2x Wallcharger + Subpanel Circuit Breaker sizing?

[PO44O]

Was recommended to crosspost this into correct subforum:

Hi everyone. Im very close to having everything ready and need help solving the missing piece.

I currently have 6-3 Romex running to a 14-50 NEMA outlet.

I will be replacing that outlet with a subpanel. Throwing on two seperate breakers which will be used to run two Tesla Wall Connectors. I know Ill be limited to 40A and want to split it 20A/20A when both my MY and M3 are charging at the dame time.

My question is..
1. what subpanel size should I buy?
2.what size of should those two breakers inside the subpanels be?

Thank you.

 

[miimura]

1. A 100A panel is cheap and I don't see any reason to go smaller.
2. Each breaker should be 50A because that's the size of the upstream breaker. That way you can use the full capacity for a single car charging. You could use a smaller one, but why would you?

Be sure to properly configure Power Sharing when you commission the Wall Connectors.

I gave some sample parts for this exact situation in this other thread:

Charging two Teslas

@athostmadsen - Buy two of these, hire a "Tesla Certified Installer" and have them set up Group Power Management. This way you won't burn your house down.

teslamotorsclub.com

 

[PO44O]

1. A 100A panel is cheap and I don't see any reason to go smaller.
2. Each breaker should be 50A because that's the size of the upstream breaker. That way you can use the full capacity for a single car charging. You could use a smaller one, but why would you?

Be sure to properly configure Power Sharing when you commission the Wall Connectors.

I gave some sample parts for this exact situation in this other thread:

Charging two Teslas

@athostmadsen - Buy two of these, hire a "Tesla Certified Installer" and have them set up Group Power Management. This way you won't burn your house down.

teslamotorsclub.com

Thanks for the direct answer!

 

[PO44O]

1. A 100A panel is cheap and I don't see any reason to go smaller.
2. Each breaker should be 50A because that's the size of the upstream breaker. That way you can use the full capacity for a single car charging. You could use a smaller one, but why would you?

Be sure to properly configure Power Sharing when you commission the Wall Connectors.

I gave some sample parts for this exact situation in this other thread:

Charging two Teslas

@athostmadsen - Buy two of these, hire a "Tesla Certified Installer" and have them set up Group Power Management. This way you won't burn your house down.

teslamotorsclub.com

Just to be sure. I have a 50A breaker on the main paneling pulling to the said nema 14-50. Wouldnt the 100A subpanel never trip? I thought 100A subpanel comes with a 100A breaker installed on it or does 100A just mainly tell you how big the real estate of the panel is?

 

[jjrandorin]

Just to be sure. I have a 50A breaker on the main paneling pulling to the said nema 14-50. Wouldnt the 100A subpanel never trip? I thought 100A subpanel comes with a 100A breaker installed on it or does 100A just mainly tell you how big the real estate of the panel is?

Someone will correct me if I am incorrect here (as I mentioned I am not an electrician, and we have many members here who are very experienced with electrical setups)....

With the above being said, you dont need the breaker for the sub panel to trip, you need the individual breakers in that sub panel to trip. I dont think Its any different than your main panel, which probably has something like a 200amp (or possibly more service) with multiple breakers of various sizes in it.

I dont have a sub panel at my house, but this is how I believe it works.

 

[MN-MS100D]

Correct. Install a Main Lugs Only (MLO) panel, not a Main Circuit Breaker (MCB) panel. Keep the neutral separated from the grounds at the sub panel. No N-G bond.

 

[miimura]

Just to be sure. I have a 50A breaker on the main paneling pulling to the said nema 14-50. Wouldnt the 100A subpanel never trip? I thought 100A subpanel comes with a 100A breaker installed on it or does 100A just mainly tell you how big the real estate of the panel is?

The rating of the 100A sub panel is telling you the rating of the bus in the panel. The particular panel that I linked has lugs for you land the upstream conductors (ie. the existing wires going to your 14-50 outlet) and doesn't come with any breakers. The breaker (50A) in the main panel is to protect those conductors and any usage in this sub-panel must remain below that level. The Power Sharing feature will do that. You can only over subscribe a panel like this when there is an active power control system managing the total draw. When I say "over subscribe" I mean installing two 50A breakers when the upstream breaker is only 50A. In a normal situation without a power control system, you would have to follow the normal load calculations.

 

[quitepossibly]

If you're using the Tesla Universal Wall Connector (not the Gen 3), you can actually daisy chain the UWC off each other, which would eliminate the need for the subpanel and possibly reduce your installation costs.

The UWC has a second set of terminals inside that allow another UWC to be wired to it.