Home charging - is 100 amp worth an extra $1,200 over 60 amp

Home charging - is 100 amp worth an extra $1,200 over 60 amp

I received a bid for installation of a wall connector. I am bidding it both with 60 amp service and 100 amp service.

The electrician is only adding $350 for the 100 amp breaker and wiring, however he is noting some potential additional costs that the city might require- load calc and a concrete encased trench + $875.

I have a feeling the load calc and concrete-encased trench could be avoided with the 60 amp service so I am debating whether the 100 amp is worth it.

I certainly don't need 100 amp for my model S given my commute. My only reason for kicking it around is that there's a good chance we'll pick up a model 3 at some point.

Having said that, the 60 amp will still charge pretty fast and neither me nor my wife drive that much that we'll absolutely have to be charging at the same time.

I think I answered my own question - no - it's not worth it, but I'm open to any input before I make the decision.

akikiki | October 13, 2018

Bill_ that makes sense too. A little more wire and another breaker in the box would not be a big deal. Do-able too.

murphyS90D | October 14, 2018

Run a 100 amp feed to a sub panel in the garage. Put two 50 amp breakers in the sub panel to feed the two 14-50s.

Yodrak. | October 14, 2018

"Would it not be like having another 120v outlet located on a different wall or different room in the house?"

Not the same. The use of the circuits is different. Even with 120 volt circuits, a distinction in the intended use of a circuit is recognized by having some areas of the house served with 15 amp circuits and other areas served with 20 amp circuits.

At 240 volts, circuits are invariably installed to serve specific individual loads. You don't see an electric dryer and an electric oven on the same circuit on the theory that both won't be used at the same time, but if they are the breaker will trip and save the house.

Going back to 120 volts, high-wattage appliances such as microwave ovens and dishwashers are served by dedicated circuits.

p.c.mcavoy | October 14, 2018

Boonedocks | October 13, 2018
Unless you bought dual chargers it won’t make any difference. 40amp default 80amp if you have dual chargers

@Boonedocks - The 40 amp std/80 am dual configuration only pertains to cars before mid-2016. The refresh front end configuration changed to a 48 amp or 72 amp configuration. Initially the 48 amp was std with the 72 amp optional as an upgrade, but in latter part of 2016 (if I recall timing correct) they went to the 48 amp as the standard on the shorter range batteries (60/70/75) and the 72 amp standard on the 90/100 batteries.

@ann.blackwood - You might want to check the spec of your 90D on whether you have the 48 amp vs. the 72 am on-board charger. If you have the 48 amp then anything more than a 60 amp circuit will not give you any benefit. If you do have a 72 amp, then you will get some increase up to a 90 amp circuit. You will charge 1.5 times faster with a 90-100 amp circuit vs. a 48 amp circuit.

My 50 amp NEMA 14-15 charges at 40 amps which yields a rate of about 30 miles/10% per hour which has been more than sufficient for my needs. Rarely if ever do I have the need to charge mid-day and quickly add 50-100 miles which would be the scenarios where the higher charging rate would be nice.

Yodrak. | October 14, 2018

"My 50 amp NEMA 14-15"


p.c.mcavoy | October 14, 2018

Yodrak - NEMA 14-15 on a 50 amp circuit ... I stated it charges at 40 amps which is the max the UMC can/will/should pull on a 50 amp circuit.

Bill_75D | October 14, 2018

p.c. means 14-50, not 14-15.

p.c.mcavoy | October 14, 2018

Bill_75D is correct ... typo on my park ... twice!

Boonedocks | October 14, 2018

@p.c.mcavoy True...but the OP didn’t say which year he purchased so I was giving him the benefit of doubt.

Rocky_H | October 15, 2018

@akikiki, Quote: “@everybody here, anyone know if (in general) electrical code would allow us to put 2 NEMA 14-50 outlets on the same 50 am circuit? As in one closer to the location of "the second Tesla"?”

That used to be kind of a gray area thing, but as of the 2017 update to NEC, that is absolutely outlawed. It says that any outlet installed for the purpose of EV charging MUST be on its own dedicated circuit.

jpcollins9 | October 16, 2018

I charge two Teslas on one 100 amp service that has about 90 amps available at any given time. I have two 240/50 amp plugs on this one service and plug both cars in and use the timer to set when one starts and when the other starts. If for any reason the first hasn't finished when the timer for the second is released, the second car won't start charging until the first is finished (the plug in on the side of the second car will turn red until the first is finished.) Anyone who requires a dedicated service for each car doesn't understand how the Tesla charging works.

Rocky_H | October 16, 2018

@jpcollins9, Quote: " Anyone who requires a dedicated service for each car doesn't understand how the Tesla charging works."

...or gives a flying &#ck about complying with electric code.

Yodrak. | October 16, 2018

"I charge two Teslas on one 100 amp service "

That's nice, but code aside the question was "anyone know if (in general) electrical code would allow us to put 2 NEMA 14-50 outlets on the same 50 am circuit?" Emphasis on the "50 am(sic) circuit".

akikiki | October 17, 2018

Thanks Rock_H, and I am not trying to argue against code. My question was simply like tihis example One single 50 amp circuit, and its has just one NEMA 14-50 outlet mounted on the south wall and another NEMA 14-50 outlet mounted on the north wall. It nice to be able to use south wall outlet with Tesla 1's UMC and at a different time, Tesla 2 begins charging using its own UMC. Two outlets and two UMCs would allow both cars to be plugged at overnight without visiting or swapping sides in the garage. Tesla 1 could start charging at 8 p.m., and Tesla 2 at 2 a.m.

