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Wall Connector/Charger Daisy Chaining on Separate Breakers

Rocky_H

Well-Known Member
Feb 19, 2015
6,660
7,953
Boise, ID
This. And set the switches in both wall chargers to 80 amps, since that's the maximum that the circuit can deliver. The car will ask for the amount that it's capable of receiving (or set to receive if you've dialed it down in the car) and the two chargers will share the 80 amps. This is how mine looks:
I'm sure you know the proper way, and this was just a brain fart that you said it in a way that wasn't right. You don't set them both for 80A in a shared configuration. The Master one gets its current set for the continuous amps of the circuit, like 80A. The other one gets the current dial set for setting F, which just says it is a Slave and it is getting guided by the Master one.
 

Rockster

Active Member
Oct 22, 2013
3,012
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McKinney, TX
I'm sure you know the proper way, and this was just a brain fart that you said it in a way that wasn't right. You don't set them both for 80A in a shared configuration. The Master one gets its current set for the continuous amps of the circuit, like 80A. The other one gets the current dial set for setting F, which just says it is a Slave and it is getting guided by the Master one.

You are correct. Thanks for correcting me. It's been 24 months since I installed my pair and I had forgotten that point. I was just trying to convey that one doesn't set the wall unit dials based upon what the car is expected to need but, rather, what the circuit is capable of delivering.
 
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captjoemcd

Member
Nov 29, 2019
258
288
California
Thanks all for the input.

At the end of the day, I decided to go with 2-2-2-4 copper SER cable to feed the subpanel (110 feet at ~$7/ft vs $2/ft for aluminum 1/0-1/0-/1/0-2 SER), which is good for ~100A derated for 131F ambient (hot attic). From the subpanel, I'll be running 3 x #6 copper (black, black, white), #10 ground in 3/4" FMC to 2 metal switch boxes, which will hide right behind the wall chargers. One will be fed with a 60A breaker for 48A charging, one will be fed with a 40A breaker for 32A charging. Key factor driving the final config decision - I'll only be in this house another 2-3 years and will likely take the chargers with me, at which point this setup will let me swap the breakers for 50A each and stick NEMA 14-50's on the boxes, which the daisy-chained configuration wouldn't allow.

Thanks again!

Handy reference to the 2017 NEC Table 310.15(B)(16) attached.
 

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captjoemcd

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Nov 29, 2019
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Quick addendum - the city hasn't approved these plans yet, technically, copper 2-2-2-4 derated for 131F is a .76 correction factor which is 98.9A - I'm not 100% sure they'll let the single amp difference slide so they may require me to go up to 1-1-1-3. Will post back when I get the plans approved
 

MN-MS100D

Member
Dec 10, 2018
135
92
Minnesota
Two comments:

1) You can use the formula in 310.15(B)(2) and work backwards to arrive at a maximum attic temperature. Just maybe your attic temp is only 129 degrees and you're then OK.

2) Keep the installation of SE cable away from insulation or you will have to derate the cable using the 60 degree ampacity column. 338.10(B)(4)

PS: Code references are from 2014 NEC
 

Rocky_H

Well-Known Member
Feb 19, 2015
6,660
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Boise, ID
Quick addendum - the city hasn't approved these plans yet, technically, copper 2-2-2-4 derated for 131F is a .76 correction factor which is 98.9A - I'm not 100% sure they'll let the single amp difference slide so they may require me to go up to 1-1-1-3.
I don't know that I would make such a big step up in wire for that then. Maybe just find a 90A circuit breaker. They do make those for most brands.
 

captjoemcd

Member
Nov 29, 2019
258
288
California
1) You can use the formula in 310.15(B)(2) and work backwards to arrive at a maximum attic temperature. Just maybe your attic temp is only 129 degrees and you're then OK.

