Using old AC lines for a new NEMA14-30 outlet

[Afgncaap]

Apologies if this question has already been asked. I did see this thread:

https://teslamotorsclub.com/tmc/threads/replace-6-30-outlet-with-14-30-without-neutral-connected.129468/

Read all the discussion, but I think my situation is different enough to warrant some new input.

My garage is in a separate building from my townhouse, and it is wired for 120AC. The house is 25' away and happens to have an old non-functional air-conditioning unit in the back, which is wired to a 40A breaker in a sub-panel inside. That wire comes from the sub-panel to a j-box in the back of the house, so easy access for me. Turns out what's inside the box is 3 wires, hot-hot-neutral. All are 10AWG solid copper, but the neutral is bare until it enters the Romex inside the wall.

I went ahead and installed a NEMA14-30 outlet in the garage, and ran 4 wires from it through PVC conduit all the way up to the j-box. I used individually insulated 6AWG stranded copper (red, black, white, green), to cover the full 25'. (I could actually cut off about 3' when I'm done.)

The trouble is what to do now. Obviously I can connect the two hot and ground wires, and the Tesla will happily suck down 30A (actually 24A on a NEMA14-30). The trick is what to do with the neutral. I know Tesla won't use it, but I'd like my wiring to be safe even if someone plugs in a dryer or something.

Can I just tie neutral to ground in the j-box? That would seem to be better than leaving it floating. Could I instead tie it to the neutral or ground of the existing AC line in the garage? But then, I measured less than an ohm between the j-box neutral and the garage ground, so would that make a difference?

 

[drawfour]

My recommendation is if you don't already know what to do, then you should be hiring an electrician to do it.

 

[Kermee]

That wire comes from the sub-panel to a j-box in the back of the house, so easy access for me.

How hard would it be for you to run a neutral wire from the sub-panel neutral bus-bar (if one) to the j-box? Then you wouldn't have to worry...

 

[jdcollins5]

Apologies if this question has already been asked. I did see this thread:

https://teslamotorsclub.com/tmc/threads/replace-6-30-outlet-with-14-30-without-neutral-connected.129468/

Read all the discussion, but I think my situation is different enough to warrant some new input.

My garage is in a separate building from my townhouse, and it is wired for 120AC. The house is 25' away and happens to have an old non-functional air-conditioning unit in the back, which is wired to a 40A breaker in a sub-panel inside. That wire comes from the sub-panel to a j-box in the back of the house, so easy access for me. Turns out what's inside the box is 3 wires, hot-hot-neutral. All are 10AWG solid copper, but the neutral is bare until it enters the Romex inside the wall.

I went ahead and installed a NEMA14-30 outlet in the garage, and ran 4 wires from it through PVC conduit all the way up to the j-box. I used individually insulated 6AWG stranded copper (red, black, white, green), to cover the full 25'. (I could actually cut off about 3' when I'm done.)

The trouble is what to do now. Obviously I can connect the two hot and ground wires, and the Tesla will happily suck down 30A (actually 24A on a NEMA14-30). The trick is what to do with the neutral. I know Tesla won't use it, but I'd like my wiring to be safe even if someone plugs in a dryer or something.

Can I just tie neutral to ground in the j-box? That would seem to be better than leaving it floating. Could I instead tie it to the neutral or ground of the existing AC line in the garage? But then, I measured less than an ohm between the j-box neutral and the garage ground, so would that make a difference?

Neutral is only connected to ground at one place, and one place only, at the Main Panel where the utility service comes in to the Main Panel. DO NOT connect the neutral to ground.

I am not clear on how you are connecting the new 4-wire 6AWG to the existing 3-wire 10AWG. Are you connecting the new 6AWG to the 10AWG Romeo cable at the junction box? If so then you are getting rid of the bare neutral wire which would be a good thing.

If the junction box is outside, you could drive a ground rod and connect to the green ground wire. Then connect Hot-Hot-Neutral.

Like stated above, if you are not sure about this, then you need to get some experienced help.

