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10-29-2011, 10:27 AM
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#1
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Newbie
Join Date: Jul 2010
Posts: 27
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A/C condenser circuit size
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.
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10-29-2011, 10:32 AM
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#2
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Electrical Contractor
Join Date: Jun 2004
Location: Newnan GA
Posts: 5,008
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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"
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10-29-2011, 11:24 AM
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#3
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Newbie
Join Date: Jul 2010
Posts: 27
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A/C condenser circuit size
No need to increase the wire size to #8 if a 40A breaker is installed?
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10-29-2011, 11:42 AM
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#4
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Electrical Contractor
Join Date: Oct 2011
Location: KC Metro
Posts: 44
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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.
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10-29-2011, 11:51 AM
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#5
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Electrical Contractor
Join Date: Oct 2011
Location: KC Metro
Posts: 44
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A/C condenser circuit size
Quote:
Originally Posted by Rustygaff
No need to increase the wire size to #8 if a 40A breaker is installed?
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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.
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10-29-2011, 12:02 PM
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#6
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Member
Join Date: Jan 2008
Location: Long Island
Posts: 3,197
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A/C condenser circuit size
add the 30a and 40a for 70a total.. and half that for 35a go with a 40a amp
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10-29-2011, 12:35 PM
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#7
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Member
Join Date: Jun 2007
Location: South Carolina
Posts: 3,312
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A/C condenser circuit size
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.
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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.
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10-29-2011, 01:06 PM
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#8
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Electrical Contractor
Join Date: Oct 2011
Location: KC Metro
Posts: 44
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A/C condenser circuit size
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.
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10-29-2011, 02:02 PM
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#9
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Electrical Contractor
Join Date: Jun 2004
Location: Newnan GA
Posts: 5,008
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A/C condenser circuit size
Quote:
Originally Posted by Rustygaff
No need to increase the wire size to #8 if a 40A breaker is installed?
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In this case, no.
In other applications, 40 amp would need #8 wire.
__________________
Yes I am a Pirate, 200 years too late. "Jimmy Buffett"
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10-29-2011, 02:21 PM
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#10
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Lic Elect/Inspector/CPO
Join Date: Apr 2011
Location: NJ
Posts: 369
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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.
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10-29-2011, 02:41 PM
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#11
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Member
Join Date: Mar 2010
Location: PENNSYLVANIA
Posts: 1,898
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A/C condenser circuit size
30 amp 10 ga, just fine.
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10-29-2011, 04:34 PM
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#12
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Licensed Electrical Cont.
Join Date: Feb 2004
Location: NY State
Posts: 6,158
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A/C condenser circuit size
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.
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Thing is, this is and air conditioner. Art 430 does not apply. Art 440 does.
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10-29-2011, 04:36 PM
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#13
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Electrical Contractor
Join Date: Oct 2011
Location: KC Metro
Posts: 44
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A/C condenser circuit size
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.
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#12 when the MCA is 30A? Are using the 90deg column?
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10-29-2011, 04:42 PM
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#14
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Licensed Electrical Cont.
Join Date: Feb 2004
Location: NY State
Posts: 6,158
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A/C condenser circuit size
Quote:
Originally Posted by Sine
#12 when the MCA is 30A? Are using the 90deg column?
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No, it's an air conditioner.
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10-29-2011, 04:49 PM
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#15
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Electrical Contractor
Join Date: Oct 2011
Location: KC Metro
Posts: 44
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A/C condenser circuit size
Quote:
Originally Posted by Speedy Petey
Thing is, this is and air conditioner. Art 430 does not apply. Art 440 does.
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You're right, my bad. I Typically just use the name plate and don't have to refer back to Article 440.
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