If load calculation is 121A on a 125amp supply with TWC included, is that ok?

[terminally_chi]

Hello everyone,

I'm planning to install a Tesla Wall Charger (48A) at my home. My main breaker is 125A. Got a few quotes from various electricians and they all came back to me with various prices and solutions. I'm hoping you could help me out:

• Electrician 1 (who I'm leaning toward to): say my full house load including the EV is 121A, which comes a little too close to 125A. To install just a charger is around $1000, but they strongly suggest adding a Tesla Neurio Kit, which is a load monitoring/meter that can communicate to the charger to lower its output as needed. The total quote is $1800
• Electrician 2: says my full load is well below my main supply, can do it for $1056. Haven't heard back since I request the load calculation
• Electrician 3: Installation is $1000, but says they need to install a DCC Load Balancing unit ($1500) to "acquire full 60A charging" and pass inspection, total is about $2500
• Electrician 4: Need to install a "125a smart switch" next to the breaker panel, then feed the smart switch with 2-pole 60A breaker then to the charger. Says they need this to pass inspection. Quote is $2000

It's a bit wild to me that each electrician company comes up with different solutions. I was expecting they all have a similar scope of work, just different prices.

I did some load calculation myself based on this guide - How Much Electricity Do I Need for My Home? and got 93.8A without the Charger, and 117A with the charger included. I talked with the Electrician 1 and he told me he did optimal calculation method at first, but said that per code - for 125A supply, if the load result is below 100A, they can't use it. So he opt for a standard method (using sq footage of the house *3 and some other numbers). Also said that if I don't want to use the Neurio kit, they can do it without, and it will pass inspection, just that the kit option would be a better and safer choice

Who would you go with in this case? For the record, I don't really use my oven (40A breaker), maybe 1-2 times a year and I'm planning to only charge from 12am - 6am, so no dryer running as well. My stove and heat are gas. I'm wondering if I really do need a meter or load balancing unit for my use case. Should I be worry about only 4A buffer between my load and the supply? or am i worrying over nothing here? Anyone with a 125A main panel can help shed some light here?

I'm located in WA, US if that helps

tl;dr: main panel is 125A, full load calculaton is 117-121A, will i be ok?

 

[Cosmacelf]

Post a picture of your panel and we can give you our take. Or tell us your house sq ft and tell us what all the double poll breakers are connected to and their amp rating.

 

[Cosmacelf]

A Tesla Neurio Kit is normally installed with a power wall. Do you have solar and a power wall there?

 

[Eric33432]

Wow, that is a lot of different options. My first thought is that 48 amps might be too much for a 125 amp panel depending on your home's electrical requirements, but if it is the Neurio is a great way to make it work.

Edit: can a Neurio work with the Tesla Wall Connector?

You can't say you rarely use the oven, will only charge after midnight when the dryer is not being used, etc., to try and convince your building department to let you install something that will not meet their code requirements. They do not take this into consideration because they have no idea who will be living in a house for the long term.

If you really have to have 48 amp charging I would go with electrician 1's quote.

But what I would do is install the wall connector on a 50 amp circuit and commission the wall connector for 40 amp charging without the Neurio. My son and his girl friend each have their own Model 3 (a Performance model and a RWD) and share a single wall connector connected to their electrical system with a 50 amp circuit breaker, and charge at 40 amps for the Performance and 32 amps for the RWD and have no problems keeping both cars charged.

If 50 amps will not satisfy your building department, a 40 amp circuit might, which will give you 32 amps of charging, which for almost all people will still be adequate.

If you go with 50 or 40 amp circuits (for 40 or 32 amp charging) and later find you must have 60 amp (48 amp charging) you can always add the Neurio later. If I thought I might do this, I would use the appropriate size wire for 60 amps which is #6 copper if running individual wires in conduit (or MC cable), or #4 if running NM cable (a/k/a Romex). If running wires in conduit the ground should be #10 copper wire. That way, you would not have to install new wire.

Curious if the first electrician is going to get a permit? A lot of them don't. A friend of mine in North Carolina had a an electrician on the Tesla recommended list install two wall connectors and he did not bother to get a permit or have them inspected.

