NEMA 14-50 Plug Meltdown / Near Fire

[Rocky_H]

I connect the UMC Gen 2 to 10-30R dryer receptacle and limit the current at 25A.

On a 30 amp circuit you should be at a maximum of 24 amps. (80% of 30).

This indicates to me that @cfan is using one of those third party things that converts a 10-30 plug to a 14-50 receptacle. You should probably go ahead and get the proper Tesla 10-30 adapter, so it will automatically set the current at 24A for you, without a change of the car forgetting that setting and going too high.

 

[Phlier]

I actually emailed Tesla charging support about this and chastised them for not having a strip gauge on the unit

It appears that you calling them out on this worked! My HPWC had a strip gauge in the unit, although there still wasn't a strip length published in the manual... at least, that I recall. Now I'm gonna have to go look.

I usually DIY when it comes to small household electrical jobs, but a 240 volt, 100 amp breaker, 3 gauge copper, a disconnect, and bending 1.25" conduit made me call out a proper sparky. Same company I've been using for electrical and refrigeration for 25+ years now, and I trust them completely. They did a great job, and having the 240v/100a breaker with the 3 gauge copper and disconnect will allow me to put in a second HPWC and fully utilize it at the same time as the first... I just can't run both house HVAC units at the same time.

 

[eprosenx]

It appears that you calling them out on this worked! My HPWC had a strip gauge in the unit, although there still wasn't a strip length published in the manual... at least, that I recall. Now I'm gonna have to go look.

I usually DIY when it comes to small household electrical jobs, but a 240 volt, 100 amp breaker, 3 gauge copper, a disconnect, and bending 1.25" conduit made me call out a proper sparky. Same company I've been using for electrical and refrigeration for 25+ years now, and I trust them completely. They did a great job, and having the 240v/100a breaker with the 3 gauge copper and disconnect will allow me to put in a second HPWC and fully utilize it at the same time as the first... I just can't run both house HVAC units at the same time.

Nice! So is their strip gauge a sticker? Or did they change the plastic mold? I would be curious to see a picture if you have one!

Note that 3 awg should have been able to fit in 1” EMT conduit. Did they use 1.25 just to make it easier to pull? Did they do PVC or EMT?

As discussed, a disconnect is not required (just a breaker lock off clip for over 60a), but if it makes it easier to add the second unit later than by all means.

If you are worried about running the second HVAC unit at the same time then they probably did not do a proper load calculation. But if you only have one car for now it is probably OK (though you don’t really know without a load calc). Most houses don’t have 100a of spare service capacity laying around!

 

[Phlier]

Nice! So is their strip gauge a sticker? Or did they change the plastic mold? I would be curious to see a picture if you have one!

It's molded into the plastic. Darn, I should've snapped a pic of it before he installed it. I'll see if taking the top cover off will allow access to it, but I'm not sure it will... Edit: Nope, I don't think it will, as the strip gauge is on the mounting assembly that the HPWC then attaches to. : /

Note that 3 awg should have been able to fit in 1” EMT conduit. Did they use 1.25 just to make it easier to pull? Did they do PVC or EMT?

Even though it wasn't required for the HPWC, I had him pull a neutral wire also, in case I wanted to add a plug that requires a neutral at some point. He used EMT. Did a great job... very happy with it. Man, bending conduit like that is a real art.

If you are worried about running the second HVAC unit at the same time then they probably did not do a proper load calculation. But if you only have one car for now it is probably OK (though you don’t really know without a load calc). Most houses don’t have 100a of spare service capacity laying around!

I can run both house AC units and the HPWC at the same time, but when I add a second HPWC, it'll be pretty close... I'll have them do a proper load calc when the time comes.

Electricity is so cheap here that it actually doesn't make sense to use natural gas. At some point, I'd like to add another 200 amp service to the house and switch *everything* over from gas to electric, and also to give me a lot of capacity to the detached workshop/garage that'll be built when Central Accounting approves the expense.

 

[lolder]

It's important that the 14-50 receptacle be a Bryant or similar more rugged outlet than the hardware store or Lowes/ Home Depot ones. The Bryant is $40 and needs a bigger dual gang faceplate available from Zoro: Bryant 50A 4W Single Receptacle 125/250VAC 14-50R BK 9450FR | Zoro.com. They have more robust clamping methods for the #6 wire.

 

[artsci]

Just found this post and thread. Glad to hear your house was not damaged.

For reference please insist that your electrician use Hubbell branded NEMA 14-50 receptacles and plugs. They cost much more (nearly $100) for a receptacle but they provide a much larger margin for safety than Leviton or any of the other cheap stuff.

