Armchair load panel calculation

I've got an extra L2 station I should probably should sell (actually two of them, a Schneider and a CC, both 32A) but I was thinking about putting one of them in my vacation rental. I figured it might add appeal to eco tourists, serve the EV community and maybe get me a bit more revenue in the process. I'm pretty sure it won't work though, here are the deets:

3BR/3BA
100A service
No A/C (condensing gas furnace 120V)
gas range
gas water heater
almost all lighting is LED
newer fridge, energy star whatever

Heavy hitters:
Electric dryer
Hot tub (specs say 30/50 amp service, need to investigate if that is configurable, it's currently on a 40A breaker)
there's also an 1100w aux heater downstairs

If the EVSE pulled 32 + 30 for the dryer and 30 for the hot tub there isn't much of a margin left. Making the dryer and the EVSE exclusive might make it possible I suppose, but the dryer isn't in the garage. A 16A EVSE might work but I don't really want to buy anything new, as there is very low confidence anyone will be interested in renting the place for this... also wondering if that would even be enough to satisfy an eco-tourist EV traveler, which would probably be in a Tesla.

IMHO, even a 16A/240V EVSE would be desirable. After all, they'd be charging overnight, and for a Tesla that would still result in about 9+mi/hour of added range.

For example, we recently took a 800 mile trip to a destination with no charging available. I was able to find a hotel that had 5-15 outlets installed on their parking lot lamp posts. Even though those outlets were controlled by a dusk-to-dawn sensor, the car still got 9 hours of charging at 4mi/hour. Being plugged in for three nights gave us enough range to let us skip an extra stop at a SuperCharger on the trip home.

Is either EVSE switch selectable to 16A?

See NEC 220.83(A). You need to know (1) the square footage, (2) the number of laundry and kitchen counter receptacle circuits [minimum 3], and (3) the nameplate ratings of:

Range
Water Heater
Refrigerator
Electric Dryer
Hot Tub
Auxiliary heater (1100W)
EVSE
Any other appliances "that are fastened in place, permanently connected, or located to be on a specific circuit."

Then you add up 3 * the square footage from (1), 1500 * the number from (2), and all of the nameplate ratings from (3). The first 8000 VA counts at 100%, the rest counts at 40%. For a 100A, 240V service, you have 24000 VA available. So your straight sum (ignoring the 40%) can be up to 8000 + 16000 / 0.4 = 48,0000.

Usually the NEC service calculations are very conservative, it seems to me this article is not, as it effectively counts the EVSE and the hot tub at only 40%. I don't see any language requiring them to be counted at 100%, however. And in practice it will likely still be fine.

Cheers, Wayne

wwhitney said:

See NEC 220.83(A). You need to know (1) the square footage, (2) the number of laundry and kitchen counter receptacle circuits [minimum 3], and (3) the nameplate ratings of:

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Thanks very much Wayne for the clearly well-informed/authoritative response. The place is 1700 square feet heated/finished. I'm going to be out at the place next week and can collect the details on the appliances to crunch the numbers.

On one hand it seems like it would be fine but it's a ski condo where one could imagine a cold night with the hot tub, furnace and basement heater all running full tilt, somebody drying a load of clothes and maybe a couple people running hair dryers... add a P100D charging in the garage and CLICK! Guests won't be too happy, although it's probably something an EVer would understand. I thought about putting a sign over the EVSE saying not to use it when the dryer is in use.

LTLFTcomposite said:

On one hand it seems like it would be fine but it's a ski condo

Click to expand...

So I guess it's not in Florida, then. : - )

LTLFTcomposite said:

where one could imagine a cold night with the hot tub, furnace and basement heater all running full tilt, somebody drying a load of clothes and maybe a couple people running hair dryers... add a P100D charging in the garage and CLICK!

Click to expand...

Hmm, I checked some hot tub spec sheets, typically one on a 40A circuit won't draw above 32A. You'll need to check your hot tub nameplate or spec sheet. The EVSE would be drawing 32A, the dryer might draw up to 24A, the hair dryers could be 15A (if on opposite legs), the auxiliary heater is about 10A. So in your scenario you'd up to 113A. The main breaker might trip after 3 or 4 minutes (or it might never trip).

