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Electricians, did I totally miss an opportunity here?

Apologies in advance for the noob question...

Earlier this summer we had a whole house humidifier installed. A 240v line was run through the garage to the basement to power it. At the time I thought it would be "years" before we got an EV. But now I'm expecting a M3 in a couple of weeks.

I have free charging at work, so I wasn't planning on installing anything at home, but then I remembered I already have 240v running through the garage! See photo.

Problem is, the humidifier uses 11.5 amps and it's on a 40 amp breaker. So that leaves me with 20 amps for an EVSE. So I think I screwed myself by not thinking ahead and telling the electrician to future proof it (put it on a 60 amp breaker for example).

Questions:

1. Is it true that EVSE is supposed to be on its own "line" / breaker anyway? So then none of this matters?

If #1 is *not* true then...

2. I'm assuming I shouldn't have a 14-50 plug installed in this junction box right (again, see photo)? Knowing that 11.5 is used during the winter months, it should probably be a 14-30 plug (e.g. so a future owner of the house doesn't assume they have 40 amps available to them).

And last,

3. If I do install a plug on this line / junction box, my thought is during the summer I can charge at 32 amps... but I have to remember during the winter months (when I turn the humidifier back on) to dial the EVSE back down to 20 amps... How bad is it if I forget one winter? It will simply trip the breaker right?

Thanks for any info!

240JunctionBox.jpg
 
Unless you're an Uber driver 16A @ 240v is plenty.

Yeah, the more I think about it, the more I realize that it's fine. Specially since I have free charging at work as well (assuming I get in early enough to get one of the 10 spots).

One last noob question. I see the 6-20 is only $5 at Home Depot (Leviton 20 Amp Commercial Grade Double-Pole Single Outlet, White-R52-05821-0WS - The Home Depot). They are rated for 20 amps. I know that you're supposed to run 80% of the circuit breaker, so in my case:

40 amp * 80% - 11.5 (Humidifier) = 20 amps.

Can the actual outlet (rated at 20 amps) handle 20 amps continuously? Or do I also need to subtract *another* 80% for the outlet itself?

Thanks!!!
 

nwdiver

Well-Known Member
Feb 17, 2013
8,855
12,936
United States
Yeah, the more I think about it, the more I realize that it's fine. Specially since I have free charging at work as well (assuming I get in early enough to get one of the 10 spots).

One last noob question. I see the 6-20 is only $5 at Home Depot (Leviton 20 Amp Commercial Grade Double-Pole Single Outlet, White-R52-05821-0WS - The Home Depot). They are rated for 20 amps. I know that you're supposed to run 80% of the circuit breaker, so in my case:

40 amp * 80% - 11.5 (Humidifier) = 20 amps.

Can the actual outlet (rated at 20 amps) handle 20 amps continuously? Or do I also need to subtract *another* 80% for the outlet itself?

Thanks!!!

The current through any breaker shouldn't exceed 80% of its rating.
 

miimura

Well-Known Member
Aug 21, 2013
7,171
7,120
Los Altos, CA
You should not charge on a circuit that has any other load on it.

One proper way to do it is to put a small sub-panel at the junction if the breaker for that circuit is larger than it needs to be. The question in my mind is: why would there be a 40A breaker there if it wasn't needed? I would get the electrician back out to give you proper code compliant options.
 

miimura

Well-Known Member
Aug 21, 2013
7,171
7,120
Los Altos, CA
Totally get that... I'm talking about the actual outlet itself. The $5 6-20 receptacle. It's rated for 20 amps. Can it actually handle 20 amps or do I also need to apply the 80% rule to that as well??? (Sorry for the dumb questions)
Yes, you can only charge at 16A from a 20A outlet. The Tesla adapter will enforce that for you. Don't use a 3rd party plug adapter that allows you to connect a 14-50 plug.
 
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nwdiver

Well-Known Member
Feb 17, 2013
8,855
12,936
United States
Totally get that... I'm talking about the actual outlet itself. The $5 6-20 receptacle. It's rated for 20 amps. Can it actually handle 20 amps or do I also need to apply the 80% rule to that as well??? (Sorry for the dumb questions)

The 80% rule also applies to the outlet. That's why standard 110v appliances are limited to 12A. 12 is 80% of 15.
 

miimura

Well-Known Member
Aug 21, 2013
7,171
7,120
Los Altos, CA
Why? Again, I really don't know what I'm talking about, but if I have 40 amps available and the only other load is the humidifier then I know how much load I have left right? So I should be able to install a 6-20 plug in the junction box for the EVSE no?
Electrical code dictates that EV charging must be on a dedicated circuit. As I said above, if you really have spare capacity on the circuit, you can put a sub-panel there and put proper breakers for each load. I will try to post a picture with a link to a small box for that purpose.
 
