Help to understand home charging options?

[cduzz]

I believe the 2nd plug isn't grounded from this picture:

In my house when dealing with old wobbly plug attachments I've used shims like these:

When that image link breaks; it is a link from home depot for a product by a brand "ideal" named "spacer" that I found with a google search of "outlet shim"

They go between the receptacle mount and the box and you shim them out until the face plate can screw into the receptacle without (much) tension.

As far as why 240 is more efficient than 120; I suspect it is more that there is a fixed "run the charger tax" of 800 watts to run coolant pumps, battery heaters, other electronic whizmos, etc. I suspect you'd see a similar non-linear improvement if you used a "TT-30" charger which gives you 30 amps of 120v. The whizmo tax isn't a big deal in a moderate temperature garage but when you're confronted with a battery that is -20° the heater probably wants to soak up 2000w for quite a while before you can charge, and if you're running on a 1500w max budget, you'll never get up to temp and start charging but you will get a big electric bill for running a space heater outside all night.

 

[ajdelange]

The grounding wire certainly is missing from the right hand set in that picture but my question is why you got to see that picture and I didn't. I'm asking that because things sometimes seem to just disappear from this site.

As to why the "system" is so much more efficient at 240 as opposed to 120 I couldn't say. This is just based on Tesla's published numbers for the two adapters which presumably represents typical conditions. Coolant pump? Maybe. Heater: at startup it draws up to 4 kW but I doubt Tesla includes that in its estimated charge rates for these adapters. I'm thinking that the charger has to boost to 850 VDC and is probably better at doing that from 240 than from 120 as the transistors will have to switch at a faster rate to get the extra boost.

 

[Rocky_H]

The grounding wire certainly is missing from the right hand set in that picture but my question is why you got to see that picture and I didn't. I'm asking that because things sometimes seem to just disappear from this site.

As to why the "system" is so much more efficient at 240 as opposed to 120 I couldn't say. This is just based on Tesla's published numbers for the two adapters which presumably represents typical conditions. Coolant pump? Maybe. Heater: at startup it draws up to 4 kW but I doubt Tesla includes that in its estimated charge rates for these adapters. I'm thinking that the charger has to boost to 850 VDC and is probably better at doing that from 240 than from 120 as the transistors will have to switch at a faster rate to get the extra boost.

From a lot of history of the Model S and X, that showed that during the charging process, there is about a third of a kilowatt of fixed overhead keeping the car awake and running the charger. For a 120V 12A (1.4kW) input, that's nearly a fourth of the total input power that's not going into the battery. So if you can increase the total input power up to 3kW or 6kW or something, that one third of a kilowatt fixed overhead becomes barely noticeable as all of the extra is directing going to the battery, which helps the charging efficiency a lot.

The Model 3 charger system is going to be a little different but similar in principle.

 

[ajdelange]

Tesla's numbers tell us a little in this regard. The table in the store page where the adapters are listed tells us that 0.8*20*120 = 1920 watt hours if energy into the car will nominally put 4 miles of range into the battery. Looking at the what's your usage thread I see unbelievably high numbers so I am going to use 300 Wh per mile as it's a nice round number and I do see that some Model 3 drivers reporting achieving that. At that consumption rate 4 miles added means 1200 Wh are going into the battery and 1920 - 1200 = 720 W are going somewhere else. Some of that is going to warm transistors in the inverter and some of it is going to operating whatever devices are consuming power under the conditions Tesla assumed in calculating 4 mph. Now going to 240 V Tesla tells us that 0.8*20*240 = 3840 Watts puts 11 miles into the battery in an hour. At the same assumed consumption that's 3300 Wh worth. That means that 3840 - 3300 = 540 W are going somewhere else. Since presumably the base line loads. This implies that the conversion circuitry is much more efficient at 240V. Accepting the 330 W figure proposed in #46 we'd have 720 - 333 = 387 W of conversion loss at 120 V and 540 - 333 = 207 W of conversion loss at 240V. Given that twice as much power is being converted the fact that the loss is half implies that conversion efficiency is better by factor of nearly 4 (3.74).

These numbers are pretty rough being based on charging rates from Tesla rounded to 1 mph, an assumed baseline load of 333 W and a consumption assumption of 300 Wh/mi.

 

[bmah]

Moderator note: Moved a couple of personal attacks (plus one or two messages quoting them, probably innocently) to snippiness.

Name-calling or other personal attacks on other TMC members is against TMC rules. Continued violation of these rules will lead to a ban. It’s OK to disagree with each other but this needs to be done in a respectful way.

Thank you,

Bruce.

 

[Litigate28]

Alright folks, so if I may get your thoughts on what my options are. Here are some updated pictures, I went in again to see if I could identify if it's 12 or 14 gauge. And it seems like it is both?

From what I can tell, the wiring coming to the outlet on the left is 12 gauge, it is definitely thicker than the other wiring. This wire is over 1mm thick and about the size of a nickel. The wiring that connects this outlet to the outlet on the right is thinner, about 1mm thick. Then there is the other set of wires not connected to anything, and those are 1mm thick as well.