 

[eprosenx]

Apologies if this question has already been asked. I did see this thread:

https://teslamotorsclub.com/tmc/threads/replace-6-30-outlet-with-14-30-without-neutral-connected.129468/

Read all the discussion, but I think my situation is different enough to warrant some new input.

My garage is in a separate building from my townhouse, and it is wired for 120AC. The house is 25' away and happens to have an old non-functional air-conditioning unit in the back, which is wired to a 40A breaker in a sub-panel inside. That wire comes from the sub-panel to a j-box in the back of the house, so easy access for me. Turns out what's inside the box is 3 wires, hot-hot-neutral. All are 10AWG solid copper, but the neutral is bare until it enters the Romex inside the wall.

I went ahead and installed a NEMA14-30 outlet in the garage, and ran 4 wires from it through PVC conduit all the way up to the j-box. I used individually insulated 6AWG stranded copper (red, black, white, green), to cover the full 25'. (I could actually cut off about 3' when I'm done.)

The trouble is what to do now. Obviously I can connect the two hot and ground wires, and the Tesla will happily suck down 30A (actually 24A on a NEMA14-30). The trick is what to do with the neutral. I know Tesla won't use it, but I'd like my wiring to be safe even if someone plugs in a dryer or something.

Can I just tie neutral to ground in the j-box? That would seem to be better than leaving it floating. Could I instead tie it to the neutral or ground of the existing AC line in the garage? But then, I measured less than an ohm between the j-box neutral and the garage ground, so would that make a difference?

Welcome to the forums and Tesla ownership!

Lots of feedback for you:

First off, circuit breakers and wire sizing for motor loads are a totally different deal than for loads like EV charging. Motors are typically thermally protected internally and so you are more just using the circuit breaker for short circuit protection. Otherwise a 10awg line would not typically be allowed on a 30a breaker.

As to your old installation: An AC unit only needs hot hot and ground typically. So that Ian likely what’s you have since as you state, the third wire is not insulated (so therefore it can’t be a neutral).

Can you please confirm that in the sub panel that neutral and ground bus bars are NOT tied together? Also please confirm which bus the bare wire to the AC is attached to (should be ground). Please post lots of pictures if you can safely. We want to see the inside of your panels with enough resolution to see how things are hooked up, the ratings on the breaker handles, and the sticker on the door panel so we can get breaker install info and model #’s.

Now the bad news: With this setup you can’t safely use a 14-30 or the 10-30 receptacle. The only options would be to get a non UL rated adapter to 6-30 for your UMC from a third party (which also does not have the thermal probe safely feature), or buy a different J1772 EVSE that’s does officially support 6-30 (it likely also won’t have the safest feature anyway), or just hard wire in a Mobile Connector. That does not need the neutral at all.

Also, for your use case that 40a breaker is not allowed. Since it is romex wire, it is limited to the 60c rating which is 30a. The 40a breaker was likely allowed since it was an AC motor and it needed startup surge current overhead (and the motor would have been thermally protected), but for an EV use that is a no no.

Can you not just take that 6awg all the way back to the subpanel or all the way to the main? How big is your main service feed and what kind of wire and breaker feed the subpanel? If you have done the hard work already of going to the other building, it would be nice to get the full capacity of that circuit available to the EV!

Oh also, there are rules around extending electrical to other buildings I am not 100% up on. Things like needing a disconnect at that building and needing to drive a ground rod. Though just for a single circuit there may be some exception. I don’t exactly remember...

 

[Sophias_dad]

I don't think I've seen hardwiring of a mobile connector yet.

Another option is the HPWC, which similarly won't need a neutral. You'll still be limited to the 30A. though.

 

[eprosenx]

I don't think I've seen hardwiring of a mobile connector yet.

Another option is the HPWC, which similarly won't need a neutral. You'll still be limited to the 30A. though.

Ack! I was on my cell phone when I wrote that and was distracted. I did not mean that. ;-) Please don't hard wire a Mobile Connector. I meant a "Wall Connector" (formerly known as a HPWC).

Thanks for pointing this out @Sophias_dad

 

[mswlogo]

Ack! I was on my cell phone when I wrote that and was distracted. I did not mean that. ;-) Please don't hard wire a Mobile Connector. I meant a "Wall Connector" (formerly known as a HPWC).

