35 Amp Breaker?

[martinb8]

Hello,

I see where most people are going with a. 50 amp breaker and then dialing it down to 32 which I think is the max for a a Tesla currently using the mobile charger. My electrician said he could just do a 35 amp breaker and it would save some and my current box is already going to be cutting it close if I tried to use a 50 amp. Any thoughts on this? Not sure why you would really need a 50 amp unless you’re thinking of putting in the actual wall charger. Plus, with the 35, he can run 10 gauge wiring to the outlet. Truth to that? Just trying to gauge it all.

 

[ellett]

Your breaker must be rated so the maximum load is no more than 80% of the breaker rating, i.e. a 32A draw requires a 40A breaker. If your electrician is proposing a lesser margin, find a new electrician. Going out of code will invalidate your homeowner's insurance if you try to make a claim due to an electrical problem.

The Tesla Wall Connector manual, available online, has a table of breaker rating vs load.

 

[martinb8]

Your breaker must be rated so the maximum load is no more than 80% of the breaker rating, i.e. a 32A draw requires a 40A breaker. If your electrician is proposing a lesser margin, find a new electrician. Going out of code will invalidate your homeowner's insurance if you try to make a claim due to an electrical problem.

The Tesla Wall Connector manual, available online, has a table of breaker rating vs load.

Ok. So if he did a 35amp I should set it to 28 max, correct? Which is fine for me. I have zero plans to do the wall connector. Just the mobile one with an attachment so I can get away with less charge, but I need more than the typical 115.

 

[LevelHeaded]

Ok. So if he did a 35amp I should set it to 28 max, correct? Which is fine for me. I have zero plans to do the wall connector. Just the mobile one with an attachment so I can get away with less charge, but I need more than the typical 115.

What receptacle are you using? Not sure it’s up to code to wire a given receptacle for less than the amperage it’s designed to indicate. Other than some exceptions like wiring a NEMA 14-50 with a 40a circuit, etc.

Why not just wire whatever receptacle you choose for its normal amperage? Is he offering some crazy deal to cap it at 35a vs. 40 or 50?

Edit: I see the cost savings mentioned. IMO have a normal configuration installed, 30, 40 or 50a circuit.

 

[martinb8]

What receptacle are you using? Not sure it’s up to code to wire a given receptacle for less than the amperage it’s designed to indicate. Other than some exceptions like wiring a NEMA 14-50 with a 40a circuit, etc.

Why not just wire whatever receptacle you choose for its normal amperage? Is he offering some crazy deal to cap it at 35a vs. 40 or 50?

Edit: I see the cost savings mentioned. IMO have a normal configuration installed, 30, 40 or 50a circuit.

I wouldn’t say a crazy deal, but if he does 35 or less he can use 10 gauge wiring which is a big cost saving. Couple that with me being ok with 20ish miles an hour charge and my current box going to be pushed to the max if much more it’s a good idea to keep it less. Again, I have no plans to ever need faster charging or to install a wall connector.

 

[Watts_Up]

I wouldn’t say a crazy deal, but if he does 35 or less he can use 10 gauge wiring which is a big cost saving. Couple that with me being ok with 20ish miles an hour charge and my current box going to be pushed to the max if much more it’s a good idea to keep it less. Again, I have no plans to ever need faster charging or to install a wall connector.

There is no such 35 A plug. To follow the code you have to choose between

- a NEMA 14-50 - 50A and
- a NEMA 14-30 - 30A plug,​

for whitch Tesla provides UMC adapters.

You should choose 30 A, because of your panel capacity otherwise you will need to upgrade your service.
It's what I have and depending of the length of the line you can select the following wires:

Using stranded copper wires:

AWG 10 - Ampacity 30 Amps
- maximum length for a 3% voltage drop and 30 A is 93 ft.
- maximum length for a 3% voltage drop and 24 A is 116 ft.

AWG 8 - Ampacity 40 Amps
- maximum length for a 3% voltage drop and 30 A is 148 ft.
- maximum length for a 3% voltage drop and 24 A is 185 ft.

