Tesla Wall Charger Wire

[zero610]

@zero610 do you plan on running everything at the same time ? I have similar size house 4200sqft 2acs 2 ovens etc etc ...I charge over night when most of that stuff isn’t on ..I also have 200a house service ..running a 100a circuit to the wall connector ::I set car at ~40a as I don’t need fast charging overnight ..it’s only a handful of times I have used the full 80a for S or full 72a for X ...you will be fine putting a 100a breaker

Good to know. This charger will be for a model 3, so it's limited to 48 amps anyway. Theoretically, I'd like to have the car plugged in whenever it's in the garage. Charging could be during some peak electricity times (i.e. cooking dinner, with wife and kid home).

I'm guessing you use the scheduled charging on the S/X to start charging at night?

 

[NickFie]

Then the flex whip that came with the transfer panel connects the main panel to the transfer panel. It is *full* of wire!
View attachment 310198

Is either vehicle charger served by the transfer panel? Family & friends in our Zip Code had multi-day power outages earlier this year.

 

[NickFie]

30amp dryer unused (have gas)

We also replaced electric dryer with a gas unit. Our Tesla-recommended Electrician suggested replacing the dryer breakers with the HPWC breakers. That kept breaker count constant and simplified load calculation.

He had to submit pictures of main and sub-panels to Tesla for approval to install 100-Amp feed to new subpanel dedicated to HPWC, with 100 Amp breakers for HPWC.

 

[P85_DA]

...

I'm guessing you use the scheduled charging on the S/X to start charging at night?

Yes where I’m at we have time of use rates so majority of my home charging is at night

 

[eprosenx]

Is either vehicle charger served by the transfer panel? Family & friends in our Zip Code had multi-day power outages earlier this year.

No, the car draws vast amounts of energy. I only have a Honda 2000i which is good for 1600 Watts continuously. Just enough for the very basics. I can twin it with a second unit (like half a dozen friends have a compatible unit) to double that.

Between my wife and I we have three cars so I will just drive my truck if the power is out for long. Also, I can go charge at my Datacenter which will basically never loose power. It has redundant paths back to the substation all underground.

We also replaced electric dryer with a gas unit. Our Tesla-recommended Electrician suggested replacing the dryer breakers with the HPWC breakers. That kept breaker count constant and simplified load calculation.

He had to submit pictures of main and sub-panels to Tesla for approval to install 100-Amp feed to new subpanel dedicated to HPWC, with 100 Amp breakers for HPWC.

Ah interesting. This must have been to be able to remove the dryer from the load calculations. Makes sense!

Any idea why they did a sub panel with just a single breaker? Was it to convert from aluminum to copper? Or to provide future flexibility? Or to provide a local disconnect?

 

[NickFie]

Any idea why they did a sub panel with just a single breaker? Was it to convert from aluminum to copper? Or to provide future flexibility? Or to provide a local disconnect?

Sub-panel was at my request for future flexibility.

- Driveway is at far side of the house from main panel.

- Considering relative labor and materials costs, subpanel with 100 Amp service seemed worthwhile. At my request, electrician used 2/3 copper end-to-end. Figured extra cost would avoid problems with Aluminum-phobic future buyers.

- I or future home buyer can add a non-Tesla charge point with short, easy cable run and breaker swap from single 100 Amp to 60 + 40 or similar.

Sub-panel also provided a very sleek HPWC installation. HPWC is visible from the street, mounted next to Mudroom entry. Electrician ran cable into back of HPWC directly through the exterior wall. Then up inside the wall, above the ceiling and inside the opposite wall to the flush mounted subpanel.

Since subpanel is visible through the mudroom door window, Township inspector accepted it as the required visible cut-off switch.

No industrial-chic conduit or “Frankenstein” switch - just the nicely-styled HPWC.

My long-time Tesla owning friend recently visited and raved about the clean appearance. Then he connected his dual-charger S85 and pulled a solid 80 Amps. We felt the subpanel feed cable at several points after he had been charging for an hour - it wasn’t even warm. Nearly 100% charge by the time he continued his journey to northern New Hampshire that evening.

Also had the electrician connect 50-foot reel of shielded twisted pair to HPWC, with reel left above the mudroom ceiling. Should simplify installing second HPWC to share the 100 Amp service if/when I get the Model 3 of my dreams with Dual motors and SAS.

 

[NickFie]

Also, I can go charge at my Datacenter which will basically never loose power. It has redundant paths back to the substation all underground.

