Home Charging

[Mark E]

The sparky has looked at my place and also been out to visit Tesla.
He tells me that it will cost around $3k to go 3 phase, but needs to put a quote together. Meanwhile he suggested that I make a list of all of the outlets etc in the house to calculate what the real load would be.
I've done that and created a google calc sheet for it. On the sheet I also looked at the current switchboard and did a worst case and sensible load calc.

In the worst case I'd be at home on a cold night with the air conditioning pumping heat, with the dishwasher running and cooking dinner in the electric oven, making coffee using the machine and the microwave, the stereo playing a movie on my plasma while the off peak hot water kicks in. This is pretty unlikely, but adds up to 77.5A. A more realistic estimate would be around 40A, for a short time, say making coffees with the movie playing, air-co pumping warm air and the off peak hot water heating up.

This is telling me that I might be able to get away with a single phase 32A in the garage without having to go 3 phase. I'll have the dual chargers for travel, but probably won't need the HPWC installed at home.
You can look at my calcs at Google Sheets - create and edit spreadsheets online, for free.

Either way, it'll be interesting to see what the sparky comes back with.

 

[mike_j]

I am no expert on electrics, but wouldn't you be charging overnight when you aren't using all the other juice?

 

[president_ltd]

Note that everything is 'derated' and sizing is around protecting the cabling, so if you've got an 80A cable to the street its likely you have a -20% derating (63A) master switch on your main switch board.

I think you've likely added up wrong though, because while you likely have a 32A breaker on your reverse cycle air con its not likely to be more than 11A actual load. Breakers for things like large compressors and motors are way oversized based on current inrush on startup but if e.g. your reverse cycle A/C is a digital scroll or "inverter" type unit then it doesn't have that large inrush and could be a 16A breaker instead.
Your google spreadsheet lists it as worst-case 20A. Really? 20A x 230V = 4600W. COP heating for most reverse cycle A/C is >3.3, often 4 for heating, do you actually have an "18KW" A/C unit? Or a 10KW unit?

I started a thread on this exact topic at Renovate Forums where numerous sparkies hang out and can provide good advice.
see How big can an individual circuit be (Melb/VIC/single phase)

One does need to gather tha loading requirements like you state - and there is good guidance there on how to do it - but my point is that if done correctly (e.g. breaker on mains that guarantees you cannot draw more than its rating on a sustained basis) and if your wiring is up to it, yes its entirely feasible to have a HPWC @ 40A (32A actual draw since that too would be 20% derated) on what is a 'typical' 63A single phase 230V connection in Australia.

 

[Cosmacelf]

Install the charging equipment you want. If you trip the main breaker, then upgrade, until then, you're fine . Seriously though, sometimes electricians get way too anal about loads. The breakers are there to protect you against overloads, so use them.

 

[Mark E]

I think you've likely added up wrong though, because while you likely have a 32A breaker on your reverse cycle air con its not likely to be more than 11A actual load. Breakers for things like large compressors and motors are way oversized based on current inrush on startup but if e.g. your reverse cycle A/C is a digital scroll or "inverter" type unit then it doesn't have that large inrush and could be a 16A breaker instead.
Your google spreadsheet lists it as worst-case 20A. Really? 20A x 230V = 4600W. COP heating for most reverse cycle A/C is >3.3, often 4 for heating, do you actually have an "18KW" A/C unit? Or a 10KW unit?

Yes really, the A/C is fully ducted & a little overkill for the house. When ordered it was a slightly smaller unit, but Fujitsu shipped the larger one and I didn't want to wait - especially at the same price. It's an inverter unit and is 23.8A max when cooling and 19.8A max when heating. 5.7 & 4.7kW, read straight from the side of it this morning.

Cooling capacity 14.5kW, Heating 16kW.

 

[president_ltd]

Install the charging equipment you want. If you trip the main breaker, then upgrade, until then, you're fine . Seriously though, sometimes electricians get way too anal about loads. The breakers are there to protect you against overloads, so use them.

This is bad advice. Many houses here don't have a "breaker" as the main switch, rather its just a switch.

 

[Mark E]

Install the charging equipment you want. If you trip the main breaker, then upgrade, until then, you're fine . Seriously though, sometimes electricians get way too anal about loads. The breakers are there to protect you against overloads, so use them.

If the 'breaker' is the 100A service fuse, then blowing that would be bad and the house without any power for potentially quite a while. I'm not sure if Ausgrid would replace the fuse without insisting on finding any fault at the house. So extra costs and inconvenience.

