Suitability of NEMA 14-50 for EV charging -- Child Safety & Thermal Cutoff

[brycenesbitt]

I dont think a EVSE provides any supplementary overload protection, so the sync signal is its only overload protection.

Pretty sure every EVSE has current monitoring.... all the common ones do for sure.
They could detect this particular condition, and perform a soft notification of the user (for connected units) or a hard shutoff (for all units). The EVSE could drop the pilot signal completely and if the car does not back off then drop the relay under load (not idea, but better).

The advantage of doing this in the EVSE is the network connection. Network connections are not at all common in dumb GFCI devices upstream.

 

[wwhitney]

Pretty sure every EVSE has current monitoring.... all the common ones do for sure.

Really, they have CTs on individual conductors, not just one CT on all the conductors for the ground fault monitoring?

Cheers, Wayne

 

[jaggedben]

Really, they have CTs on individual conductors, not just one CT on all the conductors for the ground fault monitoring?

Cheers, Wayne

You'd only need one additional CT to measure line current.

 

[jaggedben]

At some point we opened up an EVSE and got some pics inside but I can't readily find them.

I do know for a fact that the latest IQ smart EVSE fron Enphase (updated Clipper Creek product) can measure current, because it reports charging energy to the app.

 

[jaggedben]

I'd assume most if not all of the wi-fi connected ones have that.

 

[tortuga]

Pretty sure every EVSE has current monitoring.... all the common ones do for sure.

Well from what I can tell, the UL product standard 2594 section 28.1 does not require any supplementary overcurrent protection for a EVSE.
If any do provide that they are going above and beyond the product standard, the only protection is that 1khz signal.
It would be key to get access to any stored data from a recording ammeter after a melting incident.
I suspect we'd see the chargers in question exceeding 40 amps, and it would not have to be much over.

It is a weakness in the NEMA receptacle/cord cap system that a slight overload can cause a slow meltdown that a inverse time breaker does not detect.
The simple reproducible example is take a UL listed 1.5 - 1.6 kw space heater, plug it into a standard 5-15 (120V 15Amp) receptacle with #14 NM-B on a 15A breaker, run the heater continuously on the top setting in an unheated space. Since its slightly over the receptacle's maximum continuous rating of 12 amps (1440 Watts) the plug will eventually become soft and deform.

 

[brycenesbitt]

I suspect we'd see the chargers in question exceeding 40 amps, and it would not have to be much over.

I suspect we'd find connectors not properly torqued.
Many, maybe most, of the travel chargers have a temperature sensor built into the plug. This I feel is the "right solution" because it accounts for so many potential evils.

 

[don_resqcapt19]

Well from what I can tell, the UL product standard 2594 section 28.1 does not require any supplementary overcurrent protection for a EVSE.
If any do provide that they are going above and beyond the product standard, the only protection is that 1khz signal.
It would be key to get access to any stored data from a recording ammeter after a melting incident.
I suspect we'd see the chargers in question exceeding 40 amps, and it would not have to be much over.

It is a weakness in the NEMA receptacle/cord cap system that a slight overload can cause a slow meltdown that a inverse time breaker does not detect.
The simple reproducible example is take a UL listed 1.5 - 1.6 kw space heater, plug it into a standard 5-15 (120V 15Amp) receptacle with #14 NM-B on a 15A breaker, run the heater continuously on the top setting in an unheated space. Since its slightly over the receptacle's maximum continuous rating of 12 amps (1440 Watts) the plug will eventually become soft and deform.

The product standard requires testing at the receptacles maximum rated current and not at the 80% current The maximum permitted temperature rise, as measured at the male plug blade, while carrying its maximum rated current, is 30°C. That should not be enough to cause the receptacle materials to soften.

 

[tortuga]

The product standard requires testing at the receptacles maximum rated current and not at the 80% current The maximum permitted temperature rise, as measured at the male plug blade, while carrying its maximum rated current, is 30°C. That should not be enough to cause the receptacle materials to soften.

Interesting thanks don, so whatever plastic they use is not supposed to get soft at 160F?

 

[don_resqcapt19]

Interesting thanks don, so whatever plastic they use is not supposed to get soft at 160F?

That is my assumption.

In chats with a person that works for one of the receptacle companies, it is his opinion that the receptacle failures (ones that are not caused by misuse or installation errors) are a result of manufacturing changes after the initial listing, and the failure of the listing agency to do the random follow up testing for a previously listed product.

 

[wwhitney]

receptacle failures (ones that are not caused by misuse or installation errors).

Do we have reliable data showing such failures?

Because if we just have anecdotal evidence of EVSE receptacle failures, a plausible hypothesis is that EVSEs stress the receptacle much more than dryers and range, and so far more of the misinstalled receptacles turn into failures when an EVSE is attached.

Cheers, Wayne

 

[don_resqcapt19]

Do we have reliable data showing such failures?

Because if we just have anecdotal evidence of EVSE receptacle failures, a plausible hypothesis is that EVSEs stress the receptacle much more than dryers and range, and so far more of the misinstalled receptacles turn into failures when an EVSE is attached.

