Why 210.11(C)(1) differs from 220.52(A)?

[antenna2001]

I am working on learning to solve Example D(1)(a).

When I look at 210.11(C)(1), it requires at least two 20 Amp. small appliance branch circuits. If I then calculate the capacity of each of these circuits, at 120 V, I obtain: 20 A x 120 V = 2400 VA

Then, 220.52(A) requires the load on those circuits to be 1500 VA each. This gives: 1500 VA / 120 V = 12.5 A

If I interpret these results correctly, the branch circuit conductors are rated to carry a 20-Ampere load but the actual maximum load that will be imposed on them is only 12.5 A. Am I correct?

Thanks for the replies

 

[George Stolz]

If I interpret these results correctly, the branch circuit conductors are rated to carry a 20-Ampere load but the actual maximum load that will be imposed on them is only 12.5 A.

It would be more technically correct to say that "all we're required to account for in the service calculation is 12.5A, demanded down from 20A."

The maximum load that could or will be imposed on the circuits is unknown.

The amount we have to account for is 1500VA.

It's similar to the way we're allowed to disregard much of the required lighting, a portion of more than 4 appliances fixed in place, etc. More of the same.

 

[dnem]

I am working on learning to solve Example D(1)(a).

When I look at 210.11(C)(1), it requires at least two 20 Amp. small appliance branch circuits. If I then calculate the capacity of each of these circuits, at 120 V, I obtain: 20 A x 120 V = 2400 VA

Then, 220.52(A) requires the load on those circuits to be 1500 VA each. This gives: 1500 VA / 120 V = 12.5 A

If I interpret these results correctly, the branch circuit conductors are rated to carry a 20-Ampere load but the actual maximum load that will be imposed on them is only 12.5 A. Am I correct?

Thanks for the replies

There is a difference in focus between 210 & 220 part 3.

210 tells you what the limitations are for each circuit about what loads can included on any particular circuit and how that circuit is built (wire & breaker size).

220 part 3 (220.40 thru 220.61) tells you how each circuit impacts the whole feeder and service load calculation. A circuit may be able to handle 20amps of load on that individual circuit, but that doesn't mean that 20amps are anticipated on every 12gauge 20amp circuit. Table 220.42 shows that as you add more capacity, you anticipate less of an average load on each individual circuit.

In other words, you might look at
one 20amp circuit as 20amps of load, but if you have
ten 20amp circuits, you don't assume 200amps of load.

This is an oversimplified way of explaining it, but I think it gets the point across.

The last sentence of 220.52(A) shows that small appliance circuit loads are included in the general lighting loads of Table220.12. It is my understanding that 220.52 is only used to calculate individual panel loads if there is more than one panel. But maybe someone with some design experience can jump in and speak about that.

David