Then there is the risk of fire or other damage if holding a high current close to the limit for too long. I'll be following professional advice but collecting as much info as possible.

 

[Tasdevil]

In tassie you can get a circuit breaker swapped out for your main switch next to you meters. Say an 80amp cb, that way your protecting your mains and fuse. Worse case scenario is you trip it at night and have to go outside and reset it.
If its possible, but unlikely that you will draw more than your mains cable can handle this could be an option.

 

[salamagd]

How are people doing with getting their charging infrastructure installed, particularly within apartment buildings? I've hit a bit of a roadblock with my building electrician, who claims there simply isn't the capacity to add an additional 40A circuit, so I'm looking at short-term alternatives including just using a 10A cable at home temporarily and perhaps installing the wall connector at work. Bit of a pain, and I imagine others living in multiple-dwelling units may encounter similar issues!

 

[Dborn]

I have a 3 phase supply and a dedicated line to my garage at 32amps breaker (the maximum allowable on 6 SQMM wire). It has been wired as a single phase for now to my wall connector unit, which appears to be the same one being supplied to China and Hong Kong. The sparky has set the charge current to 20amps in the wall unit. Uncertain why this should be so, since breakers in this country are supposed to be capable of sustained draw at the rated current, in contrast to the USA where the draw needs to be derated.
in order to draw 32 amps, cable sizing would be 10mm sq. (next size up). This, in a domestic situation, is not justifiable. So, my charge current maximum will be 4.8Kw. until we get our 3 phase chargers next year. not sure of the exact calculation, but the 3 phase charger will allow 24.9Kw, if the 20 amps is calculated as 60 amps total and 415 volts. (over 3 phases). The good part about the future changeover is that it will literally be a physical mounting on the wall of the new unit and hookup of the existing cable, the unused phases currently having been capped off inside the enclosure of the wall connector.

 

[meloccom]

How are people doing with getting their charging infrastructure installed, particularly within apartment buildings? I've hit a bit of a roadblock with my building electrician, who claims there simply isn't the capacity to add an additional 40A circuit, so I'm looking at short-term alternatives including just using a 10A cable at home temporarily and perhaps installing the wall connector at work. Bit of a pain, and I imagine others living in multiple-dwelling units may encounter similar issues!

I spent about a year getting approval to install a 32 Amp service to my apartment garage. In the end I had to put in a separate meter specifically for the garage. It was expensive, circa $3500, and it meant going through a full load analysis by the electrician.
Are you adding an additional power point to your existing service? I fail to see why they can't install a 15 Amp power point at least.

 

[JOH]

I have a 3 phase supply and a dedicated line to my garage at 32amps breaker (the maximum allowable on 6 SQMM wire). It has been wired as a single phase for now to my wall connector unit, which appears to be the same one being supplied to China and Hong Kong. The sparky has set the charge current to 20amps in the wall unit. Uncertain why this should be so, since breakers in this country are supposed to be capable of sustained draw at the rated current, in contrast to the USA where the draw needs to be derated.
in order to draw 32 amps, cable sizing would be 10mm sq. (next size up). This, in a domestic situation, is not justifiable. So, my charge current maximum will be 4.8Kw. until we get our 3 phase chargers next year. not sure of the exact calculation, but the 3 phase charger will allow 24.9Kw, if the 20 amps is calculated as 60 amps total and 415 volts. (over 3 phases). The good part about the future changeover is that it will literally be a physical mounting on the wall of the new unit and hookup of the existing cable, the unused phases currently having been capped off inside the enclosure of the wall connector.

Has TESLA already sent you your Home charging unit?

 

[salamagd]

I spent about a year getting approval to install a 32 Amp service to my apartment garage. In the end I had to put in a separate meter specifically for the garage. It was expensive, circa $3500, and it meant going through a full load analysis by the electrician.
Are you adding an additional power point to your existing service? I fail to see why they can't install a 15 Amp power point at least.

Thanks for the info! Yeah, I figured it was going to involve something like what you've described. Individual apartment meters ara currently on each floor, so short of running something back down from the meter down the riser to the garage, there probably isn't any getting around the additional meter. If I take something lower in current, like a 10A or 15A outlet, I might be able to get the management onside to have me just connecting to the common power and then making a contribution back to them to cover the power utilisation.

 

[Tasdevil]

la dedicated line to my garage at 32amps breaker (the maximum allowable on 6 SQMM wire).
in order to draw 32 amps, cable sizing would be 10mm sq. (next size up).

I don't mean to sound rude, but this simply isn't true.

It may be your situation requires a larger cable for voltage drop reason. (I'm guessing your garage is 50m+ away? And/or your house is internal and not on the street?

