60A Breaker -> 4 gage or 6 gage wire?

[mongo]

A test anyone can run:

Look at the charging page on your app or the Tesla display. Plug in the power connector. Note the voltage right when you see the amps start out at low 1 or 2. Now wait till the amps reach 48 and note the voltage again. If it drops more than 10 volts you have a major problem. Watts equals volts times amps, so that would be almost 500 watts being dissipated in the conductors, and I am fairly sure less than 100 of those watts are burning off in the 18' cable!

I have about 25 feet of #6 from the 60A breaker to the TWC. I'm losing 6 volts across the current path. Wow. Charging starts at 241 volts, and as the current ramps up to 48 amps, it drops to 235 volts. Holy ****. That's almost 300 watts (6 * 48) being dissipated in the conductors and the cable. At 48 amps, the conduit gets warm after a couple of hours in a 65 deg garage. Wait till Phoenix summer when the garage is at 110! Scary. For reference the 18' TWC charging cable also gets warm-ish. I assume that's by design.



This is the answer I needed. Thanks! Much of the other info here is all over the place and seems to be theoretical and focus on saving a nickel or two at elevated risk. I'll go with the safe / code way. Again THANK YOU!! My electrician will be back out in a week to replace the #6 in 3/4" conduit with #4 in 1" conduit.

Those of you running Tesla Wall Connectors and charging at 48 amps, after 2 hours of 48 amp charging, please go out and feel the conductors that run from your 60 Amp breaker out to the TWC, especially if they are unprotected romex. If you feel more than gentle warmth, think about spending money (OMG!) and protecting your house and family.

The voltage drop is not just in the branch circuit, it is in everything up to and including the power company transformer. A 6V drop at 240V is only 2.5%. NEC guidance for feeder and branch circuit combined is 5%, with 3% for branch effects. #6 copper wire is 0.3951 mOhm per foot. Your 50 ft round trip branch circuit has a drop of 0.95V, 45.5W total. Less than 2W per foot. 5 volts of drop (83%) is due to the feeder to your breaker panel, the breaker, and charge cord.

#4 gas a resistance of 0.2485 and will give a drop of 0.6V and power loss of 28.6W.

#6 NM-B is undersized for 60A, but #6 copper THHN is not. As to warm to the touch, 60C is 140F, 20F hotter than the maximum water heater temperature. 75C(THHN) is 167C rated.

 

[tga]

This is the answer I needed. Thanks! Much of the other info here is all over the place and seems to be theoretical and focus on saving a nickel or two at elevated risk. I'll go with the safe / code way. Again THANK YOU!! My electrician will be back out in a week to replace the #6 in 3/4" conduit with #4 in 1" conduit.

#6 THHN in conduit is the safe/code compliant way. Although if you insist upon giving your electrician more money to convert to #4, he probably won't say no...

Those of you running Tesla Wall Connectors and charging at 48 amps, after 2 hours of 48 amp charging, please go out and feel the conductors that run from your 60 Amp breaker out to the TWC, especially if they are unprotected romex. If you feel more than gentle warmth, think about spending money (OMG!) and protecting your house and family.

Romex != THHN in conduit. Romex is limited to 60C; 6ga=55A@60C. THHN is good to 75C (most THHN is rated to 90C, but the 75C terminals on your breaker are the weak link and limit you to a 75C rating), 6ga=65A@75C.

Charging at 48A via 6ga romex is definitely not code compliant. The 29 people who voted for 6/3 romex for a 60A circuit are just plain wrong. They are advocating a non-code compliant, unsafe, and possibly illegal installation.

(I chose "other", because I would use 6ga THHN in conduit, or 4/2 romex if I could find it. /3 romex is a waste of money - the neutral is unnecessary)

 

[davezforce]

For 60amp breaker 6 gauge in Emt conduit or mc cable. 4 gauge Romex. Good for 48amps continuous.

 

[Spartan86]

Thanks everyone! 6 AWG THHN in conduit is probably my best bet as I want the full 48a capability of the HPWC. I haven’t seen as much discussion of the ground wire however. 8? 10? Thx!