Good luck and let us know how it goes!

 

[davewill]

If it will pass inspection without the extra monitoring device, then I'd say install without it. You can always install a 60a circuit and be ready to downgrade to 50a or 40a if the inspector says no.

 

[terminally_chi]

Post a picture of your panel and we can give you our take. Or tell us your house sq ft and tell us what all the double poll breakers are connected to and their amp rating.

Here's a picture of my panel. Yeah I tried to research for neurio kit and most I can find is application with power wall & solar, which I don't have.

According to Electrician 1, this is a new solution that they were given by Tesla (they went down to a Tesla installer convention of some sort last month)

 

[Cosmacelf]

So, after seeing that panel (which isn’t overloaded or anything), I would go with electrician 1, just put in a 50A circuit for the Wall Connector (charge at 40A rather than 48A, you won’t notice the difference), don’t do the Neurio and call it a day.

The problem with saying you’ll only charge at night is that once a year, you’ll need to charge during the day after a long trip or something.

Regardless, you don’t need a load balancer.

 

[terminally_chi]

If I set my charger to 48A but adjust the charge setting on my car to 40A, would that accomplish the same thing? I'd prefer the flexibility if that's achievable, instead of just hardwire limit the charger itself. Thanks so much for all the replies

 

[jcanoe]

You don't set the charging amperage on the Tesla Wall Connector. You provision the Tesla Wall Connector for the circuit, i.e. 50A or 60A. The Wall Connector automatically calculates/follows the 80% rule and limits the maximum amperage accordingly, i.e. 40A on a 50 amp circuit or 48A on a 60 amp circuit. You cannot safely provision the Wall Connector for higher than the installed circuit (wiring and breaker.) That would be a clear code violation and an invitation to an electrical fire.

You can set the charging amperage in the Tesla vehicle or Tesla app however you like but the charging amperage used will never exceed the maximum charging amperage as controlled by the Wall Connector (or Mobile Connector if using a plug.) You can set the charging amperage using the Tesla app or the Tesla charging screen to be lower than the maximum for the circuit if you want to. (The ability for the user to limit the charging amperage does not apply to Supercharging.)

 

[Sophias_dad]

I'm still trying to figure out how OP gets from "93.8A without the Charger, and 117A with the charger included. ", for a 48A charger. That's only 23.8A of difference.

I'd definitely want to avoid extra >stuff<, so I'd go with @Cosmacelf's idea of electrician 1 and wire it for a 50 amp breaker/40 amp charging. People seldom need more than 24 amp charging anyway once they actually look at their usage. Even 12 amp 240V is ~10 mi/hr, or 100 miles overnight. Do you regularly drive more than 100 miles a day? Make it 24A, and that's 200 miles a day!

 

[terminally_chi]

You don't set the charging amperage on the Tesla Wall Connector. You provision the Tesla Wall Connector for the circuit, i.e. 50A or 60A. The Wall Connector automatically calculates/follows the 80% rule and limits the maximum amperage accordingly, i.e. 40A on a 50 amp circuit or 48A on a 60 amp circuit. You cannot safely provision the Wall Connector for higher than the installed circuit (wiring and breaker.) That would be a clear code violation and an invitation to an electrical fire.

You can set the charging amperage in the Tesla vehicle or Tesla app however you like but the charging amperage used will never exceed the maximum charging amperage as controlled by the Wall Connector (or Mobile Connector if using a plug.) You can set the charging amperage using the Tesla app or the Tesla charging screen to be lower than the maximum for the circuit if you want to. (The ability for the user to limit the charging amperage does not apply to Supercharging.)

Yeah some I'm planning to provision the charger to 48A (60a breaker), but when charging at home, I tell my car to only charge at 40a. Does that tell the charger to only use 40a to charge my car? Or not really?

I think 40a would be plenty for my everyday use, I just like to keep 48a open in case of any events where I need that extra 1hour faster charging for some reason. Because based on load calculations, even if I have everything + the charger turned on, I'll still be at 121a. I just like to keep a bigger buffer between my full load and main breaker for everyday usage.