PS: Code references are from 2014 NEC

Yeah I spoke with our city's chief electrical inspector and he said to use the 140F column... maybe they'd be cool with one step down but further than that will be a tough sell. I'm in the central valley (Bakersfield), and summer temps outside the attic are rountinely 110F-115F. Charging will take place primarily at night but the attics hold a lot of heat (concrete tile roof)

2) Keep the installation of SE cable away from insulation or you will have to derate the cable using the 60 degree ampacity column. 338.10(B)(4)

PS: Code references are from 2014 NEC
Fortunately we're switching over to the 2017 NEC in a few weeks and they're cool with submitting plans using it. The 2017 NEC gets rid of that requirement for #8 and bigger SER. Here's a good discussion: 338.10(B)(4) SE Cable. Installation Methods for Branch Circuits and Feeders.

Relevant code from 2017 NEC
338.10(B)(4) Installation Methods for Branch Circuits and Feeders.

(a) Interior Installations. In addition to the provisions of this article, Type SE service-entrance cable used for interior wiring shall comply with the installation requirements of Part II of Article 334, excluding 334.80.

For Type SE cable with ungrounded conductor sizes 10 AWG and smaller, where installed in thermal insulation, the ampacity shall be in accordance with 60°C (140°F) conductor temperature rating. The maximum conductor temperature rating shall be permitted to be used for ampacity adjustment and correction purposes, if the final derated ampacity does not exceed that for a 60°C (140°F) rated conductor.
 

ToddB

Member
May 13, 2019
17
14
Lexington, MA
HELP! I've done lots of residential wiring, but never before used 3AWG wire or installed a car charger. Here is my planned NEW Installation configuration: Two Tesla Wall chargers on a single 100 A breaker (wall chargers each set to 80A), 3 wires run from sub panel - black, red and green ground 40' to junction box, which is located 10' from each wall charger. Daisy chain communications low-voltage connection between the two wall chargers in its own conduit. Six questions: 1. Does wiring from junction box to each wall charger also need to be 3 AWG? 2. Does ground wire from panel to junction box need to be 3AWG? 3. Any recommendations on most suitable junction box or junction box fittings? 4.What is correct torque on terminations? 5. Conduit size/type required for wires from panel to junction box? from junction box to wall charger? 6.Is 1/2" PVC conduit acceptable for low voltage connection between wall chargers?
 
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captjoemcd

Member
Nov 29, 2019
258
288
California
Quick addendum - the city hasn't approved these plans yet, technically, copper 2-2-2-4 derated for 131F is a .76 correction factor which is 98.9A - I'm not 100% sure they'll let the single amp difference slide so they may require me to go up to 1-1-1-3. Will post back when I get the plans approved
Ok, final answer: 1-1-1-3 Copper SER BFBA8409-90C0-44F6-ABDC-B360B666C73E.jpegE1313E73-5A75-4940-A166-85B1803C2761.jpeg15610B90-4751-4915-9C4E-C0F98F62F884.jpeg E9250331-750E-4E8B-9A1A-BDD7D2631605.jpeg
 

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captjoemcd

Member
Nov 29, 2019
258
288
California
HELP! I've done lots of residential wiring, but never before used 3AWG wire or installed a car charger. Here is my planned NEW Installation configuration: Two Tesla Wall chargers on a single 100 A breaker (wall chargers each set to 80A), 3 wires run from sub panel - black, red and green ground 40' to junction box, which is located 10' from each wall charger. Daisy chain communications low-voltage connection between the two wall chargers in its own conduit.

Sounds like a good plan - i just went through all of this and had lots of back and forth on the best design. One wall charger will be set to 80A, and the other will be set to "slave". This tells the master that it has 80A to distribute across the two chargers, and the slave takes whatever the master sends. You may want to consider pulling a neutral to the junction box as well. Even though it isn't needed now, it'll give you better options if you move.

Six questions: 1. Does wiring from junction box to each wall charger also need to be 3 AWG? 2. Does ground wire from panel to junction box need to be 3AWG?