But for someone with short cable runs you can use smaller cable.

 

[TesAus]

I don't mean to sound rude, but this simply isn't true.

It may be your situation requires a larger cable for voltage drop reason. (I'm guessing your garage is 50m+ away? And/or your house is internal and not on the street?

But for someone with short cable runs you can use smaller cable.

I agree with Tasdevil based upon advice I have received and installation that has been completed yesterday.

My electrician determined that up to 40A could be run on 6mm sq cable for the run in our house (approx 35m from main switchboard to Tesla Connector unit) using a type C circuit breaker.

It obviously depends a lot on individual circumstances.

 

[Dborn]

My total cable run from meter box to wall unit is 27 m. And yes, a different sparky told me 40 amps. The breaker installed is 32 amps, so why they derated the wall box is a mystery. This sparky told me 32 amps max on 6 mm wire. So, ultimately who do you believe? Can someone point me to the official tables used to calculate these things?

- - - Updated - - -

Has TESLA already sent you your Home charging unit?

yes.

 

[GSP]

In North America, the breaker and circuits can only run 80% of rating for a continuous load (EVs are the mother of all continuous loads). So a 40 A breaker and wiring can charge at 32 A max. In Europe equipment is rated for continuous load, so a 16A circuit and breaker can charge at the full 16 A. I don't know about Australia, but maybe this background will help.

GSP

 

[Tasdevil]

Hey DBorn, official table is actually a book called AS3008. I have one, but I don't know if you could find one on the net, or find out how to use it. It's not quite as simple as Xmm = Xamps
Generally a 6mm cable can have a 40A breaker. Most common derating factors are; how it's installed (laying in roof insulation is worse than installed underground), the length of cable run, if the cable is run in a bunch with 4 or more cables, ambient temperature...
I can only assume that you must have just come under the 40amp current carrying capacity and that if the charger installation manual is the same as the USA charger? It says a 32amp cb needs the charger set at 20amp for their derating factors? (Sorry trying to write this off my memory)

 

[Johnwill]

My total cable run from meter box to wall unit is 27 m. And yes, a different sparky told me 40 amps. The breaker installed is 32 amps, so why they derated the wall box is a mystery. This sparky told me 32 amps max on 6 mm wire. So, ultimately who do you believe? Can someone point me to the official tables used to calculate these things?

There is a lot more to it than just choosing the cross-sectional area of the cable listed in a table. E.g. Length, volt drop, how the cable is enclosed, insulation material, type of breaker/fuse, possible fault current, etc.

That's why we train and sit exams to become qualified.

Seriously though, sometimes electricians get way too anal about loads.

It might have something to do with the loss of licence, fines or jail time that can be imposed. Not to mention the loss of property or life that can result if you burn someones home down.


For those attempting to guess their own Maximum Demand calculation. It's not a matter of what you think your load is. There is a set formula that must be adhered to regardless of what one might estimate each devices current draw to be. The formula calculates what your main is legally allowed to support under the regulations. You are not allowed to exceed your maximum load as per the proper calculation and doing so could risk prosecution.

I know I'm posting from NZ but AS/NZS 3000, known as the Australia/New Zealand Wiring Rules, is a joint standard. Home - Wiring Rules - Standards Australia Limited

Also local regulations and other standards have to be taken into consideration as well as the Wiring Rules.

 

[Dborn]

There is a lot more to it than just choosing the cross-sectional area of the cable listed in a table. E.g. Length, volt drop, how the cable is enclosed, insulation material, type of breaker/fuse, possible fault current, etc.

That's why we train and sit exams to become qualified.





It might have something to do with the loss of licence, fines or jail time that can be imposed. Not to mention the loss of property or life that can result if you burn someones home down.


For those attempting to guess their own Maximum Demand calculation. It's not a matter of what you think your load is. There is a set formula that must be adhered to regardless of what one might estimate each devices current draw to be. The formula calculates what your main is legally allowed to support under the regulations. You are not allowed to exceed your maximum load as per the proper calculation and doing so could risk prosecution.

I know I'm posting from NZ but AS/NZS 3000, known as the Australia/New Zealand Wiring Rules, is a joint standard. Home - Wiring Rules - Standards Australia Limited

Also local regulations and other standards have to be taken into consideration as well as the Wiring Rules.

happy to accept all that. However, I do have two sparkys who agree that a 32 amp breaker is correct for my situation. So, I have also been told that the wiring rules state that the breaker installed must be capable of the rated sustained load. So, why derate the charging capacity of the wall unit?