 

[mongo]

Thanks everyone! 6 AWG THHN in conduit is probably my best bet as I want the full 48a capability of the HPWC. I haven’t seen as much discussion of the ground wire however. 8? 10? Thx!

10 gauge copper is NEC spec for a 6 gauge 60 amp circuit. If you upsized the phase conductors due to length, you also need to upsize the ground.

 

[Spartan86]

10 gauge copper is NEC spec for a 6 gauge 60 amp circuit. If you upsized the phase conductors due to length, you also need to upsize the ground.

Thank You.

 

[Bob Denny]

Once gain all and especially @tga and @mongo , THANK YOU!! I get it now. Also @mongo you are right. I needed to measure the voltage on the 240 at the panel (via my unloaded 14-40 dryer outlet). I will do that. That would eliminate everything upstream. I suspect you're gonna be right about that being part of it (I have a 200 amp panel).

Again thanks all.

 

[eprosenx]

Once gain all and especially @tga and @mongo , THANK YOU!! I get it now. Also @mongo you are right. I needed to measure the voltage on the 240 at the panel (via my unloaded 14-40 dryer outlet). I will do that. That would eliminate everything upstream. I suspect you're gonna be right about that being part of it (I have a 200 amp panel).

Again thanks all.

Yeah, so it would be interesting to measure the 240 voltage at the main panel (or the dryer outlet is fine) without the car charging, and then again with it charging. If it is different with the car charging then that drop is happing upstream of your panel... (voltage drop will be zero on an unloaded circuit so measuring at the dryer is fine)

 

[tga]

Yeah, so it would be interesting to measure the 240 voltage at the main panel (or the dryer outlet is fine) without the car charging, and then again with it charging. If it is different with the car charging then that drop is happing upstream of your panel... (voltage drop will be zero on an unloaded circuit so measuring at the dryer is fine)

Agreed, this is a good way to check, without pulling the cover off your main panel (which, if you don't know what you're doing, is very risky)

 

[ElectrkBugaloo]

Can someone help me identify this wire? It's 6 ga... is it the NM-B?

 

[qdeathstar]

yes. It should say on the wires insulation tho

 

[qdeathstar]

Thanks everyone! 6 AWG THHN in conduit is probably my best bet as I want the full 48a capability of the HPWC. I haven’t seen as much discussion of the ground wire however. 8? 10? Thx!

You can use the emt as the ground..

 

[qdeathstar]

@KJD, you are incorrect.

https://www.nema.org/Technical/Documents/Steel Conduit and EMT-Proven to Meet the NEC Reg.pdf

 

[mongo]

@KJD, you are incorrect.

https://www.nema.org/Technical/Documents/Steel Conduit and EMT-Proven to Meet the NEC Reg.pdf

That is a general use case, and calls out:

Section 250.122 covers the sizing of equipment grounding conductors and includes Table 250.122 Minimum Size Equipment Grounding Conductors for Grounding Raceway and Equipment. The conductor sizes in Table 250.122 may not be adequate to comply with 250.4(A)(5) – Effective Ground-Fault Current Path (Grounded Systems)- and 250.4(B)(4) – Path for Fault Current (Ungrounded Systems) and may have to be evaluated to ensure that they can provide the effective ground path. (See Note at the bottom of Table 250.122)

Equipment installation instructions take precedence when more restrictive.
Gen 3 installation instructions:

Grounding Connections
Wall Connector must have a ground path back to the main equipment earthing point on site. Without a proper ground connection, the Wall Connector will fault during a ground assurance test. Equipment grounding conductor must be run with the circuit conductors and connected to the equipment grounding terminal in the wirebox. Install a ground (PE) wire sized according to local electrical code.

 

[eprosenx]

You can use the emt as the ground..

Yeah, code does seem to allow this, but around here at least I almost never see it. Most metal conduit installs are all done in commercial settings and I think commercial electricians just don't trust it. I worry that each and every connection between conduit segments might not be properly tight.