1. Yes 2. Ground should be 5 AWG throughout. This is the reason I decided to go with individual circuits on separate breakers to two chargers, since you use #6 on a 60A breaker for each, which is another potential option for you if you have space in your panel for 2 60A breakers. Max draw on a single charger is 48A, so the 80A daisy-chained solution doesn't get you a whole lot of extra benefit with two chargers. Primary exception is for those lucky few who have the 72A onboard charger in their Tesla.

3. Any recommendations on most suitable junction box or junction box fittings? 4.What is correct torque on terminations?
Use a NEMA rectangular box. Make sure you confirm it is big enough by box-fill calculations. You'll have 6 #3 AWG, 3 #5 AWG, plus fittings. I'm almost 100% positive 8x8x6 works. Like this: WIEGMANN NEMA1 8 in. x 8 in. x 6 in. Carbon Steel Screw Cover Wall-Mount-SC080806 - The Home Depot

Splice connectors like these are great: Polaris 3/0 - 6 AWG Bagged Insulated Multi-Tap Connector, Black-IPL3/0-3B - The Home Depot

Correct torque on terminations is part of the listing. Each breaker, splice nut, termination, etc will tell you what the proper torque is by wire size and copper/aluminum. Get a proper toque screwdriver (i like the T-handle ones)

5. Conduit size/type required for wires from panel to junction box? from junction box to wall charger?
There's a max fill calc for conduits that will tell you that you'll need 1" at a minimum. In reality, you'll want to use 1.5" at a minimum because pulling the wire through the conduit is a pain and the more volume you have the better. You can have a max of 360 degrees in bends between pull points. Conduit must be fully assembled prior to installation of wire and then wire pulled through. You should be able to use either FMC or EMT, but check with your local inspector to be sure.

6.Is 1/2" PVC conduit acceptable for low voltage connection between wall chargers?
Low voltage wiring can be run in the same conduit as the 240V, provided that its insulation meets or exceeds the 240V insulation. Otherwise, 1/2" PVC should be fine. Again, check with your local inspector to be sure.
 
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captjoemcd

Member
Nov 29, 2019
258
288
California
It’s not balancing the load to the (sub) panel. It’s. Balancing the load on a single circuit. Maybe it can do what your thinking as well but I’m not sure that would meet code (two (or more) 60A breakers on a 100A panel).

God damnit, one month too late for me:
upload_2020-1-15_17-7-24.png


This is literally exactly what I wanted to do, and they even show a 100A subpanel with multiple 60A branch circuits/wall connector
https://www.tesla.com/sites/default...ng/Gen3_WallConnector_Installation_Manual.pdf
 
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mswlogo

Well-Known Member
Aug 27, 2018
6,123
4,736
MA, NH
God damnit, one month too late for me:
View attachment 500644

This is literally exactly what I wanted to do, and they even show a 100A subpanel with multiple 60A branch circuits/wall connector
https://www.tesla.com/sites/default...ng/Gen3_WallConnector_Installation_Manual.pdf

What’s the one month to late mean?

The page on the right does make some sense. But I’m surprised that meets code and I suspect some inspectors would flip out. Because your putting 4 60 Amp breakers in a 100 A panel. Those circuits could go any where and someone might think they could swap wall connectors for 14-50 outlets and poof. But with Wall Connectors communicating it should never pull more than 80A.

Is there a setting on the Wall Connector to allow 80A total and 48A per Wall Connector?

Or would the Max total still be 48A?

How would Wall Connector(s)know the Subpanel is 100A (80 A load)?
 

captjoemcd

Member
Nov 29, 2019
258
288
California
What’s the one month to late mean?
The discussion that kicked off this post was trying to get two wall chargers to share the incoming power to a subpanel. In the end I just bought two 2nd Gen wall connectors a little over a month ago for a new 100A subpanel in the garage, and ended up deciding to run #6 wiring to both of them, with one on a 60A breaker and one on a 40A breaker, since there was no way to daisy-chain 2nd gen wall connectors without running #3 to a junction box and #3 to each wall connector. The 3rd Gen would have let me run 60A breakers for both.

