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NEMA 14-50 40amp circuit

AA Hubs

Member
Apr 28, 2021
18
32
Toronto ON
Hi All,

I had an electrician come to the house and look at the garage panel. He said I have only 40amp coming into the garage panel from the house. His comment was I will be able to charge "just slower"

If I install the NEMA 14-50 outlet on the 40amp circuit then I can only draw 30amp from that outlet? (80% rule)

If you have a 50amp circuit I see people suggesting you can draw 40amp, to my understanding is the gen 2 14-50 adapter from Tesla only rated for 32amp? can you pull 40amp safely with that adapter? or is it locked to 32amp?

I'm looking at potentially getting a line run from the house panel instead and just plugging the car in outside ( not an issue as this is my temporary living for the next 2-3 years)

Upgrading the garage to 50 or 60amp is also not at option cost wise and with my living situation
 

jcanoe

Active Member
Oct 2, 2020
2,176
2,153
Maryland
By code, you cannot install a 14-50 outlet on a circuit that's rated for only 40 amps. That would require a 50A circuit.

As already suggested, the 14-30 would be your best option.
Actually the NEC does permit installing a 40A breaker with the NEMA 14-50 receptacle. The reason is that there is no specific receptacle for 40A. As long as the receptacle is clearly labeled 40A there would be no confusion.
 

jcanoe

Active Member
Oct 2, 2020
2,176
2,153
Maryland
Hi All,

I had an electrician come to the house and look at the garage panel. He said I have only 40amp coming into the garage panel from the house. His comment was I will be able to charge "just slower"

If I install the NEMA 14-50 outlet on the 40amp circuit then I can only draw 30amp from that outlet? (80% rule)

If you have a 50amp circuit I see people suggesting you can draw 40amp, to my understanding is the gen 2 14-50 adapter from Tesla only rated for 32amp? can you pull 40amp safely with that adapter? or is it locked to 32amp?

I'm looking at potentially getting a line run from the house panel instead and just plugging the car in outside ( not an issue as this is my temporary living for the next 2-3 years)

Upgrading the garage to 50 or 60amp is also not at option cost wise and with my living situation
Actually on a 40A circuit the charging amperage limit is 32A (80% of 40 is 32.)

Your electrician can install a 40A breaker for use with a 14-50 receptacle (this exception is allowed by code.) SInce you only have 40A coming into the garage then installing a 30A breaker would probably be the best option. The Tesla Mobile Connector will charge at 24A when used on a 30A circuit. This is good for up to 21 miles per hour of added range while charging. Worst case scenario where you start charging at midnight and have to finish charging by 0600 this is more than 120 miles of range added to the battery pack overnight. The NEMA receptacle for the Gen2 Mobile Connector would be the 14-30.

Although the Tesla Gen2 Mobile Connector can be used with a NEMA 14-50 receptacle when used with the NEMA 14-50 plug adapter the maximum amperage when using the Tesla Gen2 Mobile Connector is limited to 32A for an added margin of safety. If you need to charge at 40A there is a fixed plug version of the Tesla Mobile Connector, the Corded Mobile Connector. This version of the Mobile Connector has a fixed NEMA 14-50 power plug, heavier gauge wire.
 
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Rocky_H

Well-Known Member
Feb 19, 2015
6,271
7,326
Boise, ID
I had an electrician come to the house and look at the garage panel. He said I have only 40amp coming into the garage panel from the house.
I see this often. You seem to have pre-decided on a 14-50 (as if thinking that was your only option) before even finding out if your electrical setup will be able to do that. That's putting the cart before the horse. Find out what size circuit you can add, and then that will help to determine what you should install.

Now my next question is: since you only have 40A going to the garage, don't you have lights or other outlets or a garage door opener already using some of that 40A total? A charging circuit basically uses all of the capacity of the circuit it's on, so you shouldn't use that whole 40A if it's sharing with other things.

A 14-30 is probably your best bet. There is a pigtail on the Tesla store for it. You'll still get 21 MPH charging
I agree that a 30A circuit would be a better idea.
 

AA Hubs

Member
Apr 28, 2021
18
32
Toronto ON
I see this often. You seem to have pre-decided on a 14-50 (as if thinking that was your only option) before even finding out if your electrical setup will be able to do that. That's putting the cart before the horse. Find out what size circuit you can add, and then that will help to determine what you should install.

