Feeder Sizing - 215 or 220?

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PerryLackowski

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Location
Cleveland, Ohio, USA
I'm working on a hotel space, and effectively one floor of rooms will be fed from a single panel, so I'm trying to size the feeders for that panel. I'm a bit confused though, because 215 and 220 seem to have conflicting instructions for sizing the feeders. I'm working from the 2023 NEC.

Starting with 220. It's important to qualify here that the hotel rooms will not contain kitchenettes, so they do not qualify as dwelling units. Additionally, the mechanical loads are fed from separate panels. So in 220, we head to Part III for Feeder and service load calculations. 220.40 says the calculated load should be not less than the sum of the loads on the branch circuits supplied, per Part II. Part II (220.10) says the branch loads can be calculated based on 220.44 for hotels, which sends us back to Part III. 220.44 says that effectively all the lighting and receptacles in the room can be can be rolled into one VA/Sq Ft calculation using table 220.42(A), so 1.7VA*292 sq ft = 496.4VA.

Let's look at 215 next. 215.2 says the feeders must be sized as not less than the larger of the non-continuous + 125% continuous loads, and the load after any correction factors have been applied in 310.14. So basically a straight load calculation. I can't know the exact loads for the devices, but we estimated:
Mini Fridge & Coffee - 10 Amps
Bathroom - 10 Amps (running a hair dryer)
General Rec and LTG - 6 Amps
If we anticipate these loads per room, it will be 26 A per room, or 26*120=3120VA.

The 215 results are over six times larger than the minimum from 220. They also haven't factored in the diversity - there's no way every room on the floor is using both their coffee machine and hair dryer at the same time. However, I see no exceptions in 215 allowing you to consider diversity in your calculation. And my understanding is that both 215 and 220 apply, so we're stuck with much larger loads. At the panel, if we have 29 rooms, it's the difference between 80A and 252A, which is the difference between a 100A panel and a 400A panel.

Does anyone have any thoughts on this interpretation? Do we need to go with the oversized panels or is there something I'm missing?
 
PerryLackowski said:
I'm working on a hotel space, and effectively one floor of rooms will be fed from a single panel, so I'm trying to size the feeders for that panel. I'm a bit confused though, because 215 and 220 seem to have conflicting instructions for sizing the feeders. I'm working from the 2023 NEC.

Starting with 220. It's important to qualify here that the hotel rooms will not contain kitchenettes, so they do not qualify as dwelling units. Additionally, the mechanical loads are fed from separate panels. So in 220, we head to Part III for Feeder and service load calculations. 220.40 says the calculated load should be not less than the sum of the loads on the branch circuits supplied, per Part II. Part II (220.10) says the branch loads can be calculated based on 220.44 for hotels, which sends us back to Part III. 220.44 says that effectively all the lighting and receptacles in the room can be can be rolled into one VA/Sq Ft calculation using table 220.42(A), so 1.7VA*292 sq ft = 496.4VA.

Let's look at 215 next. 215.2 says the feeders must be sized as not less than the larger of the non-continuous + 125% continuous loads, and the load after any correction factors have been applied in 310.14. So basically a straight load calculation. I can't know the exact loads for the devices, but we estimated:
Mini Fridge & Coffee - 10 Amps
Bathroom - 10 Amps (running a hair dryer)
General Rec and LTG - 6 Amps
If we anticipate these loads per room, it will be 26 A per room, or 26*120=3120VA.

The 215 results are over six times larger than the minimum from 220. They also haven't factored in the diversity - there's no way every room on the floor is using both their coffee machine and hair dryer at the same time. However, I see no exceptions in 215 allowing you to consider diversity in your calculation. And my understanding is that both 215 and 220 apply, so we're stuck with much larger loads. At the panel, if we have 29 rooms, it's the difference between 80A and 252A, which is the difference between a 100A panel and a 400A panel.

Does anyone have any thoughts on this interpretation? Do we need to go with the oversized panels or is there something I'm missing?
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Yes, when you have a known load being plugged in to a a receptacle, that load is not part of the square foot load and should be counted for branch circuit, but the code doesn't say it has to be and frankly a coffee pot in a hotel room would have a huge diversity. The bathroom receptacle is clearly included per 220 along with the general receptacles and lighting.

I think you may be mixing up some terms here though. The only "feeder" in your scenario is the one that feeds the subpanel. Read the definitions is article 100. Only circuits that end in overcurrent protection like circuit breakers or fuses are feeders.
 
Strathead said:
Yes, when you have a known load being plugged in to a a receptacle, that load is not part of the square foot load and should be counted for branch circuit, but the code doesn't say it has to be and frankly a coffee pot in a hotel room would have a huge diversity. The bathroom receptacle is clearly included per 220 along with the general receptacles and lighting.

I think you may be mixing up some terms here though. The only "feeder" in your scenario is the one that feeds the subpanel. Read the definitions is article 100. Only circuits that end in overcurrent protection like circuit breakers or fuses are feeders.
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I'm believe we are in agreement on the definitions - I merely used one room to illustrate the example, but my intent is to size the feeder which feeds the panel servicing the floor, hence the final step of multiplying these room loads by 28 rooms/floor or rooms/panel.

