I can now charge at 80A, should I?

[wk057]

This is incorrect. At 80A of continuous current, the conductors and breaker will indeed become warm. Touch-warm is fine, touch-hot or "hot electronics smell" is not.

On the conductor size, you're incorrect - there is no "over-designing by 1/3" rule. Electricians follow the NEC (or CEC in Canada), as well as local amendments. NEC dictates that an EV charging loads be considered "continuous loads". Continuous loads require that conductors, over-current protection devices (breakers and fuses), and load calculations be rated for 125% of the charging current. In this case, that means the circuit must be sized for 100A. If you consult article 310 of the NEC, you'll find an ampacity table. #3 wire is good for 100A at the 75 degree termination rating, which is the rating for most modern breakers, panels, and other equipment (older equipment may require 60 degree termination, which would be #2). NM cable ("Romex") is not permitted for 80A HPWC installs because it must be used at the 60 degree column (see section 334.80) and that's only good to 95A (remember, 100 is required).

Your statement on ground and jumping to neutral is not only wrong, but completely unsafe and illegal. The EGC is never permitted to act as the neutral. In all new construction (post-1996), neutral and ground are separated, and joined in only one location at the main service panel.

For more information, see my FAQ located here:
FAQ: Home Tesla charging infrastructure QA

+10^10

Glad I'm not the only one chasing around and correcting misinformation these days. Seems to stem from a very persistent few.

In any case, I echo FlasherZ's previous advice, and my own... charge however you want or need to charge. It's not going to make a difference. Just leave it at 80A, charge, and be done with it.

 

[WentOffGrid]

but jumper ground to neutral at the plug.

NO! NO! NO!!!

As FlasherZ points out, you must NEVER connect ground and neutral together downstream!
This creates a "bootleg ground" that can be very dangerous as neutral current will flow through all grounding paths on the way back to the original neutral-ground bond at the main service (or another transformer)

 

[Quantum`]

mod note:Some others have raised an issue with this post and the safety of following it so read accordingly

This is incorrect. At 80A of continuous current, the conductors and breaker will indeed become warm. Touch-warm is fine, touch-hot or "hot electronics smell" is not.

On the conductor size, you're incorrect - there is no "over-designing by 1/3" rule. Electricians follow the NEC (or CEC in Canada), as well as local amendments. NEC dictates that an EV charging loads be considered "continuous loads". Continuous loads require that conductors, over-current protection devices (breakers and fuses), and load calculations be rated for 125% of the charging current. In this case, that means the circuit must be sized for 100A. If you consult article 310 of the NEC, you'll find an ampacity table. #3 wire is good for 100A at the 75 degree termination rating, which is the rating for most modern breakers, panels, and other equipment (older equipment may require 60 degree termination, which would be #2). NM cable ("Romex") is not permitted for 80A HPWC installs because it must be used at the 60 degree column (see section 334.80) and that's only good to 95A (remember, 100 is required).

Your statement on ground and jumping to neutral is not only wrong, but completely unsafe and illegal. The EGC is never permitted to act as the neutral. In all new construction (post-1996), neutral and ground are separated, and joined in only one location at the main service panel.

For more information, see my FAQ located here:
FAQ: Home Tesla charging infrastructure QA

No, warm is not correct or normal. And remember I said "good electricians". Why in the world would you ever take a chance with something like this? It's stupid.

As for gauge recommendations, you can go by whatever random chart you like, but I go by the wire manufacturers' ampacity rating for the wire they make. Copper comes in various formulations, you should know. And the reason I suggested #1 is because we can not know whether every one of the connectors in his branch is rated for 75°C, and so you must de-rate to 60°C if the idea is to do it right. If you don't care about doing it right, there are a thousand other ways to do it, sure.

And on neutral, I used to think like you do, in the olden days. But I recently found out that neutral is not needed. And it is in fact Ok for ground to be slightly smaller, as (you don't know that) all the current is flowing through the hots -- ground is only there as a safety.

Now; like I say, you are free to wire things any old way, and Dude is free to let his house burn down, I don't care. But it was my obligation to at least tell him the right way. Insurance might not pay, especially when he was told the right way and chose to scoff. Have fun!

NO! NO! NO!!!

