DIYbanter - View Single Post - What size wiring for Central A/C compressor?

The Daring Dufas[_8_]

On 3/4/2013 6:13 AM, wrote:
On Mar 3, 11:16 pm, The Daring Dufas the-daring-du...@stinky-
finger.net wrote:
On 3/3/2013 9:46 PM, 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.

Greg

The circuit breaker is meant to protect the wiring not necessarily the
equipment which will normally have its own secondary protective devices.
The 20 amp breaker won't harm anything but if there is a surge current
greater than 20 amps from the AC unit starting on a hot day, you may get
nuisance tripping of the breaker. O_o

TDD- Hide quoted text -

- Show quoted text -

A 20 amp breaker is less than the rated 24 amp min
circuit capacity on the eqpt label. As others have stated, the
existing 12 gauge wiring and 40 amp breaker are
correct, meet code and no change is required.

Not around here. Every electrical inspector I know would reject a 12
gauge wired circuit with a 40 amp circuit breaker. A 40 amp circuit
uses #8 copper NM/UF 60°C cable or #8 aluminum SE/USE 75°C cable. An
electrical inspector may require #6 aluminum be used depending on the
jurisdiction's requirements which may be stricter than The NEC. This
applies to "homes" not necessarily industry which will normally use
different wiring methods and higher temperature insulated wiring. I've
wired homes, businesses and industry for a living so I know a little
about electrical wiring. I've also worked in commercial sales of
electrical products. The circuit breaker is meant to protect the wiring
and should always be sized accordingly. There are places that have no
electrical inspection department and I suppose you can do whatever you
want. I've worked in those areas too and seen extremely dangerous wiring
that was quite scary. ^_^

TDD