14-50R Install for Tesla Model 3

[dewhite04]

I recently purchased a Tesla Model 3 to replace my 2013 Chevrolet Volt. Loved the Volt, but I needed a little bigger car to suit my growing family.

I installed an OpenEVSE 240v charger in our garage when I originally bought the Volt. That charger was fed with #10 wire from a 30A 2P breaker, terminating in a 2-gang "old-work" deep box. The charger which comes with the Tesla will prefer a 14-50R receptacle, which I'm planning to feed with 6-3 NM (romex) landed to a 50A 2P breaker. I was going to reuse the existing 2-gang "old work" deep box, but it seems I may not be able to meet box-fill requirements.

Best I can figure, I need 40 c.i. minimum to enter the box with 6-3 NM and terminate all conductors to the standard double-yoke receptacle. The box I have in-place is 32 c.i. and I don't think I gain any capacity from the flush-mount trim plate.

How would a retail electrical contractor properly solve this problem? My preference would be something that looks tidy and professional, but which also meets code...

Thanks in advance for any thoughts.

 

[mike93lx]

You can get 4 square boxes at 3.5 and 4 in deep, both would be over 40 ci.

4-4-4-6 AL SER would be a lot cheaper than 6/3 NM-B, if the run is long. Or pull 2-2-2-4 and mske this the last time you upgrade the wire

 

[ard]

How would a retail electrical contractor properly solve this problem? .

Prolly use the existing box?

Not sure why a new box isnt a no brainer for you.... anything about the install that lets you replace the wire, but a new box isnt a +5 minute effort?

 

[dewhite04]

You can get 4 square boxes at 3.5 and 4 in deep, both would be over 40 ci.

4-4-4-6 AL SER would be a lot cheaper than 6/3 NM-B, if the run is long. Or pull 2-2-2-4 and mske this the last time you upgrade the wire

Mike,

Thanks for the quick reply. Plug location is 6" +/- from the main panel, so no need to oversize. I went looking for 3.5 and 4 inch deep boxes and didn't find them, so I'm thinking maybe I wasn't clear on what I have now.

What I have in the wall now is a Carlon BH234R. I apologize that I must ask you to Google that, as I do not have adequate post count to link to Home Depot or Carlon's product catalog directly. Basically this is a 2-gang deep box with kick-out wings that are designed to deploy inside a Sheetrock wall cavity and **** the box up to the back side of the wall.

This box is placed in the stud bay immediately adjacent to the main panel. I installed it 5 years ago by cutting the sheet-rock opening and reaching inside with a drill and spade bit to open a hole through the stud aligned with a 1/2" KO in the main panel. Through that 1/2" KO, I pulled #10s from the breaker into the back of the 2-gang "old-work" box, which was then pushed into the opening with its wings kicked out and tightened it into place.

Because the opening is in the middle of the stud-bay (not up against either stud) I haven't been able to find any "old-work" style 2-gang boxes to replace with that list higher than 34 c.i. capacity. I thought about going to a 3-gang box, but don't know how I'm going to find a plate with a 14-50R sized opening to cover that.

Scratching my head, thinking I have to be missing something...

 

[dewhite04]

Prolly use the existing box?

Not sure why a new box isnt a no brainer for you.... anything about the install that lets you replace the wire, but a new box isnt a +5 minute effort?

"properly"

I have no issue with replacing the existing box, but what I want to avoid is having to relocate or abandon the roughly 4" x 4" hole in the wall. if I can find something bigger or deeper that will reuse or supersede that opening in the middle of the stud-bay, that would suit me just fine! I have seen some "old-work" boxes with adequate capacity, but they work by hugging up against a stud and nailing/screwing from within the new box. The edge of the opening I have is probably 4-6" in from the nearest stud.

Geez. Maybe I'll have to install some blocking in the wall to give me something to screw to? Must be a better way...

 

[mm08822]

Assuming you have 3.5" framing, use a 3.5" deep 4" sq box with 1/2 mudring. This will also provide some extra room to fold the conductors nicely.

You need 37.5 cu in and the 2 existing old work boxes wont give you that.

Your next option is 4-11/16 sq boxes w/mudring but then you're into drywall.

 

[mm08822]

Prolly use the existing box?

Not sure why a new box isnt a no brainer for you.... anything about the install that lets you replace the wire, but a new box isnt a +5 minute effort?

Probably true but violates box fill.

 

[mm08822]

You can get 4 square boxes at 3.5 and 4 in deep, both would be over 40 ci.

