BillM
I ordered a Tesla Model 3, and sadly it's arriving sooner than I had anticipated. I have a 22kW Guardian with the service rated transfer switch. I'm going to install a 60 amp circuit for this project and I want to load shed it. In fact, I want it locked out while under generator power. I searched the forum here and I have pieced a few things together but I am not certain I'm going in the right direction.

My current plan is to purchase the Generac 6873 Smart Management Module and have the lockout switch in the enabled position so that there is no power while on generator.
Since my circuit is over the 50 amp limit of the 6873 SMM, from what I gather here on the forum, the suggestion is to purchase a magnetic latching relay from PSP Products. They even sell one with an integrated 6873 SMM in it. I've attached the picture of their relay and the General 6873 integrated into it.

1) Is there a better way to do this?
2) Does Ziller have something, I'd rather buy from Ziller and support this forum than from anyone else?
3) Is there a cheaper way to do this?

Notes: The Model 3 charges at a rate of 37 miles/hour at 50 amps, and 44 miles/hour at 60 amps. I acknowledge the difference is negligible to me and many, so putting in a 50 amp circuit would lower the costs and simplify things. However, I actually want to support 2 vehicles long term so the extra 10 amps with the 'smart' chargers is where I want to go. Yes, a bigger circuit than 60 amps makes even more sense but I'm fine with realistic usage, the technology behind the 'smart' charger balancing the power and the ease of the 60 amp run.
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78buckshot
BillM, I would use the SMM as a pilot relay and use a heavy duty contactor to act as the switch to cut the current to the 60 amp circuit, the PSP Products relay may be the ticket if it's rated for your needs.
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murphy
On a 50 amp circuit your maximum charge rate is 40 amps because it is a continuous load and must follow the 80% rule. On a 60 amp circuit the maximum charge rate is 48 amps. The Tesla does not slap the maximum charge rate on the source (electric company or generator). First it measures the voltage. Then it puts a 1 or 2 amp load on and monitors the voltage. It does a slow ramp up of current while monitoring the voltage. If the voltage drops too much it stops increasing the current. If the voltage drops radically it aborts the charge and disconnects and must be manually reset. If the car is charging when the power fails the EVSE (Electric Vehicle Supply Equipment) (Tesla Wall Connector) will enter a random start up phase of up to 30 minutes before it tries to reapply power. This is mandated by the EV charging specifications so all of the cars that were dropped by the power failure do not try to come back online at the same time.

I have a pre-refresh model S with dual chargers that can accept up to 80 amps. I have a 100 amp sub panel in my garage that is fed with 2 gauge copper wire. I only use 80 amps when I need a fast charge. Normally I charge at 32 amps because that is where the supply voltage starts to drop below 240 volts. 2 gauge wire is "big" wire but it still has resistance and wastes energy as heat at high current.

That said, the heavy duty contactor, mentioned above, is still a good idea. If you are interested in how much energy the car is using for charging, now is the time to include a kWh meter in the circuit to measure what the car uses. I use this one.

[url]https://www.ekmmetering.com/collections/electric-meters-kwh-meters/products/120-240-volt-pass-through-kwh-meter-3-wire-2-hots-1-neutral-100a-60hz-ekm-25ids[/url]

It will maintain the reading, in the absence of power, for ten years. It can't be reset. It measures to two decimal places. Mine is currently showing slightly over 8300 kWh. The maximum reading is 99999.99 kWh.
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nrp3
The only thing that I don't like that they have changed on the SMM is that it now the generator has to be overloaded before it will lock out. There are other ways to wire that PSP module so that load drop occurs without the use of a SMM. There is a wiring diagram, I believe, that shows using the extra limit switch on the side of the transfer mechanism. I think I'd go that route.
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78buckshot
I agree with using the transfer limit switch, less complicated, less expense, and control with low voltage.
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Goofy4TheWorld
This may be a crazy and/or over budget solution to your goal, but consider this.

Because you anticipate two cars in the future, and because the use of an SMM and possibly a slave contactor connected to the SMM will give you two contactors which will be required to stay "energized" 364.5 days a year, along with the likely development of an audible hum from at least one of these contactors...

I would consider purchasing a 100 amp transfer switch and modifying it so that it essentially becomes a latching contactor instead of a true transfer switch.

