When I cut off my Tesla 14-50 adapter and replaced it with a Hubbell HBL9451C 14-50 plug I notice that the Tesla UMC cable has 7 conductors (2 red conductors and 2 black conductors for carrying the 40 Amps, 1 green/yellow stripe and a blue and violet signal wires). The red wires are in parallel and the black wires are in parallel. The 5 wires (2 red, 2 black & yellow/green) look to be 12 GA (could be 10 GA) it is hard to tell. I would like to see Tesla keep their charging equipment ambient temperature rise under 20 °C. I am an electrical engineer with more than 30 years experience and I agree with your electrician that the current carrying conductors are not adequate. Tesla should increase the conductor to at least the next gage bigger. I like the Roadster mobile charger.
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Scary issue with Nema 14-50 adapter melting
- Thread starter robertmgarrett
- Start date
When I cut off my Tesla 14-50 adapter and replaced it with a Hubbell HBL9451C 14-50 plug I notice that the Tesla UMC cable has 7 conductors (2 red conductors and 2 black conductors for carrying the 40 Amps, 1 green/yellow stripe and a blue and violet signal wires). The red wires are in parallel and the black wires are in parallel. The 5 wires (2 red, 2 black & yellow/green) look to be 12 GA (could be 10 GA) it is hard to tell. I would like to see Tesla keep their charging equipment ambient temperature rise under 20 °C. I am an electrical engineer with more than 30 years experience and I agree with your electrician that the current carrying conductors are not adequate. Tesla should increase the conductor to at least the next gage bigger. I like the Roadster mobile charger.
This prompted me to go look at my welder (Lincoln PowerMIG 180). It's cord has a 6-50 plug with 12Ga wiring. The 180C is rated @ 20A input, 130A/30% duty cycle output (no mention of max input current at max output of 180A, but, if linear, (180/130)*20=~28A would be a good guess). The recommended breaker is a 40A.
As FlasherZ points out, Lincoln can use a seemingly undersized cord (12Ga vs 10Ga) because of the intermittent duty cycle. I would not even consider charging @ 40A with wire smaller than 6Ga.
Yes!!! You are never going to burn up your home or garage by installing over size wire. There are 3 EVs in my family (2 Leafs and 1 Model S). I have 3 EV chargers at home (HPWC, Blink & the Nissan charger modified by EVSE Upgrade to 240 VAC, 20 AAC). I personally run 6 GA wire (or larger) for my EV connections and run only 1 EV charger on a breaker (100 Amp. for HPWC, 50 Amp. for Blink and 20 Amp. for Nissan running at 16 Amps.). So, my home chargers (knock on wood) are running cool and working well.
My work charger is where I have issues. I use the Tesla UMC at 40 Amps. Sense I replaced my Tesla 14-50 adapter with the Hubbell plug (for a 10 days now) everything on the UMC is 50 °C or less (still too hot in my opinion but working for now). In order to keep tabs on the UMC I have ordered non-reversible temperature labels from omega. I will see how that works.
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Woops, I am running 40 Amp. breaker on my Blink charger.
Just read the whole thread. Scary stuff. I'm on my 2nd UMC - Tesla replaced the first one for me for free (many months ago) because it seemed too hot to the touch for me although there was no evidence of burning. My new one seems too hot at times as well (and I'm still waiting for the new generation UMC which I haven't received in the mail yet.)
Maybe for even more safety the answer it to sheer off the end of the connector like Jim did, but instead of putting a new NEMA 14-50 plug on it, hard wire the wires directly into a junction box - that way you bypass both the NEMA 14-50 outlet and all plugs except the one that goes into the car. The only downside is that the modified UMC would no longer be a portable device so you'd need to buy an extra UMC to charge on the go. (My reason for not just getting an HPWC is that I don't have dual chargers so could never make use of above 40A and the extra cost involved in getting the HPWC.)
So for now, at a minimum I'm going to dial down my charging rate to ~24A or so for peace of mind (I charge primarily in the middle of the night) and add an extra smoke detector above the outlet. I'm wondering now if there's a way to set up a smoke detector that when the alarm goes off could automatically open a cutoff switch on the charger circuit?
Just had another thought, isn't that what AFCI breakers are for? Maybe installing a 50A AFCI breaker would be the way to go for fire/burning detection. Probably pricy though... on the other hand, this kind of burning isn't really due to arcing so that might not do any good.
Maybe for even more safety the answer it to sheer off the end of the connector like Jim did, but instead of putting a new NEMA 14-50 plug on it, hard wire the wires directly into a junction box - that way you bypass both the NEMA 14-50 outlet and all plugs except the one that goes into the car. The only downside is that the modified UMC would no longer be a portable device so you'd need to buy an extra UMC to charge on the go. (My reason for not just getting an HPWC is that I don't have dual chargers so could never make use of above 40A and the extra cost involved in getting the HPWC.)
So for now, at a minimum I'm going to dial down my charging rate to ~24A or so for peace of mind (I charge primarily in the middle of the night) and add an extra smoke detector above the outlet. I'm wondering now if there's a way to set up a smoke detector that when the alarm goes off could automatically open a cutoff switch on the charger circuit?
Just had another thought, isn't that what AFCI breakers are for? Maybe installing a 50A AFCI breaker would be the way to go for fire/burning detection. Probably pricy though... on the other hand, this kind of burning isn't really due to arcing so that might not do any good.
