# Are my calculations correct ?



## Dennis Alwon (May 9, 2009)

32 conductors is a boatload. I am not surprised and your math is correct


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## Dennis Alwon (May 9, 2009)

Work it backwards-- #4 @90 C is 95 amps
95 x .6 = 57 amps

If you use #6 you will be too small


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## Dennis Alwon (May 9, 2009)

I believe you don't need to double derate.. 

40/.6 = 67 amps-- which still means you need #4


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## active1 (Dec 29, 2009)

Without doing all that mathy stuff off my head I would do 3 #6 & #10 EG in a 1".

Ya, technically I guess you should use a #8 EG because you up-sized the ungrounded conductors. But also technically you don't need no stinking green in a steel conduit. Which makes me believe a #10 is more than fair.

Something to factor in also is startup current.
Kinda goes back to the name plate.
Sometimes the information is vage, misinterpreted and given to you, or just wrong.
All about LRA, RA, OCP, & min conductor size.
Assuming your number is the OCP size the 40A would be high in your calc.
But the startup may be closer to 200a.

Are you sure it's 240v 3PH? High Leg?

Now your math on 32 conductors would be 40% of the conductor, not 60%.
Think you would need to use the 60 degree column because the terminals are under 100a. I would come up with a #1 awg cu for the ungrounded, and guessing a #2 if you upsize the EG (not doing the circ mils calc). 

Good news is you only need 1 EG if you pull it.
Bad news is 3 #1 & a #2 may not fit in your 2" EMT with 32 other conductors.

It really becomes a point of no good return of running a ton of wire in the same conduit. Besides the price of 2" or bigger EMT & fittings, the greater time and special tools to bend, or limit on using factory bends, time to set & do monster 40 wire pull, time to identify each wire in pull, need to have 40 spools vs reusing less spools, and possible pulling equipment & wire reels. Not to mention possible problems with miss identifying, connection mistakes, and much harder to diagnose. Or 1 massive fail can take everything out. 

Not knowing the details. Just guessing I would build a rack and have about 1" conduits. Maybe 1.25". With extra space in the conduits and rack.


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## WronGun (Oct 18, 2013)

Dennis Alwon said:


> 32 conductors is a boatload. I am not surprised and your math is correct




Ok , just thought I was doing something wrong having to use 95A wire for a 40Amp circuit. 


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## WronGun (Oct 18, 2013)

The derating is 60% in Mass. not 40%

Our 2” conduit has 19 #10’s

And I figured wires for 3 condensers which I figured (12) #4’s to play safe

But, I didn’t actually think after calculations I would be pulling #4’s...

I was just trying to avoid running multiple pipes and was hoping to just run 1 larger pipe. 


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## pudge565 (Dec 8, 2007)

Are you sure that they require 40A wire or is 40 the max OCPD? If the 40 isn't the minimum circuit ampacity you may be able to use smaller wire.


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## WronGun (Oct 18, 2013)

pudge565 said:


> Are you sure that they require 40A wire or is 40 the max OCPD? If the 40 isn't the minimum circuit ampacity you may be able to use smaller wire.




Your right

This is my first job of this size and my head is scrambling all over the place 











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## active1 (Dec 29, 2009)

"And I figured wires for 3 condensers which I figured (12) #4’s to play safe"

You're figuring 4 conductors for each condenser?
Needs a neutral or are you counting a EG for each unit?


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## active1 (Dec 29, 2009)

It only draws 18.4a running.
Tells you to figure 26.5 amp wire @ 75 degrees, not 40a.


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## WronGun (Oct 18, 2013)

active1 said:


> "And I figured wires for 3 condensers which I figured (12) #4’s to play safe"
> 
> You're figuring 4 conductors for each condenser?
> Needs a neutral or are you counting a EG for each unit?




I was counting EG for each unit , that was my way of figuring Over just Incase 


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## active1 (Dec 29, 2009)

#8 awg cu at 75 deg = 50a
50a x 60% = 30a
More than 26.5a
3 #8 cu & 1 #8 EG


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## WronGun (Oct 18, 2013)

active1 said:


> It only draws 18.4a running.
> Tells you to figure 26.5 amp wire @ 75 degrees, not 40a.




Yep just realized this my error. I should’ve looked back at this picture I took at 630am. 


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## active1 (Dec 29, 2009)

Seems like you would have 12 current carrying conductors and 1 EG feeding 4 units.
NEC would be 50% on 12 ccc. Not sure about your area.

Technically you could fit 13 #8 awg in an 1.25 EMT (31.7% fill), or 1.5" (23.3% fill).


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## splatz (May 23, 2015)

25.6/.6 = 44.2 < 50 = 8 awg @ 75* 

2" EMT 
36 x 8 awg


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## active1 (Dec 29, 2009)

At 208v 18.4a is 1.8% VD.
10.9% VD at LR.


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## WronGun (Oct 18, 2013)

For Mass is 60% for 25-42 conductors 

And my calculation for 2” EMT is under by 25% of allowed conduit fill for (19) #10’s , and (13) #8’s 

I think I’m good now 



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## LeboElectric (Apr 9, 2018)

nice


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