Wire size for wall charger

[TBrownTX]

DonaldBecker in post 93 said - Reconsider running the wiring out from the side of the load center that is against the stud. I am planning exact similar installation as yours. Looks like you have ran your cable from side of load panel. Did you use NM or THHN in conduit?
Thanks

I came through a stud into the side of the box via a knockout and used a fitting to secure the wire. I did not use NM or THHN in conduit, I used NM-B Romex. It's important to use #4 wire vs #6 if you go NM-B with a 60 amp breaker.

Here's the wire I used:
https://www.lowes.com/pd/Southwire-...-Non-Metallic-Jacket-Wire-By-the-Foot/3334032

If you use 4/3 wire you will not need the neutral wire, mine is capped using heat shrink tubing. It could be used later to swap for a 14-50 plug. Some choose to use the neutral for the ground instead.

And a photo:

 

[spat12]

I came through a stud into the side of the box via a knockout and used a fitting to secure the wire. I did not use NM or THHN in conduit, I used NM-B Romex. It's important to use #4 wire vs #6 if you go NM-B with a 60 amp breaker.

Here's the wire I used:
https://www.lowes.com/pd/Southwire-...-Non-Metallic-Jacket-Wire-By-the-Foot/3334032

If you use 4/3 wire you will not need the neutral wire, mine is capped using heat shrink tubing. It could be used later to swap for a 14-50 plug. Some choose to use the neutral for the ground instead.

And a photo:
View attachment 664994

Which fittings did you use? On both ends?
Thanks for pictures.

 

[TBrownTX]

Which fittings did you use? On both ends?
Thanks for pictures.

This guy on the panel side

https://www.lowes.com/pd/Sigma-Electric-ProConnex-3-4-in-Clamp-on-Type-Service-Entrance-Connector-Conduit-Fitting/1087283

None on the connector side. The Romex sheath comes into the back of the box and the edges of the plastic hole are nice and smooth.

Coming in at an angle allows the #4 wires to make the bend, at 90 degrees with a fitting in place In not sure you’d be able to get the cover on.

Tim

 

[kishkaru]

Everyone here hopefully already knows about the wire temp ratings. For example, assuming copper, NM-B (romex) = 60C vs THHW = 75C.
So for a 60A circuit, we can use:
1. #4 NM-B, or
2. #6 THHW in conduit

However, one thing folks often overlook is the ambient temp rating! The NEC ampacity table 310.16 clearly state that the ratings are "Based on Ambient Temperature of 30°C (86°F)". The expanded NEC table shows the temp correction factors for ambient temperatures other than 30°C (86°F). Be sure to keep these correction factors in mind when deciding on cable!

For example in my case, I have to run 60 feet of cable through the attic from the breaker panel (in the back of the house) to the garage (in the front of the house). 50 ft of it is in the attic. On a hot summer day in CA, the attic will be well over 49C/120F! Even if you run the cable on the exterior of the house, it will be subject to heat and potentially direct sunlight, raising the temperature.

Thus taking the ambient temp correction factors (46–50C/114–122F) in mind, neither one of the two solutions above work:

1. (#4 NM-B): 70A * 0.58 = 40.6A
2. (#6 THHW): 65A* 0.75 = 48.75A

To make it work, we need to size up:

1. (#1 NM-B): 110A * 0.58 = 63.8A
2. (#4 THHW): 85A * 0.75 = 63.75A

When comparing prices, which one do you think is cheaper? It becomes a no brainer to use #4 THHW in conduit! #1 NM-B will be much more expensive, harder to find, and harder to work with.

Many of you are lucky to have your breaker panel already in the garage, so you don't have to go through a hot attic. But if its anything like my garage, it will still get above 90-100F in the summer (partially insulated garage). Who knows how warm it is inside the walls of a garage. So it would still be a safe bet to use the 36–40C/96–104F correction factor.

 

[TBrownTX]

Everyone here hopefully already knows about the wire temp ratings. For example, assuming copper, NM-B (romex) = 60C vs THHW = 75C.
So for a 60A circuit, we can use:
1. #4 NM-B, or
2. #6 THHW in conduit

However, one thing folks often overlook is the ambient temp rating! The NEC ampacity table 310.16 clearly state that the ratings are "Based on Ambient Temperature of 30°C (86°F)". The expanded NEC table shows the temp correction factors for ambient temperatures other than 30°C (86°F). Be sure to keep these correction factors in mind when deciding on cable!

For example in my case, I have to run 60 feet of cable through the attic from the breaker panel (in the back of the house) to the garage (in the front of the house). 50 ft of it is in the attic. On a hot summer day in CA, the attic will be well over 49C/120F! Even if you run the cable on the exterior of the house, it will be subject to heat and potentially direct sunlight, raising the temperature.

