# A/C Feeders Thoughts / Design



## jwjrw (Jan 14, 2010)

Cletis said:


> There was a nice thread on here about sizing to terminals. All I remember was you must always size to 75C ?? Cletis



You size the wire based on the terminals of the equipment. A lot of stuff is rated 60 or 75 but be careful. I have seen 60 deg only terminals on some equipment.





Cletis said:


> Is this correct? Are there panels with 90C terminals out there? This would save me some bucks allowing me to drop down a conductor size for feeder. Cletis




You only derate off of the 90Deg column. I know of no equipment rated for 90deg terminations but they may exist. If they do I have never seen them. Someone else will know I'm sure.] Cletis[/QUOTE


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## NolaTigaBait (Oct 19, 2008)

Is 22 the MCA ?...What's the max fuse size of the largest unit?


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## Cletis (Aug 20, 2010)

*AC*

I've always based feeders to sub-panel on 90C column and never been turned down. I saw the thread on here for some reason get it stuck in my head that I must now use 75C? If I could use 90C to sub-panel then I could go 
1/0,1/0/,1/0,1/0,4 for 135 amps at 90C. Then run another line for Receptacles or just go 5 wire and go to 3/0,3/0,3/0,3/0,4 and only have 1 run and save at least $ 700 or more. That would be great. 

Total load 22. Compressor 21.0 and Fan 1 

2. Not sure of MCA? Sheet only has total unit amps. I don't know if that's MCA or FLA + RLA ??? MOP = 30 amps


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## Cletis (Aug 20, 2010)

*Info*

this is all I have to work with

Electrical Data
Voltage/Phase/ Frequency 208-230/ 3/ 60 460/ 3/ 60 575/ 3/ 60
Belt-Driven Standard Max Static 1.4" 1.4" 1.4"
Outdoor Fan RLA ea. 2.40 1.20 0.90
Total Unit Amps 45 22 16
Min. Circuit Ampacity¹ 49 24 17
Max. Overcurrent Protection (amps)² 60 30 20
Entrance Power Supply & Control Voltage

Use center column


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## NolaTigaBait (Oct 19, 2008)

I seriously doubt that you can use the 90 table for this...To size the feeders..its 125% of the largest motor plus the sum of the rest...IF you have the MCA (minimum circuit ampacity) listed on the label...that number already has the 125% in the figure...Fuse size should be largest branch circuit overcurrent device plus the rest of the motors flc.


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## NolaTigaBait (Oct 19, 2008)

Ok , the way I see it(this is conservative , b/c the mca has 125 in it already)...

24x4=96 amps... so,#3 copper thwn for the feeder

Feeder OCP is:
30+24+24+24= 102, next size down is 100 amps...
It says you can go up to 250% of the largest motor plus the sum of the rest, but the Max is listed and I used that...
If you use MC, you would need #1 copper...


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## miller_elex (Jan 25, 2008)

I am thinking single hits of #6/3 aluminum MC, and a #10/2 cu for the convinience recpts. Neut required on the 3ph? Does the RTU come with an integral convinience recpt?

Zipties for support. (fat ones for the stabiloy.)

Hopefully you can free-air the controls with plenum cable.

Not sure about the feeder to your subpanel though.


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## nitro71 (Sep 17, 2009)

Since you're going to go to the trouble to set a sub panel in a area that doesn't have other power supplying it I'd upsize the feeder some. These are longer runs and there might be some voltage drop issues to consider. I'd run aluminum as you said you were looking to go lighter on the physical manhandling of the stuff. I've ran 250 MC before without working to hard, aluminum stuff. If I get time tommorow I'll try to size a feeder based on your loads for fun.


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## Cletis (Aug 20, 2010)

*Ways*

Here are the distances

Existing Service to New Sub-Panel (150 amp) 270 ft

AC 1 290 ft All measured from Main Existing Service (20 ft from Sub)

AC 2 390 ft

AC 3 490 ft

AC 4 590 ft


I'll use 75C column then and leaning towards a 2/0, 2/0, 2/0, 2/0, 4 Al XHHN-2
MC Feeder


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## NolaTigaBait (Oct 19, 2008)

Just curious, why do you need a neutral?...also, I didn;t account for voltage drop on my calcs..


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## jwjrw (Jan 14, 2010)

NolaTigaBait said:


> Just curious, why do you need a neutral?...also, I didn;t account for voltage drop on my calcs..




For his 120v recep?


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## NolaTigaBait (Oct 19, 2008)

Good point...There must be a way to get an outlet closer and cheaper than that I would think though...


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## Jlarson (Jun 28, 2009)

NolaTigaBait said:


> Good point...There must be a way to get an outlet closer and cheaper than that I would think though...


Small xformer and sub panel.


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## nitro71 (Sep 17, 2009)

What would a transformer cost for this application? Now you have me curious.


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## nitro71 (Sep 17, 2009)

Here's my feeder load calc:

3 phase/460V. Total Draw 22 amps per unit, I'm assuming this is nameplate data.

460v x 22amps x 1.732 = 17,527.8 watts x 4 units = 70,111.4 watts

70,111.4w / (480v x 1.732) = 84 amps minumum feeder size

A #1 aluminum MC feeder to a sub panel would limit your voltage drop to 2% at the panel with a load of 84 amps. You could then size your branch circuits to limit voltage drop to 3% or less and keep it under 5% total voltage drop.


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## nitro71 (Sep 17, 2009)

Here's a 15KVA transformer:

http://www.grainger.com/Grainger/ACME-ELECTRIC-Transformer-4WTZ5?Pid=search

Before I spent the 1300 on it I'd probably pull a 20 amp 120v circuit over there with your feeder.


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## Jlarson (Jun 28, 2009)

nitro71 said:


> Here's a 15KVA transformer:
> 
> http://www.grainger.com/Grainger/ACME-ELECTRIC-Transformer-4WTZ5?Pid=search


Oh my, can one say over kill.


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## Bob Badger (Apr 19, 2009)

nitro71 said:


> Here's a 15KVA transformer:
> 
> http://www.grainger.com/Grainger/ACME-ELECTRIC-Transformer-4WTZ5?Pid=search
> 
> Before I spent the 1300 on it I'd probably pull a 20 amp 120v circuit over there with your feeder.


That page is a mess.

For one thing the picture sure looks like a 75 but the dimensions 

Height (In.) 18.86
Depth (In.) 9.03
Width (In.) 20.3

look more like a 15.

And there is no way in hell I would pay $1300 for a 15 kva.:no:


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## Jlarson (Jun 28, 2009)

Bob Badger said:


> And there is no way in hell I would pay $1300 for a 15 kva.:no:


:no::no: I have gotten way bigger ones for less.


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