Electric Vehicle Wiring

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ESolar

Senior Member
Location
Eureka, CA Humboldt County
Occupation
Electrician/Contractor
The Tesla wall charger is single phase 200 - 240 AC. It operates with up to a 60 amp OCPD for 48 anp continuous. For conductors they spec the following:

"If installing for maximum power, use minimum 6 AWG, 90° C-rated copper wire for conductors.
NOTE: Upsize conductors if necessary.
For sites with multiple Wall Connectors, each Wall Connector must have its own branch circuit with L1, L2/N, and Ground."

First: Can I run wires for two Tesla plugs using four 6 AWG, 90° C in 3/4 EMT using the EMT as the EGC?

Second: Is there a need to "Upsize conductors"?

My conduiut may get hot because it's routed between the ceiling and roof (I picked 123 - 131 F).
I spec the following:
6 Gauge 90 degree C THHN (three conductors and a smaller #10 ground)
75 degree C termination
310.15(B): 65 amp conductor (based on the 75 degree C termination)
310.15(B)(2)(a): I derate the conductor for temp by 0.76
65 amps x 0.76 = 49.4 amps; Not quite 50 amps, but very close.
So I assume that am relegated to a max 45 amp OCPD (versus 50 amp) breaker and a max continuous load of 36 amps.

But then I find that this online calulator gives the Tesla answer: http://www.electrician2.com/calculators/wireocpd_ver_1_reverse.html
The calculator includes the temp rating for the terminators.
In the calculator they rate the conductor at 57 amps [(75 amps for the 90 C wire) x 0.76 = 57 amps] and spec a 60 amp OCPD for a continuous load of 48 amps.
They also recommend a #10 ground.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
Just post once, be patient and someone will come along with a reply.
Posting multiple threads with the same subject is confusing to the readers.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
The problem with running 2 circuits in the same conduit is that you need to derate for having 4 current carrying conductor's in a conduit. That is 80%.
#6 is good for 75 amps @90C but then you have 4 CCC's so that is 80%. 75x.8 = 60 amps and now you have .76 for temperature so 60 x .76 is 45 amps.

Some Tesla units can be wired with one circuit and they communicate with each other so that they never draw more than the max you have on the circuit. If you designate 48 amps then it will regulate the 2 cars. If you have a priority then you can set to charge car 1 then car 2 or whatever works.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I posted a duplicate because I was unsure where this wouldelicit an answer. NEC v Calulations
I, and probably most of us look at new posts, so we'll see it regardless of topic. It's rare that threads get moved.
 

ESolar

Senior Member
Location
Eureka, CA Humboldt County
Occupation
Electrician/Contractor
Thank you Dennis for your reply and the help. The solution is the Tesla HPWC (high power wall connector) as you suggested - it can negotiate two cars (I think from discussions on forums).
I believe this works:

Its a 200 amp panel.
Mild future proof: two 4 AWG 90 C conductors plus 6 AWG ground in existing 3/4 EMT ( and a lot of lube).
Max OCPD = 80 amps; Select 60 amps
Conductor detrated for heat ampacity = 72.2 amps
Continuous load 48 amps (Tesla HPWC designed for maximum 60 amp OCPD)

Thoughts?
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
Thank you Dennis for your reply and the help. The solution is the Tesla HPWC (high power wall connector) as you suggested - it can negotiate two cars (I think from discussions on forums).
I believe this works:

Its a 200 amp panel.
Mild future proof: two 4 AWG 90 C conductors plus 6 AWG ground in existing 3/4 EMT ( and a lot of lube).
Max OCPD = 80 amps; Select 60 amps
Conductor detrated for heat ampacity = 72.2 amps
Continuous load 48 amps (Tesla HPWC designed for maximum 60 amp OCPD)

Thoughts?
Those conductor sizing will put your duct fill at over 38% in 3/4 EMT.
 

RumRunner

Senior Member
Location
SCV Ca, USA
Occupation
Retired EE
The Tesla wall charger is single phase 200 - 240 AC. It operates with up to a 60 amp OCPD for 48 anp continuous. For conductors they spec the following:

"If installing for maximum power, use minimum 6 AWG, 90° C-rated copper wire for conductors.
NOTE: Upsize conductors if necessary.
For sites with multiple Wall Connectors, each Wall Connector must have its own branch circuit with L1, L2/N, and Ground."

