220.60 Noncoincident loads

[Elect117]

If it is truly an OR, then (2) is redundant and not needed when speaking of just feeders and services, complying with (2) means you have automatically complied with (1), therefore (2) is simply verbose text.

I wonder if (2) exists just because inspectors can argue with the "unlikely"?

Or if kirk key interlocking could prevent a emergency board or something from needing to be added or considered if it is less than the main board? Like in a hospital or place with a lot of back up panelboards.

Or a data center where you could have multiple redundant back ups and "likely" just doesn't cut it?

 

[jaggedben]

I wonder if (2) exists just because inspectors can argue with the "unlikely"?

Or if kirk key interlocking could prevent a emergency board or something from needing to be added or considered if it is less than the main board? Like in a hospital or place with a lot of back up panelboards.

Or a data center where you could have multiple redundant back ups and "likely" just doesn't cut it?

But then why the inclusion of branch circuits in (2).

 

[Elect117]

But then why the inclusion of branch circuits in (2).

Like lighting circuits with multiple branch circuits feeding them? One circuit from an emergency board and the other from a primary board? The lights in a emergency status are dimmed? I don't know. I would have to really think about a time you would kirk key a branch circuit lol.

Maybe they just didn't want branch circuits to feel left out?

 

[jaggedben]

I think the intention is that loads on the same branch circuit must be physically 'prevented' from operating at the same time, but loads on a feeder or service merely need to be 'unlikely'. In which case 'one of the following' is the mistake. But that's all just my intuitive guess.

 

[wwhitney]

If it is truly an OR, then (2) is redundant and not needed when speaking of just feeders and services, complying with (2) means you have automatically complied with (1), therefore (2) is simply verbose text.

Precisely, that's what I've been saying.

"Feeders or services" is verbose redundancy in (2), and the meaning is unchanged by deleting those 3 words. Which apparently would improve clarity without any other effect.

Cheers, Wayne

 

[wwhitney]

In which case 'one of the following' is the mistake.

It's not a mistake. "One of the following" just means (A) OR (B) OR . . It's used 157 times in the 2017 NEC. "All of the following" (as applicable) means (A) AND (B) AND . . . It's used 103 times in the 2017 NEC.

The only "mistake" is duplicating "feeders or services" in (2), which is apparently a mistake in clarity, as it has led you and Jim astray, but which makes no difference to meaning.

Cheers, Wayne

 

[wwhitney]

I wonder if (2) exists just because inspectors can argue with the "unlikely"?

(2) exists to impose a higher standard on branch circuits for "non-coincidence" than (1) imposes on feeders and services.

Here's a non-trivial example: for some reason I want garbage disposals on both of my kitchen sinks, but as the dishwasher is on the same circuit, all 3 together would be too much load for the existing branch circuit. I put the two garbage disposals on a center-off 3-way switch, so only one of them can be powered at once.

Cheers, Wayne

 

[jaggedben]

It's not a mistake. "One of the following" just means (A) OR (B) OR . . It's used 157 times in the 2017 NEC. "All of the following" (as applicable) means (A) AND (B) AND . . . It's used 103 times in the 2017 NEC.

...

Fer chrissakes, I know what it means. I'm saying it is wrong for it to be an OR.

Looking at it again, I think the subject-object construction in 'Non-coincident loads shall be considered to be ..." is also backwards. I think what they are trying to do would be better handled like this:

... Only the following shall be considered to be noncoincident loads:

(1) For feeders or service calculations: Two or more loads that are unlikely to be in use simultaneously
(2) For branch-circuit calculations, feeders, or services: Two or more loads that are prevented from being in use simultaneously by listed equipment

(Assuming I'm understanding the intention correctly, which is perhaps an unwarranted assumption.)

 

[wwhitney]

Fer chrissakes, I know what it means. I'm saying it is wrong for it to be an OR.

How so? There's no logical problem with "OR". I'm really having trouble with understanding how there is more than one plausible reading of the text in question. But apparently there is, as both you and Jim seem to be seeing a different reading, so I'm hoping you'll explain how it's "wrong," as opposed to just redundant.

Looking at it again, I think the subject-object construction in 'Non-coincident loads shall be considered to be ..." is also backwards.

"Considered" is certainly an odd word choice, "defined" would be better. But as "defined for the purposes of this section" is clearly the intention, that's how I'm reading it.

