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!

 

[esteed]

If you're ok with trickle charge as a minimum and you have a supercharger very close, I would go with the 30a receptacle if you're nervous. You all do realize it's possible to overload a panel with just what you have in it now right? Go ahead and add up all the numbers on the breakers- I bet you bottom dollar it'll add up to way more than 100. Adding a 50a receptacle may push it closer to doing that but a load calculation would probably be a much more scientific approach.

I'm not giving electrical advice here, I'm not an electrician. But if it were me, I'd have the electrician install the 14/50 outlet. If worse comes to worse, you can downgrade to a 14/30 outlet/breaker and you already have the beefier wire installed if the panel gets upgraded at some point in the future so you can go back to 50a. Good luck and welcome to the family!!

 

[jmaddr]

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?

Not possible if you are using the included mobile charger that comes with your new Tesla. That included charger can only physically pull 32A. Further, you can set the car to pull lower, and the time of day it pulls that power. That setting has been known to “reset” with some updates, but you will never exceed the physical capacity of the mobile charger (32A). It Is impossible to draw more unless you get an older Gen 1 mobile charger which can pull 40A. Gen 1s are not manufactured any longer.
My advice, listen to your insured and certified electrician first, and run the wire gauge for a 50A circuit if you can afford it. You can change the breaker and the outlet for pennies as the wire run is the most expensive part.

 

[EVer Hopeful]

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.

I installed the HPWC and downrated it to 30A - precisely because 30A was what a Load Calculation suggested would be appropriate

I just plug her in when I get home and she's ready by the time I get up. Easy peasy

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

You might have misheard him there; maybe he said "should" instead of "would" . . .

 

[MacO512]

Personally I would probably run wire that supports a 60amp breaker, unless it's a long run with significant extra wire costs. But then I would put in a 14-50 recepticle with a 40 amp breaker.

That way you can easily upgrade to wall charger or such if electrical panel is ever upgraded, you max out the mobile connector now, you won't have someone drawing 50 amps, and you can easily switch to smaller 30amp circuit if you have load issues.

If you have an amp meter clamp see what the ac and other large loads draw first.

 

[Big Earl]

I would go back to the first electrician and ask him if the load calculation supports 32 amp charging on a 40 amp circuit (NEMA 14-50 with 40 amp breaker instead of 50). If he says yes, do that. If he says no, install the NEMA 14-30 and call it a day with 24 amp charging.

Also, it would be helpful if you posted a picture of your panel. Easy enough to do from a cell phone with this forum interface.

 

[Fourdoor]

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.

Keep in mind that even if you install a 50 amp breaker on a NEMA 14-50 outlet the most the car will draw using the included Tesla Mobile Connector is 32 amps. The load calculation on that circuit would use 50 amps because that is what it says on the breaker... but the most that circuit will ever draw with your included Tesla Mobil Connector is 32 amps. Now, if in a few years you sell the house and the new owner of the house plugs in his high power welder to that plug he could over load the main breaker. Your choice if you are concerned about future owners of your house or not but a professional electrician has to take the possible future use of the circuit into account, not just your planned use.

Keith

 

[MacO512]

If you're ok with trickle charge as a minimum and you have a supercharger very close, I would go with the 30a receptacle if you're nervous. You all do realize it's possible to overload a panel with just what you have in it now right? Go ahead and add up all the numbers on the breakers- I bet you bottom dollar it'll add up to way more than 100. Adding a 50a receptacle may push it closer to doing that but a load calculation would probably be a much more scientific approach.

I'm not giving electrical advice here, I'm not an electrician. But if it were me, I'd have the electrician install the 14/50 outlet. If worse comes to worse, you can downgrade to a 14/30 outlet/breaker and you already have the beefier wire installed if the panel gets upgraded at some point in the future so you can go back to 50a. Good luck and welcome to the family!!

This first paragraph is ridiculous. Darn near every house has way more amps in breakers than main. Otherwise we'd be installing 600 amp service in houses and wasting many thousands of dollars. Most homes most of the time are only using a fraction of the main breaker. Electricians do a load calculation to properly size electrical service.

 

[Feathermerchan]

As a point of reference, we are retired but do drive a bit. We have the charge set to 20A on both vehicles and charge once a week mostly. There are SC in the area if we need them.
AFAIK no EV uses the neutral that is required for a 14-50 or 14-30. A 6-50 or 6-30 will work and requires less wire. This can save you $.
I installed two 6-50's and have two Gen1 UMC's which allow me to charge my model 3 and Y at up to 40A but have found that we only need 20A just about all the time.

 

[EVer Hopeful]

I would put in a 14-50 recepticle with a 40 amp breaker.

