Gen 3 Wall Charger -- Conduit Inside a Wall

[UberAndy]

I am about to install a Gen 3 wall charger in my garage. The charger will be about 6 ft from the main panel.

For aesthetic reasons, I am trying to avoid using external conduit and go through the studs in the wall instead. I would like the wires to come directly from the wall into the HPWC enclosure using the openings in the back of the charger (the ones that you have to drill out), not the openings at the top or bottom of the enclosure. It appears that I have two choices:

1) Using 4-3 romex cable from Home Depot. This is pricey at about $12 a foot and I am not sure I will be able to route the #4 wires inside the HPWC. The wires have to make a sharp 90 degree turn when they enter the enclosure, and those #4 wires do not bend very easily. Has anyone had luck routing 4-3 romex when using the back opening of the HPWC?

2) The other choice is to use 3/4" flexible conduit with 2 #6 THHN wires and a #10 ground wire. The problem is that the conduit also has to make a 90 degree turn when it exits the stud and comes out of the wall. My understanding is that NEC requires a minimum bending radius of 4-6 inches for various types of 3/4" conduit. Since there is only 5.5" of depth inside the walls (assuming 6x2 studs), and the conduit will be routed through the center of the studs, making that ~5" 90 degree bend into the back opening of the HPWC doesn't appear to be possible. If you managed to successfully connect flexible conduit in this way, how did you do it and which type of conduit did you use? It appears that ENT (the blue PVC conduit) is a little more flexible than FMC (the flexible metallic type), so perhaps that's the way to go? Additionally, it looks like 1/2" FMC conduit is barely within the 40% NEC fill requirements for 2 #6 + 1 #10 wires, so maybe going with 1/2" conduit is a possible solution as well?

 

[Sophias_dad]

I'm with you on not having exposed conduit.

1) You are missing that the minimum bend radius of a cable is apparently 8 times the diameter of the cable. In the case of 4-3 romex, that's going to be about six inches. Regarding bending the individual conductors once they are in the HPWC, I'm sure it can be done.

2) the MBR of 3/4" flexible metal conduit is 4", and since you have 5.5" of space for the turn you should be fine. Be sure to plan the location of the HPWC so that the conduit isn't trying to do a quick bend as it exits the joist. You don't have to place the hole for the conduit absolutely dead center of the joist on a 2x6, either. The conduit should also displace toward the other side of the cavity and allow it to make the turn into the back of the HPWC with ease. 1/2" FMC would have a 3" MBR, so it should work even better, and yes you should also be fine with that especially if you keep that ground wire bare. ENT appears to have an MBR of 6", so its sort of dubious if you want to turn inside the wall using the conduit. Another option for either kind of conduit is to use the end-fitting to make the turn. Halex 3/4 in. 90-Degree Flexible Metal Conduit (FMC) Connector-91102 - The Home Depot but that won't work real well since it'll be inside drywall when it finishes the turn. You could do it successfully and hide it behind the HPWC, but why bother?

If it were me, I'd go with 3/4" FMC, which would leave tons of space if anyone ever wants to pull a neutral for a 14-50.

 

[john pane]

If the wires are inside the wall you do not need conduit.

 

[UberAndy]

Thank you for your reply, Sophias_dad.

3/4" FMC is in fact what I was leaning towards. Can you please point me to where it says in NEC that the MBR of FMC is 4" for 3/4"? My impression was that you had to use 348.24, which refers to Chapter 9, Table 2, column "Other Bends". That specifies a bending radius of 5". Additionally, that's the "centerline radius", plus you have a fitting at the end of the conduit that extends at least 1" inside the drywall and is not flexible. From this perspective, even if you drill the stud hole right at the edge of the stud (which isn't ideal), you can't legally use 3/4" FMC, as you would need an MBR of 5.5" (wall depth) - 1/2" (outer bend radius correction for 1" diameter conduit) - 1" (fitting offset).

BTW, ENT conduit should have the same MBR as FMC, according to 362.24 (same Chapter 9, Table 2, column "Other Bends"). Where did you see 6"?

My main problem with FMC is that I have a spool of 3/4" steel FMC from Home Depot and the stuff is actually very stiff. I don't think I can bend it to even the 5" MBR allowed by NEC. Perhaps I should try the aluminum version. ENT on the other hand is relatively flexible.

Romex MBR I believe is also 5x the diameter according to 334.24. Do you have a source for the 8x?

https://up.codes/viewer/minnesota/nfpa-70-2020/chapter/3/wiring-methods-and-materials#348

 

[UberAndy]

[ My first reply is stuck in moderation so here it is again without the NEC link ]

Thank you for your reply, Sophias_dad.

3/4" FMC is in fact what I was leaning towards. Can you please point me to where it says in NEC that the MBR of FMC is 4" for 3/4"? My impression was that you had to use 348.24, which refers to Chapter 9, Table 2, column "Other Bends". That specifies a bending radius of 5". Additionally, that's the "centerline radius", plus you have a fitting at the end of the conduit that extends at least 1" inside the drywall and is not flexible. From this perspective, even if you drill the stud hole right at the edge of the stud (which isn't ideal), you can't legally use 3/4" FMC, as you would need an MBR of 5.5" (wall depth) - 1/2" (outer bend radius correction for 1" diameter conduit) - 1" (fitting offset).

