Pre wire for EV charger

[iQB]

From the Rivian EVSE Manual, pages 21 and 22:

I can't argue with the manual, but no way I'm using #6 for continuous current draw @ 48A. The heat buildup over 4+ hours is a hazard.

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[slillie]

I can't argue with the manual, but no way I'm using #6 for continuous current draw @ 48A. The heat buildup over 4+ hours is a hazard.

A #6 AWG wire can typically handle a maximum continuous current of 55 amps. However, this can vary based on the type of insulation, length of the wire, and the environment in which it is installed. For example, a #6 AWG THHN wire can handle 105 amps. A #6 wire with a 75-degree C insulation can be protected by a 60-amp breaker. When considering long-term usage, an 80% load factor should be applied, meaning a #6 AWG wire can safely carry 44 amps over a long period.

 

[Zoidz]

I can't argue with the manual, but no way I'm using #6 for continuous current draw @ 48A. The heat buildup over 4+ hours is a hazard.

Properly installed, it's not a hazard at all. That's what NEC is all about - specifications that include a safety factor. Don't be a fearmonger.

 

[dradam]

6AWG in conduit properly installed Is ok for 48A on a 60 breaker. 6 AWG Romex is not and is derated due to heat considerations. I had wanted to run 4AWG and put this all to bed and future proof, but the connector block in the Rivian charger is specked for 6 AWG although I am told the 4 will fit.
My supplier had 6-3 AWG XHHW 2 already in flexible metal conduit. It meets code and I found this much easier to run than assembling/pulling wires in hard metal conduit.

While I can peak charge at 48 Amps and I enjoyed planning the (hardwired) setup 99.9% of the time I charge at 20 A. Either way the S is charged in the morning.

 

[Rade]

I did that when we ordered our R1T - had an electrician wire an outlet into our garage's service panel. I printed down the Rivian charger specs and gave that to him.

50amp breaker to the proper NEMA receptacle.

 

[iQB]

Properly installed, it's not a hazard at all. That's what NEC is all about - specifications that include a safety factor. Don't be a fearmonger.

Debate is healthy, resorting to name calling is childish, surprised this is the route you've taken. This will be my last response to you on this topic.

To support my comment, I've had several instances in the past 8 years of EV charging, where my 32A mobile connectors will heat up to the point that the charge rate is reduced to 16A. This is using #6 AWG on a NEMA 14-50, which shouldn't even come close to being an issue with continuous charging over a period of hours (~4+ hours). Had this been an issue with one of my properties, I'd say its probably install related, but its happened at several (all located in differing states).

 

[beatle]

6AWG in conduit properly installed Is ok for 48A on a 60 breaker. 6 AWG Romex is not and is derated due to heat considerations.

This is a small nuance, but it's relevant since the guide doesn't specify the conditions where #6 doesn't actually pass muster for a 60A circuit. When I was first learning about EVSE installation, I found this pretty confusing since I thought wire is wire. What's worse is that the code says that #6 THHN is good for 60A, and that's actually what's inside the NM (Romex) outer jacket!

 

[Zoidz]

Debate is healthy, resorting to name calling is childish, surprised this is the route you've taken. This will be my last response to you on this topic.

To support my comment, I've had several instances in the past 8 years of EV charging, where my 32A mobile connectors will heat up to the point that the charge rate is reduced to 16A. This is using #6 AWG on a NEMA 14-50, which shouldn't even come close to being an issue with continuous charging over a period of hours (~4+ hours). Had this been an issue with one of my properties, I'd say its probably install related, but its happened at several (all located in differing states).

Debate is healthy, yes. In the light of well documented and time tested NEC standards, spreading irrational fear despite those standards is not debate and is not healthy on a public forum.

 

[carsly]

I have a NEMA 14-50 in the garage with a Lectron NEMA 14-50 splitter to two Tesla Universal Wall Chargers. I have each set to charge at 32 amps (I'm on a 40 amp breaker on a 50 amp sub-panel) and they charge at different time windows overnight. Unless you have a super-long commute or are rarely home to charge, 32 amps vs 40 or 48 amps makes no practical difference. In 10 hours at 7.2KW I can put ~70kwh into a battery overnight. That's enough to drive 200+ miles in my Cybertruck AWD or 160 miles in my R1S Dual Large. Normally I'd have 12 hours at a minimum so bump each by 20%.

I also have a separate Tesla Universal Wall Charger on a 60 amp breaker hardwired to a different sub-panel. I also charge that at 32 amps. In 10 hours I can charge a Model 3 or Y from dead to 100%, not that my vehicles are ever at 0%.

There is no one answer, really depends on your situation. Either way, I'd recommend a Tesla Universal Wall Charger. Works fine with three different Teslas I've had as well as my R1S. No juggling adapters or having to think about anything.



BTW, I will note that my electrical inspector recommended never to charge above 32 amps even on the hardwired EVSE regardless of the wiring or breakers since higher amperage is going to generate more heat in the panel regardless of your panel capacity or rated service.