As FlasherZ points out, you must NEVER connect ground and neutral together downstream!
This creates a "bootleg ground" that can be very dangerous as neutral current will flow through all grounding paths on the way back to the original neutral-ground bond at the main service (or another transformer

Check your panel. Neutral is connected to ground.

First of all, there is no current in neutral for a 240V load which is working properly. Second, for a device that's malfunctioning when you've connected neutral to ground, that current flows through the ground wire back to the panel and straight to ground, where it should be for safety. If you have a GFCI in the circuit (as you should), it will sense this and cut power. What you must be thinking of is a parasitic ground, where you install a second grounding rod somewhere else around the house. This can cause a ground loop, which gives 60Hz noise in house audio appliances, etc.

I can see there are all kinds of misconceptions around this subject, most having to do with overloading circuits, which is dangerous. Personally, I'm afraid of structure fires. But maybe some need them to kill the bacteria and start fresh.

 

[Kalud]

+10^10

Glad I'm not the only one chasing around and correcting misinformation these days. Seems to stem from a very persistent few.

The good thing is, one of those persistent, will most likely get banned any day from now. At least I hope so, because he's getting annoying and clueless.

(and I'm not talking about you)

 

[andrewket]

fwiw, I charge at 72A every day. I move it up to 80A if I need to charge quickly, or if my SOC is near 0 and the 80A is needed to squeeze into my TOU window.

 

[AWDtsla]

No, warm is not correct or normal. And remember I said "good electricians". Why in the world would you ever take a chance with something like this? It's stupid.

Warm is exactly normal. ALL wiring has temperature rise, the ampacity tables are a guide to manage it. There's a reason a certain current is allowed for 60C wire and another higher current for 75C, etc.

 

[Cottonwood]

No, warm is not correct or normal. And remember I said "good electricians". Why in the world would you ever take a chance with something like this? It's stupid.

As for gauge recommendations, you can go by whatever random chart you like, but I go by the wire manufacturers' ampacity rating for the wire they make. Copper comes in various formulations, you should know. And the reason I suggested #1 is because we can not know whether every one of the connectors in his branch is rated for 75°C, and you he must de-rate to 60°C to do it right.

And on neutral, I used to think like you do, in the olden days. But I recently found out that neutral is not needed. And it is in fact Ok for ground to be slightly smaller, as all the current is flowing through the hots -- ground is only there as a safety.

Now; like I say, you are free to wire things any old way, and Dude is free to let his house burn down, I don't care. But it was my obligation to at least tell him the right way. Insurance might not pay, especially when he was told the right way and chose to ignore it. Have fun! I don't give a sh*t.



Check your panel. Neutral is connected to ground.

First of all, there is no current in neutral for a 240V load which is working properly. Second, for a device that's malfunctioning when you've connected neutral to ground, that current flows through the ground wire back to the panel and straight to ground, where it should be. What you must be thinking of is a parasitic ground, where you install a second grounding rod somewhere else around the house. This can cause a ground loop, which gives 60Hz noise in the house, etc.

Excuse me, but your reply sounds more like a rant than using factual arguments. Let me address some of your claims with some facts.

Warm is normal, correct, and OK. Just put your hand on top of a stereo, TV, or your desktop computer. They all get a little warm and that is OK. The NEC is a very safety-oriented, conservative set of rules; if anything, some would argue too conservative, but others would argue that is just reasonable safety margin.

Let's look at the actual power dissipated for each of the wire sizes being discussed. From American wire gauge — Wikipedia, we see that the resistance for #3, #2, and #1 copper wire is 0.1239, 0.1563, and 0.1970 milliOhm/ft. Because the current goes out and back the power per foot of cable (conduit) is 2*I[SUP]2[/SUP]*R. For 80 Amps that is 1.6, 2.0, and 2.5 Watts per foot. Those are small power levels and pretty small differences; very slightly warm to slightly warm.

On the neutral front, you are correct that neutral is connected at the panel. That is the correct single point ground-neutral connection. Connecting it anywhere else puts current down the ground that can cause "tingling" Voltage differences and is just unsafe and wrong in modern wiring practices. Among other safety problems, you disrupt the ability of GFCI circuits to operate correctly and add safety to locations like the kitchen, bathroom, and garage.

