Help with home charging on a new construction house...

[acarney]

Does the panel have the capacity? That you would determine from a load calculation.
Is the panel in the garage?

My panel is on the other end of the house and would require routing outside and going under two sidewalks, and 100+ ft. $5000 is considered cheap.

Is there another similar house from the builder that you could get someone to do a load analysis on?

I can walk through another model that is built and listed as for sale. It should be very similar, except maybe 400 sq ft larger because it has an upstairs bonus room. I believe it should have electric for all appliances in the kitchen and heat pump for HVAC so I can look at the panel and see how full it is. Maybe even post here or reach out to a local electrician and send over a photo example to see their input.

The panel should be in the garage, that's what I've seen with all their new builds. It might be a little "far" in the sense it's on the wrong wall. I know someone mentioned a 24 foot cable, which is great, that would certainly cover two stalls of the 3 car garage... but it's split as a two car garage on the left (when facing the house from the street) and a single car on the right. The exterior wall, likely where the panel will be, is on the left side. Because everything is so small now a days, I figure I would park in the single stall space and give my family member the two car space so they didn't have to worry about pulling in/out and storage would go around. Also since I back in, if it was on the right wall, I should be able to cover the single stall space and the middle space. If it's on the left wall... I don't think it would reach (garage is 29.5 feet wide and the charge port would be on the extreme right side since I back in) if it was on the left right next to the panel.

I would be ok with conduit running around the wall or up and across the ceiling and down again, if that's up to code....

I'll see if I can get a picture of a panel in a couple days... is the rule of thumb basically that if there are physically open spots for a 60 amp circuit then the panel can accommodate it?

 

[ewoodrick]

I can walk through another model that is built and listed as for sale. It should be very similar, except maybe 400 sq ft larger because it has an upstairs bonus room. I believe it should have electric for all appliances in the kitchen and heat pump for HVAC so I can look at the panel and see how full it is. Maybe even post here or reach out to a local electrician and send over a photo example to see their input.

The panel should be in the garage, that's what I've seen with all their new builds. It might be a little "far" in the sense it's on the wrong wall. I know someone mentioned a 24 foot cable, which is great, that would certainly cover two stalls of the 3 car garage... but it's split as a two car garage on the left (when facing the house from the street) and a single car on the right. The exterior wall, likely where the panel will be, is on the left side. Because everything is so small now a days, I figure I would park in the single stall space and give my family member the two car space so they didn't have to worry about pulling in/out and storage would go around. Also since I back in, if it was on the right wall, I should be able to cover the single stall space and the middle space. If it's on the left wall... I don't think it would reach (garage is 29.5 feet wide and the charge port would be on the extreme right side since I back in) if it was on the left right next to the panel.

I would be ok with conduit running around the wall or up and across the ceiling and down again, if that's up to code....

I'll see if I can get a picture of a panel in a couple days... is the rule of thumb basically that if there are physically open spots for a 60 amp circuit then the panel can accommodate it?

Get a picture of that panel with the descriptions. Get a picture of the garage with panel and where you want the plug to be. Get an electrician to give you a quote on installation.

 

[brainhouston]

If it's on the left wall... I don't think it would reach (garage is 29.5 feet wide and the charge port would be on the extreme right side since I back in) if it was on the left right next to the panel.

Not sure how ppl park usually but i back in on the left n forward on the right side of the garage for max driver side access..
i don't trust summon...

 

[Earl]

I guess to help understand I'm more asking... should I skip the pre-wire and panel upgrade direct from the builder. If I can just hire an electrician as soon as we close and get the keys on the finished house and they install the wall connector for me and it's like $750 or something because they don't need to upgrade the panel.... then that's golden.

BUT, if it turns out they say they have to upgrade to 320 amp and it's nearly the same cost (or more since everything is finished already, and walls and ceiling are insulated), then I just want to eat the cost now and have the builder do it...