Install a ground (PE) wire sized according to local electrical code.

For what it is worth, I know this literally says "install a wire", though I think it really is saying you need to provide an effective ground path back to the main panel per local codes (and if code allows for using the conduit as the ground then that is probably fine). But as I said, I personally don't do it.

 

[qdeathstar]

That is a general use case, and calls out:


Equipment installation instructions take precedence when more restrictive.
Gen 3 installation instructions:

The link I provided to was a study that shows it is adequate when properly installed.

Under key findings:

Comparably-sized Galvanized Steel RMC, IMC and EMT allow the flow of higher fault current than an aluminum or copper equipment grounding conductor as listed in NEC 250.118


Which means that it outperforms the requirements, eg has a lower resistance to current flow than an appropriately sized wire.

 

[qdeathstar]

For what it is worth, I know this literally says "install a wire", though I think it really is saying you need to provide an effective ground path back to the main panel per local codes (and if code allows for using the conduit as the ground then that is probably fine). But as I said, I personally don't do it.

I agree if gen 3 says you need to run a wire back to ground, it needs to be a wire.

 

[mongo]

For what it is worth, I know this literally says "install a wire", though I think it really is saying you need to provide an effective ground path back to the main panel per local codes (and if code allows for using the conduit as the ground then that is probably fine). But as I said, I personally don't do it.

Yeah, I hear ya. GFCI breakers don't even need a ground, but in the case of EVSE with self test of the ground circuit, there could be nuisance faults due to questionable conduit connections which would work fine for phase faults.

@Spartan86, as an FYI, the manual states:
Branch Circuit Conductors and Ground Wire
If installing for less than maximum power, refer to local electrical code to select correct conductors and ground wire size that are suitable for the chosen circuit breaker.
If installing for maximum power, use minimum 6 AWG, 90° C-rated copper wire for conductors.

This can be read to say the ground must also be 6 AWG, if you are setting it up at a 60 Amp feed. However, the heading calls out ground wire vs circuit conductor, so the 6 AWG may only relate to the phase conductors.

 

[mongo]

@qdeathstar My apologies, I found where Tesla calls out conduit "permanent wiring system" as a grounding method.

WARNING: The Wall Connector must be grounded through a permanent wiring system or an equipment-grounding conductor.

This lines up with other vendors:

Chargepoint . https://www.chargepoint.com/files/home/CPH50_InstallGuide.pdf

3. Always ground the ChargePoint® charging station. Failure to ground
the charging station can lead to risk of electrocution or fire. The charging
station must be connected to a grounded, metal, permanent wiring
system, or an equipment grounding conductor shall be run with circuit
conductors and connected to the equipment grounding terminal or lead
on the Electric Vehicle Supply Equipment (EVSE). Connections to the
EVSE shall comply with all applicable codes and ordinances.

Hubbel https://hubbellcdn.com/installationmanuals/WIRING_PD2820_INSTALLINST.pdf

The EVSE must be connected to a grounded permanent wiring method that would qualify as an “Equipment Grounding Conductor” as
outlined in NEC® 250.118, or an equipment grounding conductor must be run with the circuit conductors and connected to the green
equipment grounding wire lead on the product.

Eaton https://rexel-cdn.com/Products/15B1...D0D7/15B1CD16-1B4E-4723-881E-4D3204B9D0D7.pdf:
This product must be connected to a grounded, metal, permanent
wiring system, or an equipment-grounding conductor must be
run with the circuit conductors and connected to the equipment
grounding terminal.

Clipper Creek (*note they use should instead of must, I think that's an error on their part) https://clippercreek.com/wp-content...ard-EVSE-Pedestal-Installation-Guide-v1.3.pdf:

Grounding Instructions - The charger should be
connected to a grounded, metal, permanent wiring
system; or an equipment-grounding conductor should
be run with circuit conductors and connected to a
grounding terminal or lead on the charger.
Connections to the charger should comply with all
local electrical codes and ordinances.

 

[KJD]

You can use the emt as the ground..

You are penny wise and dollar foolish.