NEC 220.82 and 220.83

[Tainted]

Suppose you have an existing dwelling unit and you're doing a renovation. You can either use 220.82 or 220.83.


Why does 220.82 require you to have conductors or service size of 100 amps minimum but 220.83 doesn't?

 

[Tainted]

It's essentially the same calculation but 220.83 is more liberal... why?

 

[wwhitney]

220.82 would cover any new construction, where 100A is the minimum per 230.79 or 225.39. So the 100A is baked in already.

Whereas 220.83 covers existing dwelling units, which might have smaller supplies from before 100A became the minimum.

Cheers, Wayne

 

[Tainted]

220.82 would cover any new construction, where 100A is the minimum per 230.79 or 225.39. So the 100A is baked in already.

Whereas 220.83 covers existing dwelling units, which might have smaller supplies from before 100A became the minimum.

Cheers, Wayne

Correct me if I'm wrong: 220.83 can't be used to size a service or feeder. It can only be used to check if the feeder or service is adequate for additional loads?

So if 220.83 calculation is above the rated existing capacity, does this mean I would have to use 220.82 or the standard method?

for example lets say existing breaker is 100 amps, I do 220.83 calculation and it comes out to 125 Amps. It means I would have to use 220.82 method since the existing 100A breaker is not adequate.

 

[wwhitney]

Correct me if I'm wrong: 220.83 can't be used to size a service or feeder. It can only be used to check if the feeder or service is adequate for additional loads?

I would say yes.

Now, since you've studied these sections more closely than I have, it seems like the only difference between 220.83 and 220.82 is that 220.83 gives a number 1200 VA smaller, is that correct? In that the 40% starts at 8 KVA instead of 10 KVA, so you get 60% * 2 KVA = 1200 VA less.

That assumes that it is implicit in 220.83(A) that you have to include the larger of the heating or cooling loads, even though it isn't explicitly stated, as to omit it would be implausibly inaccurate.

Cheers, Wayne

 

[Russell39]

I would say yes.

Now, since you've studied these sections more closely than I have, it seems like the only difference between 220.83 and 220.82 is that 220.83 gives a number 1200 VA smaller, is that correct? In that the 40% starts at 8 KVA instead of 10 KVA, so you get 60% * 2 KVA = 1200 VA less.

That assumes that it is implicit in 220.83(A) that you have to include the larger of the heating or cooling loads, even though it isn't explicitly stated, as to omit it would be implausibly inaccurate.

Cheers, Wayne

The 220.83(A) and (B) calculation does not take the A/C or Heat into account. It makes no sense to me as to why, but it never has.

 

[wwhitney]

The 220.83(A) and (B) calculation does not take the A/C or Heat into account. It makes no sense to me as to why, but it never has.

220.83(B) explicitly does consider A/C and Heat.

And while the language of 220.83(A) doesn't, it would be a violation of basic physics to ignore it.

Cheers, Wayne

 

[Russell39]

220.83(B) explicitly does consider A/C and Heat.

And while the language of 220.83(A) doesn't, it would be a violation of basic physics to ignore it.

Cheers, Wayne

I should have typed "existing A/C or Heat." I agree with you that it should be considered.
I would not say that either 220.83(A) or (B) explicitly consider existing HVAC...but it should be stated in the wording of the formula.
Section 220.83(A) and (B) even have a single line (d) for the inclusion of 'Water Heaters', but not A/C or Heat. I am not saying you shouldn't include them, just that the NEC could make it clearer.

 

[wwhitney]

The first sentence of (2017) 220.83(B) is "The following percentages shall be used for existing and additional new loads." And the subsequent table covers A/C equipment and Heating equipment.

So 220.83(B) explicitly covers existing HVAC.

Cheers, Wayne

 

[Russell39]

The first sentence of (2017) 220.83(B) is "The following percentages shall be used for existing and additional new loads." And the subsequent table covers A/C equipment and Heating equipment.

So 220.83(B) explicitly covers existing HVAC.

Cheers, Wayne

Yes...and it also applies to all existing loads (including HVAC) in 220.83(A).
I have heard this argued both ways many times...that's why I think it could be cleared up to avoid confusion.

 

[wwhitney]

Yes...and it also applies to all existing loads (including HVAC) in 220.83(A).

Ah right, I missed that 220.83(A) would cover them under the "existing loads" category. But what's weird is by not breaking the HVAC loads out in 220.83(A), they would fall into the "first 8 kVA @ 100%, rest at 40%" category. Vs being taken at 100% (usually) per 220.82 or 220.83(B).

Cheers, Wayne