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Thoughts on the HPWC, Feedback from Licensed Electricians on my Q

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islandbayy

islandbayy

Active Member
Feb 25, 2013
3,206
1,535
Greendale, Wisconsin
#1
So, installing the first of 2 HPWC's at the Sandrift Resort - The Peach on the Beach in Wisconsin Dells, WI to help with the HUGE demand they saw last year on the 14-50 outlet (At some periods of time, they actually had to take Reservations for 14-50 outlet use!). So, Anywho, last weekend, I had to do some major load management, as 3 Service entrances out of 4 were maxed. So, I now have things shifted and set, so we can have 1 HPWC on a 100amp breaker for 80 amp charging, the other HPWC FOR NOW, will be limited on a 40 amp breaker (Since the Tourist season literally starts in 2 weeks, timing sucks) as at the end of this season, I will be changing over hopefully 2 Electric Stoves/Ovens to Natural Gas giving us 60 more amps to play with.

So, anyways, I thought it best to get the 100 amp/80amp HPWC installed first, so that they can at least get Dual Charger enabled cars in and out much quicker.
I decided to "over due" the install, and am using 2AWG wiring, and 4Awg for the Ground. The Install Guide said 3 Awg is Sufficient for a 100 amp install.....

Anyways, that got me thinking, what I have been reading shows that Properly installed 3AWG is just fine. So, good, I did 2 AWG (had left over from previous crazy "project"...).

Now, whats confusing the royal heck out of me. When I opened the HPWC up and installed it, the Wire used to go from the HPWC to the CAR is only 6AWG for the AC 240v, and 8AWG for the Gound. (I believe that is fine for the ground wire). Thinking to myself, What the heck. 6 AWG? Seems a bit thin??? Best case scenario I see is 6 AWG rated at 75 amps, or using NM-B 55 Amps (6AWG is what I use for 14-50 outlets, which are, again 50 Amp outlets, rated for 40 amp continuous).

I hope I don't sound dumb asking about this. I do much electrical, and this just seems undersized to me. Thoughts? Input? When It's light out tomorrow, I will take a picture of it. I do have a video of the inside of the HPWC's I will dig up tomorrow for those who may be interested.
 
#2
I believe this was a trade off they made realizing the distance that the pig-tail cord to the car isn't very long. You could never get away with it for a 100ft run of course!
However over short distances you can 'get away' so to speak with a smaller wire - and i would bet they wanted the pigtail cable to be not too terribly thick and hard to handle..

- - - Updated - - -

Realizing my last post was a bit vague.. figured i would post the formula here..

R = pL / A

where p = the 'resistivity' of the wire material (i don't recall what it is for copper), L is the length of course, and A is the cross sectional area of the wire (thickness or gauge).

so you can see that R will decrease significantly with a very short L… all things being equal..

My physics here is a bit rusty, others can probably elaborate..
 
#3
Check the insulation on the 6ga wire in the HPWC and you will find that it is rated much higher than you might expect: 105c. I wired my home HPWC with 4 ga 105c wire and I'm drawing 70A (set on the HPWC DIPs) and it barely even gets warm.

It should be noted that the HPWC is located 2 feet from the 90A subpanel.
 
#4
I can only assume we are talking about copper instead of aluminum. Aluminum at those awg wouldn't be recommend. However if the awg is indeed 6 @ 105c then it is rated for at 105 amps. Also 4 awg @105c is rated for 140 amps.
 
#5
I run two different HPWCs, both on 100 Amp circuit breakers charging at 80 Amps, for hours sometimes. The cable and connector get warm, but not uncomfortably so.

If I remember correctly the cable from the HPWC to the car has two wires in parallel carrying the 80 Amps (two black and two red for four total wires). Putting two wires in parallel is like adding 3 to the AWG, so two #6 wires in parallel is the equivalent of one #3 wire. Was the #6 wire you were talking about, one of two in parallel?
 
#6
They are using very high-quality 105 deg C rated cable. They get away with this because it's considered an appliance and is subject to UL testing and standards instead of the NEC. Use of that cable to connect the HPWC would violate the NEC and subject you to insurance and liability implications.

The cable for the car coupling uses a single #6 conductor for each pole.

The NEC makes no distinction for 105 deg C rating because it's usually the terminations that make the difference - most breakers and terminals are only tested and rated to 75 degrees C for field installation, so even the 90 deg C rating can't be used.