 

[terminally_chi]

I'm still trying to figure out how OP gets from "93.8A without the Charger, and 117A with the charger included. ", for a 48A charger. That's only 23.8A of difference.

I'd definitely want to avoid extra >stuff<, so I'd go with @Cosmacelf's idea of electrician 1 and wire it for a 50 amp breaker/40 amp charging. People seldom need more than 24 amp charging anyway once they actually look at their usage. Even 12 amp 240V is ~10 mi/hr, or 100 miles overnight. Do you regularly drive more than 100 miles a day? Make it 24A, and that's 200 miles a day!

Yeah that just come out like after I follow this guide, but what do I know How Much Electricity Do I Need for My Home?

 

[Sophias_dad]

when charging at home, I tell my car to only charge at 40a. Does that tell the charger to only use 40a to charge my car? Or not really?

It will indeed only use 40A to charge your car if the charger is provisioned for 48A and the car has been told to use only 40. The downside is that on occasion the car will just 'forget' that 40 and take 48 instead(usually after a firmware update). That's usually not a big problem. It might be worth noting that that setting is saved with reference to the charger or location(I don't recall which), so if you drive do a 48A L2 charger down the street, the car will take 48A when there, but auto-reset to 40 when you come home.

Unless I misread, you don't really have an extra 48 in that panel to provision. Just looking at 240V loads, I see 40 amps of range and 30 amps of dryer. Assuming they are both running(and using their max, which is admittedly unlikely), you have 70 of the 125 already claimed. Throw in a microwave(15A), refrigerator(10A) and dishwasher(10A), and you are at 35 more amps, or 105 of the 125, if we assume all those appliances are running AND on the same leg of the supply, which is really a not-good assumption since the refrigerator and dishwasher are specifically NOT on the same leg, so you might have 95A in use. You also haven't turned anything else on, like the 20A furnace or any lighting at all.

 

[jcanoe]

Yeah some I'm planning to provision the charger to 48A (60a breaker), but when charging at home, I tell my car to only charge at 40a. Does that tell the charger to only use 40a to charge my car? Or not really?

I think 40a would be plenty for my everyday use, I just like to keep 48a open in case of any events where I need that extra 1hour faster charging for some reason. Because based on load calculations, even if I have everything + the charger turned on, I'll still be at 121a. I just like to keep a bigger buffer between my full load and main breaker for everyday usage.

Charging would be limited to 40A if that is what you set in the Tesla app or on the Tesla Model Y Charging Screen. Usually the Tesla Model Y will remember this charging amperage setting for a given location. Sometimes the charging amperage setting is lost and the Tesla Model Y will default back to 48A. This is not an issue since the absolute maximum charging amperage supported by the circuit is always determined by the charging equipment (i.e. Tesla Wall Connector or Mobile Connector) not the vehicle/app setting.

If you find that you don't have sufficient capacity for adding a 60A or 50A charging circuit the Tesla Gen3 Wall Connector can also be configured for use on 40A/30A/20A/15A 240V circuits. 32A charging on a 40A circuit works for me. (Actually it is a 50A circuit but the charging equipment I installed (for a longer 25 foot charging cord) is limited to 32A charging. I am able to add 25 to 27 miles of range to the battery of my 2020 Long Range Model Y per hour when charging. In practice any of the 240V charging amperages would probably be adequate for daily/nightly charging most of the time.

 

[terminally_chi]

It will indeed only use 40A to charge your car if the charger is provisioned for 48A and the car has been told to use only 40. The downside is that on occasion the car will just 'forget' that 40 and take 48 instead(usually after a firmware update). That's usually not a big problem. It might be worth noting that that setting is saved with reference to the charger or location(I don't recall which), so if you drive do a 48A L2 charger down the street, the car will take 48A when there, but auto-reset to 40 when you come home.

