main panel has 30 amp to garage panel, what are the options

[Rocky_H]

With a 30A circuit, the car draws 24A (or 20A if you dial it down in the car). So there is 6A (30-24) at 240V available on the feeder circuit from the main panel. Which is 12A at 120V.

The calculations for feeders are 100% of noncontinuous loads + 125% of continuous loads. So the 24A times 1.25 is 30 + 12 = 42. That would need at least a 42A supply to the subpanel, eh?

Normally, I wouldn't trust myself to do a more complicated load calculation on a subpanel if it is considered living space, and it has several circuits, where you have to apply some amount of watts per square foot and all of that, but this one is really simple because the 24A continuous supply to an EVSE really does consume the entirety of a 30A supply circuit, so there is zero capacity leftover for anything else at all.

 

[ItsNotAboutTheMoney]

OP, how many miles do you drive in a typical day?

 

[posity]

You should enlist the expertise of a qualified electrician rather than rely on a bunch of us Internet armchair 'experts'. There are numerous electrical code related requirements that have not been properly addressed here in this thread. For example, once you have more than two circuits in your garage subpanel, your disconnecting means must have a rating of at least 60A: your 30A breaker feeding the subpanel would no longer be sufficient. That likely means you need at least a new garage subpanel with a local disconnect rated at least 60A. And new code requires at least a 20A garage circuit for receptacles in each stall. Plus a proper installation should include a load capacity calculation to definitely demonstrate there is not too much load on that subpanel (which will, almost certainly, show your 30A 2 pole supply is undersized when adding a 20A 2 pole circuit for your EV). Depending whether your garage is attached or detached, your subpanel grounding may need to be addressed to follow recent code. Your AHJ (Authority Having Jurisdiction: the county, for example) will have rules that don't necessarily follow the NEC so all this postulating here on the Internet is interesting fodder, but your particular situation is just complex enough that it requires competent professional advice.

The advice here that a 20A 240V circuit (MY charge rate of 15 MPH) is likely sufficient for your EV use will be good input for the electrician you employ. The technique to accomplish that in the most competent, legal and cost effective manner involves enough tradeoffs that a professional electrician is definitely advisable.

But even that 20A 240V advice depends on your daily commute miles and amount of charging time you have each day - which you have not as yet answered AFAIK.

 

[tga]

For example, once you have more than two circuits in your garage subpanel, your disconnecting means must have a rating of at least 60A: your 30A breaker feeding the subpanel would no longer be sufficient.

Can you provide a code reference for this statement?

 

[hybrid>EV]

Thanks Everyone. I have electricians coming in about 10 days to explore options and provide quotes. Garage only has lights and garage door currently, and I have no plan to put anything else there. Even if I use power tools, it is unlikely I will be using them when I charge my car in the evening. I have superchargers nearby and typically drive < 30 miles / day. The circuit/wire between house and garage is underground and put in by builder, and I couldn't find it and don't know how big the pipe is or the type of wire or gauge they put in it. I will ask for 2 quotes.
1. install a 20 amp breaker and wall connector, and i will set it to 20 amp, which gets 15 mph and is totally enough for me needs
2. replace the 30 amp breakers and underground wire with something bigger. i suspect this is several times more expansive than the first option, but i want to get a quote anyways.

 

[Cosmacelf]

Thanks Everyone. I have electricians coming in about 10 days to explore options and provide quotes. Garage only has lights and garage door currently, and I have no plan to put anything else there. Even if I use power tools, it is unlikely I will be using them when I charge my car in the evening. I have superchargers nearby and typically drive < 30 miles / day. The circuit/wire between house and garage is underground and put in by builder, and I couldn't find it and don't know how big the pipe is or the type of wire or gauge they put in it. I will ask for 2 quotes.
1. install a 20 amp breaker and wall connector, and i will set it to 20 amp, which gets 15 mph and is totally enough for me needs
2. replace the 30 amp breakers and underground wire with something bigger. i suspect this is several times more expansive than the first option, but i want to get a quote anyways.

Congrats on slogging your way through our bickering

 

[Sophias_dad]

typically drive < 30 miles / day

So basically you need to install nothing at all. Plug your UMC into a 120V/15A outlet and you'll be good(4-5mi/hr). If you have a 120/20A outlet and the UMC adapter for it its even better.

 

[davewill]

So basically you need to install nothing at all. Plug your UMC into a 120V/15A outlet and you'll be good(4-5mi/hr). If you have a 120/20A outlet and the UMC adapter for it its even better.

I have to disagree. Yes, on it's face, the 120v outlet will cover his daily driving, but I can't recommend relying on an existing outlet. 120v outlets are usually chained through other outlet boxes on their way to any particular outlet.

I feel that it's important to have a dedicated circuit (of whatever size) when charging on a daily basis. EV charging is not like any other electrical use in a home. The long hours of high amperage will tend to uncover weaknesses in the underlying service. Better safe than sorry.

 

[Unclepaul]

The electricians coming out to you will tell you what their strategy is to optimize charging speeds and staying within your local codes.
Their hands on inspection of your system will give them better awareness of your situation and best strategies.

Remember, you can currently get a 30% tax deduction for installation of charging infrastructure for your EV. Might take some of the sting out of the estimates. Get a receipt for their work. Also good to keep the paperwork in case of any future need.