Never say, “Never!” Heard of a company with global business and a single data center in the ‘90s, before WAN bandwidth was plentiful and affordable.

They did everything to make it solid. Systems in underground bunker with tight entry control. Power feeds from separate substations at opposite corners of the large site. 45 minutes battery backup. Generator backup for the batteries. Monthly generator tests to ensure they were fully operational.

Then, disaster struck. A single tornado managed to take out BOTH substations. Battery backup picked up seamlessly. Then, generators failed to start. Techs scrambled to perform orderly shutdown of massive systems before batteries ran down.

They didn’t make it. Took over 24 hours after commercial power returned to unscramble key tracks on hundreds of disk drives.

The company, highly dependent on these systems for nearly every aspect of its complex operations, had to limp along on paper for the duration.

Turned out the generators had been failing the scheduled test for several months.

Since the company was in a cost-reduction drive and the generators had never yet been needed, the site’s facility maintenance staff decided to postpone purchase and installation of the repair part(s). Their department never shared the information about failed tests and postponed correction. Though likely got credit for meeting the tightened budget.

My friend speculated about whether the company achieved even larger savings by terminating responsible parties.

 

[eprosenx]

Found the website below for a quick whole house load calculation. I know it isn't exact. Showing around 155 amp load with the 48 amp tesla wall charger. Thoughts?

Whole House Load Calculator

My calculation:

Load.pdf

Nice tool! I will have to check that out. Was driving today to a vacation spot (sadly without my M3 yet!!!) so slow to respond.

A couple quick notes without diving into it too deep:
1. The Tesla load needs to be calculated as a continuous load, so unless the tool has a way to set it as such, you would need to count it as 14,400va.
2. Looks like you are at least missing one of your furnace supply fans (not a big deal - though I question their estimate of 300 watts - that seems quite low by my experience watching my "sense" with my furnace fan)
3. Because you have your Fridge and Washing Machine and Dryer on dedicated circuits, those may drive up your count of "small appliance circuits" (this is not an area of code I have read into much yet but I have seen some discussions online). You also have the outdoor kitchen which might be counted as small appliance circuits (though I would argue that the indoor and outdoor kitchens could be considered non-coincident loads since I doubt you use both at the same time).
4. This is where I am way beyond my current depth, but my guess is that you can't lump the Tesla in with regular house loads which then get "demand factor" reduced by 60% (to 40% of calculated) since they figure you will never use EVERYTHING in your house. The Tesla WILL be used for many hours so I suspect it does not get to be demand factor reduced. I will try to research this.

At the end of the day, I suspect you are going to be fine. It will just be pretty close. There is an interesting rule on the books that after all this calculation and derating, there is another rule that allows the service feed into the building to use conductors 83% of what the tables say you need. I have no idea how or why they came up with 83%, but it basically means that the feeds to everyones house can't really support the full 200 amps (or 100 or 400) that it is calculated at. The NEC is weird sometimes (I am wondering if this going to bite people now that folks are adding electric cars and actually more heavily loading their electrical services).

Also, any desire to future-proof your install (like if you got a model X or S) and do something larger than a 60a circuit? I just did the 60a circuit, but figured I would ask... Though since you are somewhat close on the whole house load, perhaps 60a is the safest.

If you have a few and could answer some of the questions in my previous post (and/or do some pics) that would be convenient!

 

[eprosenx]

Never say, “Never!” Heard of a company with global business and a single data center in the ‘90s, before WAN bandwidth was plentiful and affordable.

Yup. I have seen tons of crazy stuff. I am the infrastructure architect, so I know a few things about redundancy. ;-)

In my case, we damned well test the generators. This facility currently has 14x 2.25 megawatt generators. Each one sits on a couple thousand gallons of diesel. All of my loads are fed from two sets of UPS units on two generators. Then the main electrical switchgear is main-tie-main with two feeds from the utility back to two transformers at the substation. (actually half the facility is fed from a second substation as well)

With all that being said, things still fail. You can never predict or protect from everything. Though 100% of our critical systems have an *identical* copy running in a duplicate datacenter in a different state. It runs active/active and can instantly handle the full load of transaction processing.

But yeah, I never say never...

