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I am doing my own load calculation for a new house that I want to add a few premium features into (floor heater, jet tub, induction cooktop, etc.).

Running the NEC 220 calculator, I'm coming out to about 204A.

load calculation spreadsheet

  1. Is that going to absolutely force me to upgrade to Class 320 400A service? Or is there some wiggle room here when the utility looks at my request for 200A service?

  2. I heard about 225A service. Is that an option with most utilities? I could not find any meter panel of this size. Standard residential equipment is either 200A or Class 320/400A. It seems like anything besides these two options would be unusual and expensive.

isherwood
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Shubham
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2 Answers2

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You'll have to give them a call and discuss it with them. To be careful of the upsell though. That form already does some rounding it looks like the recommendation is 200A service.

There are a few things you can use to discount some of those loads.

Heatpumps can be used for floor heating as well. Running waterlines through the floor with the water heated by a heatpump. This system can also augment your tank water heater.

Alternatively you can use home automation to prevent all the floor heat from kicking in at the same time.

There exist smart EVSE that will actively monitor the actual whole-house load and dynamically throttle down the charging current when the bigger loads kick in. This lets you fully discount the charging current from the load calculation.

ratchet freak
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Take a load diet.

Technology Connections talks about this on their "fully electrify on 100A service" pair of videos.

Right off the bat, tank water heater goes away and gets replaced by a PURE (not "hybrid") heat pump water heater, becoming 1500W.

You should get some space on 220.55, rarely does cooking equipment calculate over 8000 VA.

All those over 8000 watts of last-century electric resistance floor heaters, bye bye! Replace with hydronic/water loop fed by an R290 monobloc heat pump of maybe 2000 watts.

EV charging - this is my favorite -- GONE! Byebye. Right out of the Load Calculation. Using EVEMS / Dynamic Load Management and readily available hardwired EV stations well under $1000. This also unbridles charging speed, max speed is now 11,520 watts (300 miles a night) using common kit, and 19,200 watts (500 miles a night) using exotic kit.

Not that charging "needs" unbridling - 20A/240V (4800W circuit giving 3840W charge) is still 100 miles a night, and that's plenty for 95% of people. That's 36,000 miles a year, 3 times what most drive.

Well, if you had more EVs maybe. Right now, we have Power Sharing where you allocate a fixed block of power (say 30A) to the lot and they split it dynamically as cars plug in and finish. We can't YET do Power Sharing on top of dynamic load management, but that's in the pipeline. Europe has had this for a few years, and it works fine.

For now my recommendation is 1 very small station (240V/15A) for minimum bite out of the Load Calc (2.88 kW), and one large EVEMS/DLM station. And of course level 1 charging for 3rd cars and beyond. Then you just make judicious choices of which car gets the big station tonight.

Use NEC 220.82 Alternate Method not standard method.

The standard method is for everything from dockyards to refineries to malls. 220.82 is specifically made for dwellings and tends to give more favorable numbers.

I recommend Sacramento's worksheet which captures 220.82 accurately. Note EVs are a 100% load.

For instance I see you have almost everything below line 3 being computed as a 75% or 100% load. That is required for EV charging and air conditioning/heat pumps in NEC 220.82, however electric space heating is a 65% load and everything else is a 40% load.

Harper - Reinstate Monica
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