50amp vs 30amp 240v Outlet

[SDDizzle]

New here! I have a Tesla Y Long Range coming soon to California. I am novice DIYer so will do my best to ask my electrical question below...

I need to install a 240V outlet in my garage and use a NEMA adapter for charging. I understand the difference between a 30A and 50A outlet and the corresponding 14-30 or 14-50 adapter, and how the charge rate is different.

I have an experienced licensed electrician that feels my total 100A panel (total for my house) is already pretty full with Air Conditioner/regular house things, and he would only recommend a 30A outlet for my EV charger b/c of this. Upgrading my total amp service is not possible at the moment.

I have another recommended licensed electrician who is convincing me that 50A would be okay b/c I'll mostly charge at night and other appliances are rarely used during those times. I don't think he is trying to upsell me or anything b/c there is not much of a cost difference, and he comes recommended from a friend.

I understand the situation and that either 30A/50A only ends up charging at 24/42A or so. I also understand you can adjust your Amp charge at the Tesla. My question is... if I decide on the 50A outlet and learn that the circuit is being overloaded (not sure the right terminology), would reducing the Amp charge at the Tesla be successful in adjusting the total Amps used? If a 30A (NEMA 14-30) uses 24A or if I adjust a 50A (NEMA 14-50) to use 24A - is it essentially the same? Or is the outlet still pulling 50A and if overloaded it will trip?

I prefer 50A obviously, but want to know if I can adjust as needed if there is a problem... or if I should avoid all risk and install it at 30A. Any thoughts or input appreciated!

 

[Sophias_dad]

Yes, reducing the Amp setting in the Tesla would be successful. In theory it'll even remember the setting so you'll only have to set it every now and again when the software is upgraded and/or the Tesla loses its mind. Notably, if you put in an HPWC, you could turn the HPWC provisioning down and then the car couldn't make the mistake of over-requesting current.

The problem won't be that your 50 amp circuit will trip and your car will stop charging. The problem will be that your main electrical breaker will trip, plunging your entire house into darkness. It may also do so after quite some time, 30-60 minutes or more.

A picture of your panel might help. The 'licensed electrician' should do a load calculation and see what your panel will really support. He's not really allowed to say "you'll only charge when other things are not in use", except in the rare case where you have both a home heating and home cooling device in the same panel(in which case the lower-current of those two can be ignored)

Do you never use AC at night in LA? How about the electric clothes dryer? Do you really need the extra charging?

 

[jjrandorin]

You can adjust it in the car, but that isnt considered an appropriate way to manage that. Either a load calculation states you have enough capacity, or it doesnt. You should ask "what does the load calculation say will fit?" (which is likely what the first electrician quoted you, but none of us know that for sure).

If standard load calculation method shows you only have 30amps left, then thats what you "should" install. People get hung up on wanting "as fast as possible" (and I get it, for sure, I have a 60amp circuit for 48amp charging myself), but unless you are buying a wall connector (which it doesnt sound like you are) the max charging speed will be 32 amps from the mobile connector.

 

[SDDizzle]

Yes, reducing the Amp setting in the Tesla would be successful. In theory it'll even remember the setting so you'll only have to set it every now and again when the software is upgraded and/or the Tesla loses its mind. Notably, if you put in an HPWC, you could turn the HPWC provisioning down and then the car couldn't make the mistake of over-requesting current.

The problem won't be that your 50 amp circuit will trip and your car will stop charging. The problem will be that your main electrical breaker will trip, plunging your entire house into darkness. It may also do so after quite some time, 30-60 minutes or more.

A picture of your panel might help. The 'licensed electrician' should do a load calculation and see what your panel will really support. He's not really allowed to say "you'll only charge when other things are not in use", except in the rare case where you have both a home heating and home cooling device in the same panel(in which case the lower-current of those two can be ignored)

Do you never use AC at night in LA? How about the electric clothes dryer? Do you really need the extra charging?

You're right - I do not need the extra charging and had accepted that I will settle for the 30A outlet. But when the second guy came along and confidently felt he can give me a 50A outlet, I was thinking "Hey sounds great!" but also had some reservations based on what others have told me.

This is the first I have heard of a load calculation, but that makes a lot of sense. Thanks for the info on that!

