Optional service calculation

[arnettda]

220.82 says to use this the feeder conductors must have a ampacity of 100 amps or greater. Does this mean my load calculation must be greater than 100 amps to use it or if my load calc comes out to less than 100 amps I just need to make my service wire 100 amp rated and everything is good. I believe else where in the code it states your service need to be 100 amps. But I want to understand 220.82

 

[iwire]

I read it as the conductors must be 100 amps or greater, the load could be 1 amp.

220.82 Dwelling Unit.
(A) Feeder and Service Load. This section applies to a
dwelling unit having the total connected load served by a
single 120/240-volt or 208Y1120-volt set of 3-wire service
or feeder conductors with an ampacity of 100 or greater. It
shall be permissible to calculate the feeder and service
loads in accordance with this section instead of the method
specified in Part III of this article. The calculated load shall
be the result of adding the loads from 220.82(B) and (C).
Feeder and service-entrance conductors whose calculated
load is determined by this optional calculation shall be permitted
to have the neutral load determined by 220.61

 

[highlakeselectric]

From what i just learned in class if the optional calc does not reach a 100 amps you must do a standard calc and it would most likely put you over a 100 .


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[iwire]

From what i just learned in class if the optional calc does not reach a 100 amps you must do a standard calc

Can you see that requirement in the section I posted?

Or is their a another section stating that?

 

[highlakeselectric]

No its interpretation of the code it might be an oregon thing but we must do standard here if the optional does not meet 100 amp or greater .


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[iwire]

No its interpretation of the code it might be an oregon thing but we must do standard here if the optional does not meet 100 amp or greater .


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So it would be against the code for me to run 100 amp conductors for a 60 amp load?

I think you may have misunderstood the teacher.

It would not be against code it just would not be practical.

 

[highlakeselectric]

Check with your building codes division in your state


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[steve66]

I read it as the conductors must be 100 amps or greater, the load could be 1 amp.

I agree. That's the way the paragraph reads.

And it just wouldn't make any sense to allow an optional calculation for a larger calculated load, but not for a smaller load.

If that were the case, there would be situations where adding more load to the feeder would allow you to reduce the feeder size.

And there would be situations where removing load would make you increase the feeder size.

 

[iwire]

Check with your building codes division in your state

Unless they have amendments the NEC says what it says.

 

[Toppcatt22]

It has to do with the conductor ONLY

It has to do with the conductor ONLY

According to the code book itself, "ampacity", has to do with the current that the conductor can carry without exceeding its temperature rating. So, this article has nothing to do with the load value. It has to do with a single service for a dwelling unit, with conductors rated at 100A.