Thanks for pointing this out @Sophias_dad

Why do you say earlier that that 10 AWG is not allowed on a 30A Breaker, did you mean 40A?

Also over sizing the wire to 6 AWG on a 30A or 40A circuit is frowned upon. I know there are rules and recommendations on sizing wire up for long distances. But sizing it that much would never pass inspection around here. It’s misleading what the capacity of the circuit is.

I agree that a wall connector is your best bet.

 

[Sophias_dad]

I am not an electrician by trade, but the ampacity of 10 awg a 60C temperature limit is 30 amps. I understand that because the EV load is considered continuous, you can't even run 30 amps continuous through it, but rather only 80% thereof, aka 24 amps, leaving 6 amps unused to keep connections and the 30 amp circuit breaker cool.

I'd hope that anyone connecting anything to a 6 AWG wire would have the sense to go look at the other end. Until you reach the connection-size-limit of the breaker, I'd hope that any size increase should be allowed. 6 awg on a 40 amp circuit is entirely reasonable, especially if its a long run.

 

[Cosmacelf]

As eprosenx stated, what you most likely have is two hots and a ground. So the only receptacle you can use is a NEMA 6-30. There is no way to wire in a 14-30 and have it be safe, let alone be to code.

Unfortunately, Tesla doesn't make a 6-30 adapter, but this company does: NEMA 6-30 Adapter for Tesla Model S/X/3 Gen 2

Finally, you'll need to replace that 40A breaker with a 30A breaker. When you take the cover off the panel that has the old 40A breaker, take a look at the wire and make sure it is the same romex as what you see in the junction box.

So, assuming there aren't any other surprises, you're good to go.

 

[mswlogo]

As eprosenx stated, what you most likely have is two hots and a ground. So the only receptacle you can use is a NEMA 6-30. There is no way to wire in a 14-30 and have it be safe, let alone be to code.

Unfortunately, Tesla doesn't make a 6-30 adapter, but this company does: NEMA 6-30 Adapter for Tesla Model S/X/3 Gen 2

Finally, you'll need to replace that 40A breaker with a 30A breaker. When you take the cover off the panel that has the old 40A breaker, take a look at the wire and make sure it is the same romex as what you see in the junction box.

So, assuming there aren't any other surprises, you're good to go.

Keep in mind you are recommending a non UL approved illegal adapter with the temperature sensor hacked off.

 

[eprosenx]

Why do you say earlier that that 10 AWG is not allowed on a 30A Breaker, did you mean 40A?

Also over sizing the wire to 6 AWG on a 30A or 40A circuit is frowned upon. I know there are rules and recommendations on sizing wire up for long distances. But sizing it that much would never pass inspection around here. It’s misleading what the capacity of the circuit is.

I agree that a wall connector is your best bet.

Arg yes! Another typo on my part. I meant 40a. I need to proof read better before posting.

As far as wire sizes, I don’t know of any limits to how much you are allowed to upsize, though using multiple gauges throughout a run could easily be very misleading to someone in the future and so is likely to be frowned upon (if not outright banned) by the code and AHJ’s. But I really don’t know. I like though that you ran #6, that is smart to me for future if nothing else. Make sure to he properly rated wire connectors to join the disparate sizes. I am not sure what if anything can be done to keep that neutral wire from being “floating”. I worry that if you tied to ground at the junction box and then capped the other end, then someone in the future might see the white wire and assume it was neutral... Maybe wrapping the entire end in green electrical tape and tying it to ground at both ends?

 

[Cosmacelf]

Keep in mind you are recommending a non UL approved illegal adapter with the temperature sensor hacked off.

Keep in mind that about a hundred thousand v1 Tesla UMCs are being used daily without temperature sensors and they work just fine. There are dangerous hacks, and OK hacks. That third party 6-30 adapter is not a dangerous hack.

 

[eprosenx]

Keep in mind that about a hundred thousand v1 Tesla UMCs are being used daily without temperature sensors and they work just fine. There are dangerous hacks, and OK hacks. That third party 6-30 adapter is not a dangerous hack.