I don't have a pic handy right now, but I do think the panel is pretty full as the first electrician says. I just wanted the best solution, which I thought maybe was a 50A breaker with the option to turn it down at the car if needed. But it seems that may not be a good idea.

 

[Sophias_dad]

You're right - I do not need the extra charging and had accepted that I will settle for the 30A outlet. But when the second guy came along and confidently felt he can give me a 50A outlet, I was thinking "Hey sounds great!" but also had some reservations based on what others have told me.

This is the first I have heard of a load calculation, but that makes a lot of sense. Thanks for the info on that!

I don't have a pic handy right now, but I do think the panel is pretty full as the first electrician says. I just wanted the best solution, which I thought maybe was a 50A breaker with the option to turn it down at the car if needed. But it seems that may not be a good idea.

It might be worth noting that if you are using the UMC, its limited to 32 amps continuous anyway. This means you are really choosing between a 24 amp charge rate and a 32am charge rate. Apologies for not catching that in your first post. This might steer you into going down the 14-50 path, since the difference is pretty small. The bad bit is that potentially when you move someone will plug in a welder or kiln or just use a different EV charger that can take the full 40 amp continuous charge rate and trip the main.

 

[jcanoe]

You did not state how many miles per day you typically drive.

Tesla Model Y Charging Speeds, for 240V charging:

Circuit Amperage/Charging Amperage/Power (kW)/miles per hour added while charging / Typical NEMA Receptacle

60 / 48 / 11.5 / 42 miles (estimated) - No Tesla plug option; hard wired only using Tesla Wall Connector
50 / 40 /9.6 / 36 miles (estimated) - NEMA 14-50 (note: limited to 32A using the Gen2 Mobile Connector)
40 / 32 / 7.7 / 29 miles (estimated) - NEMA 14-50 (note: can be used with a 40A circuit when 50A is not an option)
30 / 24 / 5.7 / 21 miles (estimated) - NEMA 14-30 (commonly called the electric dryer outlet)
20 / 16 / 3.8 / 14 miles (estimated) - NEMA 6-20
15 / 12 / 2.8 / 10 miles (estimated) - NEMA 6-15

 

[Unclepaul]

Ethical electricians will do a load calculation before installing additional heavy amperage sockets.

Theory is that while you may not be intending to use all your draw at once, things may change in the future or a new owner may plug in and assume they can charge their car the same time an electric dryer, airconditioner or electric stove will be in use.

 

[SDDizzle]

You did not state how many miles per day you typically drive.

Tesla Model Y Charging Speeds, for 240V charging:

Circuit Amperage/Charging Amperage/Power (kW)/miles per hour added while charging / Typical NEMA Receptacle

60 / 48 / 11.5 / 42 miles (estimated) - No Tesla plug option; hard wired only using Tesla Wall Connector
50 / 40 /9.6 / 36 miles (estimated) - NEMA 14-50 (note: limited to 32A using the Gen2 Mobile Connector)
40 / 32 / 7.7 / 29 miles (estimated) - NEMA 14-50 (note: can be used with a 40A circuit when 50A is not an option)
30 / 24 / 5.7 / 21 miles (estimated) - NEMA 14-30 (commonly called the electric dryer outlet)
20 / 16 / 3.8 / 14 miles (estimated) - NEMA 6-20
15 / 12 / 2.8 / 10 miles (estimated) - NEMA 6-15

I have maybe a 20-25 mile commute round trip. I can live with 21 mph charge, but just wanted to install the best possible option since I have to pay for the install any way. Appreciate the chart - helps a lot!

 

[jcanoe]

I have maybe a 20-25 mile commute round trip. I can live with 21 mph charge, but just wanted to install the best possible option since I have to pay for the install any way. Appreciate the chart - helps a lot!

One consideration is if you currently or plan to enroll in one of the time of use (TOU) rate plans. Some of TOU rate plans, the ones with the lowest off-peak rates, only offer the low rate between midnight and 0600. Any of the 240V options would enable you to complete charging within the off-peak window.

Depending on how long you intend to stay in the home it may be worth upgrading the electrical service, i.e. from 100A to 200A. The cost of the electrical service upgrade would apply to your cost basis when you sell the home.