Unless I misread, you don't really have an extra 48 in that panel to provision. Just looking at 240V loads, I see 40 amps of range and 30 amps of dryer. Assuming they are both running(and using their max, which is admittedly unlikely), you have 70 of the 125 already claimed. Throw in a microwave(15A), refrigerator(10A) and dishwasher(10A), and you are at 35 more amps, or 105 of the 125, if we assume all those appliances are running AND on the same leg of the supply, which is really a not-good assumption since the refrigerator and dishwasher are specifically NOT on the same leg, so you might have 95A in use. You also haven't turned anything else on, like the 20A furnace or any lighting at all.

You don't actually add all the breaker number on the panel to determine your load. If you do that I'm sure your total breakers amp far exceed your main amp. There's an actual calculation for that and the actual amp you generally pull on the breaker is 80% of the load. That's why I will add a 60a breaker for a 48a draw for the charger. And limit my car charge to 40a just for my peace of mind

The load calculations I've been following is something like this:

Safe Watt = amp x voltage x 80%

Add together the wattage capacity of all general lighting branch circuits.
Add in the wattage rating of all plug-in outlet circuits.
Add in the wattage rating of all permanent appliances (ranges, dryers, water heaters, etc.)
Subtract 10,000.
Multiply this number by .40
Add 10,000.
Look for the full wattage rating of permanent air conditioners, and the wattage rating heating appliances (furnace plus space heaters), then add in whichever is the larger of these two numbers. (You don't heat and cool at the same time, so don't need to add both numbers.)
Divide the total by 240.

The number come out will be your suggested amperage needed to power your house. That's how I came to 117a, which is the same with what the electrician 1 come up with as well until he ran a different calculations that comes out a bit higher -121a

 

[terminally_chi]

Thank you all for your replies. I think I will go ahead with installing a 60a circuit for my charger, but limit my car charge to 40a instead of 48a for my peace of mind. Because even with 48a enabled with everything running at once, I'm at 121a total, which still below 125, I guess I'm just a bit paranoid about this.

 

[Cosmacelf]

Thank you all for your replies. I think I will go ahead with installing a 60a circuit for my charger, but limit my car charge to 40a instead of 48a for my peace of mind. Because even with 48a enabled with everything running at once, I'm at 121a total, which still below 125, I guess I'm just a bit paranoid about this.

That's fine. I guess you want to have the optionality of the occasional 48A charge if you really need to? Otherwise, you'd just install a 50A circuit and commission (tell) the Wall Connector that it is connected to a 50A circuit.

 

[Sophias_dad]

You don't actually add all the breaker number on the panel to determine your load. If you do that I'm sure your total breakers amp far exceed your main amp.

Yes, I did indeed know that! If I did not, I'd be saying something idiotic like there's 217.5 amps of load in that panel right now and you can't add any at all. (That's taking the 435 amps of handles divided by two)

You can reasonably assume there will be times when you'll be using the (range, dryer, furnace, refrigerator) all at once. Might not be frequent, but it may happen. The good thing is that you are pretty much guaranteed to be at home when that happens and your charging is going on at the same time, so if the master breaker trips you'll be able to turn it back on, so your house won't freeze solid(like if you left your car plugged in and flew to Fiji for two weeks).

I still question whether you really NEED anything like 48 amp charging. That's ~350 miles per 8 hours and I seriously hope you don't drive that much.

 

[ATPMSD]

I think I will go ahead with installing a 60a circuit for my charger, but limit my car charge to 40a

Do NOT use the car to limit charging as a permanent solution! Installing a 60a circuit on a 125a panel is really pushing it. You should go with a 50a circuit and configure the wall connector as being on a 50a circuit, this will give you a 40a charge rate.

 

[Sophias_dad]

Add together the wattage capacity of all general lighting branch circuits.
Add in the wattage rating of all plug-in outlet circuits.
Add in the wattage rating of all permanent appliances (ranges, dryers, water heaters, etc.)
Subtract 10,000.
Multiply this number by .40
Add 10,000.
Look for the full wattage rating of permanent air conditioners, and the wattage rating heating appliances (furnace plus space heaters), then add in whichever is the larger of these two numbers. (You don't heat and cool at the same time, so don't need to add both numbers.)
Divide the total by 240.

I'd like to know the actual numbers you used for each of these steps, out of curiosity. I'm getting much larger numbers than you seem to be.