Looks like the settings for the wall connector are done during setup, both max setting for each wall connector and max available to share amongst all. This is the key difference for Gen 3 - you can independently set the max available to share and the max per charger- previously it was one setting, which determined max available to an individual charger and to share, which also necessitated all the wiring being spec'd for that single max available, even though it was overkill in most cases.

As for the code comment, I totally agree - I'm not sure how they get away with that meeting code, but I guess it must somehow. Probably something about "if it's designed and listed for a specific installation" etc.
 
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mswlogo

Well-Known Member
Aug 27, 2018
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MA, NH
The discussion that kicked off this post was trying to get two wall chargers to share the incoming power to a subpanel. In the end I just bought two 2nd Gen wall connectors a little over a month ago for a new 100A subpanel in the garage, and ended up deciding to run #6 wiring to both of them, with one on a 60A breaker and one on a 40A breaker, since there was no way to daisy-chain 2nd gen wall connectors without running #3 to a junction box and #3 to each wall connector. The 3rd Gen would have let me run 60A breakers for both.

Looks like the settings for the wall connector are done during setup, both max setting for each wall connector and max available to share amongst all. This is the key difference for Gen 3 - you can independently set the max available to share and the max per charger- previously it was one setting, which determined max available to an individual charger and to share, which also necessitated all the wiring being spec'd for that single max available, even though it was overkill in most cases.

As for the code comment, I totally agree - I'm not sure how they get away with that meeting code, but I guess it must somehow. Probably something about "if it's designed and listed for a specific installation" etc.

Sorry if I mislead you. I doubled checked the manual to confirm how I thought it worked and I should have looked further.

How long have Gen 3 been around? I assume the two (two different sites) I installed are the latest gen.
 

mswlogo

Well-Known Member
Aug 27, 2018
6,123
4,736
MA, NH
Sorry if I mislead you. I doubled checked the manual to confirm how I thought it worked and I should have looked further.

How long have Gen 3 been around? I assume the two (two different sites) I installed are the latest gen.

Oh, I missed it. Gen 3 just came out that can handle the case you wanted. Phew I thought I screwed you up. I didn’t think there was a way to tell Gen 2 to do what you wanted.

It’s cool that Gen 3 has WiFi. I wonder if they depend on WiFi to talk to each other instead of RS-485.
 
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Rocky_H

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Feb 19, 2015
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Boise, ID
It’s cool that Gen 3 has WiFi. I wonder if they depend on WiFi to talk to each other instead of RS-485.
It shows right there in the wiring diagram that that is what the wi-fi is for. The units communicate directly with each other to manage the current limits. This is a pretty nice help in doing the wiring for these, because the power lines to each wall connector would be separate runs, but then you still had to deal with the annoyance of doing yet another physical wiring run of twisted pair directly from one to the next, to the next. This wireless feature eliminates that extra wiring run.
 
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captjoemcd

Member
Nov 29, 2019
258
288
California
Finally done! Fully inspected, final permit approved. I swapped out the Gen 2’s for Gen 3’s at a total cost of around $400 (shouldn’t have tossed the boxes). All drywall is closed up. Each Gen 3 is on a 60A breaker and currently set to 40A continuous until the OTA update to allow load sharing. Gen 3 installation is a huge improvement over the Gen 2. Use ferrules going into the terminal blocks - 6AWG spreads quite a bit when you torque it to 50 ft-lbs in the large round terminals if you don’t. WiFi setup was a breeze.

C13DE7F1-8DE5-4678-81B7-75DD59F0575E.jpeg 7781A4D8-9893-4FE7-92D5-D0F8441C3E0D.jpeg BF9A9483-3F08-4CD2-8CAF-3C14EDD36055.jpeg A3966D37-6D15-4E5F-8C62-15C9F0345E73.jpeg AF7D7EDE-DF1C-47E0-AD23-0B8C406ABDB9.jpeg B0A3715C-8004-4C78-9876-D42CCE41F4EF.jpeg
D4D23F25-1823-45A7-BDE4-34A328F64AFE.jpeg
 
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