4-4-4-6 AL SER would be a lot cheaper than 6/3 NM-B, if the run is long. Or pull 2-2-2-4 and mske this the last time you upgrade the wire

Conductors this size would take you right out of any standard flush install. And then you run the risk of conductors not fitting the device.

 

[mm08822]

Re: 14-50R Install for Tesla Model

Mike,

Thanks for the quick reply. Plug location is 6" +/- from the main panel, so no need to oversize. I went looking for 3.5 and 4 inch deep boxes and didn't find them, so I'm thinking maybe I wasn't clear on what I have now.

What I have in the wall now is a Carlon BH234R. I apologize that I must ask you to Google that, as I do not have adequate post count to link to Home Depot or Carlon's product catalog directly. Basically this is a 2-gang deep box with kick-out wings that are designed to deploy inside a Sheetrock wall cavity and **** the box up to the back side of the wall.

This box is placed in the stud bay immediately adjacent to the main panel. I installed it 5 years ago by cutting the sheet-rock opening and reaching inside with a drill and spade bit to open a hole through the stud aligned with a 1/2" KO in the main panel. Through that 1/2" KO, I pulled #10s from the breaker into the back of the 2-gang "old-work" box, which was then pushed into the opening with its wings kicked out and tightened it into place.

Because the opening is in the middle of the stud-bay (not up against either stud) I haven't been able to find any "old-work" style 2-gang boxes to replace with that list higher than 34 c.i. capacity. I thought about going to a 3-gang box, but don't know how I'm going to find a plate with a 14-50R sized opening to cover that.

Scratching my head, thinking I have to be missing something...

The bh234 is too small and doesnt have provision to handle 6-3 nm-b. Only old work metal boxes that i know of could handle that size cable entry but you still dont have the volume.

Were the #10's that you ran previously just loose conductors between box and panel?

Based on what you describe, the easiest way to do this is just open up the drywall between panel edge and next stud.
Mount the box properly/securely and drill the right size hole through the stud next to panel and then drill panel ko out for right size. Hole through stud is larger than ko hole.

Sheetrock is an emotional thing.

 

[dewhite04]

Assuming you have 3.5" framing, use a 3.5" deep 4" sq box with 1/2 mudring. This will also provide some extra room to fold the conductors nicely.

You need 37.5 cu in and the 2 existing old work boxes wont give you that.

Your next option is 4-11/16 sq boxes w/mudring but then you're into drywall.

First, thank you for giving a true and correct answer. I also hadn't thought about the #10 EGC in the 6/3 NM, so I agree you are correct about the 37.5 c.i.

Understanding that I have a totally unnatural aversion to float/tape/texture work, what would you think about using pieces of 2x4 inside the wall to build the structure from the existing stud to the edge of my opening and then using Carlon Model B249B, which is styled as a "new/old work" box attached from the inside with screws? It shows to have a 48.2 c.i. capacity, and specs a 3-13/16" depth for a snug fit into 2x4 construction after deducting the depth of the rock.

 

[dewhite04]

Re: 14-50R Install for Tesla Model

The bh234 is too small and doesnt have provision to handle 6-3 nm-b. Only old work metal boxes that i know of could handle that size cable entry but you still dont have the volume.

Were the #10's that you ran previously just loose conductors between box and panel?

Based on what you describe, the easiest way to do this is just open up the drywall between panel edge and next stud.
Mount the box properly/securely and drill the right size hole through the stud next to panel and then drill panel ko out for right size. Hole through stud is larger than ko hole.

Sheetrock is an emotional thing.

You are correct that I had passed the old #10 THHNs through the KO, floating inside the wall, into the current wall box. I didn't know then, but I do know now, that wasn't totally kosher. I did use an anti-short at the KO and wrapped some tape on the conductors as they entered the wall box, so there's that.

My plan, this time around, was to drill a larger hole further down the stud and come in from underneath the main panel, through a 1" KO, using a properly-sized cable clamp for the 6/3 NM.

 

[dewhite04]

Re: 14-50R Install for Tesla Model

Sheetrock is an emotional thing.

Agreed.

 

[mm08822]

I dont see the old work provisions on the b249b. It still has the same issue not being able to handle 6-3 unless there are ko's i missed.

I doubt you can securely fasten 3-4 2x4's adequately to mount a box to.

Call someone to finish the sheetrock. You'll spend mega time trying to avoid it and the finished electrical job wont be right.