Permissible without violating code?

Rocky_H | October 17, 2018

@akikiki, I was really, totally clear in my previous message, where I said "absolutely outlawed", so I'll just copy and paste it again:

"That used to be kind of a gray area thing, but as of the 2017 update to NEC, that is absolutely outlawed. It says that any outlet installed for the purpose of EV charging MUST be on its own dedicated circuit."

I do know a guy here in my town that has that exact situation you just described, with two 14-50 outlets on the same 50A circuit to charge their two Teslas, intending it to be at different times, but they have conflicted and tripped the breaker a time or two. That is the very thing that the NEC wants to avoid, so as I mentioned, they specifically and absolutely disallowed that from ever being done.

Bill_75D | October 17, 2018

"Permissible without violating code?"


Rocky_H | October 17, 2018

@akikiki, When I mentioned my friend setting that up, he did that back in 2012, when it used to not be forbidden by code. They allowed that type of situation for things like if you have one welder in a workshop, and you might need to move it from one side of the shop to the other, so you have an outlet on each wall.

But with a lot of stuff that was added in 2017, with a whole dedicated section of electric vehicle charging, they closed that loophole. It's one outlet, period.

akikiki | October 17, 2018

Rocly, Bill, Thanks. Got it. :)

milesbb | October 18, 2018

The 2017 code that does not allow two outlets is NEC 625-40.

murphyS90D | October 18, 2018

Just because the 2017 code exists does not mean that your location is using that code.

PA is still using the 2008 version of the code.

tomyip | December 8, 2018

Correct me if I'm wrong, looking at the charging speed chart:

It appears there's no speed gain if someone dial up their charger beyond 60 amps. If so why is the charger having an option to charge above 60 amps?

I'm having this question because I'm thinking to upgrade the circuits to support a wall charger. Thanks!

tes-s | December 8, 2018

Teslas have the ability to charge at 40, 48, 72, or 80 amps AC depending on the vehicle.

Mark K | December 9, 2018

I bought two Model S cars and equipped both with twin chargers. So they take in 80 amps, and I installed 100 amp breakers to handle it.

At the moment, 72 amps is the max config.

I’m hoping they push it up to 80 or 100 amps when they refresh the Model S.

The faster charging in your driveway is really nice, when you come home from a trip and then want to use your car again quickly.

Adds a mile a minute, which is awesome.

bp | December 9, 2018

For overnight charging, assuming the charge is typically kept between 10-90%, a 30 or 50 amp circuit should be enough for most charging.

We have an HPWC on a 100A circuit that used to our charge our 2012 S P85 at 80A, and is now charging our 2017 S 100D at 48A - and haven't had any problems in recharging overnight. Our 2018 X 100D can charge at up to 72A, but we have it usually connected to a 14-50 outlet and only charge it at 40A - and that's fast enough for overnight charging.

Assuming charging is primarily done overnight, there really isn't a need for charging at 72 or 80 amps, and wouldn't be surprised for Tesla to shift away from that, such as the Gen 2 UMC's that only charge to 32A.

milesbb | December 11, 2018

@murphyS90D, Your link is old, Reviewed: 6/19/2016. PA is now under 2014 code and Philadelphia is under 2017. This site appears to be up to date for all states:

ATCRomes | December 12, 2018

Unless you need what Mark K described a couple posts prior, I have been charging on a single charger equipped 2013 Model S for 5 years without ever even thinking about needing faster charging.

Prioris9 | June 20, 2019

Just got a 100amp Tesla charger in today. Model S 60 2013.
Dual chargers so it goes to 80amps and 57 miles per hour.
What I dont understand is the cost. Is it less drop to a lower amperage and charge longer or just go to 80, assuming either way it's done during off peak.

murphyS90D | June 21, 2019

It depends on the length of the run and the size of the wire. Monitor the voltage in the car charging display as charging starts and what it drops to at 80 amps. The higher the current goes the higher the heating in the wire will be. Heating in the wire is lost energy unless the entire run is inside of the house and you live where it gets cold in the winter.

My run is 75 feet. I installed #2 wire because of the length of the run. When my PV solar panels are producing the voltage goes to 246 volts. At 50 amps the voltage at the car drops to 240 volts. That is where I do most of my charging. The 50 amps is split to 25 amps through each charger in the car.

6 volts times 50 amps means 300 watts is being lost to heating the wire. That is not included in the kW display in the car but it is included in the electric bill.

Side note on a previous comment about solar.
My solar ties in at the main disconnect which is outside of the house just after the meters. It has no effect on my main panel inside of the house. Connecting solar via a breaker in the main panel, in a grid tied system, is the wrong way to do it IMHO as an electrical engineer.

reyesozaeta | August 21, 2019

Consulted an electrician to install my charger for my Model X. The main panel is on the same side where we plan to install the charger. He said I don’t need a disconnect since the main breaker in on “line of sight”. The main breaker will serve as my disconnect? Any thoughts. Also debating between 100A vs 60A

murphyS90D | August 21, 2019

Put in the 100 amp circuit. The larger wire size will mean less voltage drop ( wasted power) even at 60 amps.
If they are that close together the difference in wire cost should be minimal.

The cost for my wire was $399. Three 100' lengths (red, black, white) of #2 and one 100' length of green #8.