There are two types of TESLA charging.
The 30 Amp for the type 3 and the 60 amps for the type X. This is not counting the charging scheme where you use the regular household 20 amp plug in your living room..
For Type 3, you need 30 A. the type X will require 60 Amps. Both of which must be wired accordingly.

Your multiple Wall Charging plan that requires its own branch circuit means you intend to charge all three types of charging schemes including regular plugs which takes almost the whole night when very low charge is left.
Of course it is rare that you would run down your Tesla at almost zero charge left.

You’d be better off installing a sub-panel for this scheme. This will eliminate packing your conduit with multiple conductors.

The two chargers that are exclusively for 30 Amps and 60 Amps don’t require the neutral.

Just the two hots and a green wire.

I’ve installed both for Tesla models and the Chevy Bolt.

All for free (lol) and inspected.

And OH –I did get Gift Cards for restaurant dining for my wife and I. :)
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
I spec the following:
6 Gauge 90 degree C THHN (three conductors and a smaller #10 ground)
75 degree C termination
310.15(B): 65 amp conductor (based on the 75 degree C termination)
310.15(B)(2)(a): I derate the conductor for temp by 0.76
65 amps x 0.76 = 49.4 amps; Not quite 50 amps, but very close.
So I assume that am relegated to a max 45 amp OCPD (versus 50 amp) breaker and a max continuous load of 36 amps.
For the record, the above is not quite right. There are two types of ampacity checks, I like to think of them as terminations vs elsewhere (the latter possibly being multiple checks if there are multiple different conditions along the run).

For terminations, you just use the termination temperature ampacity, with the 125% for continuous loads (since breakers care about that), but no derating for more than 3 CCCs (because in the enclosure everything is spread out) and no derating for temperature (because ?)

For elsewhere, you can use the full insulation temperature ampacity, with no 125% for continuous loads (since the wires don't care, ampacity is a continuous rating), and with derating for more than 3 CCCs and for temperature.

So for the example above with just one circuit (which only requires 2 circuit conductors, not three, as an EVSE is a straight 240V (or 208V) device), the termination check is 60A = 48A (continuous load) * 125% < 65A (75C ampacity of #6), good.

The "elsewhere" check is 48A (continuous load) < 75A (90C ampacity of #6) * 0.76 = 57A, good.

For two circuits (4 CCCs), the termination check would not change, but now the "elsewhere" check fails: 48A > 75A * 0.76 * 0.8 = 45.6A. If the EVSE had a 45A continuous setting, that would be fine; but the next lowest setting is probably 40A continuous for use on a 50A circuit.

Or if you decide the ambient temperature does not exceed 122F, then the temperature factor becomes 0.82, and the "elsewhere" check passes, as 48A < 75A * 0.82 * 0.8 = 49.2A.

Cheers, Wayne
 

ESolar

Senior Member
Location
Eureka, CA Humboldt County
Occupation
Electrician/Contractor
Right -thanks again. Just barely over. The Southwire Calculator that I use didn't flag it, perhaps because they round down. So two 4 AWG and use the EMT as the EGC will do it.
 

ESolar

Senior Member
Location
Eureka, CA Humboldt County
Occupation
Electrician/Contractor
OK now I see all answers (replied too soon). WW - I agree. I missed the 3 or more conductor derating. It appears that I can run the two 4 AWG conductors and a #10 EGC (or use the EMT as an EGC - is that legal for an EV?) for 60 amps. Running 4 AWG v. 6 AWG potentially provides some more flexibility.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
With just 2 conductors, you only need #6 AWG for a 60 amp circuit, even after temperature derating, as I explained. That is because there is no need to apply the 0.76 temperature factor, and the 125% continuous load factor, simultaneously.

Cheers, Wayne
 

Master B

Member
I don't think using the conduit for your equipment ground is a good idea for a few reasons.
First? If/when anything, like the fittings, comes loose, you've lost it.
Second? The resistance over the conduit will be a lot more than a stranded green wire with no splices in it.
Third? It's there for more than to conduct fault current if/when things go wrong. It's a low impedance shunt to ground for noise and any spikes that can/will occur during a thunderstorm.

That green wire is the single most important wire in the system. It helps keep me from becoming a "load"!
 
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