208 vs 240

[Pommie]

My new condo has a breaker wired for 208 50 A for EV charging.

The electrician is going to include the NEMA 14-50 outlet. Right now, it's just a blank plate covering the box.

From what I have read, it will still work on 208 except it will be slightly slower. Is this correct?

Model 3 Long Range AWD. Delivery is June 4--woot!

The breaker box also includes a 50 amp breaker for a hot tub. I will not be installing one. Can the 2 50 amp breakers be combined for faster charging and what type of outlet would that involve? Not sure if I will do that right now because it's an added cost but would like to know.

Thanks!!

 

[Eno Deb]

My new condo has a breaker wired for 208 50 A for EV charging.

The electrician is going to include the NEMA 14-50 outlet. Right now, it's just a blank plate covering the box.

From what I have read, it will still work on 208 except it will be slightly slower. Is this correct?

Yes.

The breaker box also includes a 50 amp breaker for a hot tub. I will not be installing one. Can the 2 50 amp breakers be combined for faster charging and what type of outlet would that involve? Not sure if I will do that right now because it's an added cost but would like to know.

That would very likely require running new wire to the outlet, and you'd have to install the hard wired Tesla wall charger (there is no plug-based charging solution for more than 50A). It also wouldn't buy you much since the most the Model 3 can make use of is 60A (which allows charging at 48A continuous load). Unless you have an extremely long commute, it'll probably not make a difference for you.

 

[davewill]

Correct. The car will still draw the same number of amps, but with the lower voltage will get less power. You can't "combine" two circuits in the way you suggest. You could always install a bigger circuit, like 60 amps, and removing the hot tub circuit might be part of being able to do that depending on the size of your service and the size of the loads in your condo. However, that would cost a LOT more than just putting in the outlet and you would then need a hard-wired wall connector to take advantage of it. There are no practical outlets for home use greater than 50a.

One option for faster charging with what you have, though, would be a wall connector hard wired to the existing 50a circuit. That would allow 40a charging instead of the max 32a charging that the mobile connector allows. The install should not cost much, if any, more than installing the outlet.

 

[Pommie]

Thanks. No long commute. Lots of super chargers around me for road trips. I think given that the 208-50 service was paid for in the construction cost, it's the best solution. I already ordered the $35 adapter for the 14-50 online.

 

[Silicon Desert]

and just as a side note.... many commercial locations where there is a destination wall charger will also be at 208VAC, but some are 240VAC.

 

[Pommie]

Yeah I associate 208 with commercial buildings. Maybe because it's a multi-unit building, that's why he used 208 instead of 240?

 

[miimura]

Yeah I associate 208 with commercial buildings. Maybe because it's a multi-unit building, that's why he used 208 instead of 240?

Yes, in a multi-unit building it's easier to distribute power to all the units from a single three phase feed. 208V 3-phase is 120V to ground, so any single phase circuits are normal 120VAC.

It sounds like you don't need the speed up, but there are two ways to speed up the charging compared to the Gen2 Mobile Connector's 32A @ 208V.

1. A small boost transformer can be installed to bump the 208V up to 240V for your charging circuit.
2. You can use a Gen1 Mobile Connector or Gen1 Corded Mobile Connector or Wall Connector to deliver 40 amps to the car instead of the 32 amps provided by the Gen2 Mobile Connector.

 

[Pommie]

Yes, in a multi-unit building it's easier to distribute power to all the units from a single three phase feed. 208V 3-phase is 120V to ground, so any single phase circuits are normal 120VAC.

It sounds like you don't need the speed up, but there are two ways to speed up the charging compared to the Gen2 Mobile Connector's 32A @ 208V.

1. A small boost transformer can be installed to bump the 208V up to 240V for your charging circuit.
2. You can use a Gen1 Mobile Connector or Gen1 Corded Mobile Connector or Wall Connector to deliver 40 amps to the car instead of the 32 amps provided by the Gen2 Mobile Connector.

Thanks so much! These are both great ideas if I find the 208 charging lacking. It's so nice to have this forum to get help but also to learn about things like how electricity works. It seems Tesla attracts a very smart tech crowd and I dig that!

 

[Silicon Desert]

Thanks so much! These are both great ideas if I find the 208 charging lacking. It's so nice to have this forum to get help but also to learn about things like how electricity works. It seems Tesla attracts a very smart tech crowd and I dig that!

