[micahdonahue]

Hi, new here but looks like a great site and resource.

I would like to install a subpanel to feed only a new geothermal compressor (Climatemaster TTS038 3-ton split system). The air handler and such are taken care of already.

The compressor requires 25.3 min circuit amps, max fuse/HACR of 40 amps, and supply wire of AWG 10. Spec also says unit requires a "4th bonding wire per NEC 250 from unit chassis to ground rod."

I plan to use one of 3 unused 220V breakers (from unused range, dryer, and wall heater circuits) in my main panel feed this new subpanel. My main panel is pushmatics and already has one sub-panel coming off it for an old kitchen addition, if it matters.

Questions about sub-panel wiring:
-To feed from the main panel breaker to the adjacent sub-panel, what wire size and configuration?
-The sub gets its neutral bar isolated from its ground bar by not installing the "ground screw," right? Is this because it's a sub, or because it's a HACR sub?
-The sub gets a ground wire (what size?) to water pipe or earth bar(s), right? Which is preferable?

Questions about geo unit wiring:
-From sub to geo unit (30 feet), what wire size and configuration?
-Spec says unit requires a "4th bonding wire per NEC 250 from unit chassis to ground rod." Does this mean I have to add a ground wire and earth rod to both the unit and the sub, or does the ground carry from unit to sub to ground bar? If I need grounds from both sub and unit, can they go to same bar or water pipe?

Thanks so much for your help. Anyone near Newburyport, MA is welcome to quote this job.

[stanfortyman]

Why do you need a sub-panel? All you need is a service disconnect for this one circuit.
You never told us the voltage, so I assume it is straight 240v, as opposed to 12/240v. 10/2 cable is fine for this and a 30 or 40A breaker. YES, I said 40.

You do not need a ground rod for this. Those are stupid instructions, and thankfully they state as per the NEC 250, since no where in 250 is this required. All you need is a #10 grounding conductor. This is part of the cable so you are good to go.

[micahdonahue]

Thanks so much. Just a non-fused service disconnect like this?
Amazon.com: Siemens WN2060U Non-Fused AC Disconnect: Home Improvement
That'd go near the unit, I assume?

Sorry, yes, straight 240.

If I use a pushmatic 50 breaker that I already have (because these guys are hard to find), what wire size would that be? Looks like #8 if 25' or less?

Thanks again.

[micahdonahue]

After more research, here's what I plan to do:

Run 10-2 w/ ground wire from an unused 30A pushmatic 220V breaker in my existing subpanel, to a new GE 30A fused Air Conditioner disconnect box ($10.47 at Home Depot). I'll mount the disco near the heat pump (which is in my basement). I'll probably use 10-3 wire that I have, use the black/red for feeds, hook the white in panel to the white bus bar, and cap the white at the disco. I'll hook up the green too obviously. The GE disco gets me a modern HACR-rated disconnect in my supply line to the heat pump. I like adding this since I don't know if the pushmatics qualify as HACR.

Then, since they request it and I'm doing this myself, I'm going to pull a #10 ground (only) from the heat pump chassis to a pair of ground rods sunk outside. Belt and suspenders approach.

Anyone see anything wrong w/ this plan?