 

[beatle]

To support my comment, I've had several instances in the past 8 years of EV charging, where my 32A mobile connectors will heat up to the point that the charge rate is reduced to 16A. This is using #6 AWG on a NEMA 14-50, which shouldn't even come close to being an issue with continuous charging over a period of hours (~4+ hours). Had this been an issue with one of my properties, I'd say its probably install related, but its happened at several (all located in differing states).

Dropping to 16A at multiple locations sounds like an EVSE or an onboard charger issue. Even 32A is pretty low for a 50A circuit. It's unlikely that all the circuits you've charged on are incapable of safely providing 32A unless maybe the same person installed them and cut the same corner in all of them.

 

[iQB]

This is a small nuance, but it's relevant since the guide doesn't specify the conditions where #6 doesn't actually pass muster for a 60A circuit. When I was first learning about EVSE installation, I found this pretty confusing since I thought wire is wire. What's worse is that the code says that #6 THHN is good for 60A, and that's actually what's inside the NM (Romex) outer jacket!

The last install I completed, I used 6/3 Romex, so this may be the culprit. It was my understanding that using this on a 50A breaker shouldn't cause any overheating issues whatsoever, but it definitely does sporadically over extended charging sessions. I've only been charging at 32A when it has happened (receptacle directly beneath the panel).

 

[2kwik4u]

But why not get a hardwired solution when its cheaper to hardwire without expense GFCI breaker/commercial receptacle, less connection point of failure, and yes also the bonus of more power?

I went 14-50 instead of hardwired for a couple reasons.

#1, I'm in a rental. I didn't want to install a hardwired EVSE for the homeowner. Using the outlet let me keep my charging equipment separate from the home, as the lease says any "improvements" become the homeowners property. I did go ahead and make it a "full 50A" circuit though with a high quality 14-50 plug, 6AWG Romex (with a small service loop in the wall), and 50A GFCI breaker. So, if the homeowner did want to put a hardwired unit in, they have the infrastructure to do so in the future.

#2. I needed the flexibility of a plug. In the winter I park in the garage, nose in. This aligns well with the charger being near the interior wall of the house, and an easy run for the electrical. In the summer, we have a boat in that spot, and I move the charger to near the door, and run a 35ft RV style extension cord from the outlet to near the garage (secured with cable anchors along the baseboard). The lets the truck sit just outside the garage and still have access to the home charger.

#3. I didn't have to buy a dedicated EVSE. I use the mobile charger that came with the truck. Bought a cheap wall bracket to hold the connector, and the charger unit itself off the ground. This only draws 32A, but is adequate for covering my commute. This saved me some cash as I didn't have to buy a dedicated EVSE. Did have to get the more expensive GFCI breaker though.

Now, I don't have time of use rates, and I have enough consistent "down time" at home to regain nearly a full charge overnight at 32A. I know this doesn't fit everyone, but it works for me, and was the right set of compromises for the situation. If/When we get our own home in the area, I'll likely go hardwired with a separate EVSE.

 

[dradam]

This is a small nuance, but it's relevant since the guide doesn't specify the conditions where #6 doesn't actually pass muster for a 60A circuit. When I was first learning about EVSE installation, I found this pretty confusing since I thought wire is wire. What's worse is that the code says that #6 THHN is good for 60A, and that's actually what's inside the NM (Romex) outer jacket!

Yes, it was somewhat unclear, but conduit apparently allows more heat dissipation than Romex, when installed in the correct size conduit.

 

[Zoidz]

What's worse is that the code says that #6 THHN is good for 60A, and that's actually what's inside the NM (Romex) outer jacket!

That's because the outer jacket of Romex tightly and thermally couples the individual conductors and also traps heat in the overall bundle. Individual THHN conductors in a properly size conduit (per NEC max cross sectional area fill of 40% with three or more conductors) have room to dissipate heat inside the conduit and through the conduit wall. NEC specifies all of this to provide a time tested safety margin against bad things happening. Just because you could force 6 wires in a conduit doesn't mean you can and meet code. Conduit fll calcs are mandatory to meet code.

 

[beatle]

Yes, I am aware of why the difference exists, but my point was that the guide only specifies the AWG of the wire which isn't the whole story.

The last install I completed, I used 6/3 Romex, so this may be the culprit. It was my understanding that using this on a 50A breaker shouldn't cause any overheating issues whatsoever, but it definitely does sporadically over extended charging sessions. I've only been charging at 32A when it has happened (receptacle directly beneath the panel).

6/3 Romex will be fine for a 50A circuit. It's what I used on my 14-50, but my failures came from the terminals. Before I installed a hardwired EVSE, I replaced my melted 14-50R with a non-melted receptacle and kept going. Within a few hours, I noticed my breaker had tripped. I went to reset it and then noticed the breaker itself was very hot. I took it out of the panel and noticed one of the terminals was loose. Mind you this had been operating perfectly for over 2 years, and it was now overheating. Apparently the extended charging sessions at 40A had loosened the terminals. This may have been a contributing factor for the failure of the receptacle as well. I mention this as something to check that may be atypical of a breaker trip elsewhere. When I installed my Tesla UWC, I also used a torque wrench. The recommended amount of torque is surprisingly high - perhaps more than I could put into the terminal with a screwdriver alone.

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