 

[dewhite04]

I dont see the old work provisions on the b249b. It still has the same issue not being able to handle 6-3 unless there are ko's i missed.

I doubt you can securely fasten 3-4 2x4's adequately to mount a box to.

Call someone to finish the sheetrock. You'll spend mega time trying to avoid it and the finished electrical job wont be right.

I can't promise I'll follow your advice, but it is sincerely appreciated and I will consider it carefully.

 

[TRWham]

...
How would a retail electrical contractor properly solve this problem? My preference would be something that looks tidy and professional, but which also meets code...

...
Scratching my head, thinking I have to be missing something...

...Must be a better way...

What you are missing is that you have put mutually exclusive constraints on a problem and wonder why you cannot solve it. We do lots of remodel projects and, while they do work to avoid making a big mess of the walls, our electricians would simply modify the drywall as needed to install a solution to code. Someone else, usually the painter, will then come along and repair the drywall.

In this case, you might be able to use a steel 4x4 with a retro ring (RACO 232-OW with 206RAC is what I have in mind) in your current location with conduit (possibly FMC) running inside the wall to the adjacent panel. You can then use 8 AWG THHN conductors to reduce the required box size but still handle your 50 amps. A 2 1/8 deep 4x4 can handle 10 #8s. It might still be hard to do this working through the existing hole without some drywall work, however.

 

[dewhite04]

What you are missing is that you have put mutually exclusive constraints on a problem and wonder why you cannot solve it. We do lots of remodel projects and, while they do work to avoid making a big mess of the walls, our electricians would simply modify the drywall as needed to install a solution to code. Someone else, usually the painter, will then come along and repair the drywall.

In this case, you might be able to use a steel 4x4 with a retro ring (RACO 232-OW with 206RAC is what I have in mind) in your current location with conduit (possibly FMC) running inside the wall to the adjacent panel. You can then use 8 AWG THHN conductors to reduce the required box size but still handle your 50 amps. A 2 1/8 deep 4x4 can handle 10 #8s. It might still be hard to do this working through the existing hole without some drywall work, however.

Thanks for your thoughts!

I came back this morning to say that I had spent more time last night looking at my options and came upon the RACO 232-OW.

My plan, as of now, is to use that with a RACO 201 extender ring outside the wall and a Steel City RS13-10R crushed corner cover to hold the receptacle. This would total 30.3 + 22.5 + 5 = 57.8 c.i. of volume. With the leftover volume and external KOs, I could run additional conductors through this box and into surface EMT for a dedicated air compressor circuit in the future.

Anyone have thoughts on a push-in fitting for 3/4" KO that is rated to accept 6/3 NM? I see that some lock-nut clamps are only good up to 6/2 and others are good for 6/3. I can make lock-nut clamps work, but a push-in fitting would be easier coming into the bottom of the main panel...

 

[wanderer]

Am I the only one who is wondering why 7200 W from your existing service is insufficient to charge a Tesla?

 

[ripperd]

Am I the only one who is wondering why 7200 W from your existing service is insufficient to charge a Tesla?

So it charges faster? Battery is somewhere between 50KWh and 75KWh.

7200w is not the charge rate, you need to derate (and the chargers do). So its really about 5.7KW it can charge at. So more than 10 hours to get it full, from near dead, with his current setup.

 

[TRWham]

...
Anyone have thoughts on a push-in fitting for 3/4" KO that is rated to accept 6/3 NM? I see that some lock-nut clamps are only good up to 6/2 and others are good for 6/3. I can make lock-nut clamps work, but a push-in fitting would be easier coming into the bottom of the main panel...

Again, if you use conduit to get from the panel to the box, you can reduce the wire to 8 AWG THHN and avoid the issue of handling 6/3 altogether.

 

[mm08822]

Arlington NM96 – requires 1” ko. Good for 4/3 >> 8/3. PKG 25 pcs.

Make sure the 232-OW has enough solid sheetrock to mount against.

Don't let the conductors rest directly on the bottom lip of the 232-ow - wrap it with a piece of slit conductor insulation.

 

[dewhite04]

So it charges faster? Battery is somewhere between 50KWh and 75KWh.

7200w is not the charge rate, you need to derate (and the chargers do). So its really about 5.7KW it can charge at. So more than 10 hours to get it full, from near dead, with his current setup.

Bingo.

I have purchased a Model 3 "Long Range" which has a ~75kWh battery pack, and an on-board charger capable of a maximum of 11.52kW charge rate, unless using DC fast-charging.

