# sizing generator conductors



## HackWork (Oct 2, 2009)

Hello and welcome. 

2-2-2-4 copper is too big, and a waste of money on copper. Run 2-2-2-4 aluminum. 

On your profile you entered "E1 Clean energy fuel cell power" for your occupation. What does that mean? Are you an electrician?


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## thycallmespky (May 22, 2017)

i was concerned about length of the run and the voltage drop. i dont want to have any issues. 

i am an E1/E2. i currently work in the clean energy field commissioning and servicing fuel cells.


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## HackWork (Oct 2, 2009)

thycallmespky said:


> i was concerned about length of the run and the voltage drop. i dont want to have any issues.


Which generator is it and what fuel type are you using?

Even if the generator was putting out 17kW, that's only 70 amps. Many generators that are rated at 17kW only put that out with propane, natural gas is 1-2kW less.

#2 aluminum is good for 90A. I think it will be fine @ 125' for 70 or less amps. Probably WAY less.


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## nrp3 (Jan 24, 2009)

You can always step up to #1 Ser aluminum is you're worried about it.


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## joebanana (Dec 21, 2010)

thycallmespky said:


> i was concerned about length of the run and the voltage drop. i dont want to have any issues.
> 
> i am an E1/E2. i currently work in the clean energy field commissioning and servicing fuel cells.


And... installing gensets. A whole different animal. More moving parts. 
Here's the secret formula:
http://www.calculator.net/voltage-drop-calculator.html


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## thycallmespky (May 22, 2017)

its a 17KW propane Honeywell with 200a automatic transfer switch service rated. 

so am i crazy or did i majorly screw something up in my load calc for the wire sizing. 

https://www.costco.com/Honeywell-17-kW-Automatic-Standby-Generator.product.100313165.html


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## thycallmespky (May 22, 2017)

what is an acceptable voltage drop for a generator? should it be at 3%. 

The breaker on the generator is an 80A, the running current on LP, is just over 70A.


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## HackWork (Oct 2, 2009)

See post #4.


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## B-Nabs (Jun 4, 2014)

Sometimes generators (and other pieces of equipment) will say somewhere something to the effect of "copper conductors only". But you can always run Al and change to copper near the machine. 

Sent from the unmarked van outside HackWork's house.


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## splatz (May 23, 2015)

The Southwire voltage drop calculator is saying #3 Al or #4 Cu will keep you under 3% for 240V single phase at 70A at 125'. 

http://www.southwire.com/support/voltage-drop-calculator.htm


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## thycallmespky (May 22, 2017)

the terminations can use copper or aluminum. is sizing SER and different than standard THHN in pipe. 

i am confused as to which temperature column i should be using with a generator.


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## HackWork (Oct 2, 2009)

thycallmespky said:


> the terminations can use copper or aluminum. is sizing SER and different than standard THHN in pipe.
> 
> i am confused as to which temperature column i should be using with a generator.


#2 AL SER will cover all of that. Contact with insulation, voltage drop, etc. If you were OK purchasing #2 copper, you should be very happy using #2 AL which is 3 times cheaper.

Depending on your code cycle, you use either 75 degree or 60 degree column, also depending on contact with insulation. But like I said above, you are so oversized that it doesn't matter.


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## mitch65 (Mar 26, 2015)

rule of thumb for voltage drop is if you are below a foot per volt, you dont need to derate.


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## thycallmespky (May 22, 2017)

https://www.wireandcableyourway.com/4-4-4-6-copper-ser-service-entrance-cable.html

this is what im thing for SER, does this look correct:

4-4-4-6 7 7 844 70 85 95 100 585 B
3-3-3-5 7 7 910 85 100 110 110 719 B
2-2-2-4 7 7 984 95 115 130 125 887 B
1-1-1-3 19 7 1132 110 130 150 150 1117 C


http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet274


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## thycallmespky (May 22, 2017)

or this possibly:

https://www.wireandcableyourway.com/3-3-3-5-copper-ser-service-entrance-cable.html


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## thycallmespky (May 22, 2017)

or this possibly:

https://www.wireandcableyourway.com/3-3-3-5-copper-ser-service-entrance-cable.html


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## telsa (May 22, 2015)

My customers would never tolerate SER for gen-set, back-up, power.

It's pipe & wire... or forget it.

Copper is often spec'd by the customer... leaving no choice.

Whereas, I'd go with aluminum, and transition to copper only at the gen-set whip.

( Aluminum does not tolerate vibration anything like the way copper does. )


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## thycallmespky (May 22, 2017)

i plan to change over to copper for the entrance into the unit. i would prefer run copper either way, kinda why im looking at copper SER. 

out of curiosity, why would you not use SER in a residential setting for Gen power? in this situation it will stay protected. i could understand piping it if it was exposed.


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## telsa (May 22, 2015)

thycallmespky said:


> i plan to change over to copper for the entrance into the unit. i would prefer run copper either way, kinda why im looking at copper SER.
> 
> out of curiosity, why would you not use SER in a residential setting for Gen power? in this situation it will stay protected. i could understand piping it if it was exposed.


I'm in Northern California.

My market is either Commercial or the Ultra Wealthy who builds to commercial standards.

( I can't compete with Romex racers. )

I can well understand that your situation does not mirror mine. Which is why I made clear that my considerations do not revolve around Code or physics... just what my customers will accept// expect.

&&&&

BTW, it's been my experience that retro-fit cable is slow to install. Cable that would fly into the building during new construction -- when the timing is right -- is a nightmare as a retro-fit proposition.

[ Keep in mind that my AHJ flatly prohibits open stud construction even in garages. So every wall is sealed with sheet rock. Subsequently, ALL surface mounted work -- yes, including residential -- MUST be in EMT, IMC, RMC. ( Short whips in Greenfield or Sealtite are okay. ) ]

Again, this 'truth' entirely depends upon specific circumstances. There can be no hard-and-fast rule.

&&&

BTW, 125-feet... that's some McMansion !:notworthy:


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## thycallmespky (May 22, 2017)

its a lonnnnnng ranch in new england.


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## thycallmespky (May 22, 2017)

long new england ranch generator is on the garage side.


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## frenchelectrican (Mar 15, 2007)

thycallmespky said:


> i plan to change over to copper for the entrance into the unit. i would prefer run copper either way, kinda why im looking at copper SER.
> 
> out of curiosity, why would you not use SER in a residential setting for Gen power? in this situation it will stay protected. i could understand piping it if it was exposed.


You have to check the specs on that generator to see if they can take alum conductors on connection point.

Normally most useally required copper conductors in the whip and I typically use the MTW or DLO cable depending on the size I get.,, 

But check with your local codes for any addtional requirement on the codes but what those guys posted here they gave you a straight shot answer.

#2-2-2-2 alum SER is plenty fine for that useage ( ya it cheaper to buy too ) 

The other thing you may have to keep in your mind with natural gas supply you will more likey have to heavy up the gas meter to handle the fuel flow on generator. the propane verison should work ok as long have proper piping size for it.


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## active1 (Dec 29, 2009)

That would be a 6-5 CU cable in Vegas trade shows.
125' would be the length of a booth.


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