Note that I think “illegal” is a bit strong. I don’t think it is against the *law* to sell non UL approved devices. Remember the UL is not a government agency...

I should also call out though: I thought the UMC Gen 1 had some kind of thermal disconnects in the adapters that would cut off power in case of excessive overheating? Wasn’t this part of a recall they did?

But yes, lots of EVSE’s exist without thermal safety devices in the plug end I think. I don’t know how to evaluate the relative risks here. I probably would not have too much of an issue with a receptacle that I personally wired that was all new and that I did not subject to repeated daily connect/disconnect cycles.

 

[mswlogo]

Note that I think “illegal” is a bit strong. I don’t think it is against the *law* to sell non UL approved devices. Remember the UL is not a government agency...

I should also call out though: I thought the UMC Gen 1 had some kind of thermal disconnects in the adapters that would cut off power in case of excessive overheating? Wasn’t this part of a recall they did?

But yes, lots of EVSE’s exist without thermal safety devices in the plug end I think. I don’t know how to evaluate the relative risks here. I probably would not have too much of an issue with a receptacle that I personally wired that was all new and that I did not subject to repeated daily connect/disconnect cycles.

I've seen a lot of dryer outlets go bad. It was actually a common service call. In fact, any new dry install we'd automatically replace the outlet. Often in damp cellars. Never saw one that burned down a house down, but I never did a service call to replace a dryer outlet that burned down a house . But saw plenty of burned up outlets. Terminals oxidize/rust over time. The environment for EV plugs is similar. Garages, Outdoors, Cars that just came in from rain or snow. Like we discussed before, long hours, full load on the circuit during sleeping hours.

I'd put a working temp sensor (on the one and only "friction" based connection) or a wall connector.

If someone feels that strongly to run a neutral that IS NOT used in THIS application go for it. But I would not run without the temp sensor.

I agree, it's hard to evaluate the total risk.

Just because there are a bunch of those sensorless installations out there doesn't mean it's statistically the safest thing to do.

Oh and that short little unmodified Tesla 14-30 adapter cable does get warm when charging.

 

[Cosmacelf]

Be aware that the Tesla Mobile Connector has pretty sophisticated algorithms to determine, based on voltage drop patterns, whether or not resistance heating is occurring anywhere along the line.

I gotta say I’m pretty tired of this fear mongering an anything electrical. I realize that electricians see a lot of dangerous and marginal wiring setups, but it’s kinda like an emergency room doctor lamenting that trampolines are evil and should be outlawed because they see so many trampoline injuries. The chances of an average person running into these scenarios is very small. And in this particular case, with a brand new receptacle and a brand new adapter that won’t be plugged and unplugged all the time, it is more than safe enough.

And yes, “illegal” as used above is actually a false statement.

 

[davewill]

I concur, especially about the FUD. Both jumping on every newbie who has a question and fear-mongering on third party adapters is getting REALLY old. You can likely install a 6-30 and use the above adapter, or you can get a wall connector, hard wire it and set it for a 30a circuit. I'd probably do the latter since I think the wall connector is a better choice for daily charging, but I see absolutely no problem with the adapter.

BTW, do we know for sure that he DOESN'T include a temperature sensor in his adapters? It would be really easy to do so.

 

[mswlogo]

I concur, especially about the FUD. Both jumping on every newbie who has a question and fear-mongering on third party adapters is getting REALLY old. You can likely install a 6-30 and use the above adapter, or you can get a wall connector, hard wire it and set it for a 30a circuit. I'd probably do the latter since I think the wall connector is a better choice for daily charging, but I see absolutely no problem with the adapter.

BTW, do we know for sure that he DOESN'T include a temperature sensor in his adapters? It would be really easy to do so.

Do you know for sure it DOES still have that function? It would make sense to put it in the plug end (closest to the weakest link).

I wouldn't exactly call them "his" adapters. They are Tesla Adapters with the factory plug cut off (with LIKELY temperature sensor and neutral) and a screwed on plug (without a neutral and temperature sensor) at double the price.