Per 625.14, EV charging is considered continuous use (rightly so, because it will often take more than 3 hours to complete a full charge). So my existing #10s with a 30A breaker could actually provide 5.76kW max, which translates to ~22 miles of range gained per hour and a 13 hour charge time from 0-100%.

The car will come with a portable charging connector with modular pigtails to connect with either a 14-50r or a standard 5-15r (a wide assortment of other pigtails are available). When connected to the 14-50r, the included portable unit will not allow the car to draw more than 32A, presumably to protect people who might have had a code-legal 14-50r installed previously in their home with #8 wire and a 40A breaker. This combination will allow me to charge at 7.68kW, which translates to ~30 miles of range gained per hour and just under 10 hours from 0-100%.

Typical practice with these cars is to avoid depleting the battery below 20% and/or charging above 80% of capacity, unless planning for a long-distance drive. Given that 60% band of regular use and my driving habits, I expect to plug in 1-2 evenings per week and reach the intended charge level in about 6 hours.

If my driving habits were different, I could switch to more capable conductors and a hard-wired charging connector that can pull 48A continuous from a 60A breaker and provide the car with a full 11.52kW charge rate, which would translate to ~44 miles of range gained per hour and around 6.5 hours from 0-100%. Biggest downside to this option is the ~$500 cost of the hard-wire connector.

FYI, with the newest iteration of DC fast-charging, Tesla claim to be able to push up to 250kW into the car (subject to ramping up and down at beginning and end of charge to protect the battery cells from heat death). They project to be able to add 185 miles of range in 20 minutes of charging. Neat stuff.

 

[dewhite04]

Arlington NM96 – requires 1” ko. Good for 4/3 >> 8/3. PKG 25 pcs.

Make sure the 232-OW has enough solid sheetrock to mount against.

Don't let the conductors rest directly on the bottom lip of the 232-ow - wrap it with a piece of slit conductor insulation.

Good advice. I was thinking just to leave the sheathing on the 6/3 long enough to extend past the lip of the box into the extender ring. It certainly won't hurt anything to do both.

Regarding the 1" KO, would I be violating NEC by field-modifying the 232-OW with a step-bit to open up one of the 3/4" KOs to the larger 1-3/8" inch sized hole needed for a 1" fitting?

Maybe this is the catch-22 that pushes me into using #8 THHN as the other poster has suggested? If it seems like I'm being stubborn, it's because I already have the 6/3 in-hand and I haven't worked extensively in the past with FMC. Both of those things are obviously overcome with relative ease...

 

[dewhite04]

What you are missing is that you have put mutually exclusive constraints on a problem and wonder why you cannot solve it. We do lots of remodel projects and, while they do work to avoid making a big mess of the walls, our electricians would simply modify the drywall as needed to install a solution to code. Someone else, usually the painter, will then come along and repair the drywall.

In this case, you might be able to use a steel 4x4 with a retro ring (RACO 232-OW with 206RAC is what I have in mind) in your current location with conduit (possibly FMC) running inside the wall to the adjacent panel. You can then use 8 AWG THHN conductors to reduce the required box size but still handle your 50 amps. A 2 1/8 deep 4x4 can handle 10 #8s. It might still be hard to do this working through the existing hole without some drywall work, however.

So, after having a few days to think it through, I did exactly what you suggested.

I pulled (3) #8s & (3) #10s through a piece of 3/4" FMC into a RACO 206 (which fit my existing opening very well). I then attached an extension ring to that and put my recep. in a crushed corner cover on top of that. I used the #8s for H-H-N on the 14-50r. 2 of the #10s passed through the extension ring into a 1/2" EMT surface mounted conduit to provide a branch circuit to an air compressor about 10 feet away. Both circuits are landed into the main panel on a new BQC230250.

The last #10 was used as a shared EGC (sized to the 50A breaker for the 14-50r). I twisted that EGC coming from the main panel together with a #12 headed for the air compressor, a #10 pig-tail going to the 14-50r, and a #10 bonding jumper that I screwed to the back of the box using a small mechanical lug. Was that necessary? Proper?

Overall, it wasn't much harder to do things correctly, and I'm satisfied that the work is solid. Again, thanks to all for sharing good advice!