Anyway, your version is clearer, without changing the meaning.

Cheers, Wayne

 

[jaggedben]

How so? There's no logical problem with "OR". ...

Perhaps it's a rare case, but where two non-coincident loads happen to be on the same branch circuit, the feeder or service calculation should not be precluded from including the largest just because they aren't prevented from operating simultaneously by listed equipment.

 

[wwhitney]

Perhaps it's a rare case, but where two non-coincident loads happen to be on the same branch circuit, the feeder or service calculation should not be precluded from including the largest just because they aren't prevented from operating simultaneously by listed equipment.

I don't believe the 2026 First Draft text of 120.6 does preclude that. If you're doing a feeder calculation, you can use (1). And (1) doesn't say anything about whether the two loads are on the same branch circuit or not.

Cheers, Wayne

 

[Rick 0920]

The fact is if the AC is the largest motor load it should still be calculated as such. Its a noncoincident load but it's still a load. Why delete it altogether? 220.60 is just saying to use the largest of the 2 which makes sense. If only one operates at a time you would obviously calculate the largest.

Ryan, In calculating the non-coincident load, you are comparing Heat vs. A/C. Nothing else. If your heat is larger than your A/C load, and if your A/C is your largest motor, then you would factor 125% of your A/C load vs. your heat. If the heat is still larger, omit the A/C load from the calculation entirely. Then your next highest motor, (disposal, compactor, pool pump etc....) is used when adding your 25% for highest motor inrush current.
Think about this. If you have calculated your A/C load plus 25% for inrush current vs. your electric heat and your heat is still larger, then when you use your A/C, your service conductors will be more than capable of carrying the A/C load plus its starting current.

 

[wwhitney]

Ryan, In calculating the non-coincident load, you are comparing Heat vs. A/C. Nothing else. If your heat is larger than your A/C load, and if your A/C is your largest motor, then you would factor 125% of your A/C load vs. your heat.

Disagree. You have to look at the total computation two different ways, once with A/C and once with heat, rather than comparing just the A/C alone to the heat alone.

For example, say you have other loads, excluding the largest motor, of 90A, plus the largest motor is 8A, so the total load is 100A if there were no heat or A/C. Now say the heat is 34A, and the A/C is a motor load of 28A.

If you just compare 125% of the A/C to the heat, you get 125% * 28A = 35A, which is greater than the heat at 34A. So you'd pick the A/C and calculate the total load. That would be 90A + 8A (formerly the largest motor, no 125%) + 125%*28A = 133A.

But look what happens if you pick the heat as the largest load: you get 90A + 125% * 8A (largest motor) + 34A = 134A, a bigger number. That is the actual load with the two non-coincident loads.

I'm not sure what exactly the text in 220.61 about largest motor loads means or is trying to do (it's been changing every year), but the above phenomenon is what it is trying to cover. I think the CMP has just consistently failed to figure out reasonable text that can succinctly describe the above issue, and in the 2026 First Draft they stopped trying.

Cheers, Wayne

 

[Elect117]

Disagree. You have to look at the total computation two different ways, once with A/C and once with heat, rather than comparing just the A/C alone to the heat alone.

For example, say you have other loads, excluding the largest motor, of 90A, plus the largest motor is 8A, so the total load is 100A if there were no heat or A/C. Now say the heat is 34A, and the A/C is a motor load of 28A.

If you just compare 125% of the A/C to the heat, you get 125% * 28A = 35A, which is greater than the heat at 34A. So you'd pick the A/C and calculate the total load. That would be 90A + 8A (formerly the largest motor, no 125%) + 125%*28A = 133A.

But look what happens if you pick the heat as the largest load: you get 90A + 125% * 8A (largest motor) + 34A = 134A, a bigger number. That is the actual load with the two non-coincident loads.

I'm not sure what exactly the text in 220.61 about largest motor loads means or is trying to do (it's been changing every year), but the above phenomenon is what it is trying to cover. I think the CMP has just consistently failed to figure out reasonable text that can succinctly describe the above issue, and in the 2026 First Draft they stopped trying.

Cheers, Wayne

I thought if you picked the AC you wouldn't have a different largest motor because the AC is the largest?

90 + 125% * 28 = 125 A.

Am I misunderstanding?

