A/C condenser circuit size

Rustygaff · 10-29-2011, 10:27 AM

Greetings: I am planning to wire in the near future a 3.5 ton A/C condensing unit. The literature with the unit indicates a 30A min. / 40A max. 240V circuit is needed. Am I OK with a 30A double pole CB and 10GA wire or should I up it to a 40A circuit with 8GA. wire? Thanks.

jbfan · 10-29-2011, 10:32 AM

10 Gage with a 30 amp breaker, or a 40 amp breaker if you have problems.

Rustygaff · 10-29-2011, 11:24 AM

No need to increase the wire size to #8 if a 40A breaker is installed?

Sine · 10-29-2011, 11:42 AM

Follow the name plate. MCA minimum circuit ampacity, that's what you use for wire sizing. MOCP or Max fuse, is what you should use for your breaker or fuse size.

Sine · 10-29-2011, 11:51 AM

Quote:

Originally Posted by Rustygaff

No need to increase the wire size to #8 if a 40A breaker is installed?

You are allowed to increase the size of the breaker on motors. Look at table 430.52 in the N.E.C. Depending on what kind of breaker you use you can increase the breaker size by as much as 800% of the full load current.

biggles · 10-29-2011, 12:02 PM

add the 30a and 40a for 70a total.. and half that for 35a go with a 40a amp

J. V. · 10-29-2011, 12:35 PM

Quote:

Originally Posted by Sine

You are allowed to increase the size of the breaker on motors. Look at table 430.52 in the N.E.C. Depending on what kind of breaker you use you can increase the breaker size by as much as 800% of the full load current.

That is correct, but extremely rare or impossible* to find this type of breaker in a residential panel. The breakers used in most load centers are "inverse time" breakers and the maximum allowed on a single phase motor is 250%.
Being this is a DIY site, I would think neither of us intend to confuse.

* I have never seen this type, so I could be wrong.

Sine · 10-29-2011, 01:06 PM

Quote:

Originally Posted by J. V.

That is correct, but extremely rare or impossible* to find this type of breaker in a residential panel. The breakers used in most load centers are "inverse time" breakers and the maximum allowed on a single phase motor is 250%.
Being this is a DIY site, I would think neither of us intend to confuse.

* I have never seen this type, so I could be wrong.

That's why I referred the op to the NEC. I have never had to increase the breaker size by 800% either. It does say in the 2008 NEC table for single phase motors you can increase the breaker by 800% when using instantaneous trip. Realistically though, you are correct. But like I said, you can't go wrong by going with the manufacturers nameplate rating.

jbfan · 10-29-2011, 02:02 PM

Quote:

Originally Posted by Rustygaff

No need to increase the wire size to #8 if a 40A breaker is installed?

In this case, no.

In other applications, 40 amp would need #8 wire.

NJMarine · 10-29-2011, 02:21 PM

The wire size is based on minimum amperage listed. In this case 30 amp.
# 12 could be used and I have seen it many times.

COLDIRON · 10-29-2011, 02:41 PM

30 amp 10 ga, just fine.

Speedy Petey · 10-29-2011, 04:34 PM

Quote:

Originally Posted by Sine

You are allowed to increase the size of the breaker on motors. Look at table 430.52 in the N.E.C. Depending on what kind of breaker you use you can increase the breaker size by as much as 800% of the full load current.

Thing is, this is and air conditioner. Art 430 does not apply. Art 440 does.

Sine · 10-29-2011, 04:36 PM

Quote:

Originally Posted by NJMarine

The wire size is based on minimum amperage listed. In this case 30 amp.
# 12 could be used and I have seen it many times.

#12 when the MCA is 30A? Are using the 90deg column?

Speedy Petey · 10-29-2011, 04:42 PM

Quote:

Originally Posted by Sine

#12 when the MCA is 30A? Are using the 90deg column?

No, it's an air conditioner.

Sine · 10-29-2011, 04:49 PM

Quote:

Originally Posted by Speedy Petey

Thing is, this is and air conditioner. Art 430 does not apply. Art 440 does.

You're right, my bad. I Typically just use the name plate and don't have to refer back to Article 440.

10-29-2011, 10:32 AM	#2
jbfan Electrical Contractor Join Date: Jun 2004 Location: Newnan GA Posts: 5,081	A/C condenser circuit size 10 Gage with a 30 amp breaker, or a 40 amp breaker if you have problems. __________________ Yes I am a Pirate, 200 years too late. "Jimmy Buffett"

10-29-2011, 11:24 AM	#3
Rustygaff Newbie Join Date: Jul 2010 Posts: 27	A/C condenser circuit size No need to increase the wire size to #8 if a 40A breaker is installed?

10-29-2011, 11:42 AM	#4
Sine Electrical Contractor Join Date: Oct 2011 Location: KC Metro Posts: 44	A/C condenser circuit size Follow the name plate. MCA minimum circuit ampacity, that's what you use for wire sizing. MOCP or Max fuse, is what you should use for your breaker or fuse size.

10-29-2011, 12:02 PM	#6
biggles Member Join Date: Jan 2008 Location: Long Island Posts: 3,250	A/C condenser circuit size add the 30a and 40a for 70a total.. and half that for 35a go with a 40a amp

10-29-2011, 02:21 PM	#10
NJMarine Lic Elect/Inspector/CPO Join Date: Apr 2011 Location: NJ Posts: 369	A/C condenser circuit size The wire size is based on minimum amperage listed. In this case 30 amp. # 12 could be used and I have seen it many times.

A/C condenser circuit size