 

[vickh]

is frequent plugging/unplugging a factor? I'm sharing the dryer plug no, but reading this thread makes me want to go to the Tesla wall charger in our new house

 

[cfan]

On a TT-30 (30a circuit) you should be limiting current to 24 amps! 80% of 30. Your voltage drop issues may have been in part due to you over drawing on the circuit (but yeah, probably mostly due to really long wires improperly sized, or maybe loose connections too).

I usually get around 245v at 48a at home (I am close to the substation and my transformer). Very solid charging speed!!!

I have had a similar experience at some of the early model superchargers. I have noticed that the "handles" on the newer ones seem cushioned and only get warm.

I did mention it to the mobile tech who met me in a shopping center to replace my passenger side airbag. He said that Tesla has replacement cable/ connectors for the wall units, with 24 ft cable. My original cable is 18 ft. I have heard that the longer the cable, the warmer it gets. I know this is true for three-wire AC extension cords. I do not need more than 12 feet. I do not know if they can be shortened.

Tesla has short cable option for the Wall Connector. It's 8'5 i

 

[cfan]

Oh, no!

Yeah, this is vitally important that people follow that 80% rule. This is why I am really glad that EVSEAdapters finally was able to start making real-ish adapters that fit directly to the UMC and dictate the current limit. It's a bit risky for people who don't know this stuff well enough to use adapter of a 30 amp outlet to a 50 amp outlet type and think that they can run constant 30A from a 30A circuit.

80% is not a magic number. 80% is just a re

This indicates to me that @cfan is using one of those third party things that converts a 10-30 plug to a 14-50 receptacle. You should probably go ahead and get the proper Tesla 10-30 adapter, so it will automatically set the current at 24A for you, without a change of the car forgetting that setting and going too high.

80% of rating current is just a rule of thumb, not a law. You don't need to be exactly at 80%. You can set at 75% if you want. I set the limit at 25A for easy to remember.

 

[eprosenx]

It's molded into the plastic. Darn, I should've snapped a pic of it before he installed it. I'll see if taking the top cover off will allow access to it, but I'm not sure it will... Edit: Nope, I don't think it will, as the strip gauge is on the mounting assembly that the HPWC then attaches to. : /

Ah, interesting. I wonder if it has always been there and I never noticed. I did not use the optional mounting assembly (that is for conditions like conduit entering from the top).

Even though it wasn't required for the HPWC, I had him pull a neutral wire also, in case I wanted to add a plug that requires a neutral at some point. He used EMT. Did a great job... very happy with it. Man, bending conduit like that is a real art.

Ah, got it. Yeah, I probably would not have run a neutral. Really no purpose for it for EV charging. ;-) I have not seen manual benders for 1.25". Largest they sell at Home Depot is 1"? Or was it a hydraulic bender?

I can run both house AC units and the HPWC at the same time, but when I add a second HPWC, it'll be pretty close... I'll have them do a proper load calc when the time comes.

Technically if you have a 100a circuit into a Wall Connector and the Wall Connector is set as such then in my book that counts as an 80a continuous draw (which is calculated as 100a). While your car may only take 48a, if an older Model S came by and plugged in it could draw a full 80a continuous even without a second Wall Connector. ;-)

Electricity is so cheap here that it actually doesn't make sense to use natural gas. At some point, I'd like to add another 200 amp service to the house and switch *everything* over from gas to electric, and also to give me a lot of capacity to the detached workshop/garage that'll be built when Central Accounting approves the expense.

Yeah, so I presume you would upgrade from a 200a service to a 320a service (that is a continuous rating number, so it is kind of more like a 400a service - it is generally delivered as two 200a panel handoffs). My next house will of course have a 320a service since I won't even have the option of Natural Gas.

 

[eprosenx]

Just found this post and thread. Glad to hear your house was not damaged.

For reference please insist that your electrician use Hubbell branded NEMA 14-50 receptacles and plugs. They cost much more (nearly $100) for a receptacle but they provide a much larger margin for safety than Leviton or any of the other cheap stuff.

Check out this thread: Definitive 14-50 NEMA Outlet Guide

My conclusion is that the Bryant receptacle is plenty good quality and is a much better bang for your buck than the Hubbell one (which is nearly identical).

is frequent plugging/unplugging a factor? I'm sharing the dryer plug no, but reading this thread makes me want to go to the Tesla wall charger in our new house

Yes, frequent unplugging of the EV/Dryer is NOT recommended. Most consumer grade receptacles just don't handle it well.

I personally am a massive fan of the Wall Connector over any kind of receptacle/EVSE combo, but the decision criteria depends on your price sensitivity among other things...

80% is not a magic number. 80% is just a re


80% of rating current is just a rule of thumb, not a law. You don't need to be exactly at 80%. You can set at 75% if you want. I set the limit at 25A for easy to remember.

