It's not strictly against code, but it will violate the UL listing on the unit, and some jurisdictions will then say it's not up to code to be used. Years ago a friend and I installed a J1772 station meant to be hardwired, with a plug instead, and the inspector wouldn't sign off on it until we had it hardwired properly instead. Moral of that story is to just have an outlet inspected, and not be too specific about telling the inspector what's being plugged in...Tesla recommends against it because they are concerned that you'll yank it out and expose the bare wires. This can be mitigated with a proper strain relief. I don't believe it's against code to add a pigtail though. I always advocate wiring directly regardless. I just like the clean look.
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HPWC: 40 amp with pigtail vs 48 amp hardwired
- Thread starter zmarty
- Start date
SoundDaTrumpet
Member
California Electrical Code (home of Tesla) and City of Fremont disagrees (home of Tesla Factory).
"The electric vehicle charging system shall be listed by a nationally recognized testing laboratory (i.e., UL) in compliance with UL 2202 “Standard for Electric Vehicle (EV) Charging System Equipment.” (CEC 90.7)
Reference: https://fremont.gov/documentcenter/view/25378
National Recognized Testing Laboratory (NRTL) includes ETL, UL, and a few others.
Modifying by add a pigtail causes the HPWC to lose it's UL listing. Keep in mind NRTLs use the documentation provided to end-users in their tests. Tesla would have to include instructions how to modify to use a pigtail, and Tesla would have to get it tested by an NRTL for it become listed.
I am in full agreement with the UL implications of unlisted modifications. However, from a purely rule of law POV, does the fact that it would not be a permanent hardwired installation make the building code not-applicable? As in the same as any other 240V device one might acquire like a 1970s buzz box for welding.
SoundDaTrumpet
Member
Good question. The rule of law is defined by key stakeholder such as the city jurisdiction authority, the customer/homeowner, and guiding bodies (i.e. NFPA for NEC). City of Fremont treats the EV charging as a charging SYSTEM by looking at it as a whole. I guess it depends where one resides. I have seen NEC applied to systems that aren't in buildings, which I also have worked with. I do know theatrical lighting systems that I work with are considered non-permanent and stated so in NEC. One cannot simply rule out NEC just because it is not permanently installed in a building. Keep in mind that the NFPA who authors the NEC is National Fire Protection Association. When it comes to fire and safety, everybody is interested.
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I was really only saying that it doesn't outright violate NFPA 70, but I did say that other jurisdictions may require UL or other NRTLs. So I think you just provided an example, not a disagreement...
Though your example is interesting. There are some popular EVSEs that don't have UL (like the JuiceBox until fairly recently)...
(And side note: I actually work in the theatrical lighting industry as well! Electrical engineering including regulatory testing of products we sell, which I bet you use...
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dhrivnak
Active Member
I for one do this and actually have the car dialed back to 24 amps as that is normally plenty to give me a full charge. With the Model 3 going from 40 to 48 amps is 6-7 miles/hour, or going from about 38 to 45 miles/hour.
Unless you have a pretty extreme use case, the difference between the two is unlikely to ever matter operationally - you'd need to be in a situation where you didn't have time for the 40A solution to get you back the range you needed before the next trip but the 48A could. That'd probably mean driving a couple hundred miles per day or more and not having a long overnight charging session available.
I guess I should have specified the 40 amp charging is actually 32 amp charging, since that is what the new UMC can do. So from 32 to 48 amps is a difference of 16 amp. At peak that is 50% more than the UMC.
Granted. But still, you need a lot of miles and limited charging opportunities for the difference to matter.
I'm not sure what calculation that you are trying to do, but I'm pretty sure that they aren't right.
12A*120V = 1,400W = 1.4kW I'm fine with this
But when you do the next set, they don't make sense.
Wh/mile is irrespective of the charge rate.
The efficiency of charging is going to be pretty much the same irrespective of the rate. If anything, the lower charge rates are going to be slightly more efficient than higher current charging.
So this suggest that a really fast charge, like a SuperCharger is better than a destination charge
That's not the case.
This references ONE of many things that can impact a batteries storage. There are many more.
There is a fixed base load of having the car on and charger enabled, that takes up a larger fraction of the the power at lower charge rates.
The effective Wh/mile from the wall has a sweet spot in the mid range (less impact due to baseload, less impact due to high current).
The faster you charge, the less power went into keeping the car in charge mode.
Yes, there are limits but I'm only talking about relative slow charge rates possible from a home charger. In the video I linked I believe the comparison was between C/10 charging and 1C charging with the batteries charged at 1C lasting much longer. Supercharging is more like 1.5C so it falls well outside that range.
No, it doesn't
5.8 kW rate for an hour means that you put 5.8 kWh in the battery.
2.9 kW rate for two hours means that you put 5.8 kWh in the battery.
261 Wh per mile, is an average for the amount of power that it takes to drive a mile
And yes, if you have 5.8 kWh in the battery, and you use it at an average of 281 W/mile, then you get 22 miles off of the charge.
But the original author's concept that the charge rate had anything to do with the efficiency, is ludicrous.
It's like saying that I have more water if I fill a 1 gallon bucket up in 1 hours vs 30 minutes. It's still only 1 gallon to water the flowers.
if your bucket has a hole and leaks a pint an hour (base load) and you only fill it at one pint per hour, how long till it is filled?
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A bucket fills and empties at nearly 100% efficiency. For every gallon that comes out of the faucet into the bucket, the water volume increases by a gallon. There will be negligible losses to evaporation.
Electrical circuits and batteries are far from 100% efficient. A significant portion of the power that comes out of your wall is not reflected in the final stored charge in the battery and efficiency can vary with voltage/current. With a Tesla UMC at 110V/12A that loss is as high as 30%. At 220V/40A it's closer to 10%
Here's a thread where this is discussed in more detail, with actual measurements:
Model S Gen2 Charger Efficiency Testing
Note that the numbers in the above thread are all at 240V. You can do a little googling to find the measured efficiency of the 110V/12A which is much less than even 240V/5A. It looks like once you get up past 10A or so at 240V then you are pretty consistently around 90% efficiency.
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Or a 2nd Tesla. Why is nobody mentioning it? Hellooooo Y
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