 

[TRWham]

...
The last #10 was used as a shared EGC (sized to the 50A breaker for the 14-50r). I twisted that EGC coming from the main panel together with a #12 headed for the air compressor, a #10 pig-tail going to the 14-50r, and a #10 bonding jumper that I screwed to the back of the box using a small mechanical lug. Was that necessary? Proper?...

I believe what you did complies with 250.148 and is correct.

 

[mm08822]

So, after having a few days to think it through, I did exactly what you suggested.

I pulled (3) #8s & (3) #10s through a piece of 3/4" FMC into a RACO 206 (which fit my existing opening very well). I then attached an extension ring to that and put my recep. in a crushed corner cover on top of that. I used the #8s for H-H-N on the 14-50r. 2 of the #10s passed through the extension ring into a 1/2" EMT surface mounted conduit to provide a branch circuit to an air compressor about 10 feet away. Both circuits are landed into the main panel on a new BQC230250.

The last #10 was used as a shared EGC (sized to the 50A breaker for the 14-50r). I twisted that EGC coming from the main panel together with a #12 headed for the air compressor, a #10 pig-tail going to the 14-50r, and a #10 bonding jumper that I screwed to the back of the box using a small mechanical lug. Was that necessary? Proper?

Overall, it wasn't much harder to do things correctly, and I'm satisfied that the work is solid. Again, thanks to all for sharing good advice!

You did that correctly - EGC's must be connected to each metal box and continuity of the remainder of the EGC's in the circuit must be independent of any device.

The #12 EGC should be #10 Copper however.

 

[dewhite04]

You did that correctly - EGC's must be connected to each metal box and continuity of the remainder of the EGC's in the circuit must be independent of any device.

The #12 EGC should be #10 Copper however.

If that's right, I can & will pull through a bigger wire right away.

I didn't pick the #12 randomly though. I'm assuming that you're thinking about Table 250.122 where the 30A breaker would require a minimum #10 EGC?

This air compressor has one of those "cheater" motors that has a "SPeciaL" horsepower rating. The name plate FLA is 15.0 amps, and it has integrated protection from overload. That protection should be sized at 125% of the name plate FLA, so 18.75A. My understanding is that the EGC can then be sized from Table 250.122, based on the overload protection for the motor and not the breaker feeding it. 18.75A on Table 250.122 pointed me at the #12 wire for an EGC.

To cute? Misguided?

 

[TRWham]

You did that correctly - EGC's must be connected to each metal box and continuity of the remainder of the EGC's in the circuit must be independent of any device.

The #12 EGC should be #10 Copper however.

If the ungrounded conductors are 12 gage going to the compressor (which it looks like they could be if THHN in EMT), 250.122 would not require the EGC to be any larger. However, if he runs 10 AWG for the circuit the EGC would need to be upsized proportionally. It does look like he is running 10, so the 10 gage ground is correct.

 

[mm08822]

If that's right, I can & will pull through a bigger wire right away.

I didn't pick the #12 randomly though. I'm assuming that you're thinking about Table 250.122 where the 30A breaker would require a minimum #10 EGC?

This air compressor has one of those "cheater" motors that has a "SPeciaL" horsepower rating. The name plate FLA is 15.0 amps, and it has integrated protection from overload. That protection should be sized at 125% of the name plate FLA, so 18.75A. My understanding is that the EGC can then be sized from Table 250.122, based on the overload protection for the motor and not the breaker feeding it. 18.75A on Table 250.122 pointed me at the #12 wire for an EGC.

To cute? Misguided?

You are confusing a few things. Motor overload protection for a motor is not the same thing as over-current protection for a branch circuit.

You state the motor has internal overload protection. If so, then that’s over with.

The conductor sizing for the branch circuit should be based off of the HP rating of the motor from table 430-248. Since you have a SPL (Someone’s Probably Lying) rated motor, use 125% of the FLA’s for sizing. #12 Cu is the minimum and you installed 10’s – no problem.

For egc sizing, as per 250.122 D1, use the rating of the branch circuit short-circuit device. You installed a 30A cb for this ckt and have 10’s installed as the current carrying conductors (ccc), you are then required to use #10 cu egc as per 250.122A.

Read the column heading of table 250.122 – “Rating or setting of Automatic Overcurrent Protective device in circuit ahead of Equipment, conduit…” ……. basically the cb rating in the distribution panel ≠ motor overload protection.

Looking further into the install:
There are more than 3 ccc’s in the fmc. The conductors should have been derated. The 8’s should have been up-sized to 6’s. (55a x 0.8 = 44A < 50a.) It’s close, but technically not to the book. I wouldn’t change it as the compressor is at best an intermittent load.

