# A\C Load Calculation



## Magnettica (Jan 23, 2007)

What is the calculated load for this AC condenser? 

Is the RLA 26.4?


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## Magnettica (Jan 23, 2007)




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## Cletis (Aug 20, 2010)

*?*

26.4


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## Cletis (Aug 20, 2010)

*Rla*

Running Load Requirements
Running load requirements are simply a *total of all the loads to be operated simultaneously.* This can be based on actual measurements if a clamp-on probe type ac current meter is available. If the building has a traditional style disk type kilowatt-hour meter an alternative is to use a stop watch and count rotations of the disk when the loads of interest are operating. See the procedure outlined below. Otherwise, an estimate of the total running load can be made by adding up the running wattages of all items to be powered at one time. Some appliances may not list the wattage on the nameplate, but may show the rated current in amps and voltage. The wattage can estimated from these two figures by multiplying them together to get the watts.


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## McClary’s Electrical (Feb 21, 2009)

34.2


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## Cletis (Aug 20, 2010)

*?*

You sure. That's min circuit ampacity. That has nothing to do with calc load ? 

I think?


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## administr8tor (Mar 6, 2010)

It's a 3 ton so 30a if you're cheap or 40a breaker preferred 50 if it's a long run

Yes I know what the min says

You know these answer's why are you asking?


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## nitro71 (Sep 17, 2009)

I'd add up the RLA and the FLA. Count it at 100%. If you do that and take it by 1.25 it just about equals the 34.2 Min circuit ampacity.


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## B4T (Feb 10, 2009)

Mininum circuit amps.. 34.2


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## oldschool (Aug 2, 2008)

RLA-26.4 X 1.25 = 33 + 1.2 (fan)= 34.2 MCA


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## Cletis (Aug 20, 2010)

*fan*



oldschool said:


> RLA-26.4 X 1.25 = 33 + 1.2 (fan)= 34.2 MCA


I thought fan was included in rla ?


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## oldschool (Aug 2, 2008)

I dont know, the math works out to match the nameplate


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## BBQ (Nov 16, 2010)

34.2 no need to add things up it is already done for you.


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## erics37 (May 7, 2009)

BBQ said:


> 34.2 no need to add things up it is already done for you.


I like wiring HVAC equipment for that exact reason :thumbup:

However, I pay for it by somehow always managing to shred my finger on a jagged piece of sheet metal and bleeding all over the place.


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## nitro71 (Sep 17, 2009)

erics37 said:


> I like wiring HVAC equipment for that exact reason :thumbup:
> 
> However, I pay for it by somehow always managing to shred my finger on a jagged piece of sheet metal and bleeding all over the place.


That's why god made gloves :thumbsup:


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## captkirk (Nov 21, 2007)

Cletis said:


> 26.4


 thats the compressor... It tells you what the max running load is...


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## MDShunk (Jan 7, 2007)

I see people at the box stores all the time trying to order "220 wire". Go to Lowe's and order a cut length of 34.2 amp wire. :laughing:


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## erics37 (May 7, 2009)

nitro71 said:


> That's why god made gloves :thumbsup:


I wear gloves all the time! It just always happens as soon as I take them off to do some fine finger work


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## leland (Dec 28, 2007)

Cletis said:


> I thought fan was included in rla ?



Stop thinking. Please.


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## mbednarik (Oct 10, 2011)

the contractor i used to work for had an old secretary that liked to screw with people. When some would come in wanting 220 wire he would grab a piece of 14-2 and hand it to them. tell them it is actually 600 wire even better.


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## Magnettica (Jan 23, 2007)

administr8tor said:


> You know these answer's why are you asking?



Because when I took the licensing exam the A/C load calculations were listed as horsepower ratings and we had to look them up article 430. 

Thanks for the info guys.


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## Amish Electrician (Jan 2, 2010)

Forget the FLA figures. They're not relevant.

The manufacturer did all of that when he posted "Minimum circuit ampacity" and "Max fuse/ breaker" on the nameplate.

"Minimum circuit ampacity" means you size your wire from the 75 degree column to handle (in this case) 34.2 amps. No need to apply multipliers, etc.

"Max fuse/ breaker" means just that. That's how big your OCPD can be. That's right, you're going to be protection 34-A wire at 50-A. That's OK. This time.


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## electures (Oct 23, 2008)

Amish Electrician said:


> Forget the FLA figures. They're not relevant.
> 
> The manufacturer did all of that when he posted "Minimum circuit ampacity" and "Max fuse/ breaker" on the nameplate.
> 
> ...


Please explain? I thought 110.14 required 60 degree (unless all terminations and conductors are 75 degree (not mentioned in OP).


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## Amish Electrician (Jan 2, 2010)

Sorry about that. It's just been so long since I've seen any terminations that were not 75 rated, and I hardly ever run Romex. Indeed, I can't recall ever powering an A/C with Romex or UF. 

For this post, the distinction does matter. Unless, you are going with #8 anyway. Assuming you have 75-degree terminations, then you could have #10 on a 50-A breaker. See 240.4(G)


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## BBQ (Nov 16, 2010)

Amish Electrician said:


> For this post, the distinction does matter. Unless, you are going with #8 anyway. Assuming you have 75-degree terminations, then you could have #10 on a 50-A breaker. See 240.4(G)


Take a look at 334.80, you are stuck on 60C if using NM, UF or SE.


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## Cletis (Aug 20, 2010)

Hey. Can you run a 10-2 nm to that on 80 amp 2 magnetic breaker in panel and fuse at 30 in disconnect?


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## Magnettica (Jan 23, 2007)

Cletis said:


> Hey. Can you run a 10-2 nm to that on 80 amp 2 magnetic breaker in panel and fuse at 30 in disconnect?


No, the maximum overcurrent protection is clearly marked MAX 50. 

10/2 NM is rated for only 30 amps in the 60º column.


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## Cletis (Aug 20, 2010)

*Fuses*



Magnettica said:


> No, the maximum overcurrent protection is clearly marked MAX 50.
> 
> 10/2 NM is rated for only 30 amps in the 60º column.


I was using 430 rules. Fuses to protect wire at 30 and breaker in panel to protect under 300% ?? Unless 430 doesnt apply ?


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## Cletis (Aug 20, 2010)

*..*

30 overload, 80 short circuit protection


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## Amish Electrician (Jan 2, 2010)

BBQ, I did say "Indeed, I can't recall ever powering an A/C with Romex or UF."

I'm not too big on opening walls up to run a new line clear across the house just to add an A/C circuit. Plus, I usually need to run power for a service receptacle as well. 

Or, maybe, I just 'like pipe.' Failing that, there's always MC. 

Then there's the matter of the line from the disconnect to the unit. IMO, it's not proper to run Romex inside the sealtite ... and the idea of a whip of UF flapping in the breeze is simply obscene.


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## BBQ (Nov 16, 2010)

Amish Electrician said:


> BBQ, I did say "Indeed, I can't recall ever powering an A/C with Romex or UF."


That is great, but not everyone knows what is in your mind and many people do run NM, SE etc to HVAC units.


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## SHOCKnAWE (Dec 25, 2011)

If all your terminations and conductors were at least 75 degrees that A/C unit could be wired with a 10 gauge conductor and protected with a 50a breaker.


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