Umm, the 80% rule (actually the 125% rule) is written into the National Electrical Code. It is code, not a recommendation. 80% of 30a is 24a.

 

[Rocky_H]

80% is not a magic number. 80% is just a re

I presume that last word was going to be "recommendation". No, it's not just a recommendation. It is a hard limit defined in National Electrical Code. They define almost everything in there as very specific hard limits and rules and very few things they will leave up to recommendations, because they know that a lot of people will get away with whatever bad ideas they can come up with if they aren't required to follow actual rules.

80% of rating current is just a rule of thumb, not a law.

Um, nope. Following the rules of NEC when building or remodeling is considered actual law in most city codes. You don't just get to decide whether you follow those rules or not. And again, it's not just a rule of thumb. It is a defined limit.

You don't need to be exactly at 80%. You can set at 75% if you want.

Are you kidding me? Don't be purposefully dense. It is an upper limit. That means the maximum. Sure, you could run less current if you want, but the meaning of an upper limit is that you cannot run more than that. That's kind of the whole paradigm of NEC, is that you can usually run less voltages or currents if you want (Everything is safe with 0 voltage or current!) but these are upper limits that you can't go over.

The actual definition of the rule states that for the continuous current on the circuit, the circuit rating must be 125% of that continuous current--so basically an extra fourth. (Current draw being 80% of the circuit rating is just the reverse of that if you're going from the number of the breaker first.) So if you have 40 amp draw, it needs an extra 10 amps, therefore 50. 32 amps needs an extra 8, therefore 40, etc. With your 25 amp example, that would need an extra 6.25 amps to have the sufficient circuit. That would need at least a 31.25 amp circuit breaker. 30 amp does not meet that, so no, you cannot run 25 amps on a 30 amp rated circuit.

 

[Phlier]

Ah, interesting. I wonder if it has always been there and I never noticed. I did not use the optional mounting assembly (that is for conditions like conduit entering from the top).

Yup, we did the conduit entering from the top, as he had routed the conduit along the garage ceiling, then down the wall where the HPWC is mounted.

Technically if you have a 100a circuit into a Wall Connector and the Wall Connector is set as such then in my book that counts as an 80a continuous draw (which is calculated as 100a). While your car may only take 48a, if an older Model S came by and plugged in it could draw a full 80a continuous even without a second Wall Connector. ;-)

D'oh, of course! Totally makes sense for load calc.

Yeah, so I presume you would upgrade from a 200a service to a 320a service (that is a continuous rating number, so it is kind of more like a 400a service - it is generally delivered as two 200a panel handoffs). My next house will of course have a 320a service since I won't even have the option of Natural Gas.

Our little town was really surprised, and not in a good way... We only got natural gas service here in the mid '90's. Man, the natural gas company went into full hype mode, spending a ton of money around town on bill boards, radio ads, TV ads, the whole shebang. Kept telling us about how much we were going to save by switching our appliances over to natural gas! Even gave us huge discounts and credits as incentives to make the switch! We were gonna save a fortune!

Well... not so much. Turns out that our electricity is so cheap (and their natural gas so expensive) that the average utility bill went *up* for those that switched.

Unfortunately, my current house has a lot more natural gas than I'd like. And my heating units, while still heat pumps, switch over to natural gas when the heat pump can't keep up. Honestly, it would be cheaper if it was just a heat pump backed up with a resistive heater than a heat pump backed up by NG. Unfortunately (again), rather than installing the resistive units (as is traditional on heat pumps), they didn't even install the resistive backup heaters in favor of the NG. So I don't even have the option to use anything other than NG when the pump can't keep up. I honestly think that the NG company is giving kick backs to home builders that install heat pump/NG units instead of heat pump/resistive electric. It's really the only logical explanation.

I really wish we no longer had the option of natural gas.

Umm, the 80% rule (actually the 125% rule) is written into the National Electrical Code. It is code, not a recommendation. 80% of 30a is 24a.

I think in this case he's referring to the setting on the HPWC itself... the rotary dial that allows you to select how many amps it'll pull. He's saying you can back that down below 80% of your breaker rating if you want.

Edit: As per the manual, if you are going to change the rotary dial setting, de-energize the circuit before hand!

 

[vickh]

natural gas cooking is great,but that's the only thing we don't have

I almost went went CNG civic, but glad I didn't..

 

[Chickenlittle]

I agree, and even professionals can make mistakes.

