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

[okii]

I do *not* recommend doing a pigtail from a Wall Connector. In addition to limiting you to 50a (40a usable) and being against the install instructions / code, it also bypasses a key safety feature (the temp sensor in the plug end). I recently helped someone else on the forum that did this and they nearly had a fire since the receptacle was wired wrong (insulation pinched in the terminal). Luckily he was monitoring his new install closely and detected excessive heat.

Note that even if you hard wire you can absolutely still take it with you when you leave... Just cap the wires and wall plate over them (or replace with a 14-50 or 6-50 receptacle with a 50a breaker).

You are right about needing 6 AWG wire for a 50a circuit if it is NM cable (Romex). 4 AWG would be required if you wanted to support a 60a breaker and still use Romex. Note that the Wall Connector has zero use for a neutral wire and it would just be in the way. They do make 4awg romex. 4-3 W/G NM-B Wire Black

I installed my Wall Connector with conduit which allows you to use the 75c insulation rating which gives you the ability to do 60a on 6 AWG (that is what I did). Though now that I think about it only has 5 amps of headroom to use on a 60a circuit (48a continuous draw by Model 3). So technically my install is only good to about 100 degrees Fahrenheit ambient temp.

THHN is what you want for use in conduit (usually dual rated as THWN or THWN-2).

The conduit could be EMT or plastic. Many people find the plastic easier to work with, but I vastly prefer EMT. I used EMT.

You could just use "flex" as well. Just make sure to use the proper fittings on the end with bushings to make sure the sharp Flex ends don't cut the wire.

To All-

Thank you very much for your instructive responses. They were all very helpful.

 

[eprosenx]

I installed my Wall Connector with conduit which allows you to use the 75c insulation rating which gives you the ability to do 60a on 6 AWG (that is what I did). Though now that I think about it only has 5 amps of headroom to use on a 60a circuit (48a continuous draw by Model 3). So technically my install is only good to about 100 degrees Fahrenheit ambient temp.

Ack, I just realized this evening I was not thinking straight when I posted the above. I did the derating off the 75c rating which is wrong.

6 AWG copper in conduit with a breaker on one end and a Wall Connector on the other end is rated to 65 amps. I have mine set to 60 (48a continuous). But the wire is actually rated to 90c and so you can use that for your temperature derating factor. So 6 AWG copper is good to 75 amps at 90c. Applying 310.15(B)(2)(a) temperature correction factors I am good up to 122 degrees Fahrenheit which requires a .82 deration. So 75 * .82 = 61.5 amps which is still above the 60a breaker and setting on the Wall Connector (well, 48a, but you have to plan it as if it is 60a due to the continuous load aspect).

I have no idea to tell how hot the inside of my wall connector will get on a hot summer afternoon (as it will get direct sun in the late afternoon), but I am not too worried. My car on a daily basis only charges for about an hour, and even if I did come home depleted, it would not be in the direct sun for that many hours (i.e. the sun only hits the West side of the house for a limited amount of time before it goes down). Plus the wire enters the back of the Wall Connector direct through the wall in Rigid conduit, so only a few inches are in the hot Wall Connector itself (though that could be enough to melt if it was hot enough).

 

[woodguyatl]

I have received a few quotes to install my Tesla Wall Connector for my model 3. The biggest difference between the quotes is wire size. All electricians have their reasons, i’d like to know what you think

My setup:
60A circuit breaker
48A max charging amps (wall connector setting #9)
35 ft. From breaker box to connector location

Wire Ampacity Ratings
6/3 Romex = 55A
4/3 Romex = 70A

Contractor #1
6/3 Romex
NEC 240.4(B) exception allows rounding to next highest breaker size if wire ampacity is in between breaker sizes.

Contractor #2
4/3 Romex
+$220 more expensive

As a side note, what wire size are you running to your Tesla Wall Connector (HPWC)? Also I am doing the 3 wire so I can replace my HPWC with a NEMA 14-50 when I move.

I pulled #4 through conduit for mine with a 90 amp breaker so I can easily add a second charger if/when we get another Tesla. I figure I was going to blow half a day doing the install (about 40 feet total) so I added a work box near where a second charger may go. Materials (breaker, wire, conduit, clamps, etc.) came to about $225 and the whole job took about 5 hours including beer breaks.

 

[mswlogo]

Interesting, I was not aware of the rounding up rule.

Since EV charging will use the FULL capacity of the circuit, while sleeping, for very long periods I wouldn't take advantage of it and go with 4-3 if you want that full 48A. The cost difference seems negligible.

If it was a really short run maybe. But if it was a short run the cost difference wouldn't be that much.

 

[woodguyatl]

Interesting, I was not aware of the rounding up rule.

Since EV charging will use the FULL capacity of the circuit, while sleeping, for very long periods I wouldn't take advantage of it and go with 4-3 if you want that full 48A. The cost difference seems negligible.