 

[wwhitney]

I thought if you picked the AC you wouldn't have a different largest motor because the AC is the largest?

Correct.

90 + 125% * 28 = 125 A.

Am I misunderstanding?

You left out the motor which was previously largest and is not included in the 90A load figure per my hypothetical. That's another 8A.

Cheers, Wayne

 

[Elect117]

Correct.


You left out the motor which was previously largest and is not included in the 90A load figure per my hypothetical. That's another 8A.

Cheers, Wayne

Ahhhh

 

[Rick 0920]

Correct.


You left out the motor which was previously largest and is not included in the 90A load figure per my hypothetical. That's another 8A.

Cheers, Wayne

Are you saying that after you omit the A/C load, that the blower motor in the A/H/U is 8A? If it is, which would surprise me, 25% of the motor load for the A/H/U would be used in one of the last steps of your calculation. The "largest motor" in a calculation is often not the largest in hp. The largest motor in NEC terms is the motor that will have the highest amp draw on the service conductors.

 

[wwhitney]

Are you saying that after you omit the A/C load, that the blower motor in the A/H/U is 8A?

I didn't specify what the 8A motor load was, just that it was present for both the heating case and the cooling case. Maybe it's a garbage disposal, doesn't matter.

The point of my example was that you can't say in isolation which is the larger load in terms of its effect on the final load calc, a 28A A/C motor load or a 34A heater load. It depends on what other motor loads are part of the calculation.

So I was taking exception to your statement "In calculating the non-coincident load, you are comparing Heat vs. A/C. Nothing else." You may need to know what else is in the calculation in order to determine the total load with non-coincident loads.

Cheers, Wayne

 

[Rick 0920]

I didn't specify what the 8A motor load was, just that it was present for both the heating case and the cooling case. Maybe it's a garbage disposal, doesn't matter.

The point of my example was that you can't say in isolation which is the larger load in terms of its effect on the final load calc, a 28A A/C motor load or a 34A heater load. It depends on what other motor loads are part of the calculation.

So I was taking exception to your statement "In calculating the non-coincident load, you are comparing Heat vs. A/C. Nothing else." You may need to know what else is in the calculation in order to determine the total load with non-coincident loads.

Cheers, Wayne

I see what you are saying. I should've been more clear. The way I understand 220.60 is that in a dwelling, your noncoincident loads are just going to be your heat and A/C. The code states that if your A/C is the largest motor (which it would probably be), and is the smaller of the noncoincident loads, we need to multiply the FLC in T.430.248 by 125% and then compare it to the heat. If the heat load is still higher, then we can omit the A/C load entirely from the calculation. But later in the calculation, we still need to increase our largest motor (not the A/C which has been omitted) by 25%

 

[Ryan Ray]

Disagree. You have to look at the total computation two different ways, once with A/C and once with heat, rather than comparing just the A/C alone to the heat alone.

For example, say you have other loads, excluding the largest motor, of 90A, plus the largest motor is 8A, so the total load is 100A if there were no heat or A/C. Now say the heat is 34A, and the A/C is a motor load of 28A.

If you just compare 125% of the A/C to the heat, you get 125% * 28A = 35A, which is greater than the heat at 34A. So you'd pick the A/C and calculate the total load. That would be 90A + 8A (formerly the largest motor, no 125%) + 125%*28A = 133A.

But look what happens if you pick the heat as the largest load: you get 90A + 125% * 8A (largest motor) + 34A = 134A, a bigger number. That is the actual load with the two non-coincident loads.

I'm not sure what exactly the text in 220.61 about largest motor loads means or is trying to do (it's been changing every year), but the above phenomenon is what it is trying to cover. I think the CMP has just consistently failed to figure out reasonable text that can succinctly describe the above issue, and in the 2026 First Draft they stopped trying.

Cheers, Wayne

This is a paragraph out of Tom Henry's Calculations book. "When calculating the service size for a dwelling, if the largest motor is the air conditioning, but Section 220.60 allows you to omit the smaller load. Example, electric space heat=10KW.10,000w/230v=43 amps which is larger than a 5hp AC motor at 28 amps X 125%=35 amps. In calculating the service size, you can omit the smaller load, the AC motor. But you also omitted the largest motor rule of an additional 25% increase. This rule must be applied to the next largest motor in the calculation in hp or FLC." It sounds odd but that's an exact quote. Do you agree with this?