Expected cost to split existing 50A garage line in 2 and install HPWCs?

[Zaxxon]

Currently we've got a J1772 PHEV using an EVSE hooked to a NEMA 14-50 outlet. Then we've got my Model 3 using the UMC into a 120V 5-15 outlet and stealing the 40A EVSE when a fuller charge is needed. We're getting ready to replace the PHEV with a Model X, so I'm debating whether it makes sense to leave things as they are or move to an improved setup.

The wiring comes into the garage and runs in conduit along the left side wall, ending in the 14-50 outlet. I'd like to split the line where it enters the garage, replace the 14-50 with a HPWC, install another HPWC on the other wall, and add the comms line between the two. So the two HPWCs would share the 50A line and provide a total of 40A of power at any given time.

It seems to me that this should be a relatively inexpensive change (outside of buying the two HPWC) since I'm not looking to upgrade the wiring to the garage and all needed work would take place in the garage, but I'm by no means an electrician. Those of you with more experience in this area, what are your thoughts?

Side note: yes, I'm aware that it'd be ideal to have a beefier line in the garage, but our panel is pretty full and 40A should continue to meet our needs. This is really just about avoiding the need to play musical plugs periodically.

 

[commasign]

That's exactly what I did. Had an Aeroviroment 32amp EVSE which we swapped out for 3 (yes, 3) Tesla Wall Connectors in power-sharing configuration. As you point out, the benefit of this is not having to play musical plugs. We also have a 40amp Tesla Mobile Connector in the 4th garage spot that we can always use for a quicker, un-shared charge.

 

[Zaxxon]

That's exactly what I did. Had an Aeroviroment 32amp EVSE which we swapped out for 3 (yes, 3) Tesla Wall Connectors in power-sharing configuration. As you point out, the benefit of this is not having to play musical plugs. We also have a 40amp Tesla Mobile Connector in the 4th garage spot that we can always use for a quicker, un-shared charge.

Sweet. Any insight into the approximate cost? Ours is just a standard 2-car garage and the cable enters the garage near the center, so shouldn't need anything fancy from a conduit perspective.

 

[miimura]

If you install both Wall Connectors at the current outlet location it should be very inexpensive. However, that probably means that you will have to drag the 20' vehicle cables all around to reach both cars, inconveniencing you every time you use it. Putting at least one Wall Connector close to the second car's charge port location would involve more conduit and wiring. It would be hard to say how much it would cost without knowing how many bends and how many feet of wire and conduit it would require.

 

[commasign]

Sweet. Any insight into the approximate cost? Ours is just a standard 2-car garage and the cable enters the garage near the center, so shouldn't need anything fancy from a conduit perspective.

Should only be a few hundred, depending on how much new conduit is needed.

 

[Zaxxon]

Here's a terrible illustration using mad mspaint skills. Model X on the left, with existing 14-50 near its rear-left. That'd become HPWC #1. Wiring entry point is at the base of the wall in front of the X. Existing conduit in black from that point to the 14-50. New conduit that'd be needed is shown in red, leading to location of new HPWC #2, near Model 3's rear-right. I haven't taken specific measurements, but it's a standard (pretty tight) 2-car garage.

 

[LoL Rick]

@Zaxxon I had a single HPWC replaced with a pair that are sharing a 100 amp line. The old one was just a couple feet from here so the run was very short. Here is a picture of the setup along with the relevant sections of the invoice. It seemed a little steep to me but I didn't argue since this electrician has done work for me several times before and they were always fair.

 

[jmaddr]

Do you know the wire guage today? There might be a chance to up the 40a breaker to 60 or even higher to help when you share.

For the cost, it’s impossible to quote a round number. The cost is simply gonna be material cost plus labor. Either three or 4 wire run (I’ll assume you have 4 wire now for the 14-50 but the HPWC only needs 3 wire). In my location, 6 guage ranges from 0.50/ft to $1/ft. You may get by with 8 guage for 40a but it’s all dependent on distance. Multiply the per foot length by either three or four co doctors and add 20-40 for misc supplies and that will be material. Man hours is entirely dependent upon your particular installation.

 

[Zaxxon]

Do you know the wire guage today? There might be a chance to up the 40a breaker to 60 or even higher to help when you share.

Here's a photo from the crawl space where the wiring is running from the panel on the back of the house through the crawl space to the entry point in the garage:

For the cost, it’s impossible to quote a round number. The cost is simply gonna be material cost plus labor. Either three or 4 wire run (I’ll assume you have 4 wire now for the 14-50 but the HPWC only needs 3 wire). In my location, 6 guage ranges from 0.50/ft to $1/ft. You may get by with 8 guage for 40a but it’s all dependent on distance. Multiply the per foot length by either three or four co doctors and add 20-40 for misc supplies and that will be material. Man hours is entirely dependent upon your particular installation.

Thanks.

 

[Rocky_H]

Here's a terrible illustration using mad mspaint skills. Model X on the left, with existing 14-50 near its rear-left. That'd become HPWC #1. Wiring entry point is at the base of the wall in front of the X. Existing conduit in black from that point to the 14-50. New conduit that'd be needed is shown in red, leading to location of new HPWC #2, near Model 3's rear-right. I haven't taken specific measurements, but it's a standard (pretty tight) 2-car garage.

For the how-to, you would probably put your junction box or sub-panel there at the front wall then. Then you can run the two power connections around the two sides of your garage. Then, the communication twisted pair has to be run directly from one wall connector to the other, which doesn't necessarily have to go around that same path. If it's easier to go across the ceiling or something, that would be fine. There is kind of a weird requirement that if you run the signal wire in the same conduit along with the power connection wiring, it has have the same insulation voltage rating as the power wire, which is generally 600V. Needless to say, that's a little hard to find in thin twisted pair wire.
Here's the wall connector manual if you haven't looked through it yet. Appendix B is about how to wire up the load sharing setups.
https://www.tesla.com/sites/default/files/downloads/wall_connector_installation_manual_80A_en_US.pdf

 

[Zaxxon]

To circle back on this in case anyone else is interested: I got two quotes. One about $1k, the other $700.

Will split the incoming wiring, replace the 14-50 with a HPWC, run line to the other side of the garage and install a slave HPWC, and finally upgrade the 50A breaker to 60A to allow for 48A shared power.

Thanks for everyone's input.

 

[MD-2000]

My only thought was - why go around the garage where the conduit will be in the way, more chances of damage - can you go up and over? Especially if you have an attic area where conduit is not needed, you'll just need conduit up and down again - but you could go along the ceiling or up high on the wall over the garage door also. Most garage doors have plenty of clearance and a foot of front wall to follow. IIRC from the manual, the chargers can be fed from the top too. The NEMA plug box would become a junction box and about a 6-inch conduit to the nearby charger?