Service size for two car residential garage with full living space above in the EV age

[JoeNorm]

I know everyone is going to say just do a load calc but its not that easy when not everything is known.

So my question is this: In the age of EV chargers, All electric homes, and rooftop solar would I be doing the homeowner a disservice to install anything but a 200 amp service in a situation like this? This is a two car garage with a roughly 1000sqft living space above it which will include kitchen and bath.

Main house already exists so the choices would be run 125amp feed to new garage or do a service upgrade and give them a 320amp meter base. 200 to main house and 200 to new garage building.

Option two is obviously much more costly but the way i see electricity being used these days, especially with EV potential, it seems like the better way to go.

Another detail to throw in the mix is that POCO demand data for the house shows very low usage, but that could be partly due to a large grid-tied PV array.

Thoughts?

 

[Buck Parrish]

I know everyone is going to say just do a load calc but its not that easy when not everything is known.

So my question is this: In the age of EV chargers, All electric homes, and rooftop solar would I be doing the homeowner a disservice to install anything but a 200 amp service in a situation like this? This is a two car garage with a roughly 1000sqft living space above it which will include kitchen and bath.

Main house already exists so the choices would be run 125amp feed to new garage or do a service upgrade and give them a 320amp meter base. 200 to main house and 200 to new garage building.

Option two is obviously much more costly but the way i see electricity being used these days, especially with EV potential, it seems like the better way to go.

Another detail to throw in the mix is that POCO demand data for the house shows very low usage, but that could be partly due to a large grid-tied PV array.

Thoughts?

My vote - 320 upgrade 200 to the house 125 to the garage. Just done one like this.

 

[jaggedben]

In reality I think 125 is probably fine but you don't want to cut it too close. Maybe look at car chargers with shared current limiting to reduce the load calc.

If 'not everything is known' then give them the higher price and say 'maybe it could be less, but not without more info'.

 

[Dennis Alwon]

Is it possible with a 2 car garage they will have 2 electric vehicles? It may be worth putting 200 at the garage. Do the owners want the apt on a separate meter?

 

[retirede]

No all-electric home around here gets less than a 200. Even with a couple EVs, a 200 should be fine for 1000 SQFT of house.

 

[tthh]

ADU -- additional dwelling unit -- that's what they call them around here

Think of this...

The garage has two spots and there is a tenant in the ADU above the garage and they have an electric car they park in the driveway. You could easily have 3 EV charges fed off the garage panel. The ADU is probably all electric and has a stove and dryer and a heat pump and A/C.

Do you still want 125A?

 

[wwhitney]

Counterpoint for discussion: other than fairly rare occurrences, planning for 2 EVs and normal usage would suffice. And say you want to be able to recharge both EVs 100 miles overnight (12 hours). At around 350 Wh per mile, that would be 70 kWh over 12 hours. So the average charging load is only 6 kW or 25A.

Cheers, Wayne

 

[wwhitney]

So the upshot would be that it could be reasonable to supply a 2 car garage with a single 60A EVSE circuit (allowing 48A charging if the car and EVSE both support it). Which could also serve two EVSEs that do load sharing, if desired.

Cheers, Wayne

 

[gadfly56]

So the upshot would be that it could be reasonable to supply a 2 car garage with a single 60A EVSE circuit (allowing 48A charging if the car and EVSE both support it). Which could also serve two EVSEs that do load sharing, if desired.

Cheers, Wayne

That seems to be cutting it a bit fine. If you're upgrading to the 320 service, why skimp on the second panel? I recall discussions here on how a 125 panel in some areas is actually more expensive than a 200 panel.

 

[wwhitney]

That seems to be cutting it a bit fine. If you're upgrading to the 320 service, why skimp on the second panel?

I guess I'm proposing that the ADU should get a 200A panel and feeder conductors, but it would be reasonable to try supplying it with just a 125A breaker and avoiding or deferring the main house service upgrade. Assuming the load calcs work out.

Also depends on the cost of the service upgrade--I'm in an area with underground services, so upgrades are very expensive.

Cheers, Wayne

 

[gadfly56]

I guess I'm proposing that the ADU should get a 200A panel and feeder conductors, but it would be reasonable to try supplying it with just a 125A breaker and avoiding or deferring the main house service upgrade. Assuming the load calcs work out.

Also depends on the cost of the service upgrade--I'm in an area with underground services, so upgrades are very expensive.

Cheers, Wayne

Yes, there is that to consider.

 

[JoeNorm]

Yes, a service upgrade will be expensive.

One other idea I had that I rarely see is just splitting a 200 amp service between the two buildings. Why not?

It seems better than bottle necking one with a 125 amp breaker.

 

[wwhitney]

One other idea I had that I rarely see is just splitting a 200 amp service between the two buildings. Why not?

If by service you mean feeder, that's what I suggested, whether or not you do a service upgrade (and whether or not you can easily supply the 20)A feeder with a full 200A OCPD without a service upgrade).

If by service you mean service, that would avoid the need for a service upgrade at the main house.

Cheers, Wayne

 

[curt swartz]

Another detail to throw in the mix is that POCO demand data for the house shows very low usage, but that could be partly due to a large grid-tied PV array.

Does your POCO really provide demand data for residential services? I have only see that for commercial services. If you are looking at KWH that is meaningless for load calculations.

 

[JoeNorm]

Does your POCO really provide demand data for residential services? I have only see that for commercial services. If you are looking at KWH that is meaningless for load calculations.

We can get demand data off of the newer meters they are installing. Not every residence has them yet.

 

[mtnelect]

With California "Electrification" 400 amp will be the norm ... How would you like that box hanging on the outside of your home ?

 

[drcampbell]

... 400 amp will be the norm ... How would you like that box hanging on the outside of your home ?

I don't see what the big deal is. It'll look essentially the same as what we have now, just a little bigger. And like you say, it'll become the norm and we won't even notice them.

It's actually what I plan for the upgrade to my own house. (built 1927, upgraded to 60-amp service in the 1940s) Two-car detached garage, with support for two fast chargers. I plan to put the meter main on the garage and a branch panel in the house.