If I hadn't had two 50 amp circuits installed before on 200 amp panels with no one even bringing up the question of upgrading the panel I wouldn't be in this position... I just really don't know how to figure out the load and how close we might be. On one hand, when I think about all the high demand electric stuff, a 200 amp panel seems small when factoring in over 25% of it's capacity JUST for an EV. But... I was in a house built in the 60s with no electric upgrades that had electric heat (3 ton heat pump and back up electric heat elements), electric stove/oven, electric dryer, etc and they tossed a 50 amp circuit in a 200 amp panel no problem. Did I just hire a questionable electrician for that... or is the 320 amp panel overkill because the builder is setting aside a potential 100amps for the car instead of my 60 max that I need (of which the most I'll use with a single Tesla is 48)

I can't imagine it being cheaper for an electrician to upgrade the panel after construction than for the builder to do it during construction. However, if the builder is playing games with upgrades as I've heard they do, that may be a different issue. There are way too many unknown variables for us, on the internet, to be able to help much.
Without the upgrade by the builder: Will the wire to the house handle the normal house load (I'd assume at least 200 amps today, probably more) plus 20 to 40 amps per charging station that you intend to install (is it a 3 car garage?)?
If so, then, perhaps an electrician can upgrade fairly cheaply after. However, at the cost of copper today, I can see the builder using the cheapest copper wire possible.
Echoing what others say: 100 amps is not necessary for an EV and rarely even convenient. Even 48 is on the high side. We actually do have a 100 Amp EVSE but only our Roadster can pull 70 amps and I've only charged at that rate 3 or 4 times in 15 years. Most of my charging has been between 16 and 32 amps (~12 and 24 mph), plenty to replenish a 96 or 192 mile day's usage overnight.

 

[Rocky_H]

320 Amp service sounds completely unnecessary and overkill for a single car, or even 2 of them to me.

You can't overgeneralize like that. What if it's a 10,000 square foot house with 5 air conditioners and 12 hot tubs? The house capacity may be already almost full with other things. An EV does not by itself determine if it fits within a certain total service capacity.

It depends on a load calculation for THAT house.

is the rule of thumb basically that if there are physically open spots for a 60 amp circuit then the panel can accommodate it?

No, that's not it. Same answer as above:
It depends on a load calculation for THAT house.

A load calculation is just a worksheet to get some data for the house and add up the numbers. It lists the high power appliances, and then some rule-of-thumb parts for how many rooms, how many square feet, etc. to total up average usage for lights, outlets, and things like that, and that will show how many amps are considered as already being used. You subtract that from the total house supply to see how many amps are still free.

There are plenty of examples if you Google for "load calculation worksheet". Here's an example:

https://www.ladbs.org/docs/default-source/forms/inspection-forms/sfd-electrical-vehicle-charger-service-load-calculation-form-in-form-00.pdf?sfvrsn=1ca8e453_20

So it's probably better to start off with this as a question: "Do the load calculation and tell me how many amps are free for an extra circuit?" Because it's probably this 100 or whatever ridiculous amps they are assuming that's pushing it over the top into requiring the big upgrade. There probably is some room for something smaller.

 

[FLRifleman]

I'd step back and look at this more logically, rather then simply going for the maximum output. Define what you really need to recover the mileage used overnight while you sleep, and go for that. For most people, a 20 amp 240v circuit will be plenty, and with you using 10% or less now that should be good for your use as well. Adding on unnecessary high amps will have a negative impact on your build costs, which may involve the transformer as well.

 

[ucmndd]

Prior advice that it’s load dependent is of course correct.

That said, I can see no realistic reason why a 1900 square foot new construction home, even with all electric appliances and heat pump heating, would need 320 amp service to accommodate a 60 amp EVSE circuit. That is indeed massive overkill for almost every scenario.

1900 square foot home with a big pool and hot tub, big garage/shop, double electric ovens, 36” induction cooktop, 2x AC units, and tons of under-floor or baseboard resistive heating? Maybe a problem.

Reference: my ~1900sf home has 200 amp service.

