Requirements to daisy chain Tesla Universal Wall Connectors?

[owl123]

As much as I wanted to use the full 80A available with my FCSP, when my electrician showed up they didn't have copper wiring for a 100A circuit and I didn't want to use aluminum wiring due to the fire risks highlighted on State of Charge, so I decided to pivot back to my initial plan of installing a Tesla Universal Wall Connector and a Tesla Wall Connector.

However, my electrician refused to daisy chain the chargers on a 60A circuit and said that this wouldn't meet code (I'm in Maine). Is that correct? He said that even though Tesla may theoretically have some safeguards designed to stop both chargers for calling for 48A simultaneously, those could fail and you can't install two 48A chargers on one 60A circuit knowing that this failure could occur.

He did say that one solution would be installing a larger circuit (e.g., 120A) that could power the full load of each device simultaneously, but then we were back to the aluminum wiring problem.

Is my electrician right about the requirements to daisy chain Tesla UWCs? Since Tesla advertises connecting up to 6 UWCs on one circuit, I'm really questioning whether that is correct. Relatedly, is there any reason to be concerned about the safeguards built into Tesla UWCs that are daisy chained?

Ultimately, it was a relatively short double run that we had to make, so not a big deal financially, but I am now a bit concerned about the overall load on our 200A service if both chargers were pulling 48A simultaneously and we happened to be fully using our heat pumps and a (future) induction range. I've set a lower charging rate on our Model Y that should mostly mitigate this concern. I could probably lower the max amperage on the charger itself, too, but I do like the option to charge our Model Y at 48A if I'm not charging our Lightning. I felt like daisy chaining was actually the safer option and, assuming there aren't other concerns with daisy chaining, I'm not sure how expensive it would be to make that adjustment now.

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[Maquis]

Maine is on the 2020 NEC. Provisions for load sharing EVSEs was just added in the 2023 NEC. Some inspection authorities will allow for future allowances such as this. YMMV

 

[RickLightning]

I think you should look into connecting them (it's ethernet wire as I recall), which will still regulate them to the charging limit. It doesn't know they're on separate circuits.

 

[PrimeRisk]

I think you should look into connecting them (it's ethernet wire as I recall), which will still regulate them to the charging limit. It doesn't know they're on separate circuits.

The load sharing control works over WiFi and only works with v3 EVSEs IIRC.

Another thread on just this topic:
https://www.f150lightningforum.com/...sal-wall-connector-is-fantastic-device.24378/

 

[RickLightning]

The load sharing control works over WiFi and only works with v3 EVSEs IIRC.

Another thread on just this topic:
https://www.f150lightningforum.com/...sal-wall-connector-is-fantastic-device.24378/

OP was going to buy two Tesla chargers, so they'd be compatible, and the thread you linked to, in the first post, specifically states WIRING...

But if you read, you can find that the latest units use WiFi and earlier units use ethernet.

 

[PrimeRisk]

OP was going to buy two Tesla chargers, so they'd be compatible, and the thread you linked to, in the first post, specifically states WIRING...

But if you read, you can find that the latest units use WiFi and earlier units use ethernet.

The wiring he is referring to is the electrical feed.

All variants of v3 (Gen 3) Tesla EVSEs, including the Universal Wall Connector, can load share up to 6 units and they do it via WiFi.

https://www.tesla.com/support/charging/wall-connector/power-management

v2 (Gen 2) Tesla EVSEs can load share up to 4 units, using a 2-wire shielded twisted-pair communications wire, not Ethernet.

https://www.tesla.com/support/charging/gen-2-wall-connector/load-sharing

v1 (Gen 1) Tesla EVSEs are not capable of load sharing

https://digitalassets.tesla.com/tes...-1-wall-connector-installation-manual-c-d.pdf

v2 and v3 Tesla EVSEs cannot work together for any load sharing.

 

[owl123]

I think you should look into connecting them (it's ethernet wire as I recall), which will still regulate them to the charging limit. It doesn't know they're on separate circuits.

Very cool. Do you know if just anyone can use the Tesla One app? This video indicates that "Group Management" can only be set up via the Tesla One app:

 

[owl123]

Wow, that was easy! Very glad that I went with these Tesla chargers.

Confirming that I was able to use the Tesla One app (I just used my Tesla credentials to log in as an "External Partner") and configure the group management settings. Also confirming that it appears that this worked despite the wall connectors being on two separate circuits (we're getting some snow right now and I'm not going to move my truck just to test).

I set my Tesla UWC as my "leader" and my Tesla v3 WC as my "follower" and set a shared maximum output of 48A.

I think my electrician could have run a hardwired communication cable which I probably would have preferred over just relying on wifi, but this is still a major improvement and should provide some extra peace of mind. Once I get some time to play around with it, I'll try testing to see how these charge without wifi.

 

[Heliian]

As much as I wanted to use the full 80A available with my FCSP, when my electrician showed up they didn't have copper wiring for a 100A circuit

Did you not explain to your electrician the install requirements?

And no, you can't have 2 appliances on the same circuit if the current rating isn't high enough. That's why the fcsp has a mechanical current setting, so that it can be adjusted to meet the circuit needs and not rely on software for derating. You also have to take into account the total in the panel.

 

[PrimeRisk]

Did you not explain to your electrician the install requirements?

And no, you can't have 2 appliances on the same circuit if the current rating isn't high enough. That's why the fcsp has a mechanical current setting, so that it can be adjusted to meet the circuit needs and not rely on software for derating. You also have to take into account the total in the panel.

In the US, as long as your area has adopted the 2023 National Electric Code, actually you can have multiple devices sharing a single branch circuit that exceeds the current rating when combined as long as they have energy management to prevent overload. Many jurisdictions will allow look-forward on NEC standards if they haven't formally adopted the 2023 NEC yet, but YMMV.

Virtually every EVSE out there leverages software or firmware for derating and the solution has proven to be very reliable. I have been running my JuiceBox that is capable of 48A for 10 years software limited to 40A because I only had a 50A plug in my garage. The breaker hasn't ever tripped.

Even if the input to the logic board being a physical switch instead of a setting on a configuration page, it is still the performance and accuracy of the software that is doing the current limiting. A bug in the software could still create an overcurrent situation regardless of how the setting is made. This is why we have circuit breakers to prevent fires from breaking out.

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