What's up with HPWC?

[TechVP]

Here is my situation and resulting questions (please note that I am neither an electrician nor do I know much about electric circuits. I will hire an electrician for the install, right now I am just trying to figure out whether I need to buy one or two HPWCs):

Saw your post, and I have thought through a similar process as yourself.
One or Two HPWC's aside, I would definitely try to justify keeping your NEMA 14-50 as a backup. In case either of your HPWC's fail to charge your car(s) you have the next best option available at all times.

Next up your power budget. You mentioned that 100A is your max. This limit may not let you charge at a 80A continuous load. Fortunately you do have the option of dialing down to the next highest settings on the HPWC.
It may help to explain what limitations you have: Cable gauge, old wiring, distance, Main panel loading, attached or detached garage, etc.

There is a brief section you should read in the FAQ: Home Tesla charging infrastructure Q&A:
Jump to the section titled:
WHAT DO YOU RECOMMEND IF I WANT TO INSTALL AN HPWC AND HAVE A 14-50R AVAILABLE FOR ANOTHER EV OR BACKUP?
I believe this gives you the most flexibility to add a 2nd HWPC. As you are aware, two or more HPWC's share the load, and are designed not exceed the rated current. Having 2 HPWC's appears to be a smarter charging method, from my perspective. If, you can go that route.
Meanwhile, do try to keep a NEMA 14-50 as standby if it will pass inspection.

Comments / Suggestions welcome.

 

[boaterva]

Apologies if this has been explained before, but I could not find the answer reading through this thread. Here is my situation and resulting questions (please note that I am neither an electrician nor do I know much about electric circuits. I will hire an electrician for the install, right now I am just trying to figure out whether I need to buy one or two HPWCs):

Situation:
- I currently have a NEMA 14-50 for my Model S with a regular single charger charging at 40 Amps
- I have a Model X on order with the upgraded 72 Amp charger
- I am planning on getting the HPWC to use the full 72 Amp on the Model X
- The total amperage going to my garage is 100 Amp and don't think I can get it any higher
- Other than a few lights in the garage I don't have anything else going on there

Questions:
- Should I replace the existing NEMA 14-50 with a second HPWC and daisy chain the two HPWCs?
- Or can I have one HPWC on the Model X and the NEMA 14-50 on the Model S?

First, to correct one common 'error' you can't 'daisy chain' HPWC's. You run the same circuit to two of them (where it branches off in a 'Y' fashion. The only 'daisy-chain' is the data connection between the 2 (or 3 or 4, if you like) on the same circuit, which is where the confusion in terminology comes from in the manual. See my pictures (signature) for how mine was done.

Also, ideally (and we can't always have it, of course), you would have two HPWCs for two Teslas, so that both are plugged in all the time, AND a backup 14-50. See how my electrician wired the 14-50 off the subpanel with a 'transfer switch' so that only the circuit to the HPWCs OR the 50 Amp circuit to the 14-50 was hot at any one time. That will satisfy even the most picky inspector!

As for whether you can actually use 80 Amps for the HPWCs, you will need to have your electrician do a load calculation to see if the 100 Amp circuit you want to add is doable. If there is a 100 A feed to the garage and there really is no other load except lighting, it may work. But they need to do an official calculation to be sure. You may need to end up with a 90 A circuit and 72 A to the HPWCs, etc.

 

[davewill]

Yes, you should replace the existing 14-50 with a second HPWC and daisy chain. With only 100a for the whole garage, taking 50a for the 14-50 would not leave you with enough capacity to do 72a charging on the X.

 

[swesson]

Apologies if this has been explained before, but I could not find the answer reading through this thread. Here is my situation and resulting questions (please note that I am neither an electrician nor do I know much about electric circuits. I will hire an electrician for the install, right now I am just trying to figure out whether I need to buy one or two HPWCs):

Situation:
- I currently have a NEMA 14-50 for my Model S with a regular single charger charging at 40 Amps
- I have a Model X on order with the upgraded 72 Amp charger
- I am planning on getting the HPWC to use the full 72 Amp on the Model X
- The total amperage going to my garage is 100 Amp and don't think I can get it any higher
- Other than a few lights in the garage I don't have anything else going on there

Questions:
- Should I replace the existing NEMA 14-50 with a second HPWC and daisy chain the two HPWCs?
- Or can I have one HPWC on the Model X and the NEMA 14-50 on the Model S?

I'm not an electrician, but I have definitely paid to put a couple of their kids through college over the years! From my experience, you will need the 100amp just to drive the 72amp HPWC in your garage. I don't know how much milage both of your cars drive, but in my case, I just got the extra long cable to reach both bays in my garage and use a single charger now for both cars. The 72amp charges so fast that I've never had a problem. You can always pull more power to the garage if you need it, by the way. You would just have to spend some money on a sub-panel if it is worth it to you. One other thing, my electrician tells me that older homes do have more load on their garages than you think. Before people started putting 2nd refrigerators in their garages, home builders would often put bathrooms on the same circuits, so if you have a home more than 20 years old and fridge and a couple of ladies in your home using hairdryers, you may be loading the garage circuit more than you think.

 

[cbutters]

Relevant:

 

[boaterva]

Relevant:

Nice installation! The only thing my electrician did differently was to do the 'break out' to the two HPWCs at the junction box that goes to the two units. Probably to save wire, which gets pricey for a 100 Amp circuit (which mine was). Not much point in going all the way back to the original starting point with the wiring!

This video does show excellently how two HPWCs are connected in a load sharing setup, however.

 

[cbutters]

Nice installation! The only thing my electrician did differently was to do the 'break out' to the two HPWCs at the junction box that goes to the two units. Probably to save wire, which gets pricey for a 100 Amp circuit (which mine was). Not much point in going all the way back to the original starting point with the wiring!

This video does show excellently how two HPWCs are connected in a load sharing setup, however.

Thanks!

I definitely considered doing it as you mentioned. What deterred me was that I would have to mount a much larger box on the ceiling to accommodate that type of splice/junction, and it also would have required two splices and two sets of polaris connectors and grounding bars instead of 1 since my garage entry wire was already cut. (I was replacing a NEMA 14-50 line with this setup.)

 

[boaterva]

Thanks!

I definitely considered doing it as you mentioned. What deterred me was that I would have to mount a much larger box on the ceiling to accommodate that type of splice/junction, and it also would have required two splices and two sets of polaris connectors and grounding bars instead of 1 since my garage entry wire was already cut. (I was replacing a NEMA 14-50 line with this setup.)

Exactly, for you, and the cost of the connectors, it may have been cheaper and easier. For a 100 Amp circuit, I think my (electrician's lol) way was better.

He also seemed to use a sort of T-tap where the wires didn't all 'go into a block' but the block squeezed over one (stripped) wire and the third one came out the T, which made the 'bending' less or non-existent.

 

[TechVP]

Wondering what NEC says about running a low voltage data wire in the same conduit as the 240 lines?
Not pointing an out an error, per say; but seeking info from those who will know.
Super job with the video. Much work, for certain. Many will benefit from your illustration.
-TechVP

 

[boaterva]

Wondering what NEC says about running a low voltage data wire in the same conduit as the 240 lines?
Not pointing an out an error, per say; but seeking info from those who will know.
Super job with the video. Much work, for certain. Many will benefit from your illustration.
-TechVP

Haven't had a chance to look in the NEC, but I assume Tesla did and their manual says:

If the signal wire is routed in the
power conduit with the power wires,
the insulation rating of the signal wire
should be equal to or greater than
that of the power wires.