One such as [url]https://www.zillerelectric.com/collections/generac-residential-transfer-switches/products/generac-rxsc100a3-100-amp-automatic-transfer-switch[/url]

You would feed your 60 amp circuit from your home's main panel into the utility side of the "2nd switch" and connect the wire going to the car onto the load side of the 2nd switch. You would not connect anything to the "generator input" side of the second switch, and you would piggy back ONLY the two 12VDC control wires from the 1st switch into the 2nd switch. After one more modification (see below) you would have a setup where every time the generator sends the "switch to generator" signal it sends it to both transfer switches, and since the car charging circuit has nothing connected to the generator side of it's contactors, it will effectively kill the charging circuit.

OF NOTE, because these Generac switches REQUIRE 240VAC to be present on the "generator side" of the switch in order to actually move the contactor to generator input (which for your setup the generator input would be EMPTY) you will have to move the two tiny control wires from the generator terminals of the switch up to the utility side of the switch. The would mean you would have two tiny wires tied to each side of "UTILITY" in order to feed 240VAC to both sides of the little ice cube relay that makes the contactors change position.

It's possible that there is something I am missing that would cause unintended consequences, so maybe someone else will come along and confirm or deny what I envision would work.

But IMO I would think these transfer switches would be a far more reliable load shedding device than using any of the SMM modules, especially when you will exceed 50 amp circuitry.
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BillM
78buckshot;n58822 wrote:
BillM, I would use the SMM as a pilot relay and use a heavy duty contactor to act as the switch to cut the current to the 60 amp circuit, the PSP Products relay may be the ticket if it's rated for your needs.


Yes, the PSP model that I would use is rated up to 100 amps, so that's my initial plan, driven in part by cost.
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BillM
murphy;n58824 wrote:
On a 50 amp circuit your maximum charge rate is 40 amps because it is a continuous load and must follow the 80% rule. On a 60 amp circuit the maximum charge rate is 48 amps. The Tesla does not slap the maximum charge rate on the source (electric company or generator). First it measures the voltage. Then it puts a 1 or 2 amp load on and monitors the voltage. It does a slow ramp up of current while monitoring the voltage. If the voltage drops too much it stops increasing the current. If the voltage drops radically it aborts the charge and disconnects and must be manually reset. If the car is charging when the power fails the EVSE (Electric Vehicle Supply Equipment) (Tesla Wall Connector) will enter a random start up phase of up to 30 minutes before it tries to reapply power. This is mandated by the EV charging specifications so all of the cars that were dropped by the power failure do not try to come back online at the same time.

I have a pre-refresh model S with dual chargers that can accept up to 80 amps. I have a 100 amp sub panel in my garage that is fed with 2 gauge copper wire. I only use 80 amps when I need a fast charge. Normally I charge at 32 amps because that is where the supply voltage starts to drop below 240 volts. 2 gauge wire is "big" wire but it still has resistance and wastes energy as heat at high current.

That said, the heavy duty contactor, mentioned above, is still a good idea. If you are interested in how much energy the car is using for charging, now is the time to include a kWh meter in the circuit to measure what the car uses. I use this one.

[url]https://www.ekmmetering.com/collections/electric-meters-kwh-meters/products/120-240-volt-pass-through-kwh-meter-3-wire-2-hots-1-neutral-100a-60hz-ekm-25ids[/url]

It will maintain the reading, in the absence of power, for ten years. It can't be reset. It measures to two decimal places. Mine is currently showing slightly over 8300 kWh. The maximum reading is 99999.99 kWh.


Please forgive the dumb question; but why does the supply voltage drop? Is that something specific to region, install or just the way it is?

I do want to bling out the install with a meter, thank you for the suggestion. I was initially going to go for 70 amps at the charger, via a 75 amp breaker but if the most I'm going to get is 32 amps, there's no point. I'd be fine with 32, but seems silly to install more.

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BillM
nrp3;n58825 wrote:
The only thing that I don't like that they have changed on the SMM is that it now the generator has to be overloaded before it will lock out. There are other ways to wire that PSP module so that load drop occurs without the use of a SMM. There is a wiring diagram, I believe, that shows using the extra limit switch on the side of the transfer mechanism. I think I'd go that route.


