On Mon, 4 Mar 2013 03:46:05 +0000 (UTC), gregz
wrote:

Mikepier wrote:
I'm running new electric in a friends basement and so far uncovered a
lot of bad wiring jobs, buried splice boxes, you name it. So now I
noticed that the central A/C compressor is wired with 10 guage wire.
I'm pretty sure its suppose to be 8 guage. And also the existing 10
guage wire is hooked up to a 40 A breaker, which of course is not
right, its suppose to be a 30A breaker.
So since everything is wide open now, I was wondering should I run
new 8 guage wire to the A/C? The unit is a Lennox, I beleive a 3 ton
unit, and the plate says "Min circuit ampacity 24.4 amps" and it also
says " Max fuse or ckt bkr 40A".
Even if the unit has been running fine all these years, I'm wondering
what happens down the road if it needs to be replaced with a new unit
that needs more amperage. the existing 10 guage wire will not be
sufficient I'm thinking.

I had a 3.5 ton installed. They used 10 gauge and 30 amp breaker. After
reading data plate and measuring operating current I switched to 20 amp
breaker.
It's only drawing 6.5 Amps and no problems. Never hurts to use thicker
wire.

If you figure a SEER of 12, 3.5T (42,000BTU/HR) is 3.5kW or 14.5A. To
get to 6.5A you'd have to have a SEER of 27! Something's not adding
up here.