Air Conditioning Wire Sizing

JesseETG

Member
Location
Bakersfield California
Occupation
Electrician
I am aware that you size Air conditioner conductors based off the Minimum circuit amps on the nameplate of the unit. However do you add the 125 percent continuous load adjustment to size your wire ?
The air conditioner may possibly run for more than three hours on a hot day I would assume.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
I am aware that you size Air conditioner conductors based off the Minimum circuit amps on the nameplate of the unit. However do you add the 125 percent continuous load adjustment to size your wire ?
The air conditioner may possibly run for more than three hours on a hot day I would assume.

It doesn't really matter if the unit runs for 3 hours or not because all motors must be sized at 125% for the conductors.
 

Lucia1222

Member
Location
Pennsylvania
Occupation
HVAC tech
Where I’m am from in Pittsburg I feel like nobody knows this I kinda see it as a problem that even tech support for the air conditioners we sell don’t know this I think the person training doesn’t know then the manufacturer should have to put it in manual list the code or something I have 2 electricians that said it’s wrong the electric supply store said it was wrong but trying to prove this that don’t believe it is impossible I tried 3 different tech support guys all told me I was wrong about sizing wire for ac to mca
 

mtnelect

HVAC & Electrical Contractor
Location
Southern California
Occupation
Contractor, C10 & C20 - Semi Retired
This might help explain.
 

Attachments

  • Electrical Wiring Residential - Air Conditioning Part 1.pdf
    143.3 KB · Views: 34
  • Electrical Wiring Residential - Air Conditioning Part 2.pdf
    200.4 KB · Views: 12

Lucia1222

Member
Location
Pennsylvania
Occupation
HVAC tech
That will help I think I’m the young guy in the room here this argument didn’t go so well for me in a class of 10 people none of them agreed lol thank you
 

mtnelect

HVAC & Electrical Contractor
Location
Southern California
Occupation
Contractor, C10 & C20 - Semi Retired
That will help I think I’m the young guy in the room here this argument didn’t go so well for me in a class of 10 people none of them agreed lol thank you
HVAC is a specialty and doesn't follow common motor calculations. Of the most common questions asked on this site and the most misunderstood is HVAC.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Show them NEC 240.4(G), and 440 parts III and IV that it directs you to.

HVAC and other motor loads are permitted to exceed normal ampacities to allow for starting currents, and because those loads contain their own over-current protection, and the breakers protect against shorts.
 
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Lucia1222

Member
Location
Pennsylvania
Occupation
HVAC tech
HVAC is a specialty and doesn't follow common motor calculations. Of the most common questions asked on this site and the most misunderstood is HVAC.
That’s where my issue is I’m installing it I need to know the correct rules if a smart customer calls me out and I don’t the right answer I’m the one who looks like a idiot now the manufacturer pays people to train on that equipment they should be teaching the correct thing not just telling me I can’t put 10 wire on a 40 Im willing to say at least half or more of the techs in my area do not know this there’s a possibility that half the electricians don’t either thank for the help I appreciate it
 

Lucia1222

Member
Location
Pennsylvania
Occupation
HVAC tech
Show them NEC 240.4(G), and 440 parts III and IV that it directs you to.

HVAC and other motor loads are permitted to exceed normal ampacities to allow for starting currents, and because those loads contain their own over-current protection, and the breakers protect against shorts.
I’m working that but when you try to show your boss and the guy your boss trust it’s like they just went deaf
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
My experience tells me that there are millions of A/C condensor units installed with conductors that a are much larger than required. All do to a lack of understanding of the NEC and NRTL requirements. This goes for both the electricians and the AHJ folks. Sad indeed and also just increases costs unnecessarily.
 

mtnelect

HVAC & Electrical Contractor
Location
Southern California
Occupation
Contractor, C10 & C20 - Semi Retired
That’s where my issue is I’m installing it I need to know the correct rules if a smart customer calls me out and I don’t the right answer I’m the one who looks like a idiot now the manufacturer pays people to train on that equipment they should be teaching the correct thing not just telling me I can’t put 10 wire on a 40 Im willing to say at least half or more of the techs in my area do not know this there’s a possibility that half the electricians don’t either thank for the help I appreciate it

This is a great resource for all Electricians. Mike Holt teachings are known world wide.
 

Lucia1222

Member
Location
Pennsylvania
Occupation
HVAC tech
My experience tells me that there are millions of A/C condensor units installed with conductors that an are much larger than required. All do to a lack of understanding of the NEC and NRTL requirements. This goes for both the electricians and the AHJ folks. Sad indeed and also just increases costs unnecessarily.
I’ve watch people rip out the wire that would’ve been fine re run it bigger instead of just changing the breaker
 

mtnelect

HVAC & Electrical Contractor
Location
Southern California
Occupation
Contractor, C10 & C20 - Semi Retired
My experience tells me that there are millions of A/C condensor units installed with conductors that a are much larger than required. All do to a lack of understanding of the NEC and NRTL requirements. This goes for both the electricians and the AHJ folks. Sad indeed and also just increases costs unnecessarily.

In California, no more "Rule of Thumb", Heat Load Engineering Study" are now required. See Attachment
 

Attachments

  • Mountain Electric - By Room Each Component .pdf
    65.5 KB · Views: 12
  • Mountain Electric DuctReport .pdf
    9.5 KB · Views: 5
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