So you might be better off reconfiguring the hot tub for a 30A circuit, or using an EVSE for a 30A circuit. Or you could put in a gas dryer, or figure out how to interlock the EVSE with the electric dryer (tricky).

Cheers, Wayne

jlv said:

IMHO, even a 16A/240V EVSE would be desirable. After all, they'd be charging overnight, and for a Tesla that would still result in about 9+mi/hour of added range.

For example, we recently took a 800 mile trip to a destination with no charging available. I was able to find a hotel that had 5-15 outlets installed on their parking lot lamp posts. Even though those outlets were controlled by a dusk-to-dawn sensor, the car still got 9 hours of charging at 4mi/hour. Being plugged in for three nights gave us enough range to let us skip an extra stop at a SuperCharger on the trip home.

Is either EVSE switch selectable to 16A?

Click to expand...

The ones I have on hand are a Schneider EVlink and a CC HCS40. Near as I can tell neither are selectable for the current. 16A would be a safer bet for the available service but it isn't what I have and given the seemingly low probability of getting "customers" I don't want to throw any more money at it other than some romex and a breaker. Also if someone arrived at 6pm and wanted to leave say, at 8am, 14 hrs * 9 miles/hr is only 126 miles... it would be a bummer to go to the trouble of doing this only to have disappointed guests. I suppose if they were there for a couple nights it would be more than enough, and this is certainly a sort of "destination", not necessarily an overnight stop (Park City UT).

wwhitney said:

So I guess it's not in Florida, then. : - )
...
Hmm, I checked some hot tub spec sheets, typically one on a 40A circuit won't draw above 32A. You'll need to check your hot tub nameplate or spec sheet. The EVSE would be drawing 32A, the dryer might draw up to 24A, the hair dryers could be 15A (if on opposite legs), the auxiliary heater is about 10A. So in your scenario you'd up to 113A. The main breaker might trip after 3 or 4 minutes (or it might never trip).

So you might be better off reconfiguring the hot tub for a 30A circuit, or using an EVSE for a 30A circuit. Or you could put in a gas dryer, or figure out how to interlock the EVSE with the electric dryer (tricky).

Cheers, Wayne

Click to expand...

It's in Park City.

I need to investigate the hot tub situation further when I'm out there. It's a Caldera brand, the parent company is "Watkins" (apparently owned by an outfit called MASCO). I think the "nameplate" may be behind an access panel and I was just getting the electrical requirements from the sales brochure that listed it as "30/50". Not sure if it's configurable or if there are different heater elements that can be installed. The number on the breaker in the main panel was very hard to read but I think it's a 40. I suppose that jives with the 80% rule, same as for EVSEs. When the tub is filled with c-c-c-cold water the heater will easily run nonstop for a full day.

Edit: Mine is a 2005 model but near as I can tell it's the same as this from 2007 (the "Hawaiian"):
https://watkinsdealer.s3.amazonaws.com/Documents/Caldera%20Spas/Owner%27s%20Manuals/PARADISE/2007-Paradise-Owners-Manual.pdf

On page 38 it talks about 30 or 50 amp, but on page 10 it only specifies supplying the subpanel with 50A.

wwhitney said:

See NEC 220.83(A). You need to know (1) the square footage, (2) the number of laundry and kitchen counter receptacle circuits [minimum 3], and (3) the nameplate ratings of:

Range
Water Heater
Refrigerator
Electric Dryer
Hot Tub
Auxiliary heater (1100W)
EVSE
Any other appliances "that are fastened in place, permanently connected, or located to be on a specific circuit."

Then you add up 3 * the square footage from (1), 1500 * the number from (2), and all of the nameplate ratings from (3). The first 8000 VA counts at 100%, the rest counts at 40%. For a 100A, 240V service, you have 24000 VA available. So your straight sum (ignoring the 40%) can be up to 8000 + 16000 / 0.4 = 48,0000.

Usually the NEC service calculations are very conservative, it seems to me this article is not, as it effectively counts the EVSE and the hot tub at only 40%. I don't see any language requiring them to be counted at 100%, however. And in practice it will likely still be fine.

Cheers, Wayne

Click to expand...

CEC section 8 under services and feeders require a 100% demand factor for Hot tubs Rule: 8-200 sub rule 1 paragraph (v) and more specifically EVSE @100% paragraph (vi)
This is a realistic demand in practice.