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

[dsm363]

Wouldn't getting it inspected and signed off on anyway be worth it to protect the business?

 

[Cottonwood]

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.

As FlasherZ said, check Voltages at the various points you can get access to. Ohm's Law: V = I*R. 60 Amps should be fine for your investigation. You can use the App on your phone to turn charging on and off remotely to check Voltage changes with current. Even if other loads are changing, a couple of on/off cycles at each test point should let you see the Delta-V caused by your Delta-I.

Cold to the touch can still cause a Voltage drop if there is very good heat dissipation at that point. The Volt Meter is the test instrument of choice for this problem.

A good puzzle can be a pleasure to solve! Good Luck!!

 

[islandbayy]

As FlasherZ said, check Voltages at the various points you can get access to. Ohm's Law: V = I*R. 60 Amps should be fine for your investigation. You can use the App on your phone to turn charging on and off remotely to check Voltage changes with current. Even if other loads are changing, a couple of on/off cycles at each test point should let you see the Delta-V caused by your Delta-I.

Cold to the touch can still cause a Voltage drop if there is very good heat dissipation at that point. The Volt Meter is the test instrument of choice for this problem.

A good puzzle can be a pleasure to solve! Good Luck!!

Sounds good. I will have 4 test points, HPWC, Load Center in Garage, Main Service Entrance into Main Panel, and a Meter thats 15 Ft from the transformer on another structure. I'm going to have someone take a peak at the transformer today and see if they can tell what it's kVa rating is. I do know it's ancient as heck and extremely rusty, so it wouldnt be beyond me that it's under-rated.

 

[rdrcrmatt]

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.

Yea I thought so too till I had a licensed electrician assist me with my HPWC install. There are gotchas that aren't obvious.

Oh, and cutting conductors out of a wire to make it fit is a hack job.

 

[FlasherZ]

Sounds good. I will have 4 test points, HPWC, Load Center in Garage, Main Service Entrance into Main Panel, and a Meter thats 15 Ft from the transformer on another structure. I'm going to have someone take a peak at the transformer today and see if they can tell what it's kVa rating is. I do know it's ancient as heck and extremely rusty, so it wouldnt be beyond me that it's under-rated.

Yeah, I'd be willing to bet that you're stressing that transformer pretty heavily. Call the PoCo, ask them to consider upgrading as your load is going to increase. If they refuse, bring a few more Teslas and boil the oil out of it so they have to replace it.

 

[islandbayy]

Yeah, I'd be willing to bet that you're stressing that transformer pretty heavily. Call the PoCo, ask them to consider upgrading as your load is going to increase. If they refuse, bring a few more Teslas and boil the oil out of it so they have to replace it.

I'm leaning towards transformer as well. asked around today, Apearantly the transformers fuse blows on a yearly basis.... don't even know where to start with that one. will test voltages this weekend and see what I turn up.

 

[Lloyd]

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.View attachment 47632

I would have placed the disconnect 3 feet from the HPWC! In California code does not require a disconnect in residential applications, but having it against the HPWC defeats the purpose!

 

[islandbayy]

Yeah, I'd be willing to bet that you're stressing that transformer pretty heavily. Call the PoCo, ask them to consider upgrading as your load is going to increase. If they refuse, bring a few more Teslas and boil the oil out of it so they have to replace it.

as for bringing more teslas, on May 17, Sandrift is hosting a large tesla get together. already have six model s's, Chevy volt, and three Prius RSVP'd.

 

[Cottonwood]

as for bringing more teslas, on May 17, Sandrift is hosting a large tesla get together. already have six model s's, Chevy volt, and three Prius RSVP'd.

If your panels have the temporary capacity, this sounds like a time to connect several "temporary" 14-50 receptacles, maybe even at some neighboring houses. With a little coordination, I bet you could really stress the transformer then. :wink:

Sandrift is a little bit of a drive from Colorado, or I would love to join you. Have Fun!

 

[Cottonwood]

Speaking of wire sizes, see Supercharger protocol for diy CHAdeMO adapter - Page 8 where they were snooping at the other side of the charging connector inside the car. The claim is that the wire is a #2 AWG. With 120 kW Supercharging, this wire is carrying 333 Amps. That works out to 17 Watts per foot, each way, resistive loss. I'm sure that Tesla has done the thermal calculations, but it does show how much Tesla pushes current carrying capacity of the wire beyond the very conservative NEC.