Thus taking the ambient temp correction factors (46–50C/114–122F) in mind, neither one of the two solutions above work:

1. (#4 NM-B): 70A * 0.58 = 40.6A
2. (#6 THHW): 65A* 0.75 = 48.75A

To make it work, we need to size up:

1. (#1 NM-B): 110A * 0.58 = 63.8A
2. (#4 THHW): 85A * 0.75 = 63.75A

When comparing prices, which one do you think is cheaper? It becomes a no brainer to use #4 THHW in conduit! #1 NM-B will be much more expensive, harder to find, and harder to work with.

Many of you are lucky to have your breaker panel already in the garage, so you don't have to go through a hot attic. But if its anything like my garage, it will still get above 90-100F in the summer (partially insulated garage). Who knows how warm it is inside the walls of a garage. So it would still be a safe bet to use the 36–40C/96–104F correction factor.

I’m in Texas, so it’s pretty hot. But I’m not sweating the 8’ of cable in my garage wall, so to speak. Also most folks charge overnight when the temperatures are much less extreme.

Tim

 

[kishkaru]

I agree, most folks charge overnight after midnight for those sweet super-off-peak rates.

But the point is that the NEC code doesn't discriminate based on the time the circuit is used. The code applies to the circuit at all times since it can be used at all times. 99% of the time, you'll charge over night, but that 1% of the time where you need to head out the door quickly and charge in the middle of summer heat on #4 NM-B, that's when you'll get into trouble. The NEC code tries to take this into account.

It's the same argument as installing a 60A circuit but only using 40A. It doesn't matter what your intentions are, the code applies to what is possible in the worst case (60A pull).

Whether or not you sweat 8 ft of cable in your garage wall is up to your inspector. If s/he is happy with the installation, then you pass.

 

[TBrownTX]

I agree, most folks charge overnight after midnight for those sweet super-off-peak rates.

But the point is that the NEC code doesn't discriminate based on the time the circuit is used. The code applies to the circuit at all times since it can be used at all times. 99% of the time, you'll charge over night, but that 1% of the time where you need to head out the door quickly and charge in the middle of summer heat on #4 NM-B, that's when you'll get into trouble. The NEC code tries to take this into account.

It's the same argument as installing a 60A circuit but only using 40A. It doesn't matter what your intentions are, the code applies to what is possible in the worst case (60A pull).

Whether or not you sweat 8 ft of cable in your garage wall is up to your inspector. If s/he is happy with the installation, then you pass.

I agree, most folks charge overnight after midnight for those sweet super-off-peak rates.

But the point is that the NEC code doesn't discriminate based on the time the circuit is used. The code applies to the circuit at all times since it can be used at all times. 99% of the time, you'll charge over night, but that 1% of the time where you need to head out the door quickly and charge in the middle of summer heat on #4 NM-B, that's when you'll get into trouble. The NEC code tries to take this into account.

It's the same argument as installing a 60A circuit but only using 40A. It doesn't matter what your intentions are, the code applies to what is possible in the worst case (60A pull).

Whether or not you sweat 8 ft of cable in your garage wall is up to your inspector. If s/he is happy with the installation, then you pass.

No wires in standard residential buildings are upsized like this, even in long Texas attic runs for A/C, ovens, dryers, or the like.

Also never seen any reports of an electrician installing, or an inspector requiring larger than #4 cable for a Gen3 wall connector for the dozens of installs reported here or on the local FB group. There are even folks using #6 Romex without issue.

Not going to argue the technicalities here, but in real world application I’d argue it’s not really a problem for folks to stress over.

Tim

 

[kishkaru]

I'm just pointing out the NEC code here, just as many of you made the argument against #6 NM-B based on the code. I'd argue that not taking the ambient temp into account (#4 NM-B @40A) is far worse than using #6 NM-B (55A at ambient) for 60A.

Ultimately, it's your home and you decide what you want to do.

 

[TBrownTX]

I'm just pointing out the NEC code here, just as many of you made the argument against #6 NM-B based on the code. I'd argue that not taking the ambient temp into account (#4 NM-B @40A) is far worse than using #6 NM-B (55A at ambient) for 60A.

Ultimately, it's your home and you decide what you want to do.

One other thought... my in-wall wiring easily exceeds the size of the cable installed on the wall connector itself. If this were a real world issue, wouldn't the 18' cord on the wall connecter be like #1 or #0? They have to be designed for indoor/outdoor use in all climates. Imagine charging in the sun in AZ during summer, or example.

