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48 amp wall connector on 50 amp circuit for track days?

destructure00

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Mar 2, 2019
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Scottsdale, AZ
I've been struggling to find ways to keep my 3 charged up during track days. Most local tracks I visit have 14-50 outlets available. Started with the original Gen II UMC, which adds about 10% per hour at 32 amps. Not enough to get me through four 20 minute sessions without supercharging. Recently bought a Gen I UMC, adds about 12.5% per hour at 40amps. Better, but still not enough.

Saw an idea posted in another thread to get a HPWC and attach a 14-50 plug to it and set it to 48 amps. This would give me about 15% per hour charge and may be enough to where I could do a full track day without having to leave to supercharge. I know it wouldn't meet code, but it also wouldn't be a permanent installation, and my understanding is a "continuous" load is one that runs for 3 hours or more. I doubt I'd be charging continuously for any more than 2 hours on a track day. On paper, 48 amps is less than 50, so seems like it would work. Would that hold true in practice as well, or is there a good chance I'd be tripping the breaker when I tried to use it?
 
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VT_EE

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Apr 22, 2017
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Per code, you cannot run a continuous load higher than 40amp on a 50 amp circuit. The wiring and outlet are not rated for the heat that would be generated with a 48 amp continuous load.
 

SSedan

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Jul 24, 2017
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Greenville Wisconsin
my understanding is a "continuous" load is one that runs for 3 hours or more. I doubt I'd be charging continuously for any more than 2 hours on a track day. On paper, 48 amps is less than 50, so seems like it would work. Would that hold true in practice as well, or is there a good chance I'd be tripping the breaker when I tried to use it?

Per code, you cannot run a continuous load higher than 40amp on a 50 amp circuit. The wiring and outlet are not rated for the heat that would be generated with a 48 amp continuous load.

Quick googling does say 3 hours+ is the definition of continuous load.

Not saying this makes what the OP proposes technically "right" but I would say working a loophole.
 
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destructure00

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Mar 2, 2019
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Scottsdale, AZ
I would worry about tripping the breaker and not having access to reset.

I would also watch voltage like a hawk with a sag during sustained use indicating an overheating point somewhere.

Yeah this is what I'd be concerned about. Wondering what real-world experience is with a scenario like this.

Not saying this makes what the OP proposes technically "right" but I would say working a loophole.

Yep, that's the spirit :cool:
 
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doghousePVD

My grandfather’s car
Dec 3, 2018
644
507
New England, USA
If I has access to the breaker I would do it. This isn’t really a safety issue, mostly a pop the breaker annoyance. The wiring from the outlet to the car is all well ventilated and easy to monitor.

That said, I wouldn’t walk away and comeback in three hours. I was charging at a 14-50 drawing only 32A this summer, and the breaker popped in an hour or two. I finished sharing at 25A. YMMV
 
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destructure00

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Mar 2, 2019
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Scottsdale, AZ
Good thoughts. The longest gap between sessions I've seen is 2 hours, and I keep a close eye on charging status through the app between sessions. Breaker panels also seem to be easily accessible. I'm going to keep an eye out for a deal on a HPWC and give this a shot I think. Can set the dial for 48 amps and turn it down inside the car if ever needed.
 

Feathermerchan

Active Member
Sep 21, 2018
1,190
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Euless, Tx
Attaching an HPWC to a 14-50 plug would violate code but drawing up to 50A for 3 hours is OK per code. You may have one but one of those infra red thermometers would be a handy way of telling what was going on with the plug, receptacle and cord. As well as breaker if so inclined. The Gen1 cord gets plenty hot at 40A as does the wand. The HPWC should have bigger wire on it but keep an eye on it anyway. Also in the hot Ariz weather, you may be limited in charging due to temp and/or the cooling system having to run.
 
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magudaman

Member
Apr 14, 2019
26
17
SF Bay Area
I’ve done 48a at the Sonoma and Laguna seca 14-50s. My though was the same as op, not continuous load. No issues with nuisance trips. Too bad most 14-50s at the tracks are 208v circuits, we could use the additional power! I’m using an old juice box for my field charging.
 

destructure00

Active Member
Mar 2, 2019
1,476
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Scottsdale, AZ
I’ve done 48a at the Sonoma and Laguna seca 14-50s. My though was the same as op, not continuous load. No issues with nuisance trips. Too bad most 14-50s at the tracks are 208v circuits, we could use the additional power! I’m using an old juice box for my field charging.