Now my next question is: since you only have 40A going to the garage, don't you have lights or other outlets or a garage door opener already using some of that 40A total? A charging circuit basically uses all of the capacity of the circuit it's on, so you shouldn't use that whole 40A if it's sharing with other things.


I agree that a 30A circuit would be a better idea.

You are correct, I did assume my current setup would allow for a 14-50 outlet, Without knowing we assumed are newly renovated garage would have had 50a coming in. My electrical knowledge is basic at best. But for $50 for the tesla 14-50 adapter I've invested so far I can get a different adapter required if my current setup doesn't allow it.

Next we are having him check our house panel to see if we can run an exterior line to the corner of the house. and if we can get more than 30a.

Obviously not ideal but my current situation is unique.
 
Oct 3, 2020
205
211
Seattle
Actually the NEC does permit installing a 40A breaker with the NEMA 14-50 receptacle. The reason is that there is no specific receptacle for 40A. As long as the receptacle is clearly labeled 40A there would be no confusion.

I stand corrected. Thanks for clarifying. I was thinking about the other scenario where the breaker is larger than the wire/receptacle capacity, sorry for the confusion.
 
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THF2021MY

Member
May 18, 2021
14
3
Florida
Folks I need two pieces of advice. I have two sub panels in my home. One installed in 1996-97 when the home was new. It is a Challenger/Eaton. Several electricians (and handymen electrical guys) have stated I should replace the Challenger/Eaton due to the risk of possible fire. Others have said it’s fine. It is filled with CB’s and in order to put in a new circuit for my Tesla MY SR they would need to make room.

The other panel was put in in 2010 for an addition to the home. That one can handle whatever I need to put in. However, it is 75’ to where the charging outlet/receptacle would be. So,…

1. Should I replace the Challenger/Eaton? ($$$)
2. If I don’t replace it should I make room for a new CB?
3. Or just use the second panel?

The second piece of advice is about circuits. I’m confused. My car can only charge at 32A. I would be using the mobile connector. Tesla does not sell a 14-40 adapter so how does that work.

4. If I install a 50A line and a 50A breaker and buy a 14-50 adapter will I damage my car? Even if the setting is set to 32A in the car won’t it be sending 40 or 50A to the car? My understanding is the mobile connector and the onboard charger would keep things safe.
5. If I install a 40A line and breaker I’ll have to use a 14-50 adapter to get the max amount of charging. Is that safe. Is it to code? Will it work?
6. One electrician wants to use “Romex“ #6 on a 40 or 50A circuit to avoid running conduit. Is that safe?

Thanks in advance for your replies. If I’m not asking the right questions please ask and answer them for me.

Tom
 

Johnny Vector

Member
Jun 21, 2020
177
243
Maryland
The second piece of advice is about circuits. I’m confused. My car can only charge at 32A. I would be using the mobile connector. Tesla does not sell a 14-40 adapter so how does that work.

4. If I install a 50A line and a 50A breaker and buy a 14-50 adapter will I damage my car? Even if the setting is set to 32A in the car won’t it be sending 40 or 50A to the car? My understanding is the mobile connector and the onboard charger would keep things safe.
5. If I install a 40A line and breaker I’ll have to use a 14-50 adapter to get the max amount of charging. Is that safe. Is it to code? Will it work?
6. One electrician wants to use “Romex“ #6 on a 40 or 50A circuit to avoid running conduit. Is that safe?

Thanks in advance for your replies. If I’m not asking the right questions please ask and answer them for me.

Tom

A 50 amp circuit won't hurt your car. In electrical parlance, the current rating of a circuit is a capability. The actual current is determined by what you plug into the receptacle, in all cases. In this particular case, the current is set by the mobile connector, which will only draw 32 amps. The 50A rating of the circuit means that if you draw more than 50 amps the breaker will trip and all of a sudden you'll be drawing 0 amps!

Yes, Romex (NM-B) 6 AWG is fine for a 50 A circuit.

From a purely technical standpoint, a 14-50 with a 40 A breaker on 40 A rated wire is not a fire hazard. Meeting code is another question. I think it does, but your electrician should know for sure.
 

THF2021MY

Member
May 18, 2021
14
3
Florida
Thank you Johnny V.

My original plan was to build for the future. Put in a 60A line for a 60A breaker but use a 50A breaker and use the 14-50 adapter on the mobile charger. But the electricians say running the wire and conduit 75’ for the 60A circuit is expensive. The 18’ length of the mobile charger is problematic, but do-able.