The use of #4 to wire an HPWC set to 100A breaker size is violating the NEC (at a minimum, failure to follow manufacturer's instructions which voids the listing, but also conductor size, etc. rules) regardless of whether it's 105 deg C or not. The NEC considers things like heat rise in a conduit, heat rise when conduits are all grouped together in risers, heat rise in electrical enclosures where many of these circuits would generate heat, etc. The HPWC's cable is always in open air, so they can make assumptions about convective heating that don't have to be considered in the broader system.

Truth is that in most situations, the #6 would work ok (but be warm) -- you just don't want to be the exception that burns your home or business down.
 
Last edited:
#7
spdntckt said:
I believe this was a trade off they made realizing the distance that the pig-tail cord to the car isn't very long. You could never get away with it for a 100ft run of course!
However over short distances you can 'get away' so to speak with a smaller wire - and i would bet they wanted the pigtail cable to be not too terribly thick and hard to handle..

- - - Updated - - -

Realizing my last post was a bit vague.. figured i would post the formula here..

R = pL / A

where p = the 'resistivity' of the wire material (i don't recall what it is for copper), L is the length of course, and A is the cross sectional area of the wire (thickness or gauge).

so you can see that R will decrease significantly with a very short L… all things being equal..

My physics here is a bit rusty, others can probably elaborate..
Click to expand...

Thank You for the explanation! It does help.

- - - Updated - - -

Brick Pilot said:
Check the insulation on the 6ga wire in the HPWC and you will find that it is rated much higher than you might expect: 105c. I wired my home HPWC with 4 ga 105c wire and I'm drawing 70A (set on the HPWC DIPs) and it barely even gets warm.

It should be noted that the HPWC is located 2 feet from the 90A subpanel.
Click to expand...


I'll take a look, thanks!
 
#8
FlasherZ said:
They are using very high-quality 105 deg C rated cable. They get away with this because it's considered an appliance and is subject to UL testing and standards instead of the NEC. Use of that cable to connect the HPWC would violate the NEC and subject you to insurance and liability implications.

The cable for the car coupling uses a single #6 conductor for each pole.

The NEC makes no distinction for 105 deg C rating because it's usually the terminations that make the difference - most breakers and terminals are only tested and rated to 75 degrees C for field installation, so even the 90 deg C rating can't be used.

The use of #4 to wire an HPWC set to 100A breaker size is violating the NEC (at a minimum, failure to follow manufacturer's instructions which voids the listing, but also conductor size, etc. rules) regardless of whether it's 105 deg C or not. The NEC considers things like heat rise in a conduit, heat rise when conduits are all grouped together in risers, heat rise in electrical enclosures where many of these circuits would generate heat, etc. The HPWC's cable is always in open air, so they can make assumptions about convective heating that don't have to be considered in the broader system.

Truth is that in most situations, the #6 would work ok (but be warm) -- you just don't want to be the exception that burns your home or business down.
Click to expand...

All great points!

If memory serves me correctly the UMC and the Supercharger cables use two paralleled wires, but you are correct, the HPWC uses single wires. I went out and opened mine to verify.

If you look at American wire gauge - Wikipedia, #6 copper wire has a resistance of 0.4 milliOhms per foot, double that for the two directions and you get 0.8 milliOhms per foot. Because resistive power loss is I^2*R, that means with 80 Amps, the power per foot is about 5 Watts. Given the size of the cable, 5 Watts is not bad, and supports my observations that the cable gets warm, but not uncomfortably so.

As FlasherZ points out, this is a different situation (out in the garage, not buried in a wooden wall) regulated by different bodies.

As for #4 for house wiring, that can be used with a 90 Amp breaker for 72 Amp MS charging, and should be considered as a very reasonable alternative. #3 can be a little hard to find, and getting #2 into the HPWC can be a real wrestling match in a very small space...

As I have posted elsewhere, I am completely comfortable using my HPWC's at 80 Amps, but for most charging, I set the current to 57 Amps (80/sqrt[2]). That's more than enough for day to day charging, cuts resistive heating in half, and still tests both of my dual chargers.
 
#9
Cottonwood said:
I run two different HPWCs, both on 100 Amp circuit breakers charging at 80 Amps, for hours sometimes. The cable and connector get warm, but not uncomfortably so.