Well you aren't going to see a huge difference from 208 to 240. Example on my MX when charging at 208 with 64 amps, it reports roughly 36 kWh. When I charge at 240 with same amperage it goes to about 41 kWh. So, as expected an approximate 13% difference. Noticeable, but not earth shattering.

 

[miimura]

(Probably dumb questions, but...)

Can a NEMA 14 outlet and a Tesla Mobile Connector really work with only two out of the three phases from the three-phase 208V circuit?

If so, would the resultant voltage actually be 208V, or would it be less since it's missing one phase?

Yes, with 208V 3-phase service you connect any two hots and the neutral and you get 208V and 120V at the outlet.
If you have 240V split-phase service you connect two hots and the neutral and you get 240V and 120V at the outlet.

 

[lolder]

It would not be a "small" booster transformer so don't consider that. The difference between 208 and 240 is whether the feed to the site is a residential 240 v split ( single ) phase or a feed to a commercial or multi-resident site which is three-phase with neutral 208 v. The difference in charging speed in "miles per hour" is about 26 vs. 31.

 

[COrocket]

Did the electrician verify behind the blank plate to ensure that the 4 wires (hot-hot-neutral-ground) for a 14-50 are present? Reason I ask is if it was wired for an EV charger like a Tesla wall connector or J1772 connector, those only use 3 wires (hot-hot-ground). If that’s the case, you’d need a 6-50 outlet and adapter.

 

[TexasEV]

Your car will charge overnight at 208V 32A. Don’t worry about what time during the night it finishes charging.

 

[Pommie]

Did the electrician verify behind the blank plate to ensure that the 4 wires (hot-hot-neutral-ground) for a 14-50 are present? Reason I ask is if it was wired for an EV charger like a Tesla wall connector or J1772 connector, those only use 3 wires (hot-hot-ground). If that’s the case, you’d need a 6-50 outlet and adapter.

I asked for a 14-50 with the job site superintendent who relayed it to the electrician. I hope that he knows whether or not he can install it vs the 6-50. I have already ordered the adapter for the 14-50 but I guess I could sell it or return it if I find out he ended up running a 6-50. Thanks for pointing this out to me

 

[Pommie]

Your car will charge overnight at 208V 32A. Don’t worry about what time during the night it finishes charging.

Interesting you bring this up. Colorado sells electricity on different rate plans and I can opt for cheaper electricity based on what hours I charge between. I am interested to see whether it's better to pay the flat rate or the reduced off-hour rate. I think the cheap rates begin at 9 pm so there is some benefit to charging faster. Can't remember the cutoff but I think it's 7 am? I guess that gives me 10 hours so it should be enough. I don't drive much. Mostly use a bike to run most of my errands.

 

[MrMassTransit]

If it is truly 9 PM to 7 AM you’ll be fine. That should allow you to charge about 80% of your LR battery’s full capacity. On a routine basis you don’t want to charge much over 80% anyway unless you need the range, and you most likely won’t be pulling in with the battery down to the single digits on most occasions. If you ever decide you want faster charging, just replace the 14-50 with an HPWC or use a corded mobile connector, but you can definitely skip it for now.

 

[Eno Deb]

Interesting you bring this up. Colorado sells electricity on different rate plans and I can opt for cheaper electricity based on what hours I charge between. I am interested to see whether it's better to pay the flat rate or the reduced off-hour rate. I think the cheap rates begin at 9 pm so there is some benefit to charging faster. Can't remember the cutoff but I think it's 7 am? I guess that gives me 10 hours so it should be enough. I don't drive much. Mostly use a bike to run most of my errands.

Well, living in Colorado you won't have a big issue anyway. I have a friend who lives in Boulder (also a Tesla owner) and his highest peak rate costs as much as my lowest off-peak rate in the middle of the night.

 

[eprosenx]

It would not be a "small" booster transformer so don't consider that. The difference between 208 and 240 is whether the feed to the site is a residential 240 v split ( single ) phase or a feed to a commercial or multi-resident site which is three-phase with neutral 208 v. The difference in charging speed in "miles per hour" is about 26 vs. 31.

