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#221976 10/25/22 05:16 PM
Joined: Jan 2005
Posts: 5,445
Likes: 3
Cat Servant
Member
Wow …
An ongoing job has really brought home how our trade has changed over the years.
It started with restoring service to an older house. The house had been stripped of wires by “scrappers.”
First built in 1935, the house had been added to and remodeled many times. As a result, the service drop had to be relocated. The hardest part has been convincing the homeowner that simply continuing to use the old 40-amp (you read that right) ungrounded system was not possible.

My load calculations came to 154-amps required, without considering the likely replacement of two destroyed outbuildings. The easiest selection was to install a 200-amp service.
As might be expected, the customer is still complaining that I did “too much.”
I think the worst thing I can call a customer is “family.”

Now for the kicker: She’s talking about getting a Tesla. So, it was time to look at Tesla’s charging specs. Tesla calls for a 60-amp circuit (48 amp continuous). That’s as much as I used for the sub-panel that serves the basic house needs.
FWIW, Tesla claims a maximum charge rate of 44 miles per hour of charging. This means most folks will need three hours of charging per day. With that load, my 200-amp service is already two amps undersized.

I also note a directive from Tesla regarding GFCI protection: GFCI is integral to the power outlet, do NOT use a GFCI breaker.

I’m open to any advice or experience you might have to share.

I also doubt EV advocates have any idea of the Pandora’s box they’ve opened.

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Joined: Jul 2004
Posts: 9,942
Likes: 34
G
Member
EC&M has been running articles about EVs for the last few months. They are rethinking the 24/7 requirement for sizing but it is still a NEC continuous load. I am not sure which load calc you used but there is usually more wiggle room in the "optional" calc. Tesla also offers a 30a charger that might be plenty for a fairly low mileage driver who charges overnight.
I agree this electric car thing will have us rethinking a lot about load sizing. I am sure there will be some filthy rich folks who want the level 3 charger and want us to get the PoCo to supply 480v 3p.


Greg Fretwell
Joined: Apr 2002
Posts: 7,386
Likes: 7
Member
Not in Renos wheelhouse but, I see an average of 8-10 resi car charger applications a week. About half include a 200 amp resi service upgrade. Most are Tesla.

Side note; Amazon is gearing up for electric delivery vans. 2 locations here are installing 36 charge stations each. Package is all a drop ship from some mfg, via Amazon. Feeds are 277/480 volt at 600 amps to distribution box for 18 stations.I have not seen any of the vans yet, but they are supposed to be Rivians.

Yes, Reno, try the optional calc.if that's not the way you went.


John
Joined: Jan 2005
Posts: 5,445
Likes: 3
Cat Servant
Member
Both are good replies.
On reflection, I think we’ve gone about this EV thing exactly backwards. You don’t create / inspire progress by passing a law. Is was bad enough when the NEC unilaterally went against countless rental leases and mandated “laundry receptacles” in ALL residential units. Look at what that did to apartment design!

With ambitious EV mandates scheduled to kick in by 2035, just imagine what the effect will be. I might make my fortune selling antacid tablets to PoCo engineers. Imagine the effects on city neighborhoods, many of which already face decaying power grids.

Add in replacing gas heat with electric, and we might see individual apartments calling for 200-amp services and modest homes moving into CT-metered services. At that point, single family homes will become a thing of the past.

As for my customer: I’m comfortable “reviewing” my calculations until the 200-amp service sails past inspection. I’m certain, for example, that I can free up plenty of watts simply by actually measuring the inside room dimensions, rather than using the assessor’s recorded square footage. Or, as Greg suggested, using a smaller charger.

Joined: Jul 2004
Posts: 9,942
Likes: 34
G
Member
We don't have much in the way of fossil fuel appliances here and we get by on 150-200a services for houses around 2000 sq/ft. The crunch for me was a 70a spa. (11 KW heat, 3/4 and 2.5HP pumps). Actual draw is less than 70a but that is not what we design for. Car chargers could get pretty close to being my spa tho. If it wasn't for load diversity I would be in trouble.


Greg Fretwell
Joined: Mar 2004
Posts: 814
B
Member
One thing service calculations don't take into consideration is occupancy. A single occupant will easily get by using less than a family. In my area we only have to provide calculations for upgrades in the county, the city doesn't require it. The county is ridiculous, I've had a county inspector come to inspect an upgrade that was already approved by the planning dept. load calcs and all and argue that it "had too many 50 amp breakers" for a 200 amp service rolleyes He would not pass it till I called his boss, apparently he got a scolding and we weren't on great terms after that.

The county also wants calcs for car chargers but not the city. Incidentally you can set the Tesla HPWC internally to limit it's maximum draw.

Last edited by BigB; 10/30/22 05:26 PM.
Joined: Jul 2004
Posts: 9,942
Likes: 34
G
Member
I suspect as these chargers get smarter they will have CTs on the service and ramp up when demand is low. They already do time of day considerations to take advantage of lower rate times if you have them. Utilities might get more control too. It is clear a large number of car chargers i n one area will have an effect on demand if they are not coordinated some way.


Greg Fretwell

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