Electric oven
Induction cooktop
4 ton AC
48 amp Tesla wall connector
32 amp EVSE for second car
50 amp hot tub circuit
200 square foot office with its own 4kw heat/AC unit
Electric clothes dryer
The “normal” number of light/plug circuits you’d have for a home this size

If I had EVERYTHING running at the same time - let’s say it’s Thanksgiving, we’re cooking a big meal, have the heat blasting, kids playing in the hot tub, and we’re charging two of our family member’s cars at the same time while finishing a load of laundry - then we could hypothetically draw a bit north of 50kw and trip our main (200 amps at 240v is 48kw).

In practice, my home has never drawn more than 30kw at any given time, and I doubt it ever will.

 

[Earl]

I'd step back and look at this more logically, rather then simply going for the maximum output. Define what you really need to recover the mileage used overnight while you sleep, and go for that. For most people, a 20 amp 240v circuit will be plenty, and with you using 10% or less now that should be good for your use as well. Adding on unnecessary high amps will have a negative impact on your build costs, which may involve the transformer as well.

While I agree that 240v 20a is sufficient for most daily commutes: You don't want to undersize it either since it will generally be cheapest during initial build than retrofitting in the future.
Be sure too cover at least two 240v 20 circuits since all driving will soon be electric. Additionally, I recommend going with one or both 40 amp circuits if at all reasonable since future vehicles may not be as energy efficient as today's (Trucks, minivans?).

 

[Eric33432]

So many of these threads end like this... just end cold...curious what the OP ended up doing.

Many comments here say you should do a load calculation, and they are right. That is the only way to know for sure what you need. Below is a link to an app you can install on your phone to do your own load study. To get a general idea of what you need you can use the default numbers for most devices (dishwashers, laundry equipment, water heater, range, etc.) if you do not know the exact amps or watts. You might want to fine tune it with the exact numbers for watts or amps before you make a final decision, especially for heating and air conditioning.

Electrical Toolbox

www.mikeholt.com

Once you have done your load calculation you can use it to have a more educated and intelligent conversation with your builder and/or electrician.

That said, I have never seen 400/320 amp service installed on a 1900 s.f. all electric house.

It took me less than 5 minutes to run a calculation for a 1900 s.f. house with a heat pump and all the normal electric devices (but no pool, no hot tub). I used 30 amps for the heat pump and 9,600 watts for the supplemental heat; since it is a heat pump both the heat pump and supplemental heat can both run at the same time. While I used typical numbers for the heat pump you would need to plug in your actual numbers.

Without EVSE equipment, the house requires 150 amp service. With one 48 amp EVSE requires 175 amp service. With two 48 amp EVSE requires 200 amp service.

Below is the load study with two 48 amp EVSE. Good luck.

USER INPUTS​

A. General Lighting/Receptacles:

Living Area in Sq. Ft.:

1900sq. ft.

Small Appliance Circuits: 2 Circuits

Laundry Circuit(s): 1 Circuit(s)

B. Fixed Appliances and Equipment:

Dishwasher(s), 120V:1Unit(s),15 Amperes

Disposal(s), 120V:1Unit(s),15 Amperes

Electric Vehicle Charger(s), 240V:2Unit(s),48 Amperes

Microwave(s), 120V:1Unit(s),1800 VA

Water Heater(s), 240V:1Unit(s),4500 VA

Electric Dryer(s), 240V:1Unit(s),5000 VA

Range (Cooktop/Oven)(s), 240V:1Unit(s),14000 VA

C. Cooling/Heating Load(s):

Cooling Load: AC/Condenser
30A and Fan 2A, 240V

Heating Load: Heat
9600 VA and Fan 2A, 240V

COPPER RESULTS​

1. Service Disconnect Rating: 200A
2. Service Conductor Size:
2/0 AWG, rated 175A at 75°C
3. Service Neutral Conductor Size: 6 AWG, rated 65A at 75°C
4. Supply-Side Bonding Jumper: 6 AWG
5. Raceway Size: 2 Inch