I agree, for me, it doesn't make me comfortable.
However, I am that guy.....the one who installs the generator which triggers the phenomena of never losing power. In my 4 years of the generator being online, my total utility loss is somewhere around 90 seconds with all incidents combined.

I will use the SMM in lockout mode. I have no ambitions of charging the vehicle while on generator power. If I have to toggle the lockout switch in some unforeseen event I will cross that bridge when I get to it. However, out of the gate, by default, I want the car charger locked out.
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BillM
78buckshot;n58826 wrote:
I agree with using the transfer limit switch, less complicated, less expense, and control with low voltage.


Thanks, now the thing I have to decide is if I want to install 2 boxes on my garage wall. The SMM and then the relay in it's own enclosure or if I want to buy their relay that has the Generac SMM embedded into it, as in the picture in my original post. The pro's are it's one box, all integrated, less intrusive looking. The con is it might be harder for me to troubleshoot if it goes south.
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BillM
Goofy4TheWorld;n58827 wrote:
This may be a crazy and/or over budget solution to your goal, but consider this.

Because you anticipate two cars in the future, and because the use of an SMM and possibly a slave contactor connected to the SMM will give you two contactors which will be required to stay "energized" 364.5 days a year, along with the likely development of an audible hum from at least one of these contactors...

I would consider purchasing a 100 amp transfer switch and modifying it so that it essentially becomes a latching contactor instead of a true transfer switch.

One such as [url]https://www.zillerelectric.com/collections/generac-residential-transfer-switches/products/generac-rxsc100a3-100-amp-automatic-transfer-switch[/url]

You would feed your 60 amp circuit from your home's main panel into the utility side of the "2nd switch" and connect the wire going to the car onto the load side of the 2nd switch. You would not connect anything to the "generator input" side of the second switch, and you would piggy back ONLY the two 12VDC control wires from the 1st switch into the 2nd switch. After one more modification (see below) you would have a setup where every time the generator sends the "switch to generator" signal it sends it to both transfer switches, and since the car charging circuit has nothing connected to the generator side of it's contactors, it will effectively kill the charging circuit.

OF NOTE, because these Generac switches REQUIRE 240VAC to be present on the "generator side" of the switch in order to actually move the contactor to generator input (which for your setup the generator input would be EMPTY) you will have to move the two tiny control wires from the generator terminals of the switch up to the utility side of the switch. The would mean you would have two tiny wires tied to each side of "UTILITY" in order to feed 240VAC to both sides of the little ice cube relay that makes the contactors change position.

It's possible that there is something I am missing that would cause unintended consequences, so maybe someone else will come along and confirm or deny what I envision would work.

But IMO I would think these transfer switches would be a far more reliable load shedding device than using any of the SMM modules, especially when you will exceed 50 amp circuitry.


I wouldn't call it crazy, but it's more than I want to tackle. It took me literally 3 months to self-install my generator. That included scheduling electrical inspections and plumbing help with the gas. The rest of it I did in my free time. The thought of putting another transfer switch in makes my head explode. But the first reason for me to go with plan A is budget.
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murphy
BillM;n58834 wrote:


Please forgive the dumb question; but why does the supply voltage drop? Is that something specific to region, install or just the way it is?

I do want to bling out the install with a meter, thank you for the suggestion. I was initially going to go for 70 amps at the charger, via a 75 amp breaker but if the most I'm going to get is 32 amps, there's no point. I'd be fine with 32, but seems silly to install more.



It's basic electricity. A wire, no matter its size, is a resistor. A really small resistor, but still a resistor. Ohm's Law states that E=IR, or in words voltage = current times resistance. I'm ignoring the fact that it is really AC and not DC. AC calculations can get complicated really fast. DC is very straight forward. 100 feet of 2 gauge wire has a resistance of 0.016 ohms. A circuit requires two conductors so the total resistance of a 100 foot circuit is 0.032 0hms. If 100 amps is flowing through that circuit the voltage drop at the load end of the circuit is 0.032 times 100 = 3.2 volts. So 240 volts at one end becomes 236.8 volts at the other end of the circuit. The energy lost to heat in that circuit is equal to I squared times R = 100 times 100 times 0.032 = 320 watts. If it's cold outside that helps heat the house so it's not really wasted. However in the summer time it's 320 watts that the air conditioner has to get rid of.