There is only one receptacle on the compressor ckt?

 

[mm08822]

If the ungrounded conductors are 12 gage going to the compressor (which it looks like they could be if THHN in EMT), 250.122 would not require the EGC to be any larger. However, if he runs 10 AWG for the circuit the EGC would need to be upsized proportionally. It does look like he is running 10, so the 10 gage ground is correct.

What if? He stated he ran 10’s.

 

[dewhite04]

You are confusing a few things. Motor overload protection for a motor is not the same thing as over-current protection for a branch circuit.

You state the motor has internal overload protection. If so, then that’s over with.

The conductor sizing for the branch circuit should be based off of the HP rating of the motor from table 430-248. Since you have a SPL (Someone’s Probably Lying) rated motor, use 125% of the FLA’s for sizing. #12 Cu is the minimum and you installed 10’s – no problem.

For egc sizing, as per 250.122 D1, use the rating of the branch circuit short-circuit device. You installed a 30A cb for this ckt and have 10’s installed as the current carrying conductors (ccc), you are then required to use #10 cu egc as per 250.122A.

Read the column heading of table 250.122 – “Rating or setting of Automatic Overcurrent Protective device in circuit ahead of Equipment, conduit…” ……. basically the cb rating in the distribution panel ≠ motor overload protection.

Looking further into the install:
There are more than 3 ccc’s in the fmc. The conductors should have been derated. The 8’s should have been up-sized to 6’s. (55a x 0.8 = 44A < 50a.) It’s close, but technically not to the book. I wouldn’t change it as the compressor is at best an intermittent load.

There is only one receptacle on the compressor ckt?

All of your assumptions are correct. This is a dedicated motor circuit without any cord/plug or other devices. I know where I got into trouble. I originally sized the EGC based on the required conductor size of #12, before I thought to de-rate for CCCs and ambient, which pushed to the #10 conductors. If I had stayed with #12 then 250.122(A) would have allowed the #12 EGC on a 30A breaker because the EGC can't be required to be larger than the circuit conductors.

Bottom line is I should use that #12 as a pull-string to bring in a piece of #10 for the motor circuit EGC. Easily done.

This is a nice place on the Internet. All of your help is very much appreciated.

 

[TRWham]

What if? He stated he ran 10’s.

Yeah, I said that. My post was just stating for his understanding what I deduced to be your reasoning.

 

[dewhite04]

You are confusing a few things. Motor overload protection for a motor is not the same thing as over-current protection for a branch circuit.

You state the motor has internal overload protection. If so, then that’s over with.

The conductor sizing for the branch circuit should be based off of the HP rating of the motor from table 430-248. Since you have a SPL (Someone’s Probably Lying) rated motor, use 125% of the FLA’s for sizing. #12 Cu is the minimum and you installed 10’s – no problem.

For egc sizing, as per 250.122 D1, use the rating of the branch circuit short-circuit device. You installed a 30A cb for this ckt and have 10’s installed as the current carrying conductors (ccc), you are then required to use #10 cu egc as per 250.122A.

Read the column heading of table 250.122 – “Rating or setting of Automatic Overcurrent Protective device in circuit ahead of Equipment, conduit…” ……. basically the cb rating in the distribution panel ≠ motor overload protection.

Looking further into the install:
There are more than 3 ccc’s in the fmc. The conductors should have been derated. The 8’s should have been up-sized to 6’s. (55a x 0.8 = 44A < 50a.) It’s close, but technically not to the book. I wouldn’t change it as the compressor is at best an intermittent load.

There is only one receptacle on the compressor ckt?

Checking-in to say that I pulled through that #10 for the air compressor EGC today. I had to fish around in my parts bin for a while to find a blue wirenut big enough to twist (4) #10s together. Once again, I very much appreciate your bringing this mistake to my attention.

On the matter of derating the #8s, I believe that is a non-issue because Table 310.15(B)(2)(a) provides, as its 3rd exception:

Derating factors shall not apply to conductors in ******* having a length not exceeding 600 mm (24 in.).

My ******, being the piece of 3/4" FMC, measured just over 5 inches long. Even if that were not the case, the connected charging equipment is internally limited to 32A continuous draw, and that's the only thing I intend will ever be connected to this receptacle. If I didn't have that exception to lean on, I suppose I could have gone back and changed for a 40A breaker which would have satisfied all requirements equally well.