I'm waiting for someone who actually knows what they're saying here (unlike me) to point out that a 40A breaker on a circuit with a 50A outlet is ... not a good idea

You (I probably mean the OP) just spent way over fifty grand on the vehicle, so just drop a few more bucks into doing it properly and get the wall connector. You can run that at whatever amperage you want, I have mine set to 30A (which btw, is more than enough) because I had a load calculation done which suggested 30 was the way to go. It made the wire run cheaper too and puts less stress on the equipment

I sleep for maybe eight hours a night, so guarantee I won't be needing the vehicle for at least those hours

 

[jcanoe]

I'm waiting for someone who actually knows what they're saying here (unlike me) to point out that a 40A breaker on a circuit with a 50A outlet is ... not a good idea

It is fine; If there is insufficient capacity for adding a 50A circuit with a 14-50 receptacle the NEC allows for using a 40A circuit breaker with the 14-50 receptacle. The receptacle should be clearly labeled as 40A. (The reasoning is unlike 15/20/30/50A circuits there is no specific plug and receptacle specified for 40A.)

 

[EVer Hopeful]

Then I take it back - lol

I understand that logic

Placarding ... I like placarding! - and yes mine is. I did think about adding a requirement for a weekly check to verify it hadn't reset itself, but then I'd need a log sheet to record the observations (which then required an audit process), and even for me that seemed a little over the top




... and this is because I know nobody here believes me

 

[rudholm]

I second (third? fourth?) the suggestion to put in a 14-50 or 6-50 receptacle (as has been pointed out, the 6-50 omits the unnecessary Neutral conductor, saving you money on wire) and put it on a 40 amp breaker. Use thicker wire than you need so that if you ever upgrade the main panel, you can convert this circuit to a higher amperage capacity circuit by just changing the breaker. (probably 8 or 6 gauge). That way you could go to the full 50 amps the outlet supports, or max out a Tesla Wall Connector with a 60 amp circuit.

Put a label on the de-rated 6-50 or 14-50 outlet that says "40A Maximum, 32A Max Continuous Load". As has been pointed out, this is allowed per the electric code. I also agree with the poster who said not to worry too much about the numerous breakers you already have, as that's not how capacity planning works.

 

[Feathermerchan]

For that 50A breaker you'd want #6 wire. I think #6 is code anyway. With my setup I can charge up to 40A. At 40A that #6 gets pretty warm.
As for the 8 hours sleeping, Charging at 24A (80% of a 30A circuit) for 8 hours would be about
(8 X 24 X 240) ÷ 1,000 = 46 kWh. At 300Wh/mile that's about 150 miles.

 

[jcanoe]

When specifying wire gauge, for the maximum amperage the type of wire matters. #8 gauge NM-B (i.e. Romex) can support up to 40A. #8 gauge THWN (75C) can support 50A and #8 THHN (90C) can support up to 55A. #6 gauge would be adequate for up to 50A with NM-B, 65A with THWN (75C) and 75A with THHN (90C) wire.

There are other considerations including the length of the wire and if the wire will be run through an attic where the temperature inside the attic can become quite hot in summer (my attic exceeds 130F, probably above 140F at the highest point inside the attic just underneath the roof.)

Cerrowire Resources - Ampacity Charts

 

[Feathermerchan]

What jcanoe said is correct. Allowable wire amperage is dependent on the temperature capability of the insulation and the conditions in which it is installed. The requirement is to not exceed the temperature limits of the insulation.

 

[EVer Hopeful]

As for the 8 hours sleeping, Charging at 24A (80% of a 30A circuit) for 8 hours would be about
(8 X 24 X 240) ÷ 1,000 = 46 kWh. At 300Wh/mile that's about 150 miles.

True, but then comes an hour of breakfast etc etc

Personally I'd like a 60A setup and if we were to move, that'd be a condition, but as it is, 30A is more than enough for the amount of driving (and sleeping) I do

 

[jcanoe]

There are other considerations when configuring a home charging circuit. Assuming that there is adequate capacity then being able to precondition in winter, while plugged in, without using charge from the battery would favor a 50A or 60A circuit. My non-Tesla home charging setup matches the Tesla Gen2 Mobile Connector when fitted with the 14-50 plug adapter. I nominally can charge at 7.7kW, typically 7.5kW rate. This tracks closely with the power used to precondition the Tesla vehicle in cold weather. In my setup a 20 minute preconditioning cycle could use a small % of the battery to precondition even when plugged in. The battery level will recover with an additional 5 or 10 minutes charge.

 

[NotDeadYet]

You're main limiter is current available, so a 240V connection will provide twice the charge at the same current as a 120V. Unless you are trying to avoid installing anything, you do not ever want 120V.

If you are willing to pay the price of a Tesla Wall Charger, it can be programmed to various levels lower than maximum to accommodate
lower current limitations. The Tesla Wall Charger is more convenient to use. None of the NEMA connectors are designed for repeated plugging and unplugging.

 

[turnbowm]

For a 100A service panel, 30A outlet would be my call. I don't think a 50A outlet would pass inspection.