It seems you missed the 80% rule. In the USA a continuous load cannot exceed 80% of the circuit breaker rating. In Canada I think it was recently reduced to 70%. So with a 75 amp breaker the most you can use for charging is 60 amps (80% of 75).

Smaller wire sizes have higher resistance values, which means a higher voltage drop and more heat generated

So the answer to your question is "That is just the way that it is".
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BillM
murphy;n58839 wrote:


It's basic electricity. A wire, no matter its size, is a resistor. A really small resistor, but still a resistor. Ohm's Law states that E=IR, or in words voltage = current times resistance. I'm ignoring the fact that it is really AC and not DC. AC calculations can get complicated really fast. DC is very straight forward. 100 feet of 2 gauge wire has a resistance of 0.016 ohms. A circuit requires two conductors so the total resistance of a 100 foot circuit is 0.032 0hms. If 100 amps is flowing through that circuit the voltage drop at the load end of the circuit is 0.032 times 100 = 3.2 volts. So 240 volts at one end becomes 236.8 volts at the other end of the circuit. The energy lost to heat in that circuit is equal to I squared times R = 100 times 100 times 0.032 = 320 watts. If it's cold outside that helps heat the house so it's not really wasted. However in the summer time it's 320 watts that the air conditioner has to get rid of.

It seems you missed the 80% rule. In the USA a continuous load cannot exceed 80% of the circuit breaker rating. In Canada I think it was recently reduced to 70%. So with a 75 amp breaker the most you can use for charging is 60 amps (80% of 75).

Smaller wire sizes have higher resistance values, which means a higher voltage drop and more heat generated

So the answer to your question is "That is just the way that it is".


Ok, thank you. I'm absorbing it all slowly. Check my logic here from a current point of view: I'm going to run less than 45 feet of 4-3 NM-B from my main panel, serviced by a 60 amp breaker. This will transition inside PVC as it penetrates into the garage. It is entering the garage around baseboard height'ish. It will go up and terminate into one of those $6 A/C non fused cutoff switch you typically have outside. From there it then will go to the load management side of the world and from there, into the Tesla. So, I'm under the belief that my usable power is going to be 48 amps. How am I doing so far?

I'm using the $6 A/C cutoff switch because it's cheap, and I want some way to 'kill' the power without having to run down into the basement to hit the breaker.
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murphy
4-3 is fine for the run from the panel to the cutoff switch. From the cutoff switch to the Tesla wall connector it is too many wires. The Tesla wall connector does not have a place to land a neutral connection. It is a 240 volt appliance which only uses 2 hot wires and building ground. If the wires to the Tesla wall connector are stranded wire, copper ferrules should be put on the ends of the wires so the screws in the wall connector have a solid surface to clamp down on.

Does the cutoff switch have an insulated neutral connection point in addition to a ground connection point? The neutral and ground can't be tied together in the switch. If it doesn't, then you only need 4-2 wire. My A/C cutoff switch only has provision for 2 hot wires and building ground since an A/C compressor is a 240 volt appliance that does not use a neutral. You can use 4 gauge wire that just has a black and a white 4 gauge wire plus a ground wire IF you wrap the exposed white wire, at both ends of the cable, with red electrical tape so the white insulation is completely covered by red tape.

Food for thought:
Think about what you might need in the garage in the future.
I didn't and have done the 75 foot run from the main panel to the garage three times.
First was a 20 amp run in early 2013 for charging a Ford Fusion Energi.
Second was a 50 amp run in late 2014 for charging an S85 with a single charger.
Third was a 100 amp run in 2017 for charging an S90D with dual chargers.
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BillM
murphy;n58846 wrote:
4-3 is fine for the run from the panel to the cutoff switch. From the cutoff switch to the Tesla wall connector it is too many wires. The Tesla wall connector does not have a place to land a neutral connection. It is a 240 volt appliance which only uses 2 hot wires and building ground. If the wires to the Tesla wall connector are stranded wire, copper ferrules should be put on the ends of the wires so the screws in the wall connector have a solid surface to clamp down on.