BTW, ENT conduit should have the same MBR as FMC, according to 362.24 (same Chapter 9, Table 2, column "Other Bends"). Where did you see 6"?

My main problem with FMC is that I have a spool of 3/4" steel FMC from Home Depot and the stuff is actually very stiff. I don't think I can bend it to even the 5" MBR allowed by NEC. Perhaps I should try the aluminum version. ENT on the other hand is relatively flexible.

Romex MBR I believe is 5x the diameter according to 334.24. Do you have a source for the 8x?

 

[Sophias_dad]

Here's my goto for FMC, note that some get down to 2" min bend radius, which I'm pretty surprised at.

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

I'm a big fan of McMaster in general. I use them for most of my project odds and ends.

ENT bend radius:

https://carlonsales.com/techinfo/brochures/electrical/ENT_2B43.pdf

You are right about the 5x MBR for romex.

 

[UberAndy]

2" MBR for 3/4" FMC is pretty insane. Unfortunately that conduit is not UL listed. Also, the NEC requirements (5" MBR for both 3/4" FMC and ENT) still take precedence over what the manufacturer specifies in their brochure.

I would like to install the charger before the end of the year to take advantage of the 30% federal tax credit, so likely no time to order from McMaster. Will try 3/4" Aluminum FMC from Home Depot next.

 

[Sophias_dad]

2" MBR for 3/4" FMC is pretty insane. Unfortunately that conduit is not UL listed. Also, the NEC requirements (5" MBR for both 3/4" FMC and ENT) still take precedence over what the manufacturer specifies in their brochure.

I would like to install the charger before the end of the year to take advantage of the 30% federal tax credit, so likely no time to order from McMaster. Will try 3/4" Aluminum FMC from Home Depot next.

McMaster almost always arrives next-day for me, at no extra charge. I also really doubt the taxman will be knocking on your door at 12:01 on 1/1/2022 to see if your charger is installed

I'd be willing to bet that if carlton says 6" and you bend it to 4" MBR, the conduit will break.

Stumbled across this, but its for IMC and threaded rigid conduit:

https://carlonsales.com/techinfo/brochures/electrical/ENT_2B43.pdf

 

[ATPMSD]

Using 4-3 romex cable

As I recall, this is 4-gauge wire with 3-conductors + a ground (Hot-Hot-Neutral-Ground). The Wall Connector does not utilize the neutral so can save money by using 4-2 wire.

 

[Sophias_dad]

As I recall, this is 4-gauge wire with 3-conductors + a ground (Hot-Hot-Neutral-Ground). The Wall Connector does not utilize the neutral so can save money by using 4-2 wire.

Yes, but I don't think 4-2 is available.

 

[ATPMSD]

Yes, but I don't think 4-2 is available.

Probably right, but I think you still have options. You could buy two lengths of 4-gauge wire and for the ground, you don’t need 4-gauge, I believe 8-gauge will do. Not sure as to the wire type(s).

 

[kayak1]

You might look at 6/2 w/Ground, MC cable.

I had a fairly short run, I used #6 thhn copper (and #10 for the ground) in 3/4 conduit as it's rated for 65 amps at 75°C.

I used a 60 AMP QO breaker which allows for 48amp to the car.

 

[Rocky_H]

You haven't even mentioned the other option. You never even mentioned what rating of circuit you're using. It sounds like you think the wall connector can only be installed on a 60A circuit, hence you thinking you need to use 4 gauge Romex. It's a variable setting device.

3) Use 6 gauge Romex and do a 50A circuit. 6 gauge should be very readily available and cheaper. Done.

 

[Sophias_dad]

You haven't even mentioned the other option. You never even mentioned what rating of circuit you're using. It sounds like you think the wall connector can only be installed on a 60A circuit, hence you thinking you need to use 4 gauge Romex. It's a variable setting device.

3) Use 6 gauge Romex and do a 50A circuit. 6 gauge should be very readily available and cheaper. Done.

Yes, and you can even get 6-2 NMB.

 

[Bernt]

If the wires are inside the wall you do not need conduit.

True for romex, not true for THHN.

 

[john pane]

True for romex, not true for THHN.

Also true for SE cable.

 

[Mrbrock]

You haven't even mentioned the other option. You never even mentioned what rating of circuit you're using. It sounds like you think the wall connector can only be installed on a 60A circuit, hence you thinking you need to use 4 gauge Romex. It's a variable setting device.

3) Use 6 gauge Romex and do a 50A circuit. 6 gauge should be very readily available and cheaper. Done.

Depends on if the OP is getting or has a Standard M3 or something else (Standard M3 only needs 40A circuit for max charging so 8/2 NM-B would work there). And if his car is capable of 48A (or higher) charging then he would need to weigh 40A charging and lower cost and more flexibility vs 48A charging and harder/more expensive install.