(incidentally, the car charger is not on UPS or generator, but it does get protection from the dual utility feeds - the substation we are fed from has four transmission lines into it, soon to be five - actually, the other two car charging stations on the opposite end of the building are fed from yet a second pair of utility feeders from that second substation - so yeah, if none of that is working, charging my Tesla is probably not top of my mind) ;-)

 

[zero610]

1. The Tesla load needs to be calculated as a continuous load, so unless the tool has a way to set it as such, you would need to count it as 14,400va.

Isn't the load calculated as volts * amps of the item? It looks like your 14,400 is 240 * 60 (circuit breaker). I was using 240 * 48 (tesla continuous charge) = 11,520. Am I thinking about that wrong?

 

[zero610]

4. This is where I am way beyond my current depth, but my guess is that you can't lump the Tesla in with regular house loads which then get "demand factor" reduced by 60% (to 40% of calculated) since they figure you will never use EVERYTHING in your house. The Tesla WILL be used for many hours so I suspect it does not get to be demand factor reduced. I will try to research this.

The tool actually has an EV charging as one of the items in the pull down menu. I just separated the Tesla so I could get a more accurate energy usage with numbers I know. That tool could definitely be flawed though. However, I like the idea of scheduled charging it at night. My electricity rates don't vary but at least I'd know I won't overload the main circuit.

2. Looks like you are at least missing one of your furnace supply fans (not a big deal - though I question their estimate of 300 watts - that seems quite low by my experience watching my "sense" with my furnace fan)
3. Because you have your Fridge and Washing Machine and Dryer on dedicated circuits, those may drive up your count of "small appliance circuits" (this is not an area of code I have read into much yet but I have seen some discussions online). You also have the outdoor kitchen which might be counted as small appliance circuits (though I would argue that the indoor and outdoor kitchens could be considered non-coincident loads since I doubt you use both at the same time).

Also agree on the 300 watts for the furnace; however, I can't imagine a gas furnace having any significant impact on energy usage.

The outdoor kitchen circuit is just a few unused outlets. No frig or high powered appliances out there. Even the "freezer" circuit I added in the calculation is unused now - just added it in case we ever decide we need a separate frig/freezer.

Like you said, I think I'll be fine adding on the main circuit. If I do ever run into any problems, what will be my first indication? Main 200 amp circuit trip? Anything else?

 

[wwu123]

The tool actually has an EV charging as one of the items in the pull down menu. I just separated the Tesla so I could get a more accurate energy usage with numbers I know. That tool could definitely be flawed though. However, I like the idea of scheduled charging it at night. My electricity rates don't vary but at least I'd know I won't overload the main circuit.



Also agree on the 300 watts for the furnace; however, I can't imagine a gas furnace having any significant impact on energy usage.

Most furnaces, except for higher-end variable speed models, have a single-speed PSC-type motor that runs at 500 watts or higher any time the air is blowing; shouldn't be a big energy draw if your heating needs are modest, but if you're one of those that leave the fan setting on the thermostat on 24 x 7 to recirculate air and even out temps, it's a lot of energy usage....

 

[eprosenx]

Isn't the load calculated as volts * amps of the item? It looks like your 14,400 is 240 * 60 (circuit breaker). I was using 240 * 48 (tesla continuous charge) = 11,520. Am I thinking about that wrong?

Yeah, so continuous loads I think have to be planned (feeder capacity and service capacity wise) as if they were 25% larger (so multiple by 1.25). So 240*48*1.25 = 14,400

The tool actually has an EV charging as one of the items in the pull down menu. I just separated the Tesla so I could get a more accurate energy usage with numbers I know. That tool could definitely be flawed though. However, I like the idea of scheduled charging it at night. My electricity rates don't vary but at least I'd know I won't overload the main circuit.

Also agree on the 300 watts for the furnace; however, I can't imagine a gas furnace having any significant impact on energy usage.

The outdoor kitchen circuit is just a few unused outlets. No frig or high powered appliances out there. Even the "freezer" circuit I added in the calculation is unused now - just added it in case we ever decide we need a separate frig/freezer.

Like you said, I think I'll be fine adding on the main circuit. If I do ever run into any problems, what will be my first indication? Main 200 amp circuit trip? Anything else?

Yeah, so this is where the load calculations thing is so complex and fuzzy. There are two ways to think about it: One is the hard and fast letter of the rules NEC calculation. This will determine whether you get inspector approval or not (if they want to throw the book at you). Though in my experience even the inspectors don't understand all the details and they just kind of handwave over it unless they are materially concerned about loads. I get the idea that a lot of what that code is about is to keep electricians on spec homes and apartments from doing something below the absolute bare minimum. On the larger custom homes which are often "cost plus" you just don't have those issues.