If I remember correctly the cable from the HPWC to the car has two wires in parallel carrying the 80 Amps (two black and two red for four total wires). Putting two wires in parallel is like adding 3 to the AWG, so two #6 wires in parallel is the equivalent of one #3 wire. Was the #6 wire you were talking about, one of two in parallel?
Click to expand...

I can't comment for the early versions, but the HPWC's I have use single #6 for each conductor.
2x6AWG for 240v, 1x8AWG for Gound, and 2xLooks like 16AWG for control wires.
 
#12
#2 is tough to wrestle with but they left enough room to connect it - it's much better than other things I've seen. My biggest problem on installation was wrestling the wires through the 1" LB that connected to the left side of the HPWC, and that wasn't too bad.

Using a #4 for ground is overkill, though, and is likely to clog up things. 100A circuits only call for #8 (NEC table 250-122), and I can't recall if the grounding lugs in the HPWC will accept a #4 (I believe they're limited to #6 in the instruction manual).
 
#13
Gjackson2434 said:
Cottonwood, I don't have my hpwc yet but you said it was very hard to get a awg 2 in the hpwc. Does it not have enough room? Do you have a pic of the inside? I'm ordering three hpwc and will be using awg 2.
Click to expand...

It can be done, but Tesla optimized the HPWC for style and not ease of install. Count on some frustration and leave yourself extra time for the HPWC end. The connector in the HPWC is rated for #2 wire, but just. In addition, the way the HPWC is designed, you have to route the wires 90˚ from the entry into the HPWC to the connector in a very small space. This makes it really hard to keep the multi-strand wires together to get into the connector.

If you can get #3 wire, I would do so, to ease the difficulty at the HPWC end. The circuit breaker box and circuit breaker connections are easy with about 10x as much space and connectors rated for larger wire.

YMMV. Good Luck!
 
#16
I did finish the first HPWC install today. I used 2AWG wire. Actually, no problem connecting it inside the HPWC (Wrestling it through). It was slightly too big to fit in the hoes provided to be lugged down, I had to snip 3 of the core wires that make up the 2AWG to fit it in, still much thicker then 4 or 3. I still like to "over-do" things.
I am having some issues tripping the Model S Current limiter though :(
House has 200 Amp service, garage the HPWC is connected to has 100 amp sub-panel connected with 1 AWG Aluminum, which should be rated for 100-115 amps. The run from House to Garage is about 15 Ft, so not very long.

The run from the Sub-Panel to the HPWC is literally exactly 12ft (Had 24ft of wire, and had just enough to get it into the breaker for both legs) of 2AWG copper.
Starting voltage is 247v. At 40 amps, which this garage had a 14-50 before, voltage drop was 237, much better then the 14-50 with it's 6AWG copper which at 40 amps was at 230 (no current limiting on the 14-50).

At the Full 80 Amps, voltage is about 225v. If left at 80, it backs down to 60 amps, voltage goes up to about 230. Anything above 65 amp charging speed, and the car cuts current to 60 amps. No further current cuts from their.

But curious about the voltage drop, all wiring stays cold to the touch (accept from the HPWC to the car, the HPWC whip gets slightly warm at 80 amps). The Copper from the HPWC to Sub Panel in garage is cold, breaker is slightly warm, Aluminum from the Garage to the house is cold. 100 amp breaker for garage in main panel is slightly warm. Main 200 amp house breaker is cold as are the mains.

Input requested: Seems that the issue is not my install, possibly over-loaded transformer? The house is a bit far away from transformer, about 400 ft, 3 individual houses are connected to it, as well as Sandrift Resort - The Peach on the Beach in Wisconsin Dells, WI , which at this time has 3x200 amp meters that are fairly loaded during the summer. This house would make Sandrift's 4th meter. Sandrift is not open for the season and the house with the HPWC and the 2 other houses are vacant (summer rentals).
Do you all think this is Voltage drop due to the length of run? I would have preferred installing it directly on the house, however, the HPWC Cable would not have reached the driveway.
Unfortunately, I ran out of time today to check voltages during charging at the main panel, I will need to do that next weekend when I am back to "Tidy Up" and start installing another HPWC on the Office.
 
#17
islandbayy said:
It was slightly too big to fit in the hoes provided to be lugged down, I had to snip 3 of the core wires that make up the 2AWG to fit it in, still much thicker then 4 or 3. I still like to "over-do" things.
Click to expand...

