220.60 - noncoincident loads - the final sentence is messing me up

[Nathanael47]

The concept of noncoincident loads laid out in 220.60 makes a lot of sense: If you have two loads that will never be on at the same time – like a heater and an air conditioner – you only need to count the larger of the two.

However, the final sentence seems to contradict what I just said:

“If a motor or air-conditioning load is part of the noncoincident load and NOT the largest of the noncoincident loads, 125 percent of either the motor load or air-conditioning load, whichever is larger, shall be used in the calculation.”

So take the example above: an HVAC load with air-conditioning and a heat strip. Assume the resistance heat is the larger load. The sentence quoted above says now we need to include 125% of the AC load as well right?

That doesn't make any sense to me.

 

[Eddie702]

yes because the 125 % is starting current. If the unit has a name plate the starting current is already figured in the minimum circuit amps.
there just telling you not to forget the starting current for a motor driven appliance. In other word don't compare the eletric heater amps and the motor or ac amps without including the 125% for starting. But they are all continuous loads anyhow.

 

[Nathanael47]

yes because the 125 % is starting current. If the unit has a name plate the starting current is already figured in the minimum circuit amps.
there just telling you not to forget the starting current for a motor driven appliance. In other word don't compare the eletric heater amps and the motor or ac amps without including the 125% for starting. But they are all continuous loads anyhow.

So you are saying the code is saying - figure out if the electric heater or AC amps is bigger (without forgetting to multiply by 125%) and then only use the larger of these two noncoincident loads?
I'm not sure that's correct. Because if the AC is the LARGER load I'm multiplying by 125% anyway. If it was saying "don't forget!" why wouldn't it just say: “If a motor or air-conditioning load is part of the noncoincident load, and NOT the largest of the noncoincident loads, 125 percent of either the motor load or air-conditioning load, whichever is larger, shall be used in the calculation.”
Or am I just not understanding?

 

[Dennis Alwon]

The statement says if the a/c or motor load is part of the noncoincident load but neither are the largest..

That means, imo there must be another load involved

 

[don_resqcapt19]

The statement says if the a/c or motor load is part of the noncoincident load but neither are the largest..

That means, imo there must be another load involved

I don't think that is what the words say.

If you have heat and air conditioning, and the heat is the largest of the two, but the AC is the largest motor in the building, you count both the heat and the AC. The heat as the largest non-coincident load and the AC as the largest motor load.

This make zero sense to me and some of the code making panel members also say it makes zero sense

 

[Dennis Alwon]

I don't think that is what the words say.

If you have heat and air conditioning, and the heat is the largest of the two, but the AC is the largest motor in the building, you count both the heat and the AC. The heat as the largest non-coincident load and the AC as the largest motor load.

This make zero sense to me and some of the code making panel members also say it makes zero sense

I agree that it makes zero sense

 

[ramsy]

In other word don't compare the eletric heater amps and the motor or ac amps without including the 125% for starting. But they are all continuous loads anyhow.

Eddie, water heater conductors / fuses are sized for 125% for continuous, but isn't HVAC nameplate only?

Did not realize HVAC conductors & loads must be calculated as continuous x 1.25% ?

I thought typical motor appliances without nameplate predominance are pool motors, well, or sump pumps (without speed drives), perhaps FAU & condenser blowers & washing machines?

 

[Eddie702]

Hvac already includes the 125% built in on the name plate=MCA--minimum circuit amps

 

[Psychlo]

So many folks are confused by this sentence. And now the change in 2023 has only compounded the confusion (for a separate discussion).

It seems to me that their intent here was likely to reclaim the extra 25% of the largest motor, even though it is omitted from the calc due to being the smaller of the two noncoincident loads. If that's the case, they should have written "25 per cent" instead of "125 per cent". Typo perhaps? But even that is not very clear.

IMO, it is not sensible to include the larger load AND ALSO the smaller load @125%. Way overkill.

Would have been easier to say "Calculate the largest motor load at 125%, then compare it to the other noncoincident load, and then take the larger of the two." IF that is what they are after, that seems to cover all bases and makes their intent clear.

 

[Dennis Alwon]

It is written correctly. You would take 125% of the load. If the motor is 20 amps then 125% means 25 amps which is to be used in the calculation.

If you used 25% then you would have 20 amps x 25% = 5 amps. Then they would need to say you need to add 25% to the motor load. Imo, it is easier to say 125% of the load.

 

[Psychlo]

It is written correctly.

Are you saying that they intend for us to include both the largest of the noncoincident loads AND 125% of the smaller load (if it is the largest motor of the building) in our calculation? That's how it is written. If so, then the following would be true...

Example:
12,000w furnace
7200w AC unit
Total calculated load = 12,000+(7200x1.25) = 21,000w

That is a great leap from how we have always done it. And I wonder, what is the purpose? They are noncoincident loads. Why would we need to include both? What is the point of putting this sentence under "noncoincident loads" if we aren't going to take that into consideration? Is that really what they intended?

 

[wwhitney]

I think this section suffers from trying to cover some complexity without being wordy. Take these two examples:

Example 1) A feeder supplies just two non-coincident loads, a 110A non-continuous load and 100A FLC motor load. If just the non-continuous load is active, the feeder load is 110A. If just the 100A FLC motor load is active, the feeder load is 125% * 100A = 125A. So the latter is the worst case.

Example 2) Same as above except the feeder also supplies a 120A FLC motor load. Now if only the non-continuous load is active, the feeder load is 125% * 120A + 110A = 260A. While if just the 100A FLC motor load is active, the feeder load is 125% * 120A + 100A = 250A. So now the former is the worst case.

I think I will submit a PI that just says to calculate the total feeder load for each case of which of the noncoincident loads is active, and take the largest result.

Cheers, Wayne

 

[don_resqcapt19]

I think this section suffers from trying to cover some complexity without being wordy. Take these two examples:

Example 1) A feeder supplies just two non-coincident loads, a 110A non-continuous load and 100A FLC motor load. If just the non-continuous load is active, the feeder load is 110A. If just the 100A FLC motor load is active, the feeder load is 125% * 100A = 125A. So the latter is the worst case.

Example 2) Same as above except the feeder also supplies a 120A FLC motor load. Now if only the non-continuous load is active, the feeder load is 125% * 120A + 110A = 260A. While if just the 100A FLC motor load is active, the feeder load is 125% * 120A + 100A = 250A. So now the former is the worst case.

I think I will submit a PI that just says to calculate the total feeder load for each case of which of the noncoincident loads is active, and take the largest result.

Cheers, Wayne

That is not what the code change was trying to get at. It is looking at loads other than the non-coincident loads. Say you have heat at 30 amps, AC at 15 amps and other motor at 10 amps. What they are after in this example is to add the AC load as the largest motor. At least that is what I get from reading the inputs and comments.

 

[wwhitney]

Say you have heat at 30 amps, AC at 15 amps and other motor at 10 amps. What they are after in this example is to add the AC load as the largest motor.

Add the AC load as the largest motor when, in what case?

For the heating case, the load is 30A + 125% * 10A = 42.5A. For the cooling case, the load is 125%*15A + 10A = 28.8A. The heating case controls, and the load is 42.5A. [Assuming there isn't a 125% factor I was supposed to apply to the heating.]

Is the extra language in 220.82 requiring a different computation with a higher result? But I see no need or justification for a higher result.

Thanks,
Wayne