So secondarily, the question is more one of "will this burn my house down" or "will this blow breakers all the time due to lack of capacity". This is where more practical discussions come in of like "well we never use the outdoor kitchen"...

Note that the NEC (for good reason) does not trust humans to manage the load on their electrical system. i.e. just because you say you won't charge your car any time but in the middle of the night does not mean the next owner won't just plug in (not knowing or caring about any inherit limitations in the homes electrical system), so NEC plans for worst case scenario.

As to what would happen if you overload: Yes, the first indication you would get would be the main 200a breaker blowing. Though I don't have a lot of experience with this. Something that sketches me out is that we have this table which tells you what the ampacities of various sizes and types of wire can handle. It is the master source of truth for calculating branch circuits, feeders (subpanel feed wires), and the main service feed. But then there is 310.15(B)(7) which says that for single family residences you are allowed to take the required ampacity for the service and multiply it by .83 and then use that number instead for sizing the wire from the meter base into the main panel. That is just so crazy to me that this table is considered the master source of record for safety of carrying different amounts of current, and then there is this unexplained exception that lets you make them smaller.

I am assuming this was done since someone did a survey and found that residential main feeds were woefully under-loaded in the real world and so they did this to allow for cheaper wiring methods. However... I wonder if as EV's become more popular if we are going to get closer to the limits and this will start becoming an issue.

So I guess my call out is that if you run close to that 200a limit, you may be stressing those service entrance conductors a lot more severely than you would a branch circuit that is near its max (and its conductors are not sized with that same .83 multiplier). I think the main purpose of the 200a main is more in case there is a short that causes a fast trip rather than for overload conditions?

Most furnaces, except for higher-end variable speed models, have a single-speed PSC-type motor that runs at 500 watts or higher any time the air is blowing; shouldn't be a big energy draw if your heating needs are modest, but if you're one of those that leave the fan setting on the thermostat on 24 x 7 to recirculate air and even out temps, it's a lot of energy usage....

My furnace supply fan is ~650 watts and I have an 1850 sq ft house for what it is worse. I think it should be included in the calculation accurately along with everything else.

 

[zero610]

@eprosenx - Does your Sense give you any data on peak energy usage for your house? Can you not use that to get a rough estimate of total load?

 

[eprosenx]

@eprosenx - Does your Sense give you any data on peak energy usage for your house? Can you not use that to get a rough estimate of total load?

So it does not have an interface mode that shows you a report of your recent peaks, etc... But you can scroll back through the history and get a great idea of what peak draw actually is. I have been bugging them to give me features like that for a while now (they are focusing on all the machine learning stuff, but I just want some basic features like this first). I do highly recommend the Sense though!

So yeah, I have a huge degree of confidence about what my loads in my house look like. I am nowhere remotely close to any limits. I think it is a great tool to understand your usage patterns.

In the image below my house is using under 200 watts total right now and it is generating nearly 2000 watts of solar!

 

[eprosenx]

FYI, I have discovered 2017 NEC code section 220.83 - Existing Dwelling Unit

It is a seemingly simplified calculation to determine if a "service" (supply from utility) or "feeder" (wire to subpanel) is of sufficient capacity to allow additional loads to be added. It would appear to be more relaxed in capacity compared to what you need to size for when building a new home or putting in a new service or feeder.

Basically they don't want you building undersized stuff, but if you already have something installed they want to be able to let you use it up to the safe maximum limit.

This makes complete sense to me. Sorry I did not know it earlier and bring it up! You can get free access to the 2017 NEC via the NFPA web site. You just have to register your email address.

 

[ccutrer]

Also, as being discussed in other threads right now - Romex (NM cable) 6 gauge is NOT rated to be allowed on a 60a breaker from what I can tell. It is because it is limited to 60c insulation rating which limits ampacity to 55 amps. So if you have it on a 60a breaker I am 90% sure you are not code compliant.

Yes, you can put 6/3 NM on a 60A breaker, but only for a load rated up to 55A. NEC has an exception to let you go up a breaker size if there isn’t a standard breaker size at your required circuit size. This does NOT mean your circuit is now good to 60A/48A continuous. Everything else is still calculated as if the breaker were 55A.

