Largest Motor

[robert.mcchesney@perrytec]

I have a question about 220.50B with 220.60 and with 430.24. Since we are calculating the A/C at 125% based off 220.50B and part 4 of 440 and it is the largest motor would we have to find a different motor for the largest motor or will the A/C count. Reading 220.60 and 220.50 and 430.24 all these combined leave a little bit of confusion for me. Thank you

 

[infinity]

When you say AC are you referring to an AC unit? The nameplate should tell you what the MCA and MaxOCPD so no 125% is required.

 

[don_resqcapt19]

I have a question about 220.50B with 220.60 and with 430.24. Since we are calculating the A/C at 125% based off 220.50B and part 4 of 440 and it is the largest motor would we have to find a different motor for the largest motor or will the A/C count. Reading 220.60 and 220.50 and 430.24 all these combined leave a little bit of confusion for me. Thank you

If the AC is not a larger load than the heat, and if the AC is the largest motor (something very likely for a dwelling) you count the heat and then add the AC as the largest motor. I think this change was made starting with the 2020 code.

 

[robert.mcchesney@perrytec]

If the AC is not a larger load than the heat, and if the AC is the largest motor (something very likely for a dwelling) you count the heat and then add the AC as the largest motor. I think this change was made starting with the 2020 code.

That I understood but. But if it is the Larger between the heat and A/C, do you still find a different largest motor. I was at a CEU that did this for some reason, and it threw me off a bit.

 

[robert.mcchesney@perrytec]

When you say AC are you referring to an AC unit? The nameplate should tell you what the MCA and MaxOCPD so no 125% is required.

I am and I am not looking for OCPD but more for a load calculation.

 

[wwhitney]

If the AC is not a larger load than the heat, and if the AC is the largest motor (something very likely for a dwelling) you count the heat and then add the AC as the largest motor. I think this change was made starting with the 2020 code.

Is that what 220.60 is trying to say? That doesn't make much sense--if you have two non-coincident loads, you should do the calculations twice and take the larger. I.e. for the heating case, you should use the largest non-A/C motor load, since the A/C won't be running.

For the 2026 NEC, 220.60 is being rewritten and moved (to Part I so it applies to other than the standard calc--right now you can't use it with the optional methods), but I don't know how to look up "TG 4 FR 14" so will wait until July 10 to read the First Draft.

Cheers, Wayne

 

[wwhitney]

That I understood but. But if it is the Larger between the heat and A/C, do you still find a different largest motor. I was at a CEU that did this for some reason, and it threw me off a bit.

Not 100% clear on your question, but whatever final answer you get, there should be exactly one extra 25% contribution for the largest motor or A/C unit.

Cheers, Wayne

 

[don_resqcapt19]

Is that what 220.60 is trying to say? That doesn't make much sense--if you have two non-coincident loads, you should do the calculations twice and take the larger. I.e. for the heating case, you should use the largest non-A/C motor load, since the A/C won't be running.

For the 2026 NEC, 220.60 is being rewritten and moved (to Part I so it applies to other than the standard calc--right now you can't use it with the optional methods), but I don't know how to look up "TG 4 FR 14" so will wait until July 10 to read the First Draft.

Cheers, Wayne

Unless there was a change by the correlating committee, 220.60 will read like shown below in the First Draft Report that will be issued on July 10th.

220.6 Noncoincident Loads.
For two or more noncoincident loads, it shall be permitted to use the single largest of these loads in the calculation of the total load. Determination of the largest noncoincident load shall include treatment of any motor-operated and combination loads as specified in 220.11(A) .
Noncoincident loads shall be considered to be one of the following:
(1) For feeders or services: Two or more loads that are unlikely to be in use simultaneously
(2) For branch-circuits, feeders, or services: Two or more loads that are prevented from being in use simultaneously by listed equipment.

 

[robert.mcchesney@perrytec]

Not 100% clear on your question, but whatever final answer you get, there should be exactly one extra 25% contribution for the largest motor or A/C unit.

Cheers, Wayne

Thank you that actually helps I appreciate it