for me!

Here are the model numbers of the equipment. I'm having trouble finding the spec sheet on-line but the A/C company will be out tomorrow to review. I'm just trying to do my own research in advance and since I'm going to supply the electrical, and pad for the compressor - I'm doing my homework now. This system is expected to be installed in the next couple of weeks.

4 ton Carrier 16.5 Seer split system:

Outside the house: Carrier 24TPA748W003 Approximately 65' from circuit breaker box + 9'x2 for distance to ground (i.e., running line thru the attic and then down to unit)

Inside the Attic: Carrier 58SU0B060M1716, and ADP C48H175P159

I am supplying 240v to the compressor and 110/120v to the attic.

Thanks for all the expertise advice.

Your junction box to the water tight flex line to the outdoor unit should be within 6' of the side that takes the connection. Obviously this is a good place for the disconnect.

Per NEC:
210.63 Heating, Air-Conditioning, and Refrigeration Equipment Outlet
A 125-volt, single-phase, 15- or 20-ampere-rated receptacle outlet shall be installed at an accessible location for the servicing of heating, air-conditioning, and refrigeration equipment. The receptacle shall be located on the same level and within 7.5 m (25 ft) of the heating, air-conditioning, and refrigeration equipment. The receptacle outlet shall not be connected to the load side of the equipment disconnecting means.

You mention "pour the pad." In many installs - the pad is a plastic platform. Not sure you need a concrete base.

Something like this:

http://forums.pelicanparts.com/uploa...1710541473.jpg

I found the spec sheet for the compressor. It says I need a 40amp circuit breaker (that is what is already in my electrical panel for the existing compressor). So. it looks like I am just replacing the line to a new location and the existing setup matches the needs of the new.

The A/C company is coming by tomorrow so I will review my plans with him before I do anything.

Or a precast lightweight pad. Good catch and I think I'd look into this. One thing Sakrete has going for it is that anyone with a trunk in the car can manage this.

Yeah, Tidy, 8 ga. or 6 ga AL.

Are you sure this receptacle is req for residential? I took a quick look and I think residential is excluded. Good to have though.

I have a regular 110/120v outlet near by that is around the corner of the house. I think I will tap into that and add one near the ac compressor. I could use it in that area. As long as I am crawling around the attic, I might as well...

Due to my reading I believe so. I know we have to provide a lighting source in an attic as well as a service platform all around the air handler. so it stands to reason that a service person or owner could take a light outside at night to examine the condenser. As well as run a vacuum pump. I'd do it anyway.