ALUMINUM RESULTS​

1. Service Disconnect Rating: 200A
2. Service Conductor Size: 4/0 AWGAL, rated 180A at 75°C
3. Service Neutral Conductor Size: 4 AWGAL, rated 65A at 75°C
4. Supply-Side Bonding Jumper: 4 AWGAL
5. Raceway Size: 2½ Inch

Service Calculation[220.82(B)]

A. General Lighting/Receptacles:

Living Area: 1900 x 3 VA = 5700VA

Small Appliance Circuits: 1,500 VA x 2 = 3000VA

Laundry Circuit(s): 1,500 VA x 1 = 1500

B. Fixed Appliances and Equipment

Dishwasher(s), 120V:1Unit(s) x 15 Amperes x 120V =1800VA

Disposal(s), 120V:1Unit(s) x 15 Amperes x 120V =1800VA

Electric Vehicle Charger(s), 240V:2Unit(s) x 48 Amperes x 240V =23040VA

Microwave(s), 120V:1Unit(s) x 1800 VA = 1800 VA

Water Heater(s), 240V:1Unit(s) x 4500 VA = 4500 VA

Dryer(s), 240V:1Unit(s), 5000VA

Range (Cooktop/Oven)(s), 240V:1Unit(s), 14000VA

Subtotal: 62140VA
First 10,000 VA at 100%: 10000

Remainder 52140 VA at 40% = 20856 VA

Subtotal Demand Load: 30856 VA

C. Cooling/Heating Load(s) [220.82(C)]:

Cooling Load at 100%: 240V x (30A + 2 A) = 7680 VA

[Omit Per 220.60]

Heating Load at 65%: [9600VA +(240V x 2 A)] x 65% = 6552 VA

[Omit Per 220.60]

Cooling/Heating Demand Load: 14232 VA

Total Service Demand Load:

Service Demand VA Load (A, B, and C):45088 VA

Service Load in Amperes: 188A ( 45088 VA/240V)

NOTES:​

1. Service Disconnect Rating [240.4 and 240.6(A)]

Service disconnect sized must have an ampacity of at least 188A

Service Disconnect Rating: 200A

2. Service Conductor Size [310.15(B)(7) and Table 310.15(B)(16)]

Service conductor sized to 83% of 200A service disconnect rating.

200x 83% = 166A

3. Service Neutral Conductor Size [220.61 and Table 310.15(B)(16)]

A. General Lighting, Small Appliance, and Laundry VA Load: [220.42]

General Lighting: 1900 sq. ft. x 3 VA = 5700 VA

Small Appliance Circuits: 1,500 VA x 2 = 3000 VA

Laundry Circuit(s): 1,500 VA x 1 = 1500 VA

First 3,000 VA at 100% = 3000 VA

Remainder, 7200 VA at 35% = 2520 VA

General Lighting, Small Appliance, and Laundry Demand Load: 5520

B. Appliance(s) VA Load:​

Dishwasher(s), 120V:1Unit(s) x 15 Amperes

Total: 5400 VA x 75% = 4050 VA, 220.53

Disposal(s), 120V:1Unit(s) x 15 Amperes

Total: 5400 VA x 75% = 4050 VA, 220.53

Microwave(s), 120V:1Unit(s) x 1800 VA

Total: 5400 VA x 75% = 4050 VA, 220.53

C. Dryer(s) VA Load [220.60]​

Neutral Demand Load [220.61(B)]​

5000VA x 70% = 3500 VA, 220.54

D. Cooking Equipment VA Load [220.61] and Table 220.55​

Neutral Demand Load [220.61(B)]​

0 VA x 70% = 0 VA, 220.55

Neutral VA Demand Load(A, B, C, and D)​

5520 VA + 4050 VA + 3500 VA + 0 VA = 13070 VA

Neutral Load in Amperes:

54A ( 13070 VA/240V)

4. Supply-side Bonding Jumper Size [250.102(C)]​

Supply-side bonding jumper sized to the service conductor size.