 

[SDDizzle]

If I could upgrade to 200a, I would but I am in a townhouse situation which makes it very complicated or not possible. I have my own 100a main panel but I believe the service is somehow connected to all units.

The electrician said he would show me how my panel is operating with his amp probe, and help me decide best option. Though he’s the guy that suggested 50a, so I guess we will see. It’s going to be a little costly for me to get the outlet due to the distance from panel to garage, so I just wanted to get the best option possible. At the same time, I don’t want any risk of tripping the whole house due to car charging. I plan to ask him about the load calculation.

 

[Sophias_dad]

If I could upgrade to 200a, I would but I am in a townhouse situation which makes it very complicated or not possible. I have my own 100a main panel but I believe the service is somehow connected to all units.

The electrician said he would show me how my panel is operating with his amp probe, and help me decide best option. Though he’s the guy that suggested 50a, so I guess we will see. It’s going to be a little costly for me to get the outlet due to the distance from panel to garage, so I just wanted to get the best option possible. At the same time, I don’t want any risk of tripping the whole house due to car charging. I plan to ask him about the load calculation.

You could avoid all of this and just plug into a 120V outlet if its available and already there. 5mi/hr for even a few hours is your daily commute.

 

[SDDizzle]

You could avoid all of this and just plug into a 120V outlet if its available and already there. 5mi/hr for even a few hours is your daily commute.

Glad to hear you think that may be okay. It’s an alternative plan - “trickle charge” and supercharge as needed. There is a supercharge station less than a mile away from me too.

I figured if I’m going Tesla, might as well go all in and install a charger. But perhaps I give the trickle plan a chance and see how it goes for a few months. Are there a good number of Tesla owners that do this and happy with it? I do want a good EV experience, as this is my first electric car.

 

[jcanoe]

Glad to hear you think that may be okay. It’s an alternative plan - “trickle charge” and supercharge as needed. There is a supercharge station less than a mile away from me too.

I figured if I’m going Tesla, might as well go all in and install a charger. But perhaps I give the trickle plan a chance and see how it goes for a few months. Are there a good number of Tesla owners that do this and happy with it? I do want a good EV experience, as this is my first electric car.

120V/15A charging is adequate, in my experience, if you commute up to ~30 miles per day. Post a photo of the 120V receptacle you plan to use. That would clearly indicate whether this is a 15A or 20A circuit. If you use a 120V15A circuit expect 3 to 4 (some say 5) miles of range added per hour. If you can charge using a 120V/20A circuit you could charge at up to ~7 miles per hour. As long as you have 9+ hours when you can charge starting each evening until you leave the next morning it would be adequate for your 25 mile commute plus some other daily driving.

 

[SDDizzle]

120V/15A charging is adequate, in my experience, if you commute up to ~30 miles per day. Post a photo of the 120V receptacle you plan to use. That would clearly indicate whether this is a 15A or 20A circuit. If you use a 120V15A circuit expect 3 to 4 (some say 5) miles of range added per hour. If you can charge using a 120V/20A circuit you could charge at up to ~7 miles per hour. As long as you have 9+ hours when you can charge starting each evening until you leave the next morning it would be adequate for your 25 mile commute plus some other daily driving.

Thanks for the info. I have regular 15a receptacles; definitely not 20a.

I believe a frequent topic is to what % to charge your Tesla and battery health. I believe the idea is to charge max to 80-90% charge, right? If I charge every night or every other night but can’t get to the target 80-90% due to hours charged or distance driven - let’s say I only get to 75% Monday night, then 70% the next day, then 65%…so by Friday I have been charging throughout the week but I’m left with 50%, but then I leave it charging longer over the weekend to the 80-90% goal. Is that damaging to the battery?

Alternatively, is it bad to drive it all week down to 30-40% charge, then just charge once or twice a week to the target 80-90%?

I understand most these questions have likely been answered so I will browse the forums. But I truly appreciate all of your time and answers!

 

[Sophias_dad]

Yes, if you run a weekday deficit and catch up on the weekends it'll be fine. I wouldn't plan to charge only on weekends, but that would work too.

Be prepared to offer the condo folks some cash. I assume the 120V outlet you have access to isn't being accounted to your own meter.