 

[islandbayy]

Thought I'd update. Checked through everything today. Re-Torqued the lugs on breakers and in the panel's. I am able to sustain 70 amp charging for about a hour before it limits down to 60 amps. 60-65 amps can be sustained no problem. Voltage drop now from no load to 80 amp load goes from 247 down to 229v.
Voltage drop between car (as displayed on the car screen as viewed via the iphone app for ease) and at the main service entrance in the house panel (Supplied by thick as heck 2/0) was only 1-2v at it's worst. I'd say thats fairly good given the distance of wire (25' HPWC cord, 12ish ft from HPWC to Sub-Panel, about 15 ft of Aluminum wire from Sub to main panel).

Now, voltage at a service entrance that is 15 ft from the transformer is 250, when I start charging the car at 80 amps, the voltage at the panel near the transformer dropped to 246.

I attached a picture of the transformer. The only writing on it. Transformer was buzzing a fair bit more then usual. I'm starting to think that its the distance from the transformer to the house is where the big drop is.

I'm going to get my tripod later, their is another info plate on the other side of the transformer, but is about 3x2", and the sun it hitting it just right to make it un-readable.

 

[Cottonwood]

Thought I'd update. Checked through everything today. Re-Torqued the lugs on breakers and in the panel's. I am able to sustain 70 amp charging for about a hour before it limits down to 60 amps. 60-65 amps can be sustained no problem. Voltage drop now from no load to 80 amp load goes from 247 down to 229v.
Voltage drop between car (as displayed on the car screen as viewed via the iphone app for ease) and at the main service entrance in the house panel (Supplied by thick as heck 2/0) was only 1-2v at it's worst. I'd say thats fairly good given the distance of wire (25' HPWC cord, 12ish ft from HPWC to Sub-Panel, about 15 ft of Aluminum wire from Sub to main panel).

Now, voltage at a service entrance that is 15 ft from the transformer is 250, when I start charging the car at 80 amps, the voltage at the panel near the transformer dropped to 246.

I attached a picture of the transformer. The only writing on it. Transformer was buzzing a fair bit more then usual. I'm starting to think that its the distance from the transformer to the house is where the big drop is.

I'm going to get my tripod later, their is another info plate on the other side of the transformer, but is about 3x2", and the sun it hitting it just right to make it un-readable.

Looks like you have collected all the data and the biggest problem is not in the transformer, it's in the connection between the service entrance and the main panel.

Let summarize your numbers to make sure I have it correct, and add calculations of power lost and resistance for each segment:

1. Total Volage Drop at MS - 18 Volts at 80 Amps - 1,440 Watts - 0.225 Ohm
2. From MS to Main Panel - 2 Volts are 80 Amps - 160 Watts - 0.025 Ohm
3. Drop from Utility through transformer to Service Entrance - 4 Volts at 80 Amps - 320 Watts - 0.050 Ohm equivalent, referred back to the 240 Volt domain
4. Remainder between Service Entrance and Main Panel - 12 Volts at 80 Amps - 960 Watts - 0.150 Ohm

From this summary, it's pretty easy to see the big Voltage drop and large resistance is in the connection from the Service Entrance to the Main Panel. Because you re-torqued all the connections, you have access to see what the wire is connecting the Service Entrance to the Main Panel. Use that wire size and type to look up the resistance (milliOhms) per foot at American wire gauge - Wikipedia, the free encyclopedia.

Estimate/measure the wire run length from the Service Entrance to the Main Panel, double it for wire there and back, and do the multiplication to see if it is close to the 0.150 Ohm calculated from your measurements. If it is, your only hope to improve the situation is to up the wire size or run more wire in parallel. I'm sure FlasherZ knows the rules on paralleling wire, but I know it passed code at my house.

If this calculation is a much smaller resistance than the 0.150 Ohm you measured then there is probably a poor connection somewhere, in danger of getting hot. If you are comfortable operating the panels with the covers off, you can set your multi-meter to 20 or 2 Volt range AC and measure drops across individual connections (lugs) to find the offending connection. Just practice good safety when measuring live panels. As I am sure you know, 240 Volts AC can be a lethal Voltage!