Tim

 

[kishkaru]

You're assuming that Tesla uses 60C rated wire internally for the WC cord, which would warrant #1 NM-B wire. They are likely using 90C rated wire like THHN which would greatly reduce the AWG to just a #6 (75A rating). 90C rated wire also has much less restrictive temp correction factors. Even at the (46–50C/114–122F) correction factor, its plenty: 75A * 0.82 = 61.5A.

Also, I do believe Tesla uses multiple smaller wires in parallel per each conductor, rather than use one large-gauge wire. This helps keep the overall WC cord cable thinner/flexible. For example, if they use 3x #12 wire, then in theory that's 3x 30A = 90A ampacity.

 

[rjpjnk]

... For example, if they use 3x #12 wire, then in theory that's 3x 30A = 90A ampacity.

Do parallel conductors really add like this or is there a derating applied for multiple conductors next to one another?

 

[TBrownTX]

Also, I do believe Tesla uses multiple smaller wires in parallel per each conductor, rather than use one large-gauge wire. This helps keep the overall WC cord cable thinner/flexible. For example, if they use 3x #12 wire, then in theory that's 3x 30A = 90A ampacity.

FWIW, the romex I purchased is constructed with parallel conductors.

Tim

 

[kishkaru]

Parallel conductors are not the same thing as stranded wire. Don't get them confused.

In the former, each conductor is wrapped in an insulator, and multiple insulated wires are used in parallel. This is what Tesla uses.
In the latter, multiple wires are stranded together and wrapped in a single insulator. This is still a single conductor. This is what your Romex cable is.

The ampacity rating is different for parallel conductors vs a single conductor made of stranded wire due to how heat is dissipated in the wire due to insulation. The NEC table takes into account solid core or stranded wire and both are considered a single insulated conductor.

 

[TBrownTX]

Parallel conductors are not the same thing as stranded wire. Don't get them confused.

In the former, each conductor is wrapped in an insulator, and multiple insulated wires are used in parallel. This is what Tesla uses.
In the latter, multiple wires are stranded together and wrapped in a single insulator. This is still a single conductor. This is what your Romex cable is.

The ampacity rating is different for parallel conductors vs a single conductor made of stranded wire due to how heat is dissipated in the wire due to insulation. The NEC table takes into account solid core or stranded wire and both are considered a single insulated conductor.

Fair, but I’ll stand by my point. I’ve never seen any reports of an electrician installing, or an inspector requiring larger than #4 cable for a Gen3 wall connector for the dozens of installs reported here or on the local FB group. There are even folks using #6 Romex without issue.

Tim

 

[TBrownTX]

Here’s a fella that could use some help!

Multiple breakers tripping when I charge

I’ve seen a few posts where the wall charger GCFI trips. In my case, the charger circuit if fine but random circuit breakers trip throughout my house. New home 2020 construction with two 200 amp panels. Charging is scheduled at 11PM, and by morning there are 12 or more breakers tripped.

teslamotorsclub.com

 

[gfunkdave]

Fair, but I’ll stand by my point. I’ve never seen any reports of an electrician installing, or an inspector requiring larger than #4 cable for a Gen3 wall connector for the dozens of installs reported here or on the local FB group. There are even folks using #6 Romex without issue.

Tim

All depends on the circuit size doesn't it?

 

[TBrownTX]

So found this handy calculator, and loaded in some sample values. Is it wrong? Read the fine print, and it references the 60C rating of NM-B cable.

Ampacity Calculator

The purpose of this calculator is to determine the ampacity of conductors in conduit, cable, or directly buried. All calculations are based on the National Electrical Code®.

www.cerrowire.com

*The calculated ampacity value is the minimum of: the corrected and adjusted ampacity; the equipment temperature limitation default values as described in NEC® 110.14(C)(1); or the cable type temperature limitation. The initial input values are also shown for verification, and they will be emailed along with the calculated ampacity if the email option is chosen. The insulation temperature rating is the rated temperature of the insulation surrounding the conductor metal, and the termination temperature rating is based on the default values shown in NEC 110.14(C)(1). If a cable wiring method was chosen, the temperature limit is 60℃ for NM-B and UF-B, and it is 75℃ for SER, SEU and MC cable.

 

[MN-MS100D]

It is correct. what do you see is wrong?

 

[TBrownTX]

It is correct. what do you see is wrong?

Comparing to kishkaru's calculations above. If 4/3 nm-b in a garage is unsafe, I can easily switch out the breaker for a 50A, I don't NEED the 48A charging.

Tim

 

[TBrownTX]

All depends on the circuit size doesn't it?

Correct, although the Gen3 charger is limited to 48A w/ a 60A circuit.

Tim