 

[jcanoe]

Tesla recommends leaving the Tesla vehicle plugged in. (If Tesla the Tesla vehicle is plugged in at some point the vehicle will charge when initiated as with Scheduled Departure - Charging and the state of charge (SOC) is below the set threshold.) Some Tesla owners follow this recommendation and charge each day. Others who understand their driving habits and needs charge as needed. There are lengthy discussions re charging protocol.

If you are driving 25 miles per day you can certainly skip a day, or several, and still have plenty of range. Once you get into a routine you may find you start to plug in as a habit when you arrive home at the end of the day.

Then there is the question of what maximum and minimum charging level to use. Since you are driving perhaps 10% of the range, if you plug in each day you will never get into the bottom half of the battery state of charge.

As far as the upper charging threshold Tesla clearly denotes daily charging within the slider control in the Tesla phone app as between 50% and 90%. You can set the charge level anywhere within this range for daily charging and not be wrong. In practice up to 80% if you charge each day should be adequate. Realize that since you are charging at 120V/12A (1.4kW) on a 15A circuit if you need to take a longer trip and the battery is at 80% it will take time to charge up to 90% or beyond before you drive.

Charging at 120V/12A would add slightly less than 2% to the battery for every hour you charge. Charging from 80% to 90% would take approximately 6 hours. You might want to set the charging threshold high enough that if decide to take a longer drive the Tesla is sufficiently charged before you leave without having to first stop to charge at a Supercharger. In practice you would rarely if ever need to charge beyond 90% before starting a longer distance road trip because you would only need to start the trip with enough battery charge to reach the first Supercharger along the route.

 

[roblab]

Go with the second electrician. You'll be charging at night. As an aside, I've never even seen a "welder" at any house I've ever known with a 14-50 outlet, and no one will be welding at 2AM. OK, someone on this forum will let me know this is EXACTLY when they do all their welding, right? But these cars can be, and usually are, programmed to charge in the wee hours when prices are cheap.

Some future homeowner MAY try to run his welder, dryer, and commercial floor polisher all at the same time, but he won't do it very long. And he'll learn why people use circuit breakers while he's at it. I would guess that these outlets will be increasingly desirous to charge electric vehicles, and that new buyers will specifically look for a 240 outlet when they are checking out potential homes for purchase.

I've been charging my electric vehicles, past and present, on the same 14-50 outlet for years. The car charges sometime after midnight, and I've never had a problem.

 

[jcanoe]

Modern arc welding equipment typically uses a 6-50 receptacle anyway, not the 14-50 receptacle so you won't be doing any welding with the 14-50 receptacle.

 

[SDDizzle]

Go with the second electrician. You'll be charging at night. As an aside, I've never even seen a "welder" at any house I've ever known with a 14-50 outlet, and no one will be welding at 2AM. OK, someone on this forum will let me know this is EXACTLY when they do all their welding, right? But these cars can be, and usually are, programmed to charge in the wee hours when prices are cheap.

Some future homeowner MAY try to run his welder, dryer, and commercial floor polisher all at the same time, but he won't do it very long. And he'll learn why people use circuit breakers while he's at it. I would guess that these outlets will be increasingly desirous to charge electric vehicles, and that new buyers will specifically look for a 240 outlet when they are checking out potential homes for purchase.

I've been charging my electric vehicles, past and present, on the same 14-50 outlet for years. The car charges sometime after midnight, and I've never had a problem.

Thanks for the input. This seems to be the thought process of the electrician who thinks it’s okay to do 50a, when others have suggested 30a. I don’t have a photo of panel handy, but it’s pretty full with multiple rooms, lights, appliances, central AC, and so on. Dryer is gas which helps.

But anyway, I’m wondering if the 14-50 adapter is set to use only 32a of the 50a circuit, does it ever spike randomly and use the full 50? If so, then I guess I could be in the situation where the car charging pulls close to 50a, the AC comes on at night and spikes around 40a, then someone uses some lights or blow dryer, and the house trips! Unlikely but possible, right?

I guess I am thinking to make the “safe” decision of installing a lower 30a circuit, but also don’t want to miss out on optimal 14-50 charging (compared to 14-30). Or as mentioned, just give trickle charging a chance.

 

[charlesoris]

SCE has a ToU-D-Prime that features $.19/kWh most of the day except between 4-9 PM when it goes up to $.48.
DWP probably has a similar rate structure