5. Raceway Size [Chapter 9, Table 1]​

Based on a raceway at 40% fill, with an equipment grounding conductor.

 

[acarney]

When I got to the final sign offs with the construction manager it turned out that it is NOT a NEMA 14-50 that the sales agent thought. The construction manager actually called his head electrician for this new build area and confirmed, it’s a run sized for 100 amps to where ever I want in the garage. It’ll be behind a blank wall plate and I’ll have my electrician after I move in install a Tesla wall connector.

I still think 100amp is overkill… but who knows where we will be in 5+ years. F150 already charges at an insane rate (72 amp?) so I went with it for future proofing. They just completed the foundation this last week, so it’ll be awhile before I move in.

 

[acarney]

I should also note that I added three additional 20 amp independent circuits which could potentially see fairly high load (computers down the road) and I might add a 1.5 to 2 ton mini split to the garage down the road… so 320 was probably worth it if I was out near the edge of 200.

 

[Eric33432]

When I got to the final sign offs with the construction manager it turned out that it is NOT a NEMA 14-50 that the sales agent thought. The construction manager actually called his head electrician for this new build area and confirmed, it’s a run sized for 100 amps to where ever I want in the garage. It’ll be behind a blank wall plate and I’ll have my electrician after I move in install a Tesla wall connector.

I still think 100amp is overkill… but who knows where we will be in 5+ years. F150 already charges at an insane rate (72 amp?) so I went with it for future proofing. They just completed the foundation this last week, so it’ll be awhile before I move in.

I should also note that I added three additional 20 amp independent circuits which could potentially see fairly high load (computers down the road) and I might add a 1.5 to 2 ton mini split to the garage down the road… so 320 was probably worth it if I was out near the edge of 200.

Having a 100 amp feeder run to your garage is a great idea assuming your main panel is not located in the garage!

But you can make assumptions and possibly spend your money needlessly if you want to.

The ONLY way to know is to do a load calculation. I have done a preliminary calculation for you making some assumptions, and pointed you where to access an app so you can fine tune that yourself if you care to. Throw in a 72 amp circuit for an F-150 if you think that is necessary, although I expect it is not really necessary to charge any car at 72 amps when overnight charging at home.

Many people assume they use more amps than they actually do. If you use 4,000 kWh in a month, which few people do, (it would cost $600/month at 15¢ per kWh), your average load in amps is less than 4 amps @ 240 volts. Of course peak loads will be much higher and an electrical system needs to be designed for that.

If you install an A/C in your garage, a 1 ton mini-split will be fine, assuming you install insulated garage door(s) (and it would be foolish to install A/C in a garage without insulated garage door(s)). That is what I have in my garage and I am in sunny and hot SE Florida. A 1 ton A/C garage mini split system will not require your service to be increased to 320 amps.

If you or a future homeowner ever want to install power walls, it is much more complicated with a service over 200 amps as the Tesla gateway is designed for 200 amp service. You would have to install two gateways and have separate power walls for each gateway if you want whole-home outage protection.

My preliminary load calculation, which I invite you to study in detail and fine tune if necessary, shows 200 amp service is fine and I included two 48 amp chargers, both running simultaneously, which you can do with 200 amp service, but is not necessary as they can be configured to load share. If you do that, you are no where close to needing 200 amp service. Even without load sharing, while you are close you are not over 200 amps, and there is still capacity for your garage A/C. And you can always back the down from 48 amps to 40 amps if that is necessary.

With 48 amp charging, it takes my Model X Plaid ~5 hours to charge from 30% to 80%, and I rarely drive it down to 30%. And the Model X takes longer to charge than any other Tesla. Two EVs sharing 48 amps would always be full in the morning unless you drove both of them down to 10% and needed to charge them to 100% starting at midnight.

My son and his girl friend manage to charge their two Model 3's (one of which is a Performance model) from a single Tesla Wall Connector that they share that is on a 50 amp circuit (40 amp charging) in their 2,400 s.f. house that has a 200 amp service and an additional load you may not have of a 2 HP pool pump that runs 12 hours a day. Unless one of them has to do a lot of driving on a single day they usually alternate charging their cars every other night. It just is not a problem.

