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.

patrick40363 | April 24, 2018

I have a 40amp for my S and will use it for both S and my 3 when it arrives.

Rocky_H | April 24, 2018

This is all very dependent on what size charger is in the car you are going to use it for, which you have not mentioned. There have been 40, 48, 72, and 80 amp versions of the various chargers throughout the years, and if you only have a small charger in your car, then of course the 100A circuit is going to be a waste.

K-D-R | April 24, 2018

Good point @Rocky_H. This will be a new 100D so 72 amp. I still don't think it's worth it.

tes-s | April 24, 2018

How big is the charger in the car? 40A? 48A? 72A? 80A? Regardless of the circuit size, you are also limited by the size of the charger in the car.

How long will you be in the house? How likely you will get a second EV while you live there?

How big is the service to the house? What are your other major loads? Do you think you have the capacity available? A load calc is a good idea if you think you are close to the capacity of your service or panel.

"Only" adding $350 for the breaker and wiring? Is it a really long run?

If you are thinking about getting another Tesla, I would spend the extra money on wire, but if the city requires load calc and trench simply put in the 60A breaker. Then if you get a second Tesla (or other EV), you could put a second EVSE off the same circuit. With a Tesla, you could add a second Wall Connector on the same circuit. With a different EVSE, you would have to put in a subpanel to split the circuit between the two EVSEs.

A risk is if you do that, they will require the load calc and trench for the 60A circuit, figuring you are going to change the breaker afterwards.

Simple answer: You don't "need" more than 60A for one car. Even with 2 cars sharing a 60A circuit with two Tesla Wall Connectors would be fine for most people most of the time. If your second EV is not a Tesla, it is a bit marginal IMO.

Run4Waffles | April 24, 2018

One option is to install two HPWC’s and they will balance the load if you have to charge both cars on the same night.

It also sounds like you can install two NEMA 14-50 outlets on 50 amp breakers. (?)

The load calculation shouldn’t cost you anything.

Being forward looking, you may want to put the 100 amp in.

We have two NEMA 14-50 outlets on 50 amp breakers.

Run4Waffles | April 24, 2018

Ahhhh, 4 of us typing at the same time. :-)

Pleasanton_Ca | April 24, 2018

2016 Model S P100D. For me it was worth the extra to install the 100 amp...

fepatton | April 25, 2018

I put in a 100A sub-panel, split into two 50A outlets. For now, my wife and I share one outlet, and the other one is used occasionally for my welder. We haven't yet gotten to the point where we both needed a charge at the same time, but we have the capability to go that route in the future. The 50A is plenty to charge a nearly empty 75 in 4-5 hours. We charge after midnight, so I don't care whether it takes 2 hours or 4!

jberkow496 | April 25, 2018

I installed a 40amp with my 100d and because I charge it overnight it is and has been sufficient

ChrisH314 | April 25, 2018

Depends on the voltage, 40A at 240V is more than twice 40A at 110V. And what you need. Will you really need to charge up very fast at home very often, i.e. do you go out already charged up, drive 400km, come home, and want to charge up and get out again as quickly as possible? My home charging is limited to 32 amps single phase and has never caused me the slightest problem over the last 3 years. I always charge at night (cheaper), and that's plenty, ~ 10 hours. However, I'm in Australia and mine is 240V = ~ 7.5kW.

BarryQ | April 25, 2018

Don't waste your money on the 100 amp.

SUN 2 DRV | April 25, 2018

60 amp is plenty for one car. 100 amp would be nice for two cars.

"city MIGHT require" well that's the key point, does the city actually require it or not?

I installed 100 amp for my 2013 MS, and feel it was worth it for the occasional times I need a faster charge at home. Most days I charge at 50 amps to fit within my ToU window and finish in time for my commute.

Haggy | April 25, 2018

If you go with 60A, then it's a moot point unless you have one of the higher amperage chargers. If you get a second EV, you could add a second wall charger on the same circuit and the two can communicate with each other.

Is it likely that if you have two EVs that both would get heavy use on the same day, or is it more likely that they will have typical use on most days and one car would be used for longer trips, or things you'd be more likely to do with a spouse? If your typical use isn't out of the range of what most people use, then even if one car needs more charge and the other doesn't, you'd probably be fine with 60A.