Thanks for sharing, I'm encouraged to hear that there were no trips. Now to find a second HPWC :)
 

destructure00

Active Member
Mar 2, 2019
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Scottsdale, AZ
Ready to charge at 48 amps :)

IMG_20191102_081735.jpg
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IMG_20191102_081747.jpg
 

Feathermerchan

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Sep 21, 2018
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Euless, Tx
That looks like a super clean setup. Is that a 50A NEMA 15-50? If so you can only charge up to 40A per NEC because the corresponding plug and wiring including beaker is rated for 50A and 80% of 50 is 40. So OK for 40A but not 48A. Don't burn your house down. (The purpose of the NEC more or less)
 

destructure00

Active Member
Mar 2, 2019
1,476
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Scottsdale, AZ
That looks like a super clean setup. Is that a 50A NEMA 15-50? If so you can only charge up to 40A per NEC because the corresponding plug and wiring including beaker is rated for 50A and 80% of 50 is 40. So OK for 40A but not 48A. Don't burn your house down. (The purpose of the NEC more or less)

It's a 14-50. We discussed code several times above (yourself included)...I am well aware of the 80% rule. You remember the purpose of this setup?
 
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destructure00

Active Member
Mar 2, 2019
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Scottsdale, AZ

It's for charging at the track. My local track has 14-50 outlets around the property. Intending to take this with me to charge between sessions. Longest gap between sessions is around 2 hours give or take, so below the threshold to be considered a continuous load and require the 80% calculation. Trying to get the fastest charge possible at the track between sessions to try and avoid having to drive 35 miles round trip to supercharge over lunch break. The included Gen 2 UMC at 32 amps is not enough. I thought a Gen 1 UMC at 40 amps might work, but it's not quite enough either. I'm thinking this HPWC at 48 amps will get me there.

I have a hard wired HPWC at home on a proper 60 amp circuit for my daily charging needs.
 

hcsharp

Active Member
Jun 7, 2011
3,409
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Vermont
I've been watching this thread... curious to see what kind of responses you got. I have mixed feelings about what you're doing. I started driving an EV 9 years ago including long trips several years before superchargers existed. Back then we had to figure out how to charge fast at RV parks with 14-50 outlets. If you read some old threads in the Roadster forum you will find many interesting solutions to your 40A charging dilemma. Back then I would have encouraged your solution. Since then I have seen some bad things happen including two fires. One of them just the cable burned (in a campground). The other caught a garage on fire.

You have to ask yourself some questions. Think of the speeding analogy. If you drove for a few days consistently 20% over the speed limit, how much would that increase your risk of having an accident? Or risk of killing somebody? None of the electrical equipment to and including the 14-50 outlet is made to supply 48A for more than a few minutes at a time. A 50A breaker will get hot after an hour at 48A. The outlet will always get warm. If it's old it will also get hot. The 50A breaker will wear out much quicker at 48A than it will at 40A. You will learn early on that if you don't have access to the breaker that it will be difficult to sustain.

You may want to consider an alternative that is safer in some respects and more dangerous for electrocution risk. If you have access to two 14-50 outlets, and it's not 3-phase supply, and you implement a combiner box with breakers and test circuit, you can pull 24A from each of 2 NEMA 14-50 outlets. I've charged at 70A with this method. Your combiner box has to allow you to change polarity if necessary and also cut off power to both cables so you don't get electrocuted after plugging the first one in. If you search TMC you can find an old thread about this.
 
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destructure00

Active Member
Mar 2, 2019
1,476
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Scottsdale, AZ
The combiner box is an interesting idea.

None of the electrical equipment to and including the 14-50 outlet is made to supply 48A for more than a few minutes at a time.


I hear what you're saying but it seems to me that the NEC wouldn't put the 3 hour definition on a continuous load if it were true that a 50 amp circuit can only support a 50 amp load for a few minutes without bursting into flames. The fact that something lights on fire rather than tripping a breaker I'd think would be an indicator of a bigger problem with something not being installed correctly to begin with.

Regardless, I'll keep a close eye on it. Doesn't do me any good if the breaker trips, and I have an IR temp gun that I'll monitor cable temps with as well. Next track day is coming up in 2 weeks, so that will be the first opportunity to use this.
 
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