Note that to get 18.3 kW to the car, there is 1.44 kW lost in the wiring to get there. That is a fair amount of power and heat going somewhere and 7.9% overhead. That is a lot!

 

[FlasherZ]

75 kVA rated transformer, that's pretty beefy. Good for ~300A or so, seems about right sizing for the loads.

Based on what you're observing at the panel near the transformer, it seems like you're correct. Voltage drop due to transformer would be seen at that panel.

2/0 AL is good for about 130A or so, but distance can cause a drop. Using my handy calculation tables and Ohm's law, a voltage drop of 18V minus 4V at the transformer/service equipment minus 2V from main to car is 12V. Using Ohm's law, 12V @ 40A is a resistance of .3 Ohms (R=E/I) and using typical resistance of 2/0 AL cable (.128 Ohms per kft), this would be a round trip distance of 2.34 Kft or one-way distance of 1.17 Kft from the service entrance to the home panel. Sound about right?

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If it is, your only hope to improve the situation is to up the wire size or run more wire in parallel. I'm sure FlasherZ knows the rules on paralleling wire, but I know it passed code at my house.

NEC says parallel conductors may be used when larger than 1/0.

 

[islandbayy]

Thought it would be easier if I just drew a picture. Flasher was more right on. At the meter on the house I have the voltage drop yet.
I hope my picture is not too confusing. The voltage drop is happening between the houses meter and the transformer.

 

[Cottonwood]

75 kVA rated transformer, that's pretty beefy. Good for ~300A or so, seems about right sizing for the loads.

Based on what you're observing at the panel near the transformer, it seems like you're correct. Voltage drop due to transformer would be seen at that panel.

2/0 AL is good for about 130A or so, but distance can cause a drop. Using my handy calculation tables and Ohm's law, a voltage drop of 18V minus 4V at the transformer/service equipment minus 2V from main to car is 12V. Using Ohm's law, 12V @ 40A is a resistance of .3 Ohms (R=E/I) and using typical resistance of 2/0 AL cable (.128 Ohms per kft), this would be a round trip distance of 2.34 Kft or one-way distance of 1.17 Kft from the service entrance to the home panel. Sound about right?

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NEC says parallel conductors may be used when larger than 1/0.

Look at the write up, he was doing the measurements at 80 Amps, so the distance is down to 585 feet.

2/0 AL sounds a little light for running a business and adding a couple of HPWC's. Hope it's not 500 feet that needs upgrading...at least 2/0 is bigger than 1/0, so you can go in parallel, just keep the lengths the same for good current sharing...

 

[islandbayy]

Look at the write up, he was doing the measurements at 80 Amps, so the distance is down to 585 feet.

2/0 AL sounds a little light for running a business and adding a couple of HPWC's. Hope it's not 500 feet that needs upgrading...at least 2/0 is bigger than 1/0, so you can go in parallel, just keep the lengths the same for good current sharing...

The only aluminum that is used Not counting anything the utility has on the poles is between the house and garage. that is 2awg. everything else is on the poles governed by the utility. The service entrance to all properties is Copper.

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Looks like they used Copper on the poles when down to 240v. I made a video that might help further.

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Im going to try and get access to one of those two houses that are on the intermediate pole. That will tell me if the drop is between the last pole feeding the house and those two houses at the middle pole, or the middle pole and transformer.

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[Tedkidd]

If you know someone with an IR camera you can check wiring for hotspot quickly and safely that way.

I will be changing over hopefully 2 Electric Stoves/Ovens to Natural Gas giving us 60 more amps to play with.

That seems a shame. Making ff infrastructure investment so your electric car charges faster somehow seems contradictory. May want to check you kitchen venting, make sure it effectively vents to outdoors.

Any other way to do that for similar investment? We really need to be shifting AWAY from natural gas...


How often do you guys with dual chargers drive far enough in a day that you need more than 40 amps overnight? That a fairly regular occurrence?

 

[islandbayy]

If you know someone with an IR camera you can check wiring for hotspot quickly and safely that way.



That seems a shame. Making ff infrastructure investment so your electric car charges faster somehow seems contradictory. May want to check you kitchen venting, make sure it effectively vents to outdoors.

Any other way to do that for similar investment? We really need to be shifting AWAY from natural gas...