Now I guess running Romex #6 wire and putting a 50A breaker and using the 14-50 adapter on the mobile charger is the best option. That quote is $1500!
 

sjsharks33

Member
Apr 10, 2021
38
16
CA
Thank you Johnny V.

My original plan was to build for the future. Put in a 60A line for a 60A breaker but use a 50A breaker and use the 14-50 adapter on the mobile charger. But the electricians say running the wire and conduit 75’ for the 60A circuit is expensive. The 18’ length of the mobile charger is problematic, but do-able.

Now I guess running Romex #6 wire and putting a 50A breaker and using the 14-50 adapter on the mobile charger is the best option. That quote is $1500!
I did exactly what you described for your original plan. Bought 6 guage THHN wire and ran in conduit with a 50 amp breaker and nema 14-50 outlet. I have the 60 amp breaker already and will eventually buy the the Tesla wall connector and all I have to do is remove the breaker and 14-50 outlet. The only difference for me is I only ran 5 ft of conduit from sub panel which was rather cheap.
 

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THF2021MY

Member
May 18, 2021
14
3
Florida
I did exactly what you described for your original plan. Bought 6 guage THHN wire and ran in conduit with a 50 amp breaker and nema 14-50 outlet. I have the 60 amp breaker already and will eventually buy the the Tesla wall connector and all I have to do is remove the breaker and 14-50 outlet. The only difference for me is I only ran 5 ft of conduit from sub panel which was rather cheap.
Sweet! The cost really goes up for me because of the distance, the wire, and the conduit. I could do it all except attaching it to the sub panel.

Question: If I understand correctly Romex is all the wires in one fireproof sheathing. If I ran Romex in the conduit (easier than running four individual wires) would that be to code?

Thanks.
 

Johnny Vector

Member
Jun 21, 2020
177
243
Maryland
Sweet! The cost really goes up for me because of the distance, the wire, and the conduit. I could do it all except attaching it to the sub panel.

Question: If I understand correctly Romex is all the wires in one fireproof sheathing. If I ran Romex in the conduit (easier than running four individual wires) would that be to code?

Thanks.
I guarantee that pulling Romex through conduit is much much harder than running individual wires. If you're using conduit, you definitely want wires with a slippery outer sheathing, and separate so the overall stiffness is less. Pulling Romex through conduit is almost impossible, not necessary, and I'm pretty sure it's against code (heat will build up in the conduit and melt the insulation sooner than in free air).
 
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sjsharks33

Member
Apr 10, 2021
38
16
CA
Sweet! The cost really goes up for me because of the distance, the wire, and the conduit. I could do it all except attaching it to the sub panel.

Question: If I understand correctly Romex is all the wires in one fireproof sheathing. If I ran Romex in the conduit (easier than running four individual wires) would that be to code?

Thanks.
If your plan is to eventually go with a 60 amp breaker then 6 guage romex is not rated for 60 amps and I believe only rated at 55 amps. THHN wire however is rated for 60 amps which is what I used for the 50 amp breaker knowing I will change to 60 amps when I get the wall connector. I'm not a professional either, but romex is typically ran inside walls with no conduit.
 
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THF2021MY

Member
May 18, 2021
14
3
Florida
If your plan is to eventually go with a 60 amp breaker then 6 guage romex is not rated for 60 amps and I believe only rated at 55 amps. THHN wire however is rated for 60 amps which is what I used for the 50 amp breaker knowing I will change to 60 amps when I get the wall connector. I'm not a professional either, but romex is typically ran inside walls with no conduit.

Thanks guys. I think I understand. When I finally choose an electrician I’ll be able to tell him/her exactly what I want.

#6awg THHN wire in conduit with a 50A breaker and an industrial grade 14-50 outlet/receptacle. If I go with a 40A breaker then the 14-50 must be marked as such.

Now I just need to decide about the original sub panel.
 

Rocky_H

Well-Known Member
Feb 19, 2015
6,271
7,326
Boise, ID
I guarantee that pulling Romex through conduit is much much harder than running individual wires. If you're using conduit, you definitely want wires with a slippery outer sheathing, and separate so the overall stiffness is less. Pulling Romex through conduit is almost impossible, not necessary, and I'm pretty sure it's against code (heat will build up in the conduit and melt the insulation sooner than in free air).
Going with the yes and the no here.
I have heard that trying to put Romex through conduit is awfully difficult to try to do.
But no, it's not against code. I have seen the code section where it is allowed, and it's for transition kind of circumstances, where you need to run it inside wall for part of the way and then come out and go along a surface. Romex isn't allowed to be exposed on a surface like that, so it's listed that you then need to have it in conduit to protect it from physical damage out there.
 