Installing a 100 amp feeder for a sub panel is not what you look at when you do your load calculation. Rather, you look at the loads that will be connected to that sub panel.

Your extra computer loads are figured in to your overall square footage calculation at the top of the load calculation. Unless you are going to have a couple of racks full of high power rack mount computers mining for bit-coin, their load will be trivial.

I hope this gives you food for thought before you most likely needlessly spend money installing 320 amp service for a 1,900 square foot home.

Photo of 1 ton mini split in my two car garage and our other Tesla Model 3.

 

[acarney]

Having a 100 amp feeder run to your garage is a great idea assuming your main panel is not located in the garage!

But you can make assumptions and possibly spend your money needlessly if you want to.

The ONLY way to know is to do a load calculation. I have done a preliminary calculation for you making some assumptions, and pointed you where to access an app so you can fine tune that yourself if you care to. Throw in a 72 amp circuit for an F-150 if you think that is necessary, although I expect it is not really necessary to charge any car at 72 amps when overnight charging at home.

Many people assume they use more amps than they actually do. If you use 4,000 kWh in a month, which few people do, (it would cost $600/month at 15¢ per kWh), your average load in amps is less than 4 amps @ 240 volts. Of course peak loads will be much higher and an electrical system needs to be designed for that.

If you install an A/C in your garage, a 1 ton mini-split will be fine, assuming you install insulated garage door(s) (and it would be foolish to install A/C in a garage without insulated garage door(s)). That is what I have in my garage and I am in sunny and hot SE Florida. A 1 ton A/C garage mini split system will not require your service to be increased to 320 amps.

If you or a future homeowner ever want to install power walls, it is much more complicated with a service over 200 amps as the Tesla gateway is designed for 200 amp service. You would have to install two gateways and have separate power walls for each gateway if you want whole-home outage protection.

My preliminary load calculation, which I invite you to study in detail and fine tune if necessary, shows 200 amp service is fine and I included two 48 amp chargers, both running simultaneously, which you can do with 200 amp service, but is not necessary as they can be configured to load share. If you do that, you are no where close to needing 200 amp service. Even without load sharing, while you are close you are not over 200 amps, and there is still capacity for your garage A/C. And you can always back the down from 48 amps to 40 amps if that is necessary.

With 48 amp charging, it takes my Model X Plaid ~5 hours to charge from 30% to 80%, and I rarely drive it down to 30%. And the Model X takes longer to charge than any other Tesla. Two EVs sharing 48 amps would always be full in the morning unless you drove both of them down to 10% and needed to charge them to 100% starting at midnight.

My son and his girl friend manage to charge their two Model 3's (one of which is a Performance model) from a single Tesla Wall Connector that they share that is on a 50 amp circuit (40 amp charging) in their 2,400 s.f. house that has a 200 amp service and an additional load you may not have of a 2 HP pool pump that runs 12 hours a day. Unless one of them has to do a lot of driving on a single day they usually alternate charging their cars every other night. It just is not a problem.

Installing a 100 amp feeder for a sub panel is not what you look at when you do your load calculation. Rather, you look at the loads that will be connected to that sub panel.

Your extra computer loads are figured in to your overall square footage calculation at the top of the load calculation. Unless you are going to have a couple of racks full of high power rack mount computers mining for bit-coin, their load will be trivial.

I hope this gives you food for thought before you most likely needlessly spend money installing 320 amp service for a 1,900 square foot home.

Photo of 1 ton mini split in my two car garage and our other Tesla Model 3.

View attachment 982533

That garage floor is AMAZING! And I bet was expensive and is a pain to keep clean, lol

 

[Eric33432]

It came with the house which was built in 2006 and we bought in 2011. Actually it is very easy to keep clean. Just vacuum and wet mop.

In my experience unfinished concrete is what is hard to keep clean.

Let the group on this thread know what you decide to do (electrically) with your new house.