At 60A, a Model 3 will add 44 miles of range in an hour. With a Model S, it would be 34. So if each needed the same eight hour charging time, you'd be able to add 136 miles of range to the Model S and 176 to the Model 3. If it's more lopsided, such as one of them going a more typical 40 miles, then one might go for under an hour and you'd still be able to take a Model 3 with no range left and get up to 90% by morning with time to spare.

It would really come down to the balance of how cars are used, how likely it is that both would be used heavily on the same day (and would need a complete charge for the next day), and which chargers and what battery sizes you will have.

Hart | April 25, 2018


K-D-R | April 25, 2018

Thanks for the input everyone. I decided to do the 60amp. Even if/when we add a second Tesla we dont do cover big miles on the same day.

reed_lewis | April 26, 2018

I charge my 75D Model S on a very slow 30 amp/240V J-1772 connector that I used for a different car before. I have never had the need for faster charging, and I drive 80 miles round trip every day to and from work. Of course it helps to have charging at work also. But in 17 months and almost 35,000 miles there has never been the case where I did not have enough charge to drive wherever I needed to.

Rocky_H | April 26, 2018

@Haggy +1 Good of you to mention that. 60A will still cover two cars well with the dynamically allocated charging of two wall connectors.

milesbb | April 26, 2018

Fairly familiar with the Code. I do not believe changing from a 60 to 100 amp circuit would add the concrete encased requirement. I believe the city would require the load calc's in either case. The load calc's will tell you how large a circuit can be installed without a service upgrade. Doing the load calculations can be time consuming and requires expertise. Doing the load calculations has an associated cost.

Andrew_OH_70D | April 29, 2018

There are several of us who have two Teslas. Why hasn't Tesla developed a two corded HPWC with software to charge one car and automatically switch to charge the second car? That way, you only need one circuit. With a 100 amp circuit, each car will charge very quickly.

murphyS90D | April 29, 2018
philgrocks | April 29, 2018

I think it's worth it to future proof your possible future of having two EV. As pointed out by murphyS90D... Getting two of the HPWC is nice because they will talk and share the circuit.

With two 48A charges possible with two cars. With the 100A circuit you could charge both with 80A using a 100A circuit (40A per car) which is pretty nice.

With 60A circuit, you could only charge two cars 48A combined... So 24A per car. Would be OK, but not as nice. Seems to me that if you believe your going to get two EV at some point I would put in 100A.

luckyluciano | April 29, 2018

One of the big issues with EV’s is the long charge times. It’s up to you if you can afford to inconvenience yourself for a lousy $1.200 dollars. I could not. I would have paid more for shorter charge times. Especially in the winter when you will consume far more energy and be left with a much more depleted battery.

Can you afford to come home to consumed battery and wait multiple hours to be charged up again. I could not.

In the long run, I believe most serious EV owners will need to upgrade their electrical systems to be both more powerful and efficient. A small price to pay for the benefits of driving the best car in the world on renewable energy.

tes-s | April 29, 2018

Most people have been able to install home charging without upgrading their electrical service. Overnight charging is not that big a load - even for two cars.

Rocky_H | April 30, 2018

@luckyluciano, Quote: " It’s up to you if you can afford to inconvenience yourself for a lousy $1.200 dollars. "

You're making quite an assumption that getting anything less than the biggest thing you can possibly get is "inconveniencing". People have different levels of needs, and many people could go the rest of their lives with the 60A circuit and never be inconvenienced at all. I would consider it kind of inconvenient to lose $1,200 of my own real money for something that never did anything for me.

CraigW | April 30, 2018

Sorry but a NEMA 14-50 plug is good enough to handle both a Model S and a Model 3 - just charge them on alternating nights. Sure all this stuff is doable, but - except for very specific circumstances - why spend more to say you have a bigger charger? Sounds like a lot of other male challenges to me.

johnyi | April 30, 2018

Related question. My electrician says I can go as high as 80A to max out my 200A panel. Assuming a second EV may eventually be in my future, how much nicer would 2 HPWC's sharing an 80A circuit be compared to a 60A circuit? Yeah bigger is always better, but the chances of both cars being drained is nil, and most nights each will have only been used for 40-50 miles. Looking for real world experience from those that own 2 Tesla's now. I'm also a little anxious about leaving myself no spare capacity at all for the house.

tes-s | April 30, 2018

How much more expensive is an 80A curcuit compared to a 60A circuit? If you need capacity for something else, you can always put a smaller breaker in for the EV circuit.

johnyi | April 30, 2018

I don't know yet. I'm assuming it will require thicker wires, so probably $100-200 depending which garage bay I decide to power up. But that's a good idea about downgrading the circuit later if needed.

tes-s | April 30, 2018

Copper wire for 80A (4 gauge) vs 60A (6 gauge) should not cost that much more.

danbry39 | April 30, 2018

We have an S and 3 and have no problem keeping both charged with a Nema 14-50. Both drive maybe 2-300 miles a week. We're also anticipating getting the Y when it comes out and aren't fretting it.

