Hi folks - I live in an 30's era former rent house, slowly sorting out a lot of "owner repairs". Our central AC unit (exterior compressor, 30 amp 220v, eighties-era) was tripping breakers constantly. The AC guy noted the wires in the service panel were undersized (#10 stranded) and noticeably warm, but the wires outside to the unit were good (#6 or 8). Luckily, the wires from the panel went to a junction box about 4 feet into the crawl space and were connected to the heavier gauge wire, and it was easy to replace the last few feet (to the service panel) with #6 wire - no more tripping breaker.

What I noticed in making this upgrade was that the original wiring used is #6 or #8/2 w/ground (size not labeled on the sheath). The original installer taped the white wire with black, and the black & white wires are connected to the breaker poles and the unit. The (bare copper) ground is being used as the neutral. It's wrapped with black tape inside the junction box (where it now connects to the new #6 wire).

Should I replace the entire wire run with a #6/3, using an insulated white as neutral? Or is the bare coppr OK as the neutral?

Also, the outdoor compressor unit has no connection for a bare-copper ground; and the pull-out shutoff on the exterior wall (where the wire whip terminates) has only three lugs. Is the outdoor unit properly grounded by today's standards? Does the concrete pad provide a path to ground?

I don't mind a day in the crawl space running new wire; it'll take about 50 feet.

THANK YOU for any info!

An A/C condenser is a straight 240v load. THERE IS NO NEUTRAL.

It is perfectly legal, safe and common to use XX/2 cable to feed a 240v appliance.

The white and black are the two hots and the bare is the GROUND.

Also, #10 is probably fine for this unit. A/C units follow different codes than other things.
Can you tell us what the "Minimum circuit ampacity" is?
And also the "Maximum fuse or circuit breaker" size?
This will tell us if #10 is big enough (and I suspect it is).

I bet the problem is in the unit, not the wiring.

Thanks for the quick reply- it's pouring out today (Edge of Hurricane Ike) so I can't check the tag just yet; however, upping that one section of thinner wire instantly cured my breaker problem (and the wires are no longer warm to the touch at the panel) so it looks like that was the problem). Glad I can leave the existing wire in place - MC

If the wires are warm to the touch at the Panel, The wire(s) may have been loose, a dirty breaker, or a burnt or corroded buss.
Can't say without your specs, Like Stans post, likely needs 30 amp breaker and 10's, If you have an Amprobe clip around compressor wires, then fan wires to see what the loads are.