 

[ccutrer]

One option for you would be to do flex conduit and fish your own conductors in. I used a #10 ground wire for my 60 amp circuit wall connector - so 48 amps usable (as that was allowed by code). Though this is usually done for somewhat shorter runs. Fishing a full 50 feet might be a pain (and I am not sure if there is a limit to how far you are allowed to use flex conduit since fishing it would be a pain and could damage the conductors - though I don't know of any code section that prohibits this - it looks like any prohibition on this may have been previously removed but I would check with your inspector before making a decision).

I just fished 2 #3 plus separate ground through 40-45’ of 1” FMC (for a 100A/80A continuous wall connector install). It was a piece of cake. I fished the wires through the conduit first, laying the conduit out (relatively) straight in the front yard. Then I strung the whole assembly across the (not yet dry walled) garage. In general, fishing THHN through properly sized conduit, without too many bends is relatively easy (make sure to use fish tape. Though I didn’t even need it for my 100A circuit). If it’s tough, you’re either putting too many wires in, or using the wrong kind of wire (NM in EMT or liquidtite!), or not sized correctly.

 

[eprosenx]

Yes, you can put 6/3 NM on a 60A breaker, but only for a load rated up to 55A. NEC has an exception to let you go up a breaker size if there isn’t a standard breaker size at your required circuit size. This does NOT mean your circuit is now good to 60A/48A continuous. Everything else is still calculated as if the breaker were 55A.

Hah, yes, you are very correct. If you had a non-continuous load that was 51-55 amps, or a continuous load that was 41-44 amps (EVSE's are always considered continuous loads) then yeah, you could use 6/3 NM (Romex) and put it on a 60a breaker and be totally code compliant. But a NEMA 14-50 is only rated to 50 amps so you can't put it on a 60 amp breaker, and the Tesla Wall connector settings jump from 40 to 48 amps so there is no setting that falls in that range.

So I am not sure if it would be allowed to use the "next size up rule" since you don't have a load need to do so, but from a more practical and safety standpoint I just would not do it since it buys you nothing and I think potentially adds some risk - no reason to use a bigger breaker if you don't need it.

I just fished 2 #3 plus separate ground through 40-45’ of 1” FMC (for a 100A/80A continuous wall connector install). It was a piece of cake. I fished the wires through the conduit first, laying the conduit out (relatively) straight in the front yard. Then I strung the whole assembly across the (not yet dry walled) garage. In general, fishing THHN through properly sized conduit, without too many bends is relatively easy (make sure to use fish tape. Though I didn’t even need it for my 100A circuit). If it’s tough, you’re either putting too many wires in, or using the wrong kind of wire (NM in EMT or liquidtite!), or not sized correctly.

Hah, yeah, I think this is how most people do it, but I have heard that technically it is not allowed (I don't know what NEC article to cite though). Something about potential to damage the conductors. Also, perhaps if the flex is then installed somewhere difficult to get to and you need to replace a conductor later it may be difficult/impossible if you relied on having the conductors installed ahead of time.

 

[ccutrer]

Hah, yeah, I think this is how most people do it, but I have heard that technically it is not allowed (I don't know what NEC article to cite though). Something about potential to damage the conductors. Also, perhaps if the flex is then installed somewhere difficult to get to and you need to replace a conductor later it may be difficult/impossible if you relied on having the conductors installed ahead of time.

Shrug. I could see that with something smaller. But 3AWG in one inch, carefully coiled very loosely has minimal chance. I’m sure it would pull through just fine in-place (two very gentle 90s - up one wall, across the garage, down the other). Besides, how is it any different than NM that can be potentially damaged as you’re pulling it, and the only way to replace it after-the-fact is to tear out drywall? Summary - I can see reasoning behind such a rule, but I’m not worried about violating the spirit of it in my case. (Point of fact, I put the conductors in ahead of time at my current home before taking it over to the new home in order to reduce the time I was working at the new home - my wife can be a bit possessive of my time!)

 

[zero610]

I've been away from this thread a few days...

Yes, you can put 6/3 NM on a 60A breaker, but only for a load rated up to 55A. NEC has an exception to let you go up a breaker size if there isn’t a standard breaker size at your required circuit size. This does NOT mean your circuit is now good to 60A/48A continuous. Everything else is still calculated as if the breaker were 55A.

Does this mean I should not use a 6/2 MC cable (link below) since I'll be charging at 48A continuous?

Metal Clad MC Cable 6/2 - Type MC Copper Electrical Wire 6 Gauge 2 Conductor