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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