How often do you guys with dual chargers drive far enough in a day that you need more than 40 amps overnight? That a fairly regular occurrence?

I have been trying to rent or purchase a IR Camera for a while now. Not cheap I'd love to own one, as I could use one regularally, just hard to swallow $1-2k to purchase one.

This is a seasonal motel, open 4-5 months/year (summer). Natural Gas usage would be highly minimal.
And again, this is a Motel, and gets high Model S/EV Traffic due to being the only charging location in the midwest's largest tourist city. Got to the point last summer where they had to start taking Reservations to use the 14-50 outlet they had.

 

[FlasherZ]

Look at the write up, he was doing the measurements at 80 Amps, so the distance is down to 585 feet.

2/0 AL sounds a little light for running a business and adding a couple of HPWC's. Hope it's not 500 feet that needs upgrading...at least 2/0 is bigger than 1/0, so you can go in parallel, just keep the lengths the same for good current sharing...

Thanks. Yes, half that figure - I knew it was 80 and some of my earlier calculations were based on it but somehow I stuck 40 in there.

2/0 CU is much better than AL - I'm very surprised they used copper, but it's good for you. Table 310.15(B)(7) details a special ampacity case for cables that act as whole-house feeders from a disconnect to a structure, 2/0 CU is good to 200A rating in that case. That will address the HPWC's, but you'd be overloading it with 2 HPWC's - my guess is that if you set them both to 80A circuit size (64A charging) you'd be just fine.

With the cost of copper today, I'd be afraid at the cost of installing that cable.

One note about paralleling conductors - you may not parallel 2/0 AL and 2/0 CU - they must be exactly the same cable type. The reason for this is that current splits between the conductors in proportion to their resistance. Higher-resistance 2/0 AL will not allow current to split evenly beyond the two cables. In most cases, electricians won't parallel cables but will instead just go another gauge up.

 

[Cottonwood]

Thought it would be easier if I just drew a picture. Flasher was more right on. At the meter on the house I have the voltage drop yet.
I hope my picture is not too confusing. The voltage drop is happening between the houses meter and the transformer.
View attachment 47979

It took me a while to grok this diagram, but I think I not have a better picture. Here are a few observations. Let me know if this makes sense.

1. There are a total of six, 200-Amp service loads on this one 75 kW transformer. That seems like a lot especially if you are putting in a couple of high amp EVSE's as well as the 14-50 charge outlets at the motel. From what I think I have seen you post, it sounds like two 14-50's at the motel, a 100 Amp breaker, 80 Amp service HPWC at your house and another 60 Amp breaker, 48 Amp service HPWC somewhere else. That adds up to 2*10 kW + 20 kW + 12 kW = 52 kW continuous load just for EV charging, added to the loads that were already there for the six 200 Amp services... Seem like a bigger transformer is needed or maybe a second transformer on the power pole where you show the three-way feed split to the three houses.
2. It looks like you are getting 16 Volts of drop at your house with the HPWC and an 80 Amp load. That is 16/240 or a 6.7% Voltage drop drawing half of the possible load on your 200 Amp service. I think FlasherZ has quoted 5% as the acceptable drop at the service entrance. 6.7% is higher than that, and the 13.3% that you would get if you drew a full 160 Amps, is much higher than 5%. Sounds like it's time to start talking to the local utility.
3. Because it takes up to an hour for your charge rate to be reduced, it does not look like you are triggering a threshold immediately. But given the Voltage drops, it could easily be loads at the motel and other houses that are causing Voltage swings that trigger the current reduction.
4. If I add up the wire lengths from your house to the transformer and assume that they are all 2/0 (the run to the split for the three houses probably should be larger), then I get 330'. 2/0 copper is 0.07793 mOhm/ft or 0.15586 for two ways. 330' * 0.15586 mOhm/ft is 0.051 Ohms. 0.051 Ohms * 80 Amps is 4.1 Volts. Per your measurements there was 12 Volts drop on that set of utility wires. Maybe, it's as simple as the utility tightening some connections to reduce the drop by up to 8 Volts.

Keep up the good work installing EV charging infrastructure! Looks like you are forcing some utility upgrades in this neighborhood with those installs, but it's more sales long term for the utility, and they should support your increased use. Good Luck!!!