It shouldn't be, I was able to get #2 fully installed. Snipping strands off (even if using a larger wire size) is not good.

House has 200 Amp service, garage the HPWC is connected to has 100 amp sub-panel connected with 1 AWG Aluminum, which should be rated for 100-115 amps. The run from House to Garage is about 15 Ft, so not very long. The run from the Sub-Panel to the HPWC is literally exactly 12ft (Had 24ft of wire, and had just enough to get it into the breaker for both legs) of 2AWG copper.
Starting voltage is 247v. At 40 amps, which this garage had a 14-50 before, voltage drop was 237, much better then the 14-50 with it's 6AWG copper which at 40 amps was at 230 (no current limiting on the 14-50). At the Full 80 Amps, voltage is about 225v. If left at 80, it backs down to 60 amps, voltage goes up to about 230. Anything above 65 amp charging speed, and the car cuts current to 60 amps. No further current cuts from their.

But curious about the voltage drop, all wiring stays cold to the touch (accept from the HPWC to the car, the HPWC whip gets slightly warm at 80 amps). The Copper from the HPWC to Sub Panel in garage is cold, breaker is slightly warm, Aluminum from the Garage to the house is cold. 100 amp breaker for garage in main panel is slightly warm. Main 200 amp house breaker is cold as are the mains.

Input requested: Seems that the issue is not my install, possibly over-loaded transformer? The house is a bit far away from transformer, about 400 ft, 3 individual houses are connected to it, as well as Sandrift Resort - The Peach on the Beach in Wisconsin Dells, WI , which at this time has 3x200 amp meters that are fairly loaded during the summer. This house would make Sandrift's 4th meter. Sandrift is not open for the season and the house with the HPWC and the 2 other houses are vacant (summer rentals).
Do you all think this is Voltage drop due to the length of run? I would have preferred installing it directly on the house, however, the HPWC Cable would not have reached the driveway.
Unfortunately, I ran out of time today to check voltages during charging at the main panel, I will need to do that next weekend when I am back to "Tidy Up" and start installing another HPWC on the Office.
Click to expand...

Depends on the size of the transformer, and the size of the service conductors to the transformer. If a 50 kVA or larger transformer, it may be ok.

I've mentioned in a couple of other posts that my home's 200A service was served by 2/0 AL conductors on a 15 kVA transformer before the PoCo did an upgrade to support the Tesla, and PoCo measurements showed I was running the transformer (without the HPWC) at 2x rating during peak periods. The PoCo expressed amazement that I wasn't dimming the lights when the A/C units kicked in.

The voltage drop could be due to the length of the run, but it would be a combination of service conductor size and length of run. Larger cables will have less voltage drop.

You're on the right path -- watch the voltage at the main breaker as the charging kicks in. If your loss also occurs at the main breaker, you'll need to start looking at your service conductors and/or transformer and involve the PoCo. See if you can determine the size of the transformer (mine has a prominent "37.5" on it to denote 37.5 kVA). Ask if they'll let you break the meter seal to watch voltage at the base of the meter (to ensure it's not your service entrance conductors), and ask them to come out and help troubleshoot heavy voltage sag if they won't let you break the seal and/or you see it sag at the meter. Ask them if they have records on the service conductor size (my co-op is particularly good about discussing all of the parameters, but some PoCos consider it proprietary).
 
#18
Glad I had a good electrician put my HPWC in. Love it. Nice to not have to figure it out. I have messed up my share of things making it work.
image.jpg
 
#19
islandbayy said:
Unfortunately, I ran out of time today to check voltages during charging at the main panel, I will need to do that next weekend when I am back to "Tidy Up" and start installing another HPWC on the Office.
Click to expand...

Deducing that you are not a licensed electrician, hope that you realize you have a massive personal liability doing all this major work? We'd all hate to see you in trouble just through helping out.
 
#20
NigelM said:
Deducing that you are not a licensed electrician, hope that you realize you have a massive personal liability doing all this major work? We'd all hate to see you in trouble just through helping out.
Click to expand...

It's a family business. Install is done properly. I don't do hackjob installs. I don't know everything, and know my limitations, and when I do have questions, I ask. So, I had 2 questions for the most part, one was how exactly they get away with 6AWG from the HPWC to the car, and second was opinions on the voltage drop, which I will be investigating further.
 
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