If it was a really short run maybe. But if it was a short run the cost difference wouldn't be that much.

Tesla's use 80% of capacity. That its why a 3 charges at 48 amps on 60amp circuit.

 

[mswlogo]

Tesla's use 80% of capacity. That its why a 3 charges at 48 amps on 60amp circuit.

6-2 is 55 Amps.

So that's 48/55 = 87%

They allow the 80% rule to be broken (as discussed). I'm saying I wouldn't do it because the EV uses all 80% A LOT.
So when you take advantage of this rule you'll be using 87% A LOT.

Normally circuits don't hit that 80% very often. But EV's do. For that reason I would not take advantage of this "rounding up" to 60 Amps.

If it was say a Surge up to 87% sure. Or a very short run. Or say a Welder that doesn't have long duration and you're always around when in use.

Even perfectly installed 80% load circuits fail. This would be asking for trouble in this application.

 

[tga]

6-2 is 55 Amps.

So that's 48/55 = 87%

They allow the 80% rule to be broken (as discussed). I'm saying I wouldn't do it because the EV uses all 80% A LOT.
So when you take advantage of this rule you'll be using 87% A LOT.

Normally circuits don't hit that 80% very often. But EV's do. For that reason I would not take advantage of this "rounding up" to 60 Amps.

If it was say a Surge up to 87% sure. Or a very short run. Or say a Welder that doesn't have long duration and you're always around when in use.

Even perfectly installed 80% load circuits fail. This would be asking for trouble in this application.

You cannot round up the wire's rating, only the breaker protecting it (if no standard size breaker exists at the wire's rating). The wire's rating doesn't change.

6ga romex is limited to 60deg C, for 55A max. On a non-EV (non-continuous load) circuit, you can install a 60A breaker, since no 55A breakers exist. You cannot draw >55A without overloading the wire, however.

Charging through 6ga romex limits you to 80% of 55A, or 44A, but no such setting exists in the HPWC. Your choices are either 40A (50A breaker) or 48A (60A breaker), so you're stuck with the lower setting.

I have a SolarEdge SE10000A inverter, rated at max 42A@240V. It's connected via 6/2 romex through a 60A breaker (also the AC disconnect). Since it could run several hours at full output, you need a circuit that can handle 52.5A (42A*1.25=52.5A). The breaker roundup rule allows a 60A breaker on the circuit.

 

[mswlogo]

You cannot round up the wire's rating, only the breaker protecting it (if no standard size breaker exists at the wire's rating). The wire's rating doesn't change.

6ga romex is limited to 60deg C, for 55A max. On a non-EV (non-continuous load) circuit, you can install a 60A breaker, since no 55A breakers exist. You cannot draw >55A without overloading the wire, however.

Charging through 6ga romex limits you to 80% of 55A, or 44A, but no such setting exists in the HPWC. Your choices are either 40A (50A breaker) or 48A (60A breaker), so you're stuck with the lower setting.

I have a SolarEdge SE10000A inverter, rated at max 42A@240V. It's connected via 6/2 romex through a 60A breaker (also the AC disconnect). Since it could run several hours at full output, you need a circuit that can handle 52.5A (42A*1.25=52.5A). The breaker roundup rule allows a 60A breaker on the circuit.

So your allowed to “round up” the breaker. But the continuous load still needs to be below 80% (the weakest link, in this case the wire). I see. Thx.

I wonder how often that’s screwed up.

 

[eprosenx]

You cannot round up the wire's rating, only the breaker protecting it (if no standard size breaker exists at the wire's rating). The wire's rating doesn't change.

6ga romex is limited to 60deg C, for 55A max. On a non-EV (non-continuous load) circuit, you can install a 60A breaker, since no 55A breakers exist. You cannot draw >55A without overloading the wire, however.

Charging through 6ga romex limits you to 80% of 55A, or 44A, but no such setting exists in the HPWC. Your choices are either 40A (50A breaker) or 48A (60A breaker), so you're stuck with the lower setting.

I have a SolarEdge SE10000A inverter, rated at max 42A@240V. It's connected via 6/2 romex through a 60A breaker (also the AC disconnect). Since it could run several hours at full output, you need a circuit that can handle 52.5A (42A*1.25=52.5A). The breaker roundup rule allows a 60A breaker on the circuit.

^------ What he said!

Technically the breaker rule is the "next size up" rule (not really rounding). Basically they allow you to make use of the wire all the way up through its rating as per your load calculations (if you had to use the next-size-down breaker you would sacrifice capacity). Remember the breaker is not really the primary mechanism to avoid overload. It is just a backup in case things go wrong. Calculating your expected draw is the primary way to keep things from melting.