Haggy | April 30, 2018

I also manage an S and a 3 with one outlet, so far. It's a bit inconvenient having to move the cable each time plus I want to use night rates, so I charge every other day or balance things based on use. Worst case scenario I could use a supercharger but it's unlikely.

johnyi | May 1, 2018

FWIW they quoted me an extra $75 for the 80A upgrade if I place it near the panel, or $225 if I run it to the other side of the garage (~100ft). Seems kind of high given the wire cost is about the same at Home Depot or Lowes. But 80A CB's cost 3x the 60A, and maybe they are expecting extra labor to fish the bigger wire?

SUN 2 DRV | May 1, 2018

Yes larger cables are definitely harder to wrangle. I used 2 gauge for my HPWC and it took some detailed planning and lots of effort to get it into the 90 deg elbows.

dwarden3 | May 1, 2018

I paid about $300 to have 100 A breaker and HPWC installed. I probably didn't need it but I love having the flexibility of charging at 17 kW (72 A charger in my P100D). I never feel like I'm waiting for my car to charge.

Tropopause | May 1, 2018

I recently installed Tesla solar on my house. Due to the size of the system, Tesla has to downgrade my 200 amp main breaker to 175 Amp. I told them I have a Model 3 on the way to join my MS and plans to install two HPWC’s on a 100 amp beaker. They made a phone call to the boss and assured me I’d be okay but I’ll be upset if I get rejected when the time comes.

I still don’t understand why the installation of a 60 amp solar breaker required a main breaker downgrade from 200 to 175 amps.

GenericWilliam | May 1, 2018

Disclaimer: I am not an electrician - the below is simply my understanding, and may be incomplete, incorrect, etc.

I believe it is to protect the bus bar. The main breaker's primary purpose is to interrupt current flowing over the feeder wires from the utility to the bus bar of your main panel, to protect those utility feeder wires. Not surprisingly, the bus bar on the main panel is typically sized to handle the max load of the main breaker, so if your main panel has a 200A main breaker, the bus bar can likely handle 200A as well.

However, if an alternate energy source (i.e. solar) is feeding power to the bus bar, then their combined power could exceed the bus bar rating. In the extreme case, if you were using 258A of power (199A from the utility and 59A from the solar input), your main breaker wouldn't trip although you'd be far exceeding the bus bar rating (assuming it was rated at 200A).

Hence, de-rating the main breaker might be needed in order to keep the total combined load under the bus bar rating, since that needs protected as well as the utility feeder lines.

NOTE: Some main breaker panels (such as my Siemens MC4040S1200SC installed by SolarCity shortly before the merger) are expressly designed to avoid the need for derating the main breaker.

Short answer: If you're being told by a qualified electrician (who knows your specific situation and equipment) that you would need to derate the main breaker, I'd believe them. However, you might be able to swap in a different main panel that wouldn't require a main breaker derate if that is important to you for your situation.

tes-s | May 2, 2018

That is the reason for the lowering of the main breaker, but I think the simple solution is to put the solar feed at the other end of the bus bar as the main feed. Then even if you draw the max 260A no part of the bus bar is ever carrying more than 200A.

bp | May 2, 2018

We've had an S P85 (dual chargers) since early 2013 and an S 100D (48A charger) for a year. In our garage we have a 100A HPWC and a 14-50.

The P85 is running off the 14-50, getting 40A of charging. The 100D is on the HPWC and getting 48A.

And for overnight charging, both cars are able to get enough charge to be ready by the morning.

Even though the P85 could have charged as high as 80A on the HPWC, in 5 years of ownership, the only time we've needed to charge that fast was in the early days when we did our daily commute, came home in the evening and then left on a road trip that night. We needed a 100% charge to do the road trip, because the supercharger network wasn't in place yet - and we needed to go a long way until the next charger (getting there with about 10 miles of charge left).