 

[ucmndd]

Remember, you can currently get a 30% tax deduction for installation of charging infrastructure for your EV.

IF you live in eligible census tracts

 

[Tronguy]

At one point, the OP stated that he didn't know how the wires got from his house to the garage. They might be buried; but perhaps they're being run through some conduit.

If it's the latter and the conduit isn't hard to find or overly full, adding a (say, 60A) set of wires to the bundle might not be that big a deal. Or cost that much.

Back in the deeps of time, the SO and I had a kitchen reno done; the electrician put in a 4" diameter plastic pipe from just above the breaker box, run across the ceiling of the garage, through a wall, then up from the first floor to the second, where the kitchen lived. Interestingly, the pipe wasn't all that full and the guy left a nylon strap in there should some future electrician want to pull some additional wires. Perhaps our OP is similarly lucky.

 

[CKwik240]

At one point, the OP stated that he didn't know how the wires got from his house to the garage. They might be buried; but perhaps they're being run through some conduit.

If it's the latter and the conduit isn't hard to find or overly full, adding a (say, 60A) set of wires to the bundle might not be that big a deal. Or cost that much.

Back in the deeps of time, the SO and I had a kitchen reno done; the electrician put in a 4" diameter plastic pipe from just above the breaker box, run across the ceiling of the garage, through a wall, then up from the first floor to the second, where the kitchen lived. Interestingly, the pipe wasn't all that full and the guy left a nylon strap in there should some future electrician want to pull some additional wires. Perhaps our OP is similarly lucky.

I would definitely look into how it's currently run. Mine had several circuits (including a dryer circuit) running through an underground conduit. I pulled all the wires out and ran 3 ga THHN and installed a 100A subpanel and distributed all the garage wiring from there. I was thankful the conduit was large enough to accommodate this.

 

[Rocky_H]

The electricians coming out to you will tell you what their strategy is to optimize charging speeds and staying within your local codes.
Their hands on inspection of your system will give them better awareness of your situation and best strategies.

This gets to the advice which I think is helpful to new owners in this situation.

If you start off your request to the electrician with "I want..." they will probably take you at your word of doing exactly that, including whatever big expensive upgrades it requires to give what you literally asked for.

So in cases like this, I think the more helpful initial line would be to show the 30A subpanel in the garage and ask it as a question: "How big a 240V circuit can we add to this?"

 

[davewill]

This gets to the advice which I think is helpful to new owners in this situation.

If you start off your request to the electrician with "I want..." they will probably take you at your word of doing exactly that, including whatever big expensive upgrades it requires to give what you literally asked for.

So in cases like this, I think the more helpful initial line would be to show the 30A subpanel in the garage and ask it as a question: "How big a 240V circuit can we add to this?"

Yes, the two questions you want an answer to are:

1. What is the biggest I can put in?
2. What is the biggest I can do without incurring excessive expense?

People so often overlook the second question.

 

[BillRadio]

The 120v/15A solution is a great basic choice if you are aware of its limitations.

First, if your utility charges any type of time of use rates you will often need to charge in a more expensive period due to the longer time required for charging.

Second, in cold weather, the charge rate is lower due to the need to heat the batteries.

These don't affect some users, but for others, it can be a real problem.

 

[Cosmacelf]

So basically you need to install nothing at all. Plug your UMC into a 120V/15A outlet and you'll be good(4-5mi/hr). If you have a 120/20A outlet and the UMC adapter for it its even better.

Disagree. 120V charging is more expensive every single day for a variety of reasons (see this page for a 120V cost calculator, Advice for EV Charging in North America). If you have access to low overnight rates for EVs, then 120V charging is really expensive in comparison.

Most 120V receptacles and especially GFCIs are just not built for day in day out continuous loads. I had been using a relatively new 120V/20A GFCI receptacle for about 18 months myself and one day the GFCI just melted and burned out.

 

[tga]

I have to disagree. Yes, on it's face, the 120v outlet will cover his daily driving, but I can't recommend relying on an existing outlet. 120v outlets are usually chained through other outlet boxes on their way to any particular outlet.

I feel that it's important to have a dedicated circuit (of whatever size) when charging on a daily basis. EV charging is not like any other electrical use in a home. The long hours of high amperage will tend to uncover weaknesses in the underlying service. Better safe than sorry.

This is a really important point that I think a lot of people overlook. I hate to hear that someone is charging off an existing 120V outlet, for these reasons.

Disagree. 120V charging is more expensive every single day for a variety of reasons (see this page for a 120V cost calculator, Advice for EV Charging in North America). If you have access to low overnight rates for EVs, then 120V charging is really expensive in comparison.

Most 120V receptacles and especially GFCIs are just not built for day in day out continuous loads. I had been using a relatively new 120V/20A GFCI receptacle for about 18 months myself and one day the GFCI just melted and burned out.

EDIT - and this!

 

[Sophias_dad]

A 240V circuit would be fine and easy/cheap to install. 20A would definitely work, although I'd want to make sure the 120V loads were on different legs(than each other). Even 30A would be okay, until you break out the table saw, leaf blower or garage heater. TBH, a garage heater on the 120V leg would have a high likelihood of tripping the breaker even with a 20A(16A drawn) EV load, if it was left on for a while.