So do I have 12 gauge running to the outlet on the left, and then 14 gauge powering the the second outlet using the power from the first one? If that's the case, do I have the option of going to 6-20? If not 5-20 maybe?

Appreciate the help, especially for an electrical newbie.

 

[ajdelange]

Someone earlier here posted a most useful tip revealing that 12 Ga is about the thickness of a nickle and 14 Ga about the thickness of a dime. Furthermore, given to feed is 12 it would make sense to bridge to the single 15A outlet with 14. Thus it is almost certain that you have 12 though the jacket is white. I think there may now be a requirement that 12 be yellow but I believe that came in one of the later editions of the code. Yes, you can install either a 5-20 or 6-20 receptacle in this box but get rid of the other outlet or at least fix its earth. It looks as if the feeder earth wire is terminated at the left plug and then a piece of bare wire, subsequently cut, was looped around this. You also should verify that this is the only outlet on the breaker.

 

[ucmndd]

Agree with @ajdelange.

RE the white jacket 12awg, my California home, built in 1991, has this as well. I think the yellow standard came about later.

As for switching to the 6-20, IF this is the only outlet on the circuit AND you have space in your panel for a new 20A double pole breaker, then yes you could do this.

If either of those conditions don’t hold, replacing the receptacle with a new 5-20 and buying the necessary adapter for your UMC would be easy and cheap.

 

[Litigate28]

Thanks for the quick replies. There is another outlet on a near wall on the same circuit, and this is actually part of a double pole breaker already (this 20 amp breaker). I also need to plug in my washer/dryer on some outlet here, so I think the 5-20 would be the only solution...

Can I just replace the left with the 5-20 and keep the right one as it is with the 5-15? Or does it not work like that... I'll probably just get an electrician anyway but just wanted to know myself first before having him out there.

 

[ucmndd]

and this is actually part of a double pole breaker already (this 20 amp breaker).

The breaker you posted a picture of in the first post is called a “tandem” breaker - two circuit breakers in a single pole 120v body.

A “double pole” breaker is double the width and takes up two slots in your panel on opposite phases to make a 240 volt circuit. This is what you’d need to do to move to a 240v 6-20 outlet.

So yes, with the other outlets and the need for other loads, you probably want to stick with the 5-20 idea.

Can I just replace the left with the 5-20 and keep the right one as it is with the 5-15? Or does it not work like that... I'll probably just get an electrician anyway but just wanted to know myself first before having him out there.

You can do that, it’s fine to mix 15 and 20 amp receptacles on a 20 amp circuit. Like mentioned earlier though, if you’re going to keep that 15 amp receptacle daisy chained, get it properly grounded.

That said, based on the scenario you describe where your washer and potentially other loads will be on the same circuit, you’ll need to be careful about doing things like charging your car and washing laundry at the same time to avoid nuisance breaker trips, particularly if you have the car charging full tilt at 16 amps.

 

[ucmndd]

Here’s a pic of my garage sub panel showing the difference in breakers. 120v 20A tandem breaker on the left for regular receptacles, 240v 20A dual pole breaker on the right for a NEMA 6-20 plug that runs an air conditioner.

 

[ajdelange]

Thanks for the quick replies. There is another outlet on a near wall on the same circuit, and this is actually part of a double pole breaker already (this 20 amp breaker).

We need to be careful about terminology. A "double pole" breaker is a 240V breaker. It connects to both panel phases (black and red) and has two output terminals that go to the black and red of a 240V appliance. The 20 A breaker in the picture is a "tandem" breaker. It is single pole in that it connects to only one phase (black or red) but has two output terminals for two separate 120V feeders. If flipping one of the two toggles on this breaker off turns off one of the outlets but not the other the other is on a separate circuit and you will be fine leaving the washer connected to it. If both outlets go off when you flip one toggle that's not so good. The UMC with a 20 amp adapter will tell the car it can take 16 A and if you plug a 5 amp load into the other outlet you will be drawing 21 amps. The breaker will trip (but it might take quite some time). This is OK from the POV of the NEC but it is your responsibility to see to it that the circuit is not overloaded.

I also need to plug in my washer/dryer on some outlet here, so I think the 5-20 would be the only solution...

You can do that (i.e. leave the other outlet in - be sure to fix the ground but the same reasoning applies. If the washer draws more than 5 amps when the car is drawing 16 the breaker will eventually pop interrupting both your charge and your laundry. I described in No. 40 how to convert the circuit to the box in question to 240V and thus allow installation of a 6-20R for much faster (almost 3 times) charging. There is another piece of Romex coming into that box. it eventually makes its way back to the panel. If you can figure out where that wire goes in the panel (piece of cake with the breaker finder I mentioned in an earlier post and thus a piece of cake for an electrician equipped with one) you have the potential for having a 240V receptacle for EV charging and a 120V duplex for the washing machine on separate circuits in that same box.

