sub-panel off a subpanel

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cloudymacleod

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my question is, a friend has a large barn with a 200 amp sub panel inside the barn thats coming off the 200 amp main. with the barn being so large, he wants another 100 amp sub panel at the other side of the barn. is this possible to do without a service change. and if so. he would also need ground rods also for that 100 amp panel. would the wire size be #2alum and ##4 copper se cable 4 wire 2 hots, neutral, and grounding conductor. i would appricate the forums help thanks.
 
The service size is based on the calculated load. The number of panels/subpanels/ocpds is not material.

The ground rod is for the whole building, not the sub-panel.

You can make the wire any size you want, as long as you properly protect it at the line side and it is at least as large as your load calculations indicate it needs to be.
 
yes i work in the industry, im just not used to doing residental, just commicial. i know u can do this for commicial but dont know about res, in which he already has a 200a sub of a main. in furthermore i thought u did need a ground rod for a subpanel if its going to be used for more than 1 circuit.
 
The sub from a sub is fine. However the #4 CU is not. For a 100 amp feeder you will need a minimum of #3 CU or #1 AL.
 
to dingo, a barn is considered residental/commercial. there is barns that people make reastraunts and function halls, yes that would be considered commercial. this barnin question is behind a home for storage, its considered residental property, not commercial property.
 
cloudymacleod said:
to dingo, a barn is considered residental/commercial. there is barns that people make reastraunts and function halls, yes that would be considered commercial. this barnin question is behind a home for storage, its considered residental property, not commercial property.
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When you pull your permit, you might want to run the feeder size by the AHJ. I think Table 310.15(B)(6) is for Dwellings... then look at Article 100 for definition of Dwelling. Then you might want to look at Article 547.(2005)
 
The NEC does not really break things up by commercial or residential.

It breaks things up as Dwelling units or "Other than dwelling units"

A barn is normally "Other than dwelling units" so table 310.15(B)(6) will not apply.
 
iwire said:
The NEC does not really break things up by commercial or residential.

It breaks things up as Dwelling units or "Other than dwelling units"

A barn is normally "Other than dwelling units" so table 310.15(B)(6) will not apply.
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this is correct and forgive my outdatedness....Im going from the 99 code book right now , 220-40(b) other than dwelling unit.
for each farm building or load supplied by two or more seperate branch circuits, the load for feeders, service-entrance conductors, and service equipment shall be computed in accordance with demand factors not less than indicated in table 220-40
 
I agree with Iwire, you should not (be allowed to) use Table 310.15(B)(6) for this structure.
cloudymacleod said:
he would also need ground rods also for that 100 amp panel.
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I agree with Bob Peterson, the ground rods are connected to the first disconnect at the structure, not subpanels after that.
 
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