EV Charging Approach - Difficult Choice

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ESolar

Senior Member
Location
Eureka, CA Humboldt County
Occupation
Electrician/Contractor
There are multiple ways to run an EV Charging receptacle(s) and I'm onthe fence as to which way to go.

1. Run 6 AWG romex from existing 70 amp subpanel using a 40 amp breaker (reduced from 60 due to demand on panel) to a 14-50R. This option is not mutually exclusive, i.e., it can be completed with one of the following. AND/OR

2. Run from 200 amp main panel 3 x 1 AWG, 1 x 6 AWG (ground) in1 1/2PVC to new 100 amp subpanel in garage. The main panel is approaximately 40 feet away. Would require trenching and hydraulic bore under 4 ft wide walkway. OR

3. Run from 200 amp main panel 3 x 6 AWG plus 1 x 10 AWG (ground) through an existing 3/4" EMT to a new 50 amp subpanel. Existing EMT terminates in attic and requires additional EMT to reach garage. Total approximately 50 feet.

Thoughts?
 
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retirede

Senior Member
Location
Illinois
A couple thoughts:

Unless you know for sure that the EVSE to be used is 32A or less, you are doing the customer a disservice by installing a 14-50R on a 40A breaker.

Is the garage attached? If not, adding a second feeder would likely be a code violation.

When using EMT, pulling a wire for the EGC is not required by code.
 
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ESolar

Senior Member
Location
Eureka, CA Humboldt County
Occupation
Electrician/Contractor
The 40 amp run from the 70 amp subpanel is only down 4 feet and into ceiling cavity, then 5 feet to exterior wall adjacent to garage door (exterior mount in that location). That makes it cheap for the client. I would run 6/3 UF-B (because once it exitsthe building it is considered wet) into one of these from the back:
www.homedepot.com

Midwest Electric Products 50 Amp Temporary RV Power Outlet U054P - The Home Depot

GE Temporary RV Power Outlet is designed for outdoor electrical service to meet short-term power requirements. UL certified product for safety.
www.homedepot.com
 
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retirede

Senior Member
Location
Illinois
jaggedben said:
But not from a receptacle.
Click to expand...

Of course not. The 48A is the max the car will draw. The EVSE (which is fed from a properly sized branch circuit)tells the car what it’s capable of supplying. The car will then draw what it wants, not exceeding the EVSE’s capability.

The largest receptacle that can be used for an EVSE is a 14-50, thus 40A maximum.
 
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jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Perhaps it bears further explanation for those who might not know...

The highest amps any listed plug-in EVSE will draw is 40A. One should assume a plug-in EVSE can draw 80% of the pkug rating. Thus for a 14-50 plug it should be on a 50A breaker like you said above, just in case. For a lesser rated plug it can be less, as appropriate with 125% continuous multiplier, because any listed plug-in EVSE knows what type of receptacle it's plugged into (even if it has multiple plug adapters like Tesla's), and will limit charge accordingly.

That said, in no case will the car draw more than it wants.
 
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curt swartz

Electrical Contractor - San Jose, CA
Location
San Jose, CA
Occupation
Electrical Contractor
Pretty much all of the plug in chargers are 32 amp max (40 amp circuit). Even the plug in Tesla charger is 32 amps. I'm wondering if they can't get a listing for more than 32 amps since the NEC permits 50 amp receptacles to be fed by 40 amp circuits?

Tesla offers an optional charge cord with a factory installed 50 amp plug (not an adapter type like the standrd charge cords). In the past serveral years they have never shown the item in stock though. It might not really exist.
 
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ramsy

Roger Ruhle dba NoFixNoPay
Location
LA basin, CA
Occupation
Service Electrician 2020 NEC
curt swartz said:
Pretty much all of the plug in chargers are 32 amp max (40 amp circuit). Even the plug in Tesla charger is 32 amps. I'm wondering if they can't get a listing for more than 32 amps since the NEC permits 50 amp receptacles to be fed by 40 amp circuits?
Click to expand...
Continuous charging at over 32 Amps may not be good for modern lithium car batteries, which are the most expensive component of electric vehicles, and degrade prematurely with heat stress.

Level 4 DC fast charging stations in summer ambient may be the worst way to heat stress lithium vehicle batteries.
 
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ESolar

Senior Member
Location
Eureka, CA Humboldt County
Occupation
Electrician/Contractor
jaggedben said:
Btw many Tesla's can draw 64A with a hard-wired charger.
Click to expand...
>The Tesla Wall charger is designed to draw a maximum of 48 amps from a 60 amp circuit. You can set it to draw less.
>The Tesla mobile charger will draw various amperages depending on the pigtail design. However, the maximum that it will draw is 32 amps, even with the 14-50p pigtail.
>Note that the 40 amp breaker that I specified for the subpanel run was sized based on a 32 amp demand (0.8 x 40) so as to not "overload" the panel.
>However, the panel is a 125 amp and the feeder from, and breaker in, the main are sized at 70 amps. So in practice, I could go to 50 amps on that line without damaging the wire and bus bar. But that may result in nusance trips.

That subpanel currently has a 45 amp breaker for solar, 1400 sqft at 15 and 20 amps, central vacuum (20), and a furnace blower motor (20).
 
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wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
ramsy said:
Local commuters, within 100 miles per day, can dial down overnight charging to 20 Amps max @ 240v, and preserve battery life by avoiding thermal maximums.
Click to expand...
I don't think the difference between 4 kW charging and 7 kW charging is going to make a significant thermal difference for a car with a 40+ kWh battery. Which is basically every EV currently being made, most are 60+ kWh.

Cheers, Wayne
 
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