Service cable size

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Electriman

Senior Member
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TX
Greetings,

I am working on a project that the current load is 2kw and the service voltage 120-240 V single phase.
For some reason the owner has asked me to request for 100 A service. The length of the service cable is over 200 ft.

The question I have is do I need to calculate the voltage drop based on the real load which 2kW or based on the 100A for future?

Thank you in advance.
 
topgone said:
Please show us your calculations, then others can pick which line needs correction/s!
Click to expand...
I use this website to caculate the voltage drop.

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.
www.calculator.net www.calculator.net
Per this website 3/0 will give me almost 2% VD at 100A and 200’. But I am not sure since it is service conductor if I need to size it based in the VD. Otherwise, I can just use #3 copper conductor.

Thanks
 
With a few exceptions (fire pumps & sensitive electronic equipment), VD is not a NEC issue so it's somewhat between you and your customer.
It might be good to show him the drop using a #3 with the 2KW load and show him the cost of maintain:)ing a 3% drop with a full 100 amp load.
Most folks compromise.
 
Just watch the lugs on the 100A panel if you go with large wire. I am pretty sure the MB lugs on the square D 100's only go up to 2/0. IF you are running big wire, perhaps might as will just go with a 200. Not sure what this load is, but if it is really only 2KW with little likelihood of future increased capacity, #6 AL would easily do it (which is the minimum conductor size per 230.23(B). Depending on what this is, you may need a 60 amp service minimum 230.79(D). If you/he wants to go full 100, #1 AL would do it and is plenty cheap.
 
augie47 said:
With a few exceptions (fire pumps & sensitive electronic equipment), VD is not a NEC issue so it's somewhat between you and your customer.
It might be good to show him the drop using a #3 with the 2KW load and show him the cost of maintain:)ing a 3% drop with a full 100 amp load.
Most folks compromise.
Click to expand...
Really? I was under the impression that VD is a NEC recommendation that we have to meet. Is this for all cable sizing or just the service conductor size?
 
By definition, a "recommendation" is never something you "have to meet." Other than the examples that Gus cited, the only mention of VD in the NEC comes in a couple "Informational Notes." These are not enforceable, and they are worded in terms of "reasonable efficiency of operation." Look at Informational Note 4 following 210.19(A).
 
I see. Two questions:
1- is this recommendation applicable for service conductor sizing as well as branch circuit?
2- But I believe that IECC (energy code) has a requirement of no more than 5% voltage drop. Is this enforceable?
 
Electriman said:
I see. Two questions:
1- is this recommendation applicable for service conductor sizing as well as branch circuit?
2- But I believe that IECC (energy code) has a requirement of no more than 5% voltage drop. Is this enforceable?
Click to expand...
1- it is a recommendation period.

2 - if you have enforcement of other codes yes, but is not an NEC requirement, so enforcement is going to have to be by other codes.


Further, voltage drop is load dependent. If you have only 2kVA load but have ~100 amp conductors around 200 feet long - you shouldn't have any significant VD issues for 120 volts or more. If it is 12 volts you likely will have VD issues along with overloaded conductor even with short length. VD won't care what fuse or breaker setting is.
 
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