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Yes, AFCI's react to these types of problems, but they're expensive and typically only available at the 15/20A levels for general-purpose receptacle use. NEC calls for them only for outlets in living spaces. You're also correct in that they won't solve all these problems - the electronics in an AFCI look for the pattern of an arc-fault, but they can't detect high-resistance, high-heat scenarios where there is no arc.
So this just happened. Some facts: plug was seated all the way and supported(the unseated pic is to show damage, not how it was). Drawing 40A on 50A breaker. 99 degrees inside garage. Car continued to draw 40A as it was melting. No warning message from car. The cord was very hot. No damage whatsoever between adapter and cord like others have posted. Adapter is the updated version, not the original(I have a 2013. Is there a 3rd gen adapter out?) No smoke and definitely no flame. I simply smelled an electrical smell as I walked through my garage and ran my nose around until I found it.
An in-law that's an electrician informed me that a loose connection could have caused it. The plug for the black wire fried so it may have lost positive contact with the red wire's plug and pulled all 40A thru the black wire and melted it. Am I guessing that right? The 14-50 was existing when we bought the house so there's a good chance it's 14 years old, however I don't think it was used by the previous owner.
Regardless, I cleaned up the damage and hooked up a new 14-50. Both phases read proper voltage. The new plug is a noticeably tighter connection. The previous outlet seemed tight but this new one has zero movement. I've also set the default draw to 30A for extra margin.
If there are any other suggestions or comments, feel free.
An in-law that's an electrician informed me that a loose connection could have caused it. The plug for the black wire fried so it may have lost positive contact with the red wire's plug and pulled all 40A thru the black wire and melted it. Am I guessing that right? The 14-50 was existing when we bought the house so there's a good chance it's 14 years old, however I don't think it was used by the previous owner.
Regardless, I cleaned up the damage and hooked up a new 14-50. Both phases read proper voltage. The new plug is a noticeably tighter connection. The previous outlet seemed tight but this new one has zero movement. I've also set the default draw to 30A for extra margin.
If there are any other suggestions or comments, feel free.
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RAM_Eh
Member
Definitely a loose connection, either in the plug not seating properly in the receptacle or the wire not tight on the terminal. Either one would melt the plug with enough power running through it.
Others have addressed that it was almost certainly a loose connection, but just for education’s sake, I wanted to address this part.
AC electricity doesn’t work that way. It cannot send energy just through one wire if the car side connection is OK. (At the moment I’m not talking about shock situations, where something or someone may touch a live wire that has no current flow and accidentally makes a path to ground, which does allow current to flow in an electrocution type of event.) The loose connection in your outlet means that the contact point becomes very thin, which means the resistance goes up incredibly. Running that same power through a very thin high resistance point generates a ton of heat. If the wire were to be completely disconnected, as you are talking about, current flow would stop. In these kinds of situations, it is simply a race of whether the wire will melt through and break the connection, stopping the current (lucky), or whether the resistive point will get so hot it catches something on fire around it (unlucky).
AC electricity doesn’t work that way. It cannot send energy just through one wire if the car side connection is OK. (At the moment I’m not talking about shock situations, where something or someone may touch a live wire that has no current flow and accidentally makes a path to ground, which does allow current to flow in an electrocution type of event.) The loose connection in your outlet means that the contact point becomes very thin, which means the resistance goes up incredibly. Running that same power through a very thin high resistance point generates a ton of heat. If the wire were to be completely disconnected, as you are talking about, current flow would stop. In these kinds of situations, it is simply a race of whether the wire will melt through and break the connection, stopping the current (lucky), or whether the resistive point will get so hot it catches something on fire around it (unlucky).
I truly appreciate you taking the time to explain that. Makes sense.
Now I haven't verified this with multiple tests but after charging for a couple hours at 30A, it seemed the prong for the black wire(same wire that got hot) was much hotter than the prong for the red wire. i.e., the prong for the black one would just nearly burn you the red one was simply warm. Mind you this is with the new outlet and adapter. Could my cord be causing an asymmetric draw? Tesla doesn't think it is but wants to replace the cord to rule it out. What else could cause this, if it is indeed one wire that's overheating?
Now I haven't verified this with multiple tests but after charging for a couple hours at 30A, it seemed the prong for the black wire(same wire that got hot) was much hotter than the prong for the red wire. i.e., the prong for the black one would just nearly burn you the red one was simply warm. Mind you this is with the new outlet and adapter. Could my cord be causing an asymmetric draw? Tesla doesn't think it is but wants to replace the cord to rule it out. What else could cause this, if it is indeed one wire that's overheating?
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The car has no idea that plug is hot. In the case of a loose connection or not, the plug itself does NOT have the ability to cool itself. The cooling comes entirely from the things plugged into it from either side. For that reason, it's imperative that you use large gauge (6AWG) copper wire, and that it is torqued down properly for best heat transfer, which for that type of plug, make sure to use a square driver instead of slotted, and basically as tight as possible.
When you replace the receptacle, spend a little more and buy the one made by Hubble. It is a little more robust with stronger, larger lugs and contacts. Costs about $48 compared to ~$15 for the Leviton.
FlatSix911
Porsche 918 Hybrid
davewill
Active Member
If it's the same unit that was burnt by the outlet, it could easily have been damaged enough to be causing a poor connection on that side. Definitely replace it.
This was Tesla's advice also. The Hubble and Cooper outlet are commercial grade and are better able to handle heat and constant use. I was told this after I had already bought and installed a new Leviton outlet. I'll be getting a better outlet.
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