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Electrical code dictates that EV charging must be on a dedicated circuit. As I said above, if you really have spare capacity on the circuit, you can put a sub-panel there and put proper breakers for each load. I will try to post a picture with a link to a small box for that purpose.

This is what I was worried about. So I have these junction boxes that I can't even use :(

How bad is it if I do install a 6-20 plug and charge @ 16 amps though? Am I just violating the code or am I really creating a hazard?
 

miimura

Well-Known Member
Aug 21, 2013
7,171
7,120
Los Altos, CA
Apologies in advance for the noob question...

Earlier this summer we had a whole house humidifier installed. A 240v line was run through the garage to the basement to power it. At the time I thought it would be "years" before we got an EV. But now I'm expecting a M3 in a couple of weeks.

I have free charging at work, so I wasn't planning on installing anything at home, but then I remembered I already have 240v running through the garage! See photo.

Problem is, the humidifier uses 11.5 amps and it's on a 40 amp breaker. So that leaves me with 20 amps for an EVSE. So I think I screwed myself by not thinking ahead and telling the electrician to future proof it (put it on a 60 amp breaker for example).

Questions:

1. Is it true that EVSE is supposed to be on its own "line" / breaker anyway? So then none of this matters?

If #1 is *not* true then...

2. I'm assuming I shouldn't have a 14-50 plug installed in this junction box right (again, see photo)? Knowing that 11.5 is used during the winter months, it should probably be a 14-30 plug (e.g. so a future owner of the house doesn't assume they have 40 amps available to them).

And last,

3. If I do install a plug on this line / junction box, my thought is during the summer I can charge at 32 amps... but I have to remember during the winter months (when I turn the humidifier back on) to dial the EVSE back down to 20 amps... How bad is it if I forget one winter? It will simply trip the breaker right?

Thanks for any info!

View attachment 483253

I have never seen a US 220v circuit that was not dedicated... and yes you need a dedicated circuit but you can use an existing 220 outlet intended for a dryer, but most are 30 amps and you will charge at 24. If you are going to pay for an electrician then get at least a 40 amp circuit so you can use the mobile charger to it's full advantage. I would install a NEMA 14-50 on a 40 amp breaker and tell the electrician you are going to plug in your RV or a small arc welder so you won't get the Tesla VAT added to your bill.
 

Akikiki

A'-Lo-HA ! y'all
Nov 26, 2012
6,625
5,032
Kaneohe, HI
@JimDog, I guess you know what you are talking about because you are there and can see it. But to me, it does not make sense that an electrician installed a device (humidifier) that only uses <12 amp on a 40 amp circuit. Seems to me like a hazard considering the load that would have to build on that line or at the device to trip a 40 amp circuit breaker. Wow. Does not seem right.
 
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I have never seen a US 220v circuit that was not dedicated...

Ok, I think things are starting to make sense now... I found the installation manual for the humidifier and it says:

"With factory settings, the Model 800 draws 11 .5 amps +/- 10% . Use a minimum 20 amp dedicated circuit when installing to operate at 11.5 amps. When set to 16 amps, use a minimum 25 amp dedicated circuit"

So it looks like it is meant to be a "dedicated circuit". But why then did the electrician add the junction boxes on the way to the humidifier? Is this part of the electrical code? I've heard that 120v outlets inside the house have to be every so many feet... is it the same for this 240v line (even though it's "dedicated" to something already)???
 
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@JimDog, I guess you know what you are talking about because you are there and can see it. But to me, it does not make sense that an electrician installed a device (humidifier) that only uses <12 amp on a 40 amp circuit. Seems to me like a hazard consider the load that would have to build on that line or at the device to trip a 40 amp circuit breaker. Wow. Does not seem right.

I'm learning as I go (see my previous post in reply to @kkillebrew )... The humidifier has a dip switch and you can select between 11.5 and 16 amps. The electrician was not the same person that installed the humidifier, so my guess is he was being extra safe (not knowing which setting the plumber was going to use)?
 
@JimDog, I guess you know what you are talking about because you are there and can see it. But to me, it does not make sense that an electrician installed a device (humidifier) that only uses <12 amp on a 40 amp circuit. Seems to me like a hazard consider the load that would have to build on that line or at the device to trip a 40 amp circuit breaker. Wow. Does not seem right.
Excellent point. Who knows? You can buy a 10-30 to 14-50 adapter on Amazon and then plug your mobile charger's 14-50 adapter into that, and if you don't know to reduce the draw in the charging menu the car thinks you can support the full 32 and will pop a breaker or blow a fuse, or worse.
 

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