Incorrect EV charging

F

Familytechsupport

Member
Location
Texas
Occupation
Retired engineer
This weekend a family member charged their EV from a 30 amp dryer plug but forgot to set the charger to limit things to 24 amps so it ran in 32 amp mode. Everyone understands that this was bad and can't happen again.

The charging lasted for about 3.5 hours and the breaker never popped. The charging showed a peak power of 7400W so that implies max current was close to 31 amps. The plug was quite warm to the touch, but not so warm that it couldn't be handled with a bare hand. There were no other effects seen. There was not way to observe the in-wall wiring of the circuit. Air temperature was in the 75F range.

The question being asked is if we should assume there is hidden damage in the circuit. I know nobody can answer this definitively, but I'm trying to figure out how worried to be.
 
curt swartz said:
I take it they were using some type of homemade or non UL listed adapter?
Click to expand...
Not necessarily, the EV charger could have had a Plug. But also could have had one of those amazon unlisted cheaters that take your 30A cord for an RV and allow it to be plugged into a 50A receptacle, seen in the reverse configuration too.
Familytechsupport said:
The question being asked is if we should assume there is hidden damage in the circuit. I know nobody can answer this definitively, but I'm trying to figure out how worried to be.
Click to expand...
While others comments are probable I would suggest that you get a qualified electrician in to check for evidence of heating damage on the conductors. Best option is to have the electrician do an insulation resistance test be done for optimal safety review. Long duration heating of a conductor can cause damage more so on pinch points on a wire (staples, sharp bends etc.). But if wire was sized correctly to begin with and is newer type (of NM) the conductor is likely rated 75o or 90o C for max of 35 or 40 amps, a relatively short duration minor over current less likely to one time cause significant damage, repeated overage even minor will damage the conductors.
 
I think that most NEC/UL bits & pieces have a very large safety margin.
Circuit breakers are not close tolerance devices. 3 hours at 32 Amps is the same as 30 Amps to the breaker.
 
If the NEC sized wire was protected by a properly selected Listed OCPD, then it cannot be overloaded. This is what testing is all about.

Of course defective equipment is possible, in which case look at post #7.
 
I would not worry about this overload for this period of time.

Circuits are _intended_ to be overloaded for short periods of time, and circuit breakers are known to have a tolerance range so wire sizes are selected to be safe if the breaker operates at the top of its tolerance range. Thus I expect no acute damage to the circuit unless there was a pre-existing problem.

At worst I expect that the receptacle or circuit breaker was subjected to some 'accelerated aging'. Each time you plug a device into a receptacle and use it, the receptacle experiences some wear and tear. My _guess_ is that this time the receptacle experience wear and tear equivalent to several normal operations.

Tell your family member not to do it again, and that they owe you half a beer for the fuss :)
 
Fred B said:
Not necessarily, the EV charger could have had a Plug.
Click to expand...
If the EV charger came with a 30 amp factory cord/plug it would have been factory set to 24 amps.

I have never seen an EV charger that has come with a factory 30 amp cord/plug. Only charge cords that accept adapters like Tesla. These cords automatically set the maximum charge rate based on the adapter installed.
 
What speed skater said, so much safety margin built into NEC there is no concern, esp as ambient only 75F.

Since OP says retired engineer, will throw this in: I have a 4ksi, 4 gpm electric motor pressure washer that pulls 70A when used on 208V at the end of a 100ft extension cord. My 100 ft cord is 10AWG (e.g another 14 V drop which is why the PW pulls 70A :rolleyes: ), No visible degradation of SO cord or of plugs.
Now if someone would want to get precise and quibble with 'no effect', there is a reduction in insulation lifetime that can be calculated using Arrhenius equations. Plug can get as warm as 40C. Any degradation due to a few hours or days a 40C is ultra trivial.
 
note for those interested in numbers: 4ksi @ 4gpm = about 9.4 HP, pump eff of 90% . 70A @194V = 13.6 kW. So, running a 240Vac single phase motor at 194V show that motor is quite lossy, running at only 75% efficiency or so - thus needed to add additional cooling to motor.
 