Do not ever add additional ground-to-neutral connections beyond the single connection point in the panel!

 

[wk057]

Warm is exactly normal. ALL wiring has temperature rise, the ampacity tables are a guide to manage it. There's a reason a certain current is allowed for 60C wire and another higher current for 75C, etc.

Excuse me, but your reply sounds more like a rant than using factual arguments. Let me address some of your claims with some facts.

Warm is normal, correct, and OK. Just put your hand on top of a stereo, TV, or your desktop computer. They all get a little warm and that is OK. The NEC is a very safety-oriented, conservative set of rules; if anything, some would argue too conservative, but others would argue that is just reasonable safety margin.

Let's look at the actual power dissipated for each of the wire sizes being discussed. From American wire gauge — Wikipedia, we see that the resistance for #3, #2, and #1 copper wire is 0.1239, 0.1563, and 0.1970 milliOhm/ft. Because the current goes out and back the power per foot of cable (conduit) is 2*I[SUP]2[/SUP]*R. For 80 Amps that is 1.6, 2.0, and 2.5 Watts per foot. Those are small power levels and pretty small differences; very slightly warm to slightly warm.

On the neutral front, you are correct that neutral is connected at the panel. That is the correct single point ground-neutral connection. Connecting it anywhere else puts current down the ground that can cause "tingling" Voltage differences and is just unsafe and wrong in modern wiring practices. Among other safety problems, you disrupt the ability of GFCI circuits to operate correctly and add safety to locations like the kitchen, bathroom, and garage.

Do not ever add additional ground-to-neutral connections beyond the single connection point in the panel!

NO! NO! NO!!!

As FlasherZ points out, you must NEVER connect ground and neutral together downstream!
This creates a "bootleg ground" that can be very dangerous as neutral current will flow through all grounding paths on the way back to the original neutral-ground bond at the main service (or another transformer)

Very glad there is enough sense on this board for multiple people to correct this stuff, like above. Kudos.

https://media.giphy.com/media/P5vjklHg5MqqY/giphy.gif

 

[AmpedRealtor]

I charge at the full 80A. I figure if one or more chargers are going to fail, I'd like them to fail within the warranty period.

 

[FlasherZ]

I can see there are all kinds of misconceptions around this subject, most having to do with overloading circuits, which is dangerous. Personally, I'm afraid of structure fires. But maybe some need them to kill the bacteria and start fresh.

I see he's banned, I don't know if it's permanent or temporary... But everything said in this post is utter BS, incorrect, and VERY dangerous. For anyone reading this, please do not consider.

 

[SomeJoe7777]

I see he's banned, I don't know if it's permanent or temporary... But everything said in this post is utter BS, incorrect, and VERY dangerous. For anyone reading this, please do not consider.

Completely agree. There is one and only one set of rules in the US for the "correct" way to install electrical equipment, and that is the NEC. Anything else is at best non-compliant and won't pass inspection, or could possibly be highly dangerous at worst.

 

[Cottonwood]

I see he's banned, I don't know if it's permanent or temporary... But everything said in this post is utter BS, incorrect, and VERY dangerous. For anyone reading this, please do not consider.

Hmmm..... It seems that my post that used facts to refute Quantum's claims, also got deleted. Oh well...

 

[FlasherZ]

Hmmm..... It seems that my post that used facts to refute Quantum's claims, also got deleted. Oh well...

Not deleted - just in moderation - I presume. And yours was likely swept up because it quoted some of the illegal and dangerous recommendations he had made.

(It's why I quoted only a sentence at the end.)

On an electrician's forum I frequent, such obviously dangerous posts get a statement from the head moderator stating the illegality of the advice at the end and the thread is locked from future posts. I think our mods do the best thing they can do here.

 

[Cottonwood]

Not deleted - just in moderation - I presume. And yours was likely swept up because it quoted some of the illegal and dangerous recommendations he had made.

(It's why I quoted only a sentence at the end.)

On an electrician's forum I frequent, such obviously dangerous posts get a statement from the head moderator stating the illegality of the advice at the end and the thread is locked from future posts. I think our mods do the best thing they can do here.

That is what I figured, but I would have appreciated it if they has only redacted the quote or portions of the quote. Even a PM to me would have been polite.