AWG 6 - Ampacity 55 Amps
- maximum length for a 3% voltage drop and 30 A is 235 ft.
- maximum length for a 3% voltage drop and 24 A is 294 ft.

Use the following calculation tool from:

Copper Wire Resistance and Voltage Drop and Conductor Size Calculators

Voltage Drop Calc (.xls, 650KB)
​

You should look at the price of the hardware (wires, plugs, circuit breaker, conduit...) on web site like TheHomeDepot.
You will see that the hardware cost is a very small part of the estimate price you will get.
You can think that 90% of the estimate is Labor cost (or mark up profit) for the installer.
The difference of price between using AWG10 instead of AWG8 will be very very small.
It is possible that you will have to use 1" conduit instead of 3/4" but still small difference.
You could use a NEMA 6-50 to avoid using the Neutral wire, but not really cost saving.

 

[pdx_m3s]

Ok. So if he did a 35amp I should set it to 28 max, correct? Which is fine for me. I have zero plans to do the wall connector. Just the mobile one with an attachment so I can get away with less charge, but I need more than the typical 115.

It doesn't work like that. The entire circuit must be built support the max load for the outlet/receptacle. You have to assume that whatever is being plugged into the outlet is going to draw the maximum allowed amps for that receptacle. If you are hardwiring a wall connector, then you can do a 35 amp breaker, but you'd be limited to 28 amp charging. Unless you don't have the main panel capacity, I don't know why anyone would ever do this.

Sounds like you're just using the Mobile Connector. In that case, your options are 30 amp or 50 amp with a NEMA 14-30 or 14-50 outlet, respectively.

 

[animorph]

Relying on the car to dial down your amps is a bad idea because once in a while the car doesn't know where it is and accepts the maximum the connector allows. Mismatching socket and breaker sizes leads to hazardous use cases, especially when selling the house. If the breaker is larger than it should be you could burnout the socket. If the socket is too large you might trip the breaker by plugging in something the socket should suport. You won't be standing by it 24/7.

As far as fitting 50A or 30A into your electrical panel, you should be doing a "load calculation". There are online calculators for this that should give you an idea of what you can do. You may have space for a new breaker but not the capacity to use more current. Don't want to fry your panel.

A 30A socket and 30A circuit would be legit and within your requirements it sounds like. Be sure to chose a socket that fits one of the Tesla adapters for your mobile connector. That will let the connector know the maximum current it is allowed to draw (24A). And it won't be depending on GPS to set that maximum current. If that sounds OK, your current electrician should be adequate. Otherwise neither of you should probably be tackling car charging installations at this time.

 

[martinb8]

Thanks for everyone’s feedback! I’ll push to just do a 30amp and for the NEMA 14-30. Makes the most sense and the safest option given my current load and needs.

 

[pdx_m3s]

Thanks for everyone’s feedback! I’ll push to just do a 30amp and for the NEMA 14-30. Makes the most sense and the safest option given my current load and needs.

Right on. That's exactly what I did due to the small main panel at my old house. The slower charging rate compared to a 50 amp charger was never an issue.

 

[MY-Y]

As for saving money on wire cost, a 75' roll of 6/2 wire at Home Depot is $106.17. This wire supports a 6-50 outlet on a 50 amp breaker. Considering the cost of the car and the electrician's labor cost, the cost difference compared to a smaller wire is in the noise.

As far as panel capacity, have you measured your actual load? My main 200 amp panel has ~350 amps of breakers, yet draws less than 60 amps 99% of the time (pre-Tesla) and averages less than 1/3 of that.

 

[Rocky_H]

Thanks for everyone’s feedback! I’ll push to just do a 30amp and for the NEMA 14-30. Makes the most sense and the safest option given my current load and needs.

Thumbs up to this choice. If there are considerations about capacity in your panel and wanting to go down to 10 gauge wire for cost, fine, those are good considerations, but the 35A circuit doesn't make much sense since there isn't a 35A receptacle type. Making it a 30A with a normal 30A outlet type is just a good straightforward solution.