Thank you all for your many and rapid responses and suggestions. I assure you that, logistics permitting, many beers would be distributed.

I do want to clarify things slightly. The charger is a portable unit meant to be used with different sources and is supposed to adjust automatically. It has plugs available for everything from a 14-50 to do ~7.2kW charging down to 5-15 to do ~1.2kW charging. The problem here was that the 14-30 plug was not available so an adapter was purchased from Home Depot or Lowes (not homebrew and not intentionally fly by night). The issue is that the charger uses some pinning in the plug to know what kind of outlet it is plugged into. Since it was using the 14-50 plug it didn't know it was on a smaller circuit. What was supposed to happen was the car was to be set to do slower charging and only pull a max of 24A. The last step was missed and the fact that it was charging too fast was overlooked. So it was still an error, but it was not an attempt to get away with something.
 
Fred B said:
While others comments are probable I would suggest that you get a qualified electrician in to check for evidence of heating damage on the conductors.
Best option is to have the electrician do an insulation resistance test be done for optimal safety review. Long duration heating of a conductor can cause damage
Click to expand...
Most electricians wont have a megger tester, likely to show up without it, and demand payment for a continuity check using an Ohm meter.

Those who do carry Megger testers wont notice wet wire, or existing 600v NM, before blasting it with 500-1000 volts, causing more damage.

Anyone asking electricians in the wild, should get written bids for any Megger test, and specifying the voltage limits for existing, or wet wire.
 
Familytechsupport said:
Since it was using the 14-50 plug it didn't know it was on a smaller circuit. What was supposed to happen was the car was to be set to do slower charging and only pull a max of 24A.
Click to expand...
It only was drawing 31 amps on a 30 amp circuit so no wiring was damaged. As long as the receptacle and plug look good there is nothing to worry about.
 
Unlike hardwired wall chargers designed for 75C terminations, most plug-in mobile car chargers are listed for 50C max operating temp.

Unfortunately, most electricians size new wire for the allowed 75C limits, without checking, much less expecting 50C equipment limits.

32 Amps appears in NEC Table 310.16 in the 75C column for #10 copper, typically used on 240v electric clothes dryers.

Regardless of existing 3 prong dryer receptacles indicative of 60C wire, the 50C mobile charging equipment likely ran at 75C until either a High Temp. Detect auto shutoff engaged, or the 50C equipment was destroyed.
 
infinity said:
It only was drawing 31 amps on a 30 amp circuit so no wiring was damaged. As long as the receptacle and plug look good there is nothing to worry about.
Click to expand...
Agree with the possible exception of wiring that is so old and degraded that it was already a potential problem before the overload happened, and shouldn't even be used with a 24A EVSE.

For the OP, when was the dryer circuit installed, approximately? Not sure how old would be old enough to be concerned, but I expect 1990 or later would definitely be fine, and 1940 or earlier would definitely be questionable? [Others are probably much more knowledgeable about the evolution of wire types and what age would now be suspect.]

Cheers, Wayne
 
ramsy said:
Unlike hardwired wall chargers designed for 75C terminations, most plug-in mobile car chargers are listed for 50C max operating temp.

Unfortunately, most electricians size new wire for the allowed 75C limits, without checking, much less expecting 50C equipment limits.
Click to expand...
The equipment termination temp rating and the allowable ambient operating temp of the equipment are two different things. Not directly relatable.
 
wwhitney said:
Agree with the possible exception of wiring that is so old and degraded that it was already a potential problem before the overload happened, and shouldn't even be used with a 24A EVSE.

For the OP, when was the dryer circuit installed, approximately? Not sure how old would be old enough to be concerned, but I expect 1990 or later would definitely be fine, and 1940 or earlier would definitely be questionable? [Others are probably much more knowledgeable about the evolution of wire types and what age would now be suspect.]

Cheers, Wayne
Click to expand...
It was built in the early 2000's I believe, so 20ish years old.
 
You must log in or register to reply here.
Top