Installing 220v circuit for 3 1/2 ton Central A/C unit

[ultrasp99]

FYI... I also posted this on the Electrical forum - Just thought heating and cooling folks might have a few comments

I just purchased a 3 1/2 ton Central Air Condition unit. I was told that I need to run an 8 gage 40 amp circuit. I will have a Electrician come over and do the final hook up, what I wanted to do is mount the disconnect box and run the wire. That way I can take my time drilling the holes for the box, and line set ensuring it comes out nice and neat. This is a brand new house and I don't trust anyone anymore.

My question is... what type of wire should I buy, the run will be about 30 - 40 feet. Should it be 8-AWG 2 wire plus a ground our 3 wire plus a ground.

The disconnect box has 4 connections along top ( 2-line and 2 load) and right below a bus with 2 screws.

Like I said I just want to run the wire, mount the disconnect box, pull the wire into the disconnect box, and leave several feet at the circuit breaker box.

I did open the panel tonight and saw what I expected. For example the 50 amp range has 3 wire and a ground. The black and red are connected to the breaker, the white and copper are connected to the bus. Is that the way this 40amp circuit should be hooked up, if so which wires would be connected to what in the disconnect box.

The Minimum Circuit Ampacity is 25 and the Maximum Circuit breaker is 40.

With this information what wire gage should I use and what amp circuit breaker should I use.




Sorry for the long and unclear question.

Thanks in advance.

[Wgoodrich]

With you saying the MCA =25 A and the MOP = 40 the NEC requires that your conductor MINIMUM size be an 8 awg wire. If it were me I would install a 6 awg copper cable with a black white and bare wire reidentifying the white with rings of black tape showing it also being a hot wire. Then connect the reidentified white and black wires on a 40 amp breaker and the bare wire on the neutral bar.

Don't forget you are required a disconnect outside at the a/c unit for the repairman to work per NEC rules.

The larger 6 awg is more than minimum but the money spent can be caught back up in better running equipment and lower kw usage on such an equipment that will run so much. Then year after year you can still experience that lower kw saving and a longer lasting a/c unit per life expectancy.

Just my thoughts

Wg