Can I combine 30A and 50A 240V lines?

[Hometheatremaven]

I am having an electrician run a new 50A 240V line to my garage to charge my soon-to-be-received Tesla S. He is doing this when he replaces my existing Zinsco box.
I also have an existing 30A 240V dryer outlet that can be extended to the location of the Tesla plug.

Is there anyway to combine those two power sources to charge quicker? If so, what adapter would I use on the mobile charging cord? Or is there a different way to go?

Thanks.

 

[qwk]

Only the HPWC charges at a greater speed than a 50A receptacle.

 

[Doug_G]

Uh, no. If you want faster charging you need a 100A circuit, an HPWC, and dual chargers in the car.

Just stick with the 50A circuit. You will quickly find it's all you need.

 

[bluetinc]

Hey Hometheatremaven,

Setting aside the issues directly related to combining the circuits, the how, and the costs, the bottom line in this case is that it won't help you very much anyway. When I combine two circuits, the current splits just about evenly. Because of this the smaller circuit will limit you at 80% of the rated current, or 24A. You would then be pulling 24A from both the 30A circuit and the 50A circuit, or 48A total. So, in the end, you might pick up that ability to charge 20% faster.

Peter

 

[Lloyd]

Hey Hometheatremaven,

Setting aside the issues directly related to combining the circuits, the how, and the costs, the bottom line in this case is that it won't help you very much anyway. When I combine two circuits, the current splits just about evenly. Because of this the smaller circuit will limit you at 80% of the rated current, or 24A. You would then be pulling 24A from both the 30A circuit and the 50A circuit, or 48A total. So, in the end, you might pick up that ability to charge 20% faster.

Peter

Ummm NO you can't do that. It is expressly against NEC at sizes < AWG 1/0. You can't guarantee conduction as you think on the two different conductors. One can overheat and start a fire. Setting aside the fact that you said there are issues, this needs to be clear.

 

[FlasherZ]

When I combine two circuits, the current splits just about evenly.

In theory, you *could* do it. It will be far too complex and impractical, though... read up on Ohm's Law and parallel circuits. As Lloyd points out, against the NEC which will invalidate your homeowner's insurance.

50A is generally good enough for anyone, or you'll need to install a bigger circuit w/ HPWC.

 

[Hometheatremaven]

Thanks to everyone. Especially Flasher Z who shamed me into replacing my Zinsco box (fire hazard) with a new one ($2000) and running a new 50A line in conduit under the walkway and into the garage ($1000).
Flasher, maybe I should tell the electrician to send you the bill for the new box Haha!
Anyway the Tesla will charge faster with the new 50A line instead of the 30A dryer line (which would have cost < $100 to extend).
Okay Flasher, I'll only have him bill you $1900

 

[bluetinc]

Hey Flasher,

I'm not sure why you quoted that line, it is what I do see when I do combine circuits. That said, no argument that doing so safely is very very complex and impractical, especially for home use, which I would NEVER recommend.

Peter

In theory, you *could* do it. It will be far too complex and impractical, though... read up on Ohm's Law and parallel circuits. As Lloyd points out, against the NEC which will invalidate your homeowner's insurance.

50A is generally good enough for anyone, or you'll need to install a bigger circuit w/ HPWC.

 

[FlasherZ]

I'm not sure why you quoted that line, it is what I do see when I do combine circuits. That said, no argument that doing so safely is very very complex and impractical, especially for home use, which I would NEVER recommend.

Yes, in hindsight, I can see the confusion on my quote choice. I meant to add on to what you were saying; namely, that in the absence of some complex calculations, specialized hardware and/or specific distances of wire, etc., current will try to divide equally based upon resistance of the conductors. Managing asymmetrical currents across parallel conductors is very very difficult.

On top of that, if you have a failure of one of the conductors it can cause some problems too unless you size things appropriately.

 

[bluetinc]

Agreed!

Yes, in hindsight, I can see the confusion on my quote choice. I meant to add on to what you were saying; namely, that in the absence of some complex calculations, specialized hardware and/or specific distances of wire, etc., current will try to divide equally based upon resistance of the conductors. Managing asymmetrical currents across parallel conductors is very very difficult.

On top of that, if you have a failure of one of the conductors it can cause some problems too unless you size things appropriately.