OTOH, that is extra work, and removing the dangerous recommendations was important and the priority.

 

[boonedocks]

While I'm sure many others disagree, the chargers are designed to work at their capacity. If you were charging at 40A, then one charger was working at 40A. At 50A, both chargers were at 25A. At 80A both chargers are at 40A. So 80A and 40A makes basically no difference to the car. 20kW charging is ~1/4C for the 85/90 packs as well, not even enough to heat them up much at all through a full charge.

Well I have dual charges and 100 amp service to my HPWC but and wish I could get 80Amps to my car. Thanks to my power provider I can only get 231V and 79Amps. When we were iced in and I was running our house on the whole house generator, got a rock solid 240V/80Amps

wk057, thank you for all of your insight and sharing. There is so much misunderstanding and proliferation of misunderstanding and flat out uneducated comments about the BMS and how to how much and how often to charge our cars. You are a genuinely appreciated.

 

[ArtInCT]

I will soon be in the same boat at the OP.

Here is my advice...

I would first off assess your overall electrical usage and understand what an additional 80A draw will mean on your electrical infrastructure in the worst case.

For that reason I would suggest you start out by setting the HPWC to 80A and your S at 40A and then slowly incrementally up the S's charge setting day by day.
Monitor the wires and connectors and take the amperage turn ups in finite steps.

 

[Steve2498]

I would suggest you start out by setting the HPWC to 80A and your S at 40A and then slowly incrementally up the S's charge setting day by day.
Monitor the wires and connectors and take the amperage turn ups in finite steps.

That's basically what I've done except I went ahead and started at 80A. Everything handled the load fine and on an 80+ degree day the wires stabilized at around 110F - 115F degrees.

Just to keep things conservative I've settled on charging at 64A unless circumstances dictate getting topped off more quickly in which case I won't hesitate to use 80A.

 

[scottm]

The answer to the OP's question: Yes.


Thank you, that is all.



Been doing that since day 1, 80A full shot. Nothing burns out. No battery degradation. Handle gets warm, sure. So what?
Roll in on Empty and 4.5 hours later, good to go again. Day after day after day...

 

[TSLA Pilot]

According to Tesla's charge calculator on their own website, it is slightly more efficient to charge at 80 Amp compared to 40.

In terms of battery health, it makes no difference that would justify one or the other. Both rates are pretty low in relation to the battery size.

WK is absolutely right that these chargers are most efficient at their designed power level. Running them at lower rates doesn't increase efficiency nor does it help battery health long term. So do whatever is best for you.

There are too many blanket statements being made in this thread that are not applicable to all. Specifically, I have noted that on our P85 we can get battery cooling taking place when charging at high rates (up to 40 amps--we only use the UMC) at high temps.

Since cooling a battery to charge at a high rate is a massive waste of electricity (that ALSO makes for a much hotter garage from all this waste heat), we charge at 10 to 20 amps with nearly every charge (usually around 70-80%), unless there's a reason to go to 40 amps for a some short-notice issue where we need to step up the range ASAP. That also keeps the volts high (barely dropped, or completely unchanged) and since energy resistance is measured in amps ONLY, why not just back off on the amps and charge at a relaxed, maximum-voltage rate?

In the long-term I'd have to think it's easier on the equipment (less heat) to charge at a relaxed rate, no?

 

[AWDtsla]

There are too many blanket statements being made in this thread that are not applicable to all. Specifically, I have noted that on our P85 we can get battery cooling taking place when charging at high rates (up to 40 amps--we only use the UMC) at high temps.

Since cooling a battery to charge at a high rate is a massive waste of electricity (that ALSO makes for a much hotter garage from all this waste heat), we charge at 10 to 20 amps with nearly every charge (usually around 70-80%), unless there's a reason to go to 40 amps for a some short-notice issue where we need to step up the range ASAP. That also keeps the volts high (barely dropped, or completely unchanged) and since energy resistance is measured in amps ONLY, why not just back off on the amps and charge at a relaxed, maximum-voltage rate?

In the long-term I'd have to think it's easier on the equipment (less heat) to charge at a relaxed rate, no?

If that's a compromise for you, then sure. Around here 40A does not sufficiently heat the battery to keep it out of regen limiting even from a base temperature of ~50F, forget about needing active cooling.