Does the cutoff switch have an insulated neutral connection point in addition to a ground connection point? The neutral and ground can't be tied together in the switch. If it doesn't, then you only need 4-2 wire. My A/C cutoff switch only has provision for 2 hot wires and building ground since an A/C compressor is a 240 volt appliance that does not use a neutral. You can use 4 gauge wire that just has a black and a white 4 gauge wire plus a ground wire IF you wrap the exposed white wire, at both ends of the cable, with red electrical tape so the white insulation is completely covered by red tape.

Food for thought:
Think about what you might need in the garage in the future.
I didn't and have done the 75 foot run from the main panel to the garage three times.
First was a 20 amp run in early 2013 for charging a Ford Fusion Energi.
Second was a 50 amp run in late 2014 for charging an S85 with a single charger.
Third was a 100 amp run in 2017 for charging an S90D with dual chargers.


Thanks for the tips. I was going to run the 4-3 and tape off the end in the disconnect (haven't checked with an electrician on if that's ok), in an attempt to 'terminate' the neutral since it's not needed. I naively am thinking it's better to have the wire in case it's needed down the road. I'm going to take your food for thought note into consideration. At this point, I do have what I believe is enough electrical in the garage. Famous last words.
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murphy
If I had put the 100 amp sub panel in the garage the first time I could have avoided doing the job three times. Hind site is always 20-20.
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BillM
Goofy4TheWorld;n58827 wrote:
This may be a crazy and/or over budget solution to your goal, but consider this.

Because you anticipate two cars in the future, and because the use of an SMM and possibly a slave contactor connected to the SMM will give you two contactors which will be required to stay "energized" 364.5 days a year, along with the likely development of an audible hum from at least one of these contactors...

I would consider purchasing a 100 amp transfer switch and modifying it so that it essentially becomes a latching contactor instead of a true transfer switch.

One such as [url]https://www.zillerelectric.com/collections/generac-residential-transfer-switches/products/generac-rxsc100a3-100-amp-automatic-transfer-switch[/url]

You would feed your 60 amp circuit from your home's main panel into the utility side of the "2nd switch" and connect the wire going to the car onto the load side of the 2nd switch. You would not connect anything to the "generator input" side of the second switch, and you would piggy back ONLY the two 12VDC control wires from the 1st switch into the 2nd switch. After one more modification (see below) you would have a setup where every time the generator sends the "switch to generator" signal it sends it to both transfer switches, and since the car charging circuit has nothing connected to the generator side of it's contactors, it will effectively kill the charging circuit.

OF NOTE, because these Generac switches REQUIRE 240VAC to be present on the "generator side" of the switch in order to actually move the contactor to generator input (which for your setup the generator input would be EMPTY) you will have to move the two tiny control wires from the generator terminals of the switch up to the utility side of the switch. The would mean you would have two tiny wires tied to each side of "UTILITY" in order to feed 240VAC to both sides of the little ice cube relay that makes the contactors change position.

It's possible that there is something I am missing that would cause unintended consequences, so maybe someone else will come along and confirm or deny what I envision would work.

But IMO I would think these transfer switches would be a far more reliable load shedding device than using any of the SMM modules, especially when you will exceed 50 amp circuitry.


I've decided to run 100 AMPS to the garage via 4AWG wire in SCH40 PVC. So, upon further review, I'm liking your plan more and more. The problem is this is the most expensive option, the transfer switch at Ziller is $342.00 Buying a magnetic latching relay and a Generac SMM is cheaper. So I have to do some thinking.
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murphy
I recommend that you consult a wire gauge versus current table. A 100 amp circuit requires 2 AWG wire. 3 AWG would probably work but many suppliers don't stock the odd AWG wire sizes. 4 AWG is too small for a 100 amp breaker to protect it.
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BillM
murphy;n59377 wrote:
I recommend that you consult a wire gauge versus current table. A 100 amp circuit requires 2 AWG wire. 3 AWG would probably work but many suppliers don't stock the odd AWG wire sizes. 4 AWG is too small for a 100 amp breaker to protect it.


I should have said I was running #4 THHN Copper (90 degree C). You might be thinking Aluminum???? #4 THHN Copper is rated for 95 AMPS, I'm allowed to round up to the next breaker. I'm running 3 #4's (2 hots and the neutral). And I'm going to run a #6 ground although #8 is all I need for code. But the electrician overseeing my work insisted on #6 and I'm quoting him; "Better to protect the nice cars with a better ground which will trip faster if things turn ugly." Quite frankly, I'd rather run the #8, save 10 cents a foot and it's an easier pull, but I have to follow his advice.
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murphy
I was thinking of copper wire.