Since the Tesla Wall Connectors for the most part don't have settings for ampacities other than the common breaker sizes, I have yet to find a situation where it would be helpful to apply the "next size up" breaker rule. (note that I have provided feedback to the Wall Connector team at Tesla that I would love to see more granular ampacity settings for the Wall Connector so you can make use of every last rated amp for your wire - say provide two rotary dials that give you 1a granularity of max charge rates - not sure if J1772 supports that though)

If your wire is rated to 65a, but you can only set the Wall Connector to 60a (48a continuous), so while you could put a 70a breaker on that, it would do you no good. In fact, I am not even sure if code allows you to make use of that "next size up rule" unless you actually need it. i.e. if your load is only 60a, then no reason to go for 70a. (I should go research this)

 

[eprosenx]

I pulled #4 through conduit for mine with a 90 amp breaker so I can easily add a second charger if/when we get another Tesla. I figure I was going to blow half a day doing the install (about 40 feet total) so I added a work box near where a second charger may go. Materials (breaker, wire, conduit, clamps, etc.) came to about $225 and the whole job took about 5 hours including beer breaks.

What rotary dial / dip switch setting did you set your Wall Connector to?

If you set it to 90 amps you have violated electrical code and potentially created a latent safety hazard for some day when someone charges with a car that can pull the full 72 amps continuous.

 

[KJD]

What if a person used THHN 6 gauge copper wire (in conduit) instead ?
Could you then use a 60 amp breaker and set the Wall Connector to 48 amps ?

 

[tga]

What if a person used THHN 6 gauge copper wire (in conduit) instead ?
Could you then use a 60 amp breaker and set the Wall Connector to 48 amps ?

Yes, THHN is (usually) good to 90C, but the HPWC and breaker* terminals are only rated to 75C, so you can use the 75C column for 65A.

* - I've never found a residential breaker with 90C terminals.

 

[woodguyatl]

What rotary dial / dip switch setting did you set your Wall Connector to?

If you set it to 90 amps you have violated electrical code and potentially created a latent safety hazard for some day when someone charges with a car that can pull the full 72 amps continuous.

Wall connector is set to 80. Wire ampacity of THHN is 95 amps but I could not find a 90 degree breaker.

 

[woodguyatl]

6-2 is 55 Amps.

So that's 48/55 = 87%

They allow the 80% rule to be broken (as discussed). I'm saying I wouldn't do it because the EV uses all 80% A LOT.
So when you take advantage of this rule you'll be using 87% A LOT.

Normally circuits don't hit that 80% very often. But EV's do. For that reason I would not take advantage of this "rounding up" to 60 Amps.

If it was say a Surge up to 87% sure. Or a very short run. Or say a Welder that doesn't have long duration and you're always around when in use.

Even perfectly installed 80% load circuits fail. This would be asking for trouble in this application.

Thanks for the clarification.

 

[eprosenx]

What if a person used THHN 6 gauge copper wire (in conduit) instead ?
Could you then use a 60 amp breaker and set the Wall Connector to 48 amps ?

Yes! This is how my wall connector is configured.

However: (to clarify what @tga said)
While THHN in conduit is good to 65a at 75c, that is at 86f ambient temp.

You have to derate for temperatures over that (but you are allowed to derate using the 90c rating of the wire).

So this setup allows you to operate in an ambient temp up to 122f.

 

[eprosenx]

Wall connector is set to 80. Wire ampacity of THHN is 95 amps but I could not find a 90 degree breaker.

Yeah, the wall connector is likely only rated to 75c too, so even if you can find the breaker it won’t help.

So I guess I would call out that since your wall connector is set to 80, there is no benefit to using the 90a breaker.

 

[woodguyatl]

Yeah, the wall connector is likely only rated to 75c too, so even if you can find the breaker it won’t help.

So I guess I would call out that since your wall connector is set to 80, there is no benefit to using the 90a breaker.

The panel is in a detached garage that can get a bit warm here in ATL in the summer so I used a 90 to allow for just a bit of de-rating.

 

[eprosenx]

The panel is in a detached garage that can get a bit warm here in ATL in the summer so I used a 90 to allow for just a bit of de-rating.

Got it. Though FWIW the 80 amp breaker would already be derated to 64a since EVSE's are continuous load, so I don't think you would ever have an issue even with an 80 amp breaker.

 

[tga]

note that I have provided feedback to the Wall Connector team at Tesla that I would love to see more granular ampacity settings for the Wall Connector so you can make use of every last rated amp for your wire - say provide two rotary dials that give you 1a granularity of max charge rates - not sure if J1772 supports that though

I haven't read the J1772 spec, but the OpenEVSE allows you to select even currents from 6A to 80A (in 2A increments), plus 79A.

 

[Bob Denny]

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.

The electrician may not be aware that EV charging is considered continuous loads, not intermittent.
If you charge at 48A, the circuit needs to be rated for 125% of that or 60 Amps, which exceeds 6 AWG NM-B at 60 C.

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.