Can I just replace the left with the 5-20 and keep the right one as it is with the 5-15? Or does it not work like that...

Yes, as long as you fix the ground but see above.

I'll probably just get an electrician anyway but just wanted to know myself first before having him out there.

I hope this will help you in your discussions with him. Be sure to get a good man. Unfortunately many electricians know how to do what they have been doing for many years (and do it very well) but if asked to do anything at all unusual (conversion of a circuit to 240V might be considered unusual) are totally at sea.

 

[Litigate28]

Got it, thank you.

We need to be careful about terminology. A "double pole" breaker is a 240V breaker. It connects to both panel phases (black and red) and has two output terminals that go to the black and red of a 240V appliance. The 20 A breaker in the picture is a "tandem" breaker. It is single pole in that it connects to only one phase (black or red) but has two output terminals for two separate 120V feeders. If flipping one of the two toggles on this breaker off turns off one of the outlets but not the other the other is on a separate circuit and you will be fine leaving the washer connected to it. If both outlets go off when you flip one toggle that's not so good. The UMC with a 20 amp adapter will tell the car it can take 16 A and if you plug a 5 amp load into the other outlet you will be drawing 21 amps. The breaker will trip (but it might take quite some time). This is OK from the POV of the NEC but it is your responsibility to see to it that the circuit is not overloaded.

You can do that (i.e. leave the other outlet in - be sure to fix the ground but the same reasoning applies. If the washer draws more than 5 amps when the car is drawing 16 the breaker will eventually pop interrupting both your charge and your laundry. I described in No. 40 how to convert the circuit to the box in question to 240V and thus allow installation of a 6-20R for much faster (almost 3 times) charging. There is another piece of Romex coming into that box. it eventually makes its way back to the panel. If you can figure out where that wire goes in the panel (piece of cake with the breaker finder I mentioned in an earlier post and thus a piece of cake for an electrician equipped with one) you have the potential for having a 240V receptacle for EV charging and a 120V duplex for the washing machine on separate circuits in that same box.

Yes, as long as you fix the ground but see above.


I hope this will help you in your discussions with him. Be sure to get a good man. Unfortunately many electricians know how to do what they have been doing for many years (and do it very well) but if asked to do anything at all unusual (conversion of a circuit to 240V might be considered unusual) are totally at sea.

Thank you and ucmndd for the detailed posts. I also went and looked over your post #40 and although I understand the idea generally, I would never dare try that myself. What's interesting is I can't figure out why that breaker is labeled Master Bedroom TV plug because no outlets in the master turn off when I flipped that breaker (there are two covered plates with no outlets, so maybe those use to be on the same circuit, not sure). Nothing in the kitchen either which directly shares the wall with the garage. Here's a more distant pic showing the garage setup if that helps. On the left are the plugs we were looking at, and in the back of the picture near the shelf is the other plug that is part of this circuit. The garage is small enough that if the car is charging we can't use the laundry anyway as the car would be in the way.

 

[ajdelange]

It's clear some mods have been done to the wiring as you have the unterminated piece of ROMEX coming into the box. Is the panel in the garage?

 

[ucmndd]

I second the question about the dryer plug. A dryer buddy would be a great option.

 

[Litigate28]

I second the question about the dryer plug. A dryer buddy would be a great option.

Not sure really. It's a gas dryer so it was just plugged in to the regular 5-15 outlet.

It's clear some mods have been done to the wiring as you have the unterminated piece of ROMEX coming into the box. Is the panel in the garage?

Panel is far away in the back yard. Lines are drawn through a crawl space. Probably 50-60 feet is my guess.

 

[ucmndd]

Not sure really. It's a gas dryer so it was just plugged in to the regular 5-15 outlet

Ah. Never mind then.

 

[Litigate28]

Not sure if anyone will see this quick enough but electrician is here and put in the 5-20 on the left side. However when I plug in the UMC it blinks red for ground fault. The ground is there and was working before on the 5-15. Interestingly he has some tester plugged into the other outlet and it shows grounded but when I plug in the UMC it shows ground fault. Any ideas?

 

[Rocky_H]

Not sure if anyone will see this quick enough but electrician is here and put in the 5-20 on the left side. However when I plug in the UMC it blinks red for ground fault. The ground is there and was working before on the 5-15. Interestingly he has some tester plugged into the other outlet and it shows grounded but when I plug in the UMC it shows ground fault. Any ideas?

The ground wire may be attached onto the outlet, but maybe it's not hooked in at the panel? Also, I don't know if it is checking for ground versus which pin in the outlet is supposed to be the 0V neutral. Maybe those two are switched. But an outlet tester should notice either of those issues.

 

[Litigate28]

The ground wire may be attached onto the outlet, but maybe it's not hooked in at the panel? Also, I don't know if it is checking for ground versus which pin in the outlet is supposed to be the 0V neutral. Maybe those two are switched. But an outlet tester should notice either of those issues.

It was working before on the 5-15 outlet. And now sadly the 5-15 doesn't work either despite him putting it back the same way.