Cheers, Wayne

We will never have any "reliable" data on that issue...there is no investigation when a plug and receptacle fails.

 

[tortuga]

We will never have any "reliable" data on that issue...there is no investigation when a plug and receptacle fails.

Some light reading:

https://www.ojp.gov/pdffiles1/nij/grants/243828.pdf

 

[GeorgeB]

The simple reproducible example is take a UL listed 1.5 - 1.6 kw space heater, plug it into a standard 5-15 (120V 15Amp) receptacle with #14 NM-B on a 15A breaker, run the heater continuously on the top setting in an unheated space. Since its slightly over the receptacle's maximum continuous rating of 12 amps (1440 Watts) the plug will eventually become soft and deform.

Others have pointed out the standard requires testing at 100% load, so no more on that.

MANY have disassembled 5-15R and 5-20R devices and observed that the only difference is the T slot in the "front". Whether the contact area and pressure via construction is the same for the "horizontal" and "vertical" "white wire" spring loaded contact sets hasn't been presented. The "black wire" males are the same from what I have seen.

So, in my OPINION, a 5-15R made by a manufacturer who also makes 5-20R devices should not exceed the 30C rise. An ambient of 40C (104F) and a 30C rise gets you to 70C (158F), roughly the 160F that @don_resqcapt19 suggested (and I agree) would not result in softening of any internal components.

Could the 50A male (USUALLY molded on EVSEs I've seen pictured) be the primary heat generator? I doubt it would conduct heat from the wire termination, which seems would be the weakest portion, through the receptacle without first melting the (probably undersized) wire.

I'm with the rest here who suspect the wire to receptacle. But I'll 100% agree that the box lug design may be much of the problem. I've not seen anyone compare the Hubbell and elCheapo 14-50R devices.

 

[retirede]

I've not seen anyone compare the Hubbell and elCheapo 14-50R devices.

Hubbell on the top, Leviton below.

This one is Leviton on the top:

 

[curt swartz]

It would not surprise me if most of the failures are Leviton receptacles. Leviton's clamp terminations have always been horrible. Years ago when Leviton was my main line I would not let my guys use the clamps with solid conductors for 15/20 amp devices. You could tighten up the clamps then push the device into the box. If you pulled the device out of the box the wires would pull right out of the clamps. Any slight rotation of the conductors would cause the wires to be as loose as if you never tightened them at all.

With power receptacles I have always pre-bent the wires to line up with the terminations. I land the wires and tighten. Push the device into the box then gently pull it back out bending it enough to get to the screws. Verify connections are still tight then push device back into box and secure.

I had switched to Legrand prior to Leviton redesigning their power receptacle to have the wires enter the back. When I first saw them I was not impressed. I could easily see the connections loosening up as the installer was twisting the receptacle trying to get it into the box.

I have never had the issue of small solid conductors loosening up with slight twisting on Legrand or Hubbell devices.

 

[brycenesbitt]

All this would be solved if EVSE plugs were required to have thermal sensors. Oddly it's the 5-15 cordsets that seem to have such sensors, not the higher amperage versions. Anyone using a crappy Leviton would quickly find their EVSE shuts down with a thermal warning.

 

[electrofelon]

My opinion is that receptacles in general need to be made better and have a more rigorous product/testing standard. If I think about all the "burnt up" stuff I have seen in my career, probably 95% of them have been receps.

 

[retirede]

All this would be solved if EVSE plugs were required to have thermal sensors. Oddly it's the 5-15 cordsets that seem to have such sensors, not the higher amperage versions. Anyone using a crappy Leviton would quickly find their EVSE shuts down with a thermal warning.

If the initial failure begins where the branch circuit conductors are attached, it may be too late by the time the plug sensor can detect it.

 

[don_resqcapt19]

Well from what I can tell, the UL product standard 2594 section 28.1 does not require any supplementary overcurrent protection for a EVSE.
If any do provide that they are going above and beyond the product standard, the only protection is that 1khz signal.
It would be key to get access to any stored data from a recording ammeter after a melting incident.
I suspect we'd see the chargers in question exceeding 40 amps, and it would not have to be much over.

It is a weakness in the NEMA receptacle/cord cap system that a slight overload can cause a slow meltdown that a inverse time breaker does not detect.
The simple reproducible example is take a UL listed 1.5 - 1.6 kw space heater, plug it into a standard 5-15 (120V 15Amp) receptacle with #14 NM-B on a 15A breaker, run the heater continuously on the top setting in an unheated space. Since its slightly over the receptacle's maximum continuous rating of 12 amps (1440 Watts) the plug will eventually become soft and deform.

That is not what the UL 498 says. The standard requires the receptacle to be subjected to 50 make and break operations at 150% of the receptacle rating, and then it is tested for temperature rise at the full rating of the receptacle, so a 15 amp receptacle is tested with 15 amps of load not 12 amps. The 100% load test continues until 3 consecutive temperature measurements taken 5 minutes apart do not show any increase in temperature. The maximum permitted temperature rise over the ambient is 30°C.