Extracted from the installation manual for the Tesla HPWC>

STEP FIVE - CONNECT WIRING
NOTE: For most branch circuits of 100A, use 3 AWG (26.7 mm2), 75°C
(167°F) copper wire. For installations less than 100A, use conductors that
are sized according to local electrical codes.


[url]https://www.schneider-electric.us/en/faqs/FA175147/[/url]

The HPWC is not rated for 90 degree C wire.
Most commonly available 100 amp circuit breakers are not rated for 90 degree C wire.

Also note that to get a good connection with stranded wire, copper ferrules need to be crimped on the wire before it is inserted into the circuit breaker and the HPWC.

With 2 AWG wire there will be less voltage drop across the wire which means less wasted energy while charging the car.
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BillM
murphy;n59384 wrote:
I was thinking of copper wire.

Extracted from the installation manual for the Tesla HPWC>

STEP FIVE - CONNECT WIRING
NOTE: For most branch circuits of 100A, use 3 AWG (26.7 mm2), 75°C
(167°F) copper wire. For installations less than 100A, use conductors that
are sized according to local electrical codes.


[url]https://www.schneider-electric.us/en/faqs/FA175147/[/url]

The HPWC is not rated for 90 degree C wire.
Most commonly available 100 amp circuit breakers are not rated for 90 degree C wire.

Also note that to get a good connection with stranded wire, copper ferrules need to be crimped on the wire before it is inserted into the circuit breaker and the HPWC.

With 2 AWG wire there will be less voltage drop across the wire which means less wasted energy while charging the car.


I appreciate the help with this, but I apologize because I'm not fully understanding the thread you supplied. I looked at the wire I bought and it is 4AWG and it right on the insulation lists it's good for 90 degree's C. It says it's THHN/THWN-2 on it.

I've attached a link to the wire description and I also attached an excerpt where I'm coming up with my thought process.
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BillM
murphy;n59384 wrote:
I was thinking of copper wire.

Extracted from the installation manual for the Tesla HPWC>

STEP FIVE - CONNECT WIRING
NOTE: For most branch circuits of 100A, use 3 AWG (26.7 mm2), 75°C
(167°F) copper wire. For installations less than 100A, use conductors that
are sized according to local electrical codes.


[url]https://www.schneider-electric.us/en/faqs/FA175147/[/url]

The HPWC is not rated for 90 degree C wire.
Most commonly available 100 amp circuit breakers are not rated for 90 degree C wire.

Also note that to get a good connection with stranded wire, copper ferrules need to be crimped on the wire before it is inserted into the circuit breaker and the HPWC.

With 2 AWG wire there will be less voltage drop across the wire which means less wasted energy while charging the car.


The part in the link I am not sure I'm understanding is:
"So, circuit breakers marked for use with 75 deg. C rated conductors may be used with conductors rated for 90 deg. C if the conductors are sized per their 75 deg. C ampacity."
It's the last part that has me confused. Is it basically saying; I can use 90 deg C wire as long as I limit my circuit to 75 deg C amperage?

Or, basically, I can be legal if I change out the 100 AMP breaker in my main panel feeding this for a 90 AMP breaker? That way I can keep my #4 wire, by basically treating it as a 75 deg C wire? Am I getting closer to reality?
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BillM
murphy;n59384 wrote:
I was thinking of copper wire.

Extracted from the installation manual for the Tesla HPWC>

STEP FIVE - CONNECT WIRING
NOTE: For most branch circuits of 100A, use 3 AWG (26.7 mm2), 75°C
(167°F) copper wire. For installations less than 100A, use conductors that
are sized according to local electrical codes.


[url]https://www.schneider-electric.us/en/faqs/FA175147/[/url]

The HPWC is not rated for 90 degree C wire.
Most commonly available 100 amp circuit breakers are not rated for 90 degree C wire.

Also note that to get a good connection with stranded wire, copper ferrules need to be crimped on the wire before it is inserted into the circuit breaker and the HPWC.

