EatsShootsandLeafs
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How many amps for new 240V install?

Sat Jan 18, 2020 12:20 pm

Walls are open so we're running a 240V circuit to the garage in anticipation of a future EV (I don't have one at this time). Going to do at least 50amps. 60 the electrician is going to use thicker wire so wants another $100-150. 80 amps he can do for another $100 again on top of that.

What's a heavy duty residential install look like these days? I assume when I put in an actual charge station later I can specify the circuit size and it will charge accordingly.

Thanks!

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Nubo
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Re: How many amps for new 240V install?

Sat Jan 18, 2020 1:00 pm

AFIK, as long as the wiring can carry the load, you can size the circuit breaker according to the device you use (80% continuous load). I.e., for a 40 amp EVSE, use a 50 amp breaker. You don't want to use an 80 amp breaker for a 40 amp EVSE. But having the wire be heavier than needed is fine. In fact you'll save a small amount of power due to the lower resistance.
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powersurge
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Re: How many amps for new 240V install?

Sat Jan 18, 2020 1:37 pm

There is no reason to install wire as thick as your arm...

What will you plan to do with that installation?

A home installation is a situation where there is one thing that you have.... Time.... No one will need to plug in, and have to run out again in 20 minutes.. Even with my 30 amp setup, I can charge 30 - 35 miles per hour. So in 2 hours, it can go from 30% charge to 90-100% charge.

Is that so bad? Even if you get a really big battery, like a Tesla, a 40 amp setup will be fine to charge because you will never drive that many miles during a day that you need FAST CHARGE!!!

I would say, get a 50 amp circuit, which will handle a future 40 amp charger.

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Re: How many amps for new 240V install?

Sat Jan 18, 2020 2:48 pm

Nubo wrote:
Sat Jan 18, 2020 1:00 pm
AFIK, as long as the wiring can carry the load, you can size the circuit breaker according to the device you use (80% continuous load). I.e., for a 40 amp EVSE, use a 50 amp breaker. You don't want to use an 80 amp breaker for a 40 amp EVSE. But having the wire be heavier than needed is fine. In fact you'll save a small amount of power due to the lower resistance.
This is my understanding as well. I don't generally suggest wiring that will handle 80 amps, but it won't hurt anything as long as the breaker is sized for the device.
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EatsShootsandLeafs
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Re: How many amps for new 240V install?

Sun Jan 19, 2020 4:01 am

Thanks, all.

Seems like more than 50 amp would be a waste of money. Guessing 14-50 is the best receptacle to get. Going full 60 amps now with 14-60 receptacle might be a pain, too.

I'm going to do 50 amps for convenience now and cost but if it's only a few bucks to go with a fatter gauge wire to handle future 60 I'll possibly have him run that. Then down the road I could put in a new breaker and receptacle without it impacting cost or compatibility now.

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Re: How many amps for new 240V install?

Sun Jan 19, 2020 5:10 am

Awhile back, Tesla started including no >48 amp OBCs on the their US vehicles (https://www.tesla.com/support/home-char ... rd-charger). They used to have also have 40, 72 and 80 amp (via twin OBCs). And, 32 amp is new for the lowest end Model 3(s).

From looking at the specs for https://www.audiusa.com/models/audi-e-tron, they mention 9.6 kW AC charging, so I guess 40 amps. It seems like finally, non-Tesla powered US-market BEVs are finally getting over 32 amp OBCs. I wonder if the trend will continue and where the typical max will end up being? 40 amps? 48 amps? or still 32 amps?

Previously, you had to go with something Tesla powered to have 40+ amp OBCs.

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Re: How many amps for new 240V install?

Sun Jan 19, 2020 4:20 pm

Unless you are a super commuter 30 amp circuit and 24 amp EVSE is plenty 99% of the time.
Get 40 or 50 if you like but I would rather have 2x 30 amp for two vehicles.
If going 60+ then put it to a subpanel to split the power between multiple EVSE etc.
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Re: How many amps for new 240V install?

Sun Jan 19, 2020 7:22 pm

smkettner wrote:
Sun Jan 19, 2020 4:20 pm
Unless you are a super commuter 30 amp circuit and 24 amp EVSE is plenty 99% of the time.
Get 40 or 50 if you like but I would rather have 2x 30 amp for two vehicles.
If going 60+ then put it to a subpanel to split the power between multiple EVSE etc.
Numbers. 30 Amps 240V is 7.2kW With 12 hours of overnight charging, and 2.0 miles per kWh, commute out to 170 miles. Hard to find a super commuter doing more.
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Re: How many amps for new 240V install?

Sun Jan 19, 2020 8:46 pm

I'd ask the electrician about what it would cost to install a sub-panel in the garage. That's what I'm planning to do in my garage. I'll probably run 100A just to future-proof it although my OpenEVSE will be on a 35A circuit. Also ask about Al wire vs Cu. Al is much cheaper.

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Re: Aluminum wiring?

Sun Jan 19, 2020 9:23 pm

It's not cheaper if your house catches on fire.

Aluminum wire creeps under the pressure of the screw terminals, which results in looseness of the electrical connection, then arcing across the gap occurs and generates heat in the junction.

Special grease and fittings are used with aluminum wire in an attempt to mitigate this, but periodic inspection and re-tightening of the bolts and screws are needed. Aluminum may be used for the transformer pole-to-house wiring, but usually crimp lugs are used to make those junctions.

Use copper and sleep easy, just consider the cost difference as cheap fire insurance.

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