It absolutely would be a pretty small transformer. You would use an "autotransformer" (buck/boost) which uses a single winding for the primary and secondary windings and it only has to handle the capacity for which you are increasing or decreasing the voltage. So they are pretty small. Square D Transformer, 120/240VAC, 16/32VAC, 2kVA 2S46F | Zoro.com

Now with that being said, I would generally not recommend them. I probably would spend my money first at upgrading from a 32a EVSE (like the UMC Gen 2 that came with the car) to a 40a one (presuming you have a 50a circuit - this maxes at 40a usable, a 40a circuit maxes at 32a usable). Then beyond that I would spend my money on a 60a circuit (or larger - up to 100a/80a usable - though most Tesla's max out at 32, 48, or 72a usable - or 40a or 80a for the really old Model S units) into a Wall Connector. Even on the 50a circuit I would consider a Wall Connector too (40a max charge rate).

To the original poster:

Don't stress out about it! Give it a shot at 208v with the 14-50 you already paid for and the UMC Gen 2 that comes with the car. If you find yourself wanting faster charging, then consider upgrading once you have the car.

If you post pictures of your main electrical panel and the receptacle the electrician installed we might be able to provide more insight. I am curious what gauge wire the electrician used, whether it is in conduit the whole way or not (this impacts how much power it can handle as "romex" would be more limited), how much total capacity you have into your main panel (125a?), what other loads you have in the house, and how far it is from the main panel to the vehicle (for voltage drop reasons).

Enjoy the car!

 

[darth_vad3r]

It absolutely would be a pretty small transformer. You would use an "autotransformer" (buck/boost) which uses a single winding for the primary and secondary windings and it only has to handle the capacity for which you are increasing or decreasing the voltage. So they are pretty small. Square D Transformer, 120/240VAC, 16/32VAC, 2kVA 2S46F | Zoro.com

Now with that being said, I would generally not recommend them. I probably would spend my money first at upgrading from a 32a EVSE (like the UMC Gen 2 that came with the car) to a 40a one (presuming you have a 50a circuit - this maxes at 40a usable, a 40a circuit maxes at 32a usable). Then beyond that I would spend my money on a 60a circuit (or larger - up to 100a/80a usable - though most Tesla's max out at 32, 48, or 72a usable - or 40a or 80a for the really old Model S units) into a Wall Connector. Even on the 50a circuit I would consider a Wall Connector too (40a max charge rate).

To the original poster:

Don't stress out about it! Give it a shot at 208v with the 14-50 you already paid for and the UMC Gen 2 that comes with the car. If you find yourself wanting faster charging, then consider upgrading once you have the car.

If you post pictures of your main electrical panel and the receptacle the electrician installed we might be able to provide more insight. I am curious what gauge wire the electrician used, whether it is in conduit the whole way or not (this impacts how much power it can handle as "romex" would be more limited), how much total capacity you have into your main panel (125a?), what other loads you have in the house, and how far it is from the main panel to the vehicle (for voltage drop reasons).

Enjoy the car!

Despite the fact that you linked to a 240V to 32V transformer , 208 to 240 do exist ... but there is no point to do this to charge a Tesla. You don’t get a magical increase in power by boosting the voltage (with a transformer). The current will drop.

Your car wants more power to charge faster, not more volts.

Power is Volts x Amps.
e.g. 208V x 32A = 6.656kW
240V x 27.7A = 6.6kW

 

[darth_vad3r]

Yes, in a multi-unit building it's easier to distribute power to all the units from a single three phase feed. 208V 3-phase is 120V to ground, so any single phase circuits are normal 120VAC.

It sounds like you don't need the speed up, but there are two ways to speed up the charging compared to the Gen2 Mobile Connector's 32A @ 208V.

1. A small boost transformer can be installed to bump the 208V up to 240V for your charging circuit.
2. You can use a Gen1 Mobile Connector or Gen1 Corded Mobile Connector or Wall Connector to deliver 40 amps to the car instead of the 32 amps provided by the Gen2 Mobile Connector.

See my post above. There’s no reason to use a transformer to boost voltage for charging a Tesla.

That won’t speed up charging because increasing voltage does not mean more power unless the current doesn’t drop by the same % amount (which is going to happen with a transformer).

Charge speed is determined by power, not voltage. Power is voltage x current (Volts x Amps).

EDIT: Foot, mouth, remove
... if the breaker is 50A, and the transformer input is 40A continuous, you could get 240V x 32A out of the other side of the transformer and that would increase the charge speed by like ~29mi/hr vs ~25mi/hr (with the mobile charger that is limited to a 32A draw)