At least 2 or 3 mistakes here
1. Did home owner insist on permit, which would have required inspection of work
2. Was inspection done?
3. Electricians mistake

Bought new home and had builder install nema 14-50. I never saw any inspection done and saw no permit drawn. I demanded a permit be done despite assurances that the electrician had decades of experience. I was there for inspectors arrival and they looked at outlet and started signing off. I asked how looking at outlet could be considered an inspection of work and she told electrician to take off the face plate. While removing the face plate large click and electrician fell back (was shocked). I asked inspector whether that was a fail. He had left an exposed wire too long and it was contacting the screw. It could have been me.

 

[derotam]

At least 2 or 3 mistakes here
1. Did home owner insist on permit, which would have required inspection of work
2. Was inspection done?
3. Electricians mistake

Bought new home and had builder install nema 14-50. I never saw any inspection done and saw no permit drawn. I demanded a permit be done despite assurances that the electrician had decades of experience. I was there for inspectors arrival and they looked at outlet and started signing off. I asked how looking at outlet could be considered an inspection of work and she told electrician to take off the face plate. While removing the face plate large click and electrician fell back (was shocked). I asked inspector whether that was a fail. He had left an exposed wire too long and it was contacting the screw. It could have been me.

Yeah I love the laws that put the legal requirement on the owner to get a permit(Fairfax County, VA). It should be a legal requirement applied to whoever is actually doing the work. I've seen so many companies quote people for projects and never once say anything about a permit.

 

[Bill25cycle]

It was a Leviton brand receptacle. My electrician is a hard-working, experienced tradesman. He was on-the-job training a junior helper. What I presume is that the heavy-duty gauge of the wiring gave the impression that the connection was tight and firm. Both my 50 amp breaker and my whole-house breaker tripped simultaneously, in a conflagration/peak.

Here is a better photo of the damage done to the receptacle.View attachment 417002

I wouldn't blame the electrician here... I blame Stores like Home Depot for selling the Leviton Junk.

Years ago I installed a Leviton 6-50 and then when installing it, using only moderate torque, the white-metal threads of the attachment lug stripped. I threw the junk in the garbage and replaced it with Bryant.

I will only use Bryant or Hubbell for Continuous Loads such as EV car charging. As this Blog shows, installing Leviton is Borderline Criminal.

 

[Bill25cycle]

I wouldn't blame the electrician here... I blame Stores like Home Depot for selling the Leviton Junk.

Years ago I installed a Leviton 6-50 and then when installing it, using only moderate torque, the white-metal threads of the attachment lug stripped. I threw the junk in the garbage and replaced it with Bryant.

I will only use Bryant or Hubbell for Continuous Loads such as EV car charging. As this Blog shows, installing Leviton is Borderline Criminal.



I'm really getting sick of Leviton in general. Home Depot as a for instance sells plenty of the Leviton Crap. Pull chain basement ceiling lights break after 4 on-off cycles, after REPEATED replacement - meaning nearly 100%
of them are Junk.

(The Legrande stuff at Lowe's is also made in China, but of a better quality).

What gets me is there is NOTHING in the new 2020 NEC addressing this. They have plenty of other really silly requirements - one of which is banning NEMA 14-60 plug-in circuits for the expected avalanche of 48 ampere fixed in place, or portable charging facilities (for all the new ev's coming out with 48 ampere chargers) - limiting such to either 30 or 50 ampere receptacles max. No matter that the 50 ampere receptacles from Leviton seem to melt down. Or that you can't have adjustable 'fixed in place' EVSE's any longer. Underwriter's Laboratories has been SUSPECT for years, as a for instance, this Leviton Total Crap gets a listing. They must have insisted on a Blind, Deaf and Dumb tester.

As far as the 6-50 or 14-50 debate, I think FORD has standardized on the 14-50 for their 'occasional use cord', so that means that the 14-50 receptacles will win, just like VHS supplanted the superior Betamax. Being best has nothing to do with most popular.

Many EV drivers to the boonies stop at camp grounds with 14-50, and TT-30 , ( but no 6-50 ) receptacles... I vote for 14-50 in the interest of standardization even though I hear the complaints of added cost..

But whatever you decide to install, avoid the 'firestarter' branded receptacles.

 

[nwdiver]

which would have required inspection of work

I've seen a lot of electrical inspections. None of them checked for loose wires.

 

[Silver Rocket]

View attachment 416954 View attachment 416958 View attachment 416959

My main house breaker tripped tonight. Upon investigating, I saw black smoke curling up my garage wall and smelled burning plastic, from where my 14-50 plug is located. Turns out my electrician had installed the plug with a loose black conductor, causing the outlet and plug to meltdown. At this point I am much more relieved than upset because I was able to stop what could have been a disaster. I will be double-checking every connection myself going forward in the install of a HPWC to replace the 14-50! If you smell burning plastic, investigate!

You can’t use stranded wire!