With 2 AWG wire there will be less voltage drop across the wire which means less wasted energy while charging the car.


I believe in my first round of questions you pointed out the benefit of putting on the copper ferrules, I appreciate that suggestion. I will do that.

I think in a nutshell, if I change out the main breaker to be a 90 AMP CH breaker, instead of the 100 AMP, I should be ok??? Not ideal, as the only ideal solution would be the #3 or better wire, but I already have the wire.

If I still want to isolate this from my generator I can go back to the idea of an SMM running a magnetic latching relay.
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murphy
Do you leave your car plugged in all of the time? I don't, I only plug it in when I want to charge it and then unplug it when it is done. If there is a power failure, when power is restored the HPWC should wait a random amount of time up to 30 minutes before trying to resume charging. That is required by the EV charging specification to prevent all of the cars trying to resume charging at the exact same time which could destabilize the grid. It is likely that a load shed would have come back on line before the car tries to resume charging unless you put in a hard shed that never comes back on line when the generator is running.

Have you ever watched the car ramp up charging? It tries a few amps and monitors the voltage. It then slowly increases the current while monitoring the voltage. If there is a quick drop in voltage it stops increasing the current and stays at that current. If it continues it will go to the max for the first charger in the car which is 40 amps and it will stop there for a bit. It will then repeat the previous process to go from 40 amps to 80 amps. If at any time the voltage drop looks bad it will stop increasing the current.

90 ° C wire is allowed to heat up to 90 ° C (194 ° F). That is way hotter than I want wire in my house to reach. That is a lot of wasted energy being used to heat the wire. I used 2 AWG wire because I want the wire to be no more than lukewarm. If the wire can get to 90 ° C, whatever is connected at each end must be able to handle that temperature.

According to this table the maximum current for #4 at 75 ° C is 85 amps.

[url]http://www.usawire-cable.com/pdfs/nec%20ampacities.pdf[/url]

I can charge my car at 80 amps. Most of the time I charge it at 20 amps to avoid energy loss heating the connecting wire.

How long is the run from your main panel to the car? Mine is 75 feet. The company that installed my generator did not consider shedding the sub panel in the garage because nothing is permanently connected to it. They shed the oven in the kitchen and the air conditioner compressor. Both are hard wired to the main panel.

My only reason for going in to all of this is I don't want your car charging circuit to be a fire risk.
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BillM
murphy;n59409 wrote:


My only reason for going in to all of this is I don't want your car charging circuit to be a fire risk.


Thank you, and I appreciate all the help you are giving me. And your patience with me.

I ordered the Model 3 with the Standard Battery but it's delayed again so I may just give up on the Tesla and get the Chevy Bolt. But right now, still waiting on the car. No real life experience on it's charging. I already own the #4 wire, so that's why I'm hanging onto the size. And in the grand scheme of things, I'd be happy with a 60 amp circuit though I'd always think I should have gone bigger. I'm running a 22kW Generac generator for the house and I'm not shedding anything at this point. Mentally, I figured it wouldn't be a bad idea to shed this project. I don't have a need to, not even sure it really matters. But I was thinking, why not. I liked the PSP Products latching magetic relay initially, because it would shed the garage but gave me the ability to 'manually' bring the garage online if I wanted to without any fuss. It also allowed me to delay the garage as I saw fit. But then I started weighing costs between all my options .... including just running nomex cable and a smaller, simpler circuit. But the cost of nomex was far greater and I have #4 on hand so that's how I got to where I am. I took notes, left them for my electrician who is overseeing this project. As it sits now, I'm thinking of feeding this garage sub-panel with a 90 amp breaker, with #4 as before. But now I have to decide if I want to shed it, and if so which way. I can use the PSP Products way, or if I use a Generac 100 amp transfer switch but basically as a shedding relay, am I opening myself up to issues because it in itself has a breaker in it that is 100 amps, on a 90 amp protected circuit. I don't need/want a breaker at that position but it comes with one. I will have a 90 amp in my main panel, and I'm feeding a sub-panel (8 circuit) which in turn will have breakers for the outlet I'm putting in, the 30 amp RV circuit I'm putting in for my sisters once every 10 year visit and the car charger which I'm actually only feeding with a 60 amp circuit. The model 3 at best can only charge at 48 amps (60 amp circuit.)
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