AC power

Status
Not open for further replies.

Rewire

Senior Member
28.5 minimum circuit ampacity ,minimum HVAC breaker 50 amps. The AC guy insists that it needs number 8 romex I say 10 romex ,10 romex at 60C is rated 30 amps.
Have I missed something?
 

hillbilly

Senior Member
28.5 minimum circuit ampacity ,minimum HVAC breaker 50 amps. The AC guy insists that it needs number 8 romex I say 10 romex ,10 romex at 60C is rated 30 amps.
Have I missed something?
How far between the breaker and the unit?

If voltage drop is not a consideration, you're correct.

steve
 
Reading in Article 440, you will find the answers to your question>
I agree that your answer of a conductor rated for 30 amps is sufficient, as all of the calculations are performed by the manufacturer, and the label is written to be followed without any additional calculations performed.
 

Rewire

Senior Member
Its a short run so VD is not an issue.The AC guy was very insistant so I wanted to check with the board because if something was changed somebody here would have knowledge of it.Tango Yankee
 

SegDog

Member
Location
Philadelphia
technically correct

technically correct

I do both electrical and HVACR. Minimum #10

I've thrown-in a larger conductor for a good customer, and charged accordingly; especially if someone insists. This is a case of bigger is better.
 

Rewire

Senior Member
So much for the easy way,The AC guy insiust that using #10 will void his warrantee I asked for something from the manufacturer stating this. Has anyone had to walk an AC tech through article 440? I don't want to overload his brain so I want to keep it simple as to the code references ,where to start ,what to leave in what to leave out any suggestions.
 

C3PO

Senior Member
Location
Tennessee
So much for the easy way,The AC guy insiust that using #10 will void his warrantee I asked for something from the manufacturer stating this. Has anyone had to walk an AC tech through article 440? I don't want to overload his brain so I want to keep it simple as to the code references ,where to start ,what to leave in what to leave out any suggestions.
Good luck. I have never had much luck talking code with HVAC guys. The ones I deal with always ask for way larger conductors then what is required because they do not understand the code and usually get mad when they are questioned.
 

Smart $

Esteemed Member
Location
Ohio
Its a short run so VD is not an issue.The AC guy was very insistant so I wanted to check with the board because if something was changed somebody here would have knowledge of it.Tango Yankee
He may have you on this one...

440.12 Rating and Interrupting Capacity.
(A) Hermetic Refrigerant Motor-Compressor.
A disconnecting
means serving a hermetic refrigerant motorcompressor
shall be selected on the basis of the nameplate
rated-load current or branch-circuit selection current,
whichever is greater, and locked-rotor current, respectively,
of the motor-compressor as follows.
(1) Ampere Rating. The ampere rating shall be at least
115 percent
of the nameplate rated-load current or branchcircuit
selection current, whichever is greater.
28.5A ? 115% = 32.8A
 

Power Tech

Senior Member
So much for the easy way,The AC guy insiust that using #10 will void his warrantee I asked for something from the manufacturer stating this. Has anyone had to walk an AC tech through article 440? I don't want to overload his brain so I want to keep it simple as to the code references ,where to start ,what to leave in what to leave out any suggestions.
I have been through this with A/C men. They claim the starting load will lower the voltage with the smaller wire. I was up above the T-bar and herd an A/C start and the wire was slapping around in the conduit. Perhaps there is some truth to it but, so what. Like you said, make him show you where the OEM will void the warranty. He may be blowing smoke.
 

e57

Senior Member
It may also be in the instructions for the unit...

I recently had a debate with a Plumber about a steam unit, I forget the particulars, but the rated load would have put the thing at ~45A (50A OCP) and appropriate wire size right????? In the instructions for the unit - it required - 75A OCP!!!!! :mad: Which also killed the wire size too... As 75A was more than the next size bigger than the load and wire via 310.15....

What ticked me off most about it was the plumber withholding the intructions and actual model number from me through most of it....
 

SegDog

Member
Location
Philadelphia
consider carrying your book

consider carrying your book

For what it's worth...

I just remembered about a pretty good guy, that I worked with go goofy on me about a larger system wiring issue.

I took out the book and showed him. This was the opposite of your situation of using a larger conductor. Somehow, he was referencing 310.15 (B) (6). He relented and acknowledged the mistake. This isn't always the way that they end-up.
 

e57

Senior Member
And... The Tin Dinger may be looking at the data plate which will more than likely has a min & MAX ocp/fuse size listed he may be basing this from the max size. And some units have starting problems on the min size - FWIW :cool:
 

marti smith

Senior Member
Hey all- keep in mind that that circuit is often for both the blower and the heat strip. This would reason the larger conductor and the 50 amp breaker to go with it. If the conductor (#10) is only for a compressor circuit and it is 32.8, somebody needs to change that ocpd or else the insulation will be in crumbs in the floor of the unit. ;)
 

SegDog

Member
Location
Philadelphia
data plate or sticker

data plate or sticker

Good point Marti. Most of us are referring to A/C only, not heatpumps.
The data plate has all of the answers. The rest is upsizing, and/or some common sense.

When the equipment is not available, some of the installers don't give you enough to do research on, or look-up the specs.

I wrote about this before (broken record). My partner spoke to a geothermal contractor. The partner was nervous about the lack of info he was given, and asked me to verify the wiring a day before. I called the geo-contractor. He was obviously on a beach somewhere. I never did meet him in person, but his office is on a beach. He gave me a lot more of requirements than he told partner. We had to speak to the homeowner because now we had to upgrade the service to accomodate the additional wiring. The homeowner was fine with everything, and acknowledged that this system was getting more costly. After finishing the geo and a lot of guess-work, we went about finishing the rest of the jobs we were doing for the HO. The geo guys asked us to run an additional circuit after all was said and done. I asked them what I should mark it in the panel. They couldn't give me a straight answer. I voiced my dis-pleasure with the situation (not them), and hopefully, they told beach boss. My partner said that we were in the wrong business. My response, "So was the geo contractor." I was hoping that the HO got his moneysworth. The nicest, most cooperative people get screwed by some of these cats.

roger, over and out.
 

mcclary's electrical

Senior Member
Location
VA
I ALWAYS go by the MCA. If they want bigger , they gotta pay. Also, I've been thru this with several builders. If their A/C tells me to run a CERTAIN SIZE WIRE for rough in,,,,,when I see the machine on trim out, if he told me the wrong size wire, I"M CHARGING THE GC FOR IT,,,,these a/c guys always want a bigger wire for some reason,,,,point blank MINIMUM CIRCUIT AMPACITY is just that. If you couldn't run a #10 to this, the manufacturer's MCA would not be less than 30 amps
 
Status
Not open for further replies.
Top