For daily driving, for almost all cars, you should be able to get charged overnight (90% charge), even at 32A. And with superchargers, all you really need to have is enough charge to make it to the first supercharger.

The ability to charge faster at home is more to address "range anxiety" than actual need, based on our experience.

I've debated about getting the 72A charger upgrade on our S 100D, to bring it in line with almost all 100D's that were built - but still haven't come up with a need to charge more than 48A at home. The only reason to get a 72A charger is for road trips - if we are able to find a destination charger that can handle more than 48A, and we want to quickly get a charge after getting to the hotel.

Robert21 | May 2, 2018

Have been driving EVs for 17 years and have never needed to charge at > 32A. Our rates drop at 9 PM and if I charge until 7 AM. 10 hours at about 20 MPH = 200 miles. I usually charge a couple times a week when it gets below 100 miles and charge to 250 miles, so only need a max of 150 miles per night.
For the Tesla, I plug the portable charger into the 14-50 socket, and have a separate ChargePoint for the Rav4EV. My advice would be to put in a 50A circuit now, and leave space in the panel for another one later if you drive enough to need 2 chargers.

SUN 2 DRV | May 2, 2018

Part of the answer depends on your mindset about investing in heavy duty tools.

Do you like to get by with the minimum requirements and run things at their maximum ratings for hours on end, unsupervised, in the middle of the night? Or do you normally invest in a heavy duty version of a tool so you're not stressing it as much and hope/expect it to last longer or provide more reliable service.

Lots of supporters of either approach... which are you?

i always advocate installing a Wall Connector for anyone with a garage, and on the largest circuit you can reasonably afford. But that's just my style... I prefer running things at 50% of their rated capacity.

Bill_75D | May 2, 2018

I have a 50 amp 14-50 outlet and set my car to charge at 25 amps. The charging cable gets very warm at 40 amps and is cool at 25 amps. The car still charges to full overnight.

SCCRENDO | May 2, 2018

To those of us who have more than one Tesla this thread is a giggle. Seriously guys. when you invest over $100k in 2 cars why are we debating $600 vs $1200. Pay the extra $600 and you will sleep better at night and be well prepared for multiple Teslas over the next 10 years.

SUN 2 DRV | May 3, 2018

Bill_75D: Yep, half power is good. And that would be 16 amps for the new/current Mobile Connector.

Pleasanton_Ca | May 3, 2018

@SCCRENDO, +1...

ann.blackwood | October 13, 2018

I have an S 90D and am debating the same question. How long will it take to charge on the 60 vs. the 100amp? Thanks much.

Boonedocks | October 13, 2018

Unless you bought dual chargers it won’t make any difference. 40amp default 80amp if you have dual chargers.

60amp = 48amp useable
100amp= 80amp useable

If you are ever contemplating getting another EV definitely go with the 100amp in either case above so you can charge simultaneously and adult the amp draw as necessary.

The new Tesla wall chargers will automatically adjust and share a single 80amp circuit as needed. Works super great in that environment!!

ann.blackwood | October 13, 2018

Thanks. Unlikely to get another EV but wondering if it might make a difference in the future as the cars and charging technologies evolve.

akikiki | October 13, 2018

ann.blackwood. Among the local owners that I have talked to, most have the 14-50 installed and draw 40 amps to charge their car. The remaining charge left in the battery helps us decide at what time we start the charge at night. I have my car set to start charging at 11:00 p.m. And its usually done in 3-3.5 hours worse case. So the car is completely charged before 6 a.m. when I leave home. If for some reason there was less range one evening, it would still finish before 6 a.m. or I could start the charge cycle before 11:00 p.m. We simply learn what's best for our given situations.

akikiki | October 13, 2018

@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"?

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

Why would someone one want to do this? I think if later someone bought a second Tesla, with the second 14-50, they could plug both in, but stagger the charging start up far enough apart time-wise, so the second would would be set to start a hour or more after the first finished?

If both were to try to charge at the same time, the car is going to turn the draw down automatically or the circuit breaker would trip anyway because of the excessive load.

What-a ya think?

Bill_75D | October 13, 2018

I believe code requires a 14-50 to be connected directly to it's own circuit breaker. Two outlets would require two breakers each with it's own wire run.

But I'm no electrician.