I think there is just as much "fear-mongering" on using a 14-30 outlet without a neutral.

Can you PROOVE which is statistically safer?

I think the only 100% proper way to use a 10-2/30A circuit is a wall connector. I think we can agree on that.
All other solutions are a compromise. No one can prove which is the best compromise.

Newbies have no idea what they may be compromising. And a 6-30 to 14-30 adapter is even worse IMHO.
If anything, it might educate them enough to go with the wall connector.

I think just steering a newbie at the 6-30 modified adapter is not doing the newbie any favors.

It's really a shame Tesla doesn't offer a 6-30 adapter.

Also I think this is the first "newbie" thread other than a thread I created and the OP referenced that I've commented on that 6-30 3rd party MODIFIED adapter.

 

[johnr]

Hi, John Rowell here. I work at EVSE Adapters and actually make this adapter, so I'd be happy to answer any questions you might have here. Firstly, mswlogo is incorrect to assume that we hack off the temperature sensor. The temperature sensor is actually preserved and replaced into the new adapter. The new adapter retains the same functions - automatically setting the correct current limit, and automatic temperature derating.

Currently, these adapters are indeed assembled using OEM Tesla adapters by replacing the plug with a different one. That's the reason they're relatively pricey - besides the fact that we have to buy the original adapter at full retail price, it's a tricky process to carefully extract the circuit from the OEM adapter without damaging it. Unlike the Gen 1 adapters, these Gen 2 adapters actually contain a tiny circuit board inside the plug with its own computer chip. This circuit communicates with the UMC using a digital signal to set the correct current for that type of plug, and to reduce the current in the event of an over-temperature condition. Without this circuit, the adapter simply won't work. I've developed a technique to remove the circuit safely and efficiently, and once removed it's then reused inside the new plug. We are working on our own version of an equivalent circuit so we won't have to cut open Tesla adapters to make them, so I've had a good look at the way this circuit operates - I can't divulge much details here, but suffice it to say, it's rather impressively engineered.

 

[mswlogo]

Hi, John Rowell here. I work at EVSE Adapters and actually make this adapter, so I'd be happy to answer any questions you might have here. Firstly, mswlogo is incorrect to assume that we hack off the temperature sensor. The temperature sensor is actually preserved and replaced into the new adapter. The new adapter retains the same functions - automatically setting the correct current limit, and automatic temperature derating.

Currently, these adapters are indeed assembled using OEM Tesla adapters by replacing the plug with a different one. That's the reason they're relatively pricey - besides the fact that we have to buy the original adapter at full retail price, it's a tricky process to carefully extract the circuit from the OEM adapter without damaging it. Unlike the Gen 1 adapters, these Gen 2 adapters actually contain a tiny circuit board inside the plug with its own computer chip. This circuit communicates with the UMC using a digital signal to set the correct current for that type of plug, and to reduce the current in the event of an over-temperature condition. Without this circuit, the adapter simply won't work. I've developed a technique to remove the circuit safely and efficiently, and once removed it's then reused inside the new plug. We are working on our own version of an equivalent circuit so we won't have to cut open Tesla adapters to make them, so I've had a good look at the way this circuit operates - I can't divulge much details here, but suffice it to say, it's rather impressively engineered.

Well, until this information was shared, I HAD to assume it may not have retained that functionality.
I stand by my statements I made by the information we had at the time.
I would recommend sharing the information you just did above (abbreviated) that you do retain temperature motoring functionality [what you have is insufficient]. Just mention temperature monitoring is maintained.
I knew it still had to communicate current limits and that could have been in the other unmodified end.
All that would have been needed on the plug end is a thermo-coupler.
But all being in one circuit in the plug makes sense too.

I was correct that plug did have the temperature sensor. I went with the safest solution I could with info available.
If this information was shared with the product specs I probably would have used your adapter.

It also confirms that using a 6-30 to 14-30 adapter is a bad idea.

As my "QA" guy used to say when I would educate him verbally on how something worked in our system that wasn't properly documented.
He'd say "Now I Know". Hinting that everyone needs to know. Not just the folks reading this thread.