Hot Tub calcs

[kbrandt]

Hey guys I've looked all over the code book and can't find anything on hot tub demand factor.

I'am doing an addition to a home and adding a sub panel. Some retired county engineer did the calcs.He got the total VA 17301 with 12000 for the tub added to that total and took the first 10000 at 100% and the remainder at 40%. He came up with 54 amp demand for the sub panel. He also did receps. at 180 VA at 80%,which is not calculated for residential. (I think I right on that)

I think the hot tub is counted at 100% and not derated but can not find anything to be positive.

This addition is all gas except for hot tub, just bedroom and a bathroom are being added, and hot tub outside off of new panel.

I came up with 61 amp demand.

Lighting @ 2190 va
vacuum system @ 375 va
Total = 2565
First 10000 va @ 100%= 2565
Add hot tub @ 100% is 12000va = 14565va/240 = 60.68 amps

I'am I right or the county print.

Thanks for any input.

 

[Chamuit]

Hey guys I've looked all over the code book and can't find anything on hot tub demand factor.

. . . I came up with 61 amp demand.

Lighting @ 2190 va
vacuum system @ 375 va
Total = 2565
First 10000 va @ 100%= 2565Add hot tub @ 100% is 12000va = 14565va/240 = 60.68 amps

I'am I right or the county print.

Thanks for any input.

If this is an addition, then the lighting and vacuum system would be calculated @ 40% against the whole house because it 1st 10k would already have been counted.

Sizing the sub-panel would be figured your way. IMHO

 

[suemarkp]

What load are you calculating -- the subpanel feeder or the whole service? If just the feeder, then you'd calculate the hot tub like any other appliance. So add up all your loads, take the first 10 KVA at 100% and the remaining at 40% (fixed space heating or airconditioning being the only exception, which goes in at 100% after the fact). The lighting load should be 3 VA per square foot, and this covers general receptacle loads, so no need for 180 VA per receptacle. Assuming your numbers are right, you get:

2190 + 375 + 12000 = 14565

First 10000 at 100% = 10 KVA
Remaining 4565 at 40% = 1.8 KVA
Total feeder calculation: 11.8 KVA = 49.2A

Note that a hot tub requiring a 50A circuit most likey does not draw 50A. There's a motor or two in there which have a 125% factor on the biggest one. Plus, the load could have calculated to 41A which would require a 50A circuit.

All this calculation being said and done, I'd personally go a bit higher since the tub is a single heavy load. I'd do a 55A to 60A feeder in this case.