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Johnny Vector

Member
Jun 21, 2020
177
243
Maryland
Going with the yes and the no here.
I have heard that trying to put Romex through conduit is awfully difficult to try to do.
But no, it's not against code. I have seen the code section where it is allowed, and it's for transition kind of circumstances, where you need to run it inside wall for part of the way and then come out and go along a surface. Romex isn't allowed to be exposed on a surface like that, so it's listed that you then need to have it in conduit to protect it from physical damage out there.
Ah, thanks. That makes sense. I actually did that to cover the 6" from inside the house to the outside, switching to THWN in the 90° conduit body. Making sure the volume (clearly marked inside by the manufacturer) was sufficient for the wires in there. But that doesn't really count as pulling; I just shoved it in one end and it came out the conduit body! The hardest part was figuring out that the Southwire THHN is also rated as THWN (and THHN-2, and a couple others as well). You'd think they would make that clearer in the advertising.

I would still worry about heat buildup with a long run in conduit, but I guess the NFPA built enough margin into the code limits that it's okay.
 

Rocky_H

Well-Known Member
Feb 19, 2015
6,271
7,326
Boise, ID
Ah, thanks. That makes sense. I actually did that to cover the 6" from inside the house to the outside, switching to THWN in the 90° conduit body.
I am going to need to make use of this transition thing. I currently have my 14-50 outlet directly under my panel, about knee high, so it's just Romex down inside the wall. But I want to replace it with a wall connector to the side of my panel, and really don't want to have to do sheet rock work (sideways has studs in the way). So my intent is to get a longer piece of Romex, do the first part of it the same, down through the wall, and then come out where the outlet was, and through flex metal conduit right and up to where I want to mount the wall connector. I figure I can pre-shove the Romex through the conduit while it's mostly straight and flexible and then curve it into shape to fasten it to the wall.

I would still worry about heat buildup with a long run in conduit, but I guess the NFPA built enough margin into the code limits that it's okay.
It's already downrated a lot because of what it is and where you use it. It's made to put into the inside of walls, surrounded by insulation. There is almost no air flow, so it is rated 15 Celsius degrees (27 Fahrenheit degrees) less than regular wires in conduit, because it's going to be in stuffy areas where heat will build up. Being in a conduit, but at least outside of the wall, I think would dissipate heat as well or better than in the wall.
 

Johnny Vector

Member
Jun 21, 2020
177
243
Maryland
I am going to need to make use of this transition thing. I currently have my 14-50 outlet directly under my panel, about knee high, so it's just Romex down inside the wall. But I want to replace it with a wall connector to the side of my panel, and really don't want to have to do sheet rock work (sideways has studs in the way). So my intent is to get a longer piece of Romex, do the first part of it the same, down through the wall, and then come out where the outlet was, and through flex metal conduit right and up to where I want to mount the wall connector. I figure I can pre-shove the Romex through the conduit while it's mostly straight and flexible and then curve it into shape to fasten it to the wall.

That should be fine. It's the curves you need to worry about, or really long lengths. A few years ago I needed a 50 foot outdoor run of 10AWG to connect a single solar panel in the one sunny spot of my off-grid camp to the pumphouse, and I bought the UF before deciding I wanted more protection than direct burial, so I got some conduit and shoved it through one length at a time. Doable, but only because there were no corners. I'm more concerned about lasting 100 years than about anyone ever digging there, so plastic seemed a better choice, code notwithstanding. (The ground is glacial rubble; no way am I trenching 18" deep). Plus, y'know, 30 volts peak. If I were starting fresh, I would transition to THWN at the junction to outdoors.

It's already downrated a lot because of what it is and where you use it. It's made to put into the inside of walls, surrounded by insulation. There is almost no air flow, so it is rated 15 Celsius degrees (27 Fahrenheit degrees) less than regular wires in conduit, because it's going to be in stuffy areas where heat will build up. Being in a conduit, but at least outside of the wall, I think would dissipate heat as well or better than in the wall.

Yeah, I guess conduit isn't any worse than surrounded by insulation. I think the main reason the temperature rating is lower is mainly the properties of the insulation material (PVC vs. high-temperature Nylon). There's no prohibition about running conduit in insulated walls, right? So in that situation conduit can only make things worse, but I suspect it increases the overall R-value by like 1 or 2 percent, which is in the noise.
 

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