So if I'm understanding your interpretation, we would take the final load on the feeder to be 1.7 VA/Sq.Ft. * 292 Sq.Ft. * 29 rooms, and only add the additional identifiable loads like the refrigerator and the coffee maker (an additional 10A * 120V * 29 rooms)? This alone would get us down to 136A, so 150A panels. I'm glossing over that math a bit - I think it's probably 90W for the fridge, * 1.25 since it's continuous, so ~1A per room or ~3A during startup. And 900W for the coffee maker, so 7.5A. But I agree that there would be significant diversity on the coffee makers. Am I able to apply that?
 
Having looked at the code a little further, I see I'm making some assumptions about the fridge and coffee maker loads that the code may already be handling for me. Continuing to read part III beyond the initial 220.42 load estimate, 220.47 makes me think I should include an extra 180*29 for the coffee maker. I'm debating if the fridge qualifies for 220.47 as well, or if it belongs to 220.52(A), as a small-appliance circuit load. If the fridge qualifies for 220.52(A), it will contribute more to the final load than the coffee makers, which seems counter-intuitive.

From there, I can apply the demand factors in Table 220.45 to both the coffee and fridge loads.

Am I on the right track?
 
PerryLackowski said:
I'm believe we are in agreement on the definitions - I merely used one room to illustrate the example, but my intent is to size the feeder which feeds the panel servicing the floor, hence the final step of multiplying these room loads by 28 rooms/floor or rooms/panel.

So if I'm understanding your interpretation, we would take the final load on the feeder to be 1.7 VA/Sq.Ft. * 292 Sq.Ft. * 29 rooms, and only add the additional identifiable loads like the refrigerator and the coffee maker (an additional 10A * 120V * 29 rooms)? This alone would get us down to 136A, so 150A panels. I'm glossing over that math a bit - I think it's probably 90W for the fridge, * 1.25 since it's continuous, so ~1A per room or ~3A during startup. And 900W for the coffee maker, so 7.5A. But I agree that there would be significant diversity on the coffee makers. Am I able to apply that?
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IMO 220(M) covers you to only use the square foot load, for all lighting and power period, for the feeder. My code book 2020 doesn't have a 220.47. It isn't necessary to add anything for the mini fridge or the coffee machine. The code writes know these are common in a hotel room and didn't find it necessary to address them.
 
PerryLackowski said:
Let's look at 215 next. 215.2 says the feeders must be sized as not less than the larger of the non-continuous + 125% continuous loads, and the load after any correction factors have been applied in 310.14. So basically a straight load calculation.
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I will disagree with this part. The word "load" in 215.2 refers to the result of the applicable Article 220 calculation. It does not refer to some other "straight" load calculation.

Cheers, Wayne
 
@Strathead - 220.47 is "Receptacle Loads - Other Than Dwelling Units". Wow, so just 292*1.7*29/(208*1.732) = 39.95A for the whole floor? (I had a math error in my original post doubling this to 80A.) This seems almost too good to be true. So in theory we could feed two floors off of a single 125A panel.

@david luchini & @wwhitney - Thank you for clarifying the distinction between 215 and 220. I see how 215.2(A)(1) lets us use noncontinuous + 125% continuous, and as I was struggling to understand how you would apply that to a combined load density result, I realized that the load density Table 220.42(A) clarifies in the note that the 125% multiplier is already included. I wish this codebook was more easy to interpret sometimes, but I appreciate the guidance!
 
PerryLackowski said:
So if I'm understanding your interpretation, we would take the final load on the feeder to be 1.7 VA/Sq.Ft. * 292 Sq.Ft. * 29 rooms, and only add the additional identifiable loads like the refrigerator and the coffee maker (an additional 10A * 120V * 29 rooms)? This alone would get us down to 136A, so 150A panels. I'm glossing over that math a bit - I think it's probably 90W for the fridge, * 1.25 since it's continuous, so ~1A per room or ~3A during startup. And 900W for the coffee maker, so 7.5A. But I agree that there would be significant diversity on the coffee makers. Am I able to apply that?
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A refrigerator is not a continuous load. The compressor cycles on and off and it would be quite unlikely that the compressor would run for 3 hours or more under normal circumstances. I would expect the nameplate to include the 1.25 factor for motors/compressors, so look at the nameplates for similar sized fridges if you don't have an exact number (and I'm unclear as to whether you actually need a number for it or not). To me, the coffee pot can be ignored as it is a counter top cord and plug item (and they cycle on and off too so you'll have a lot of diversity). Likewise the blow dryer can probably be ignore unless it is built into the wall in which case one could argue it is a fastened in place item. But they are typically a short use item and diversity would be high in a hotel.

There is nothing prohibiting you from padding the load calc to give yourself more margin. Code minimum doesn't always work out well.
 
tortuga said:
See 220.44 where it says 'no additional calculations shall be required for such outlets'
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I would agree and concede that the coffee maker circuit falls under a general-use receptacle in 220.44(1) since it's placed in an accessible place on a counter. However I'd argue that the fridge receptacle is not general-use since it's usually tucked at the back of a cabinet, and perhaps 220.47 would apply here.
 
PerryLackowski said:
I would agree and concede that the coffee maker circuit falls under a general-use receptacle in 220.44(1) since it's placed in an accessible place on a counter. However I'd argue that the fridge receptacle is not general-use since it's usually tucked at the back of a cabinet, and perhaps 220.47 would apply here.
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The others will probably roast me but I have never included mini fridges, only receptacles I count separate was dedicated HVAC like those thru the wall heatpumps that are sometimes cord and plug.
 
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