Single or three phase power for new build? Thinking of car chargers

For benefit of people who stumble across this this via searches:

My understanding is that the Auckland lines company vectors "standard" residential connections are:

60A single phase (Approx 14kW)
60A three phase (Approx 41kW)

I understand that the vector charge the same monthly connection fees for the above two connection's. This is not the case in all area, some lines companies charge substantially more monthly fees for a three phase connection, something to check out if you are deciding between the two.

I understand that other area regions / lines company areas other residential connections are sometimes offered, for example:

100A single phase (Approx 23kW)
60A two phase (Approx 28kW) - I have a family members semi rural house with this setup.

For OP, the key decision points are:

Do/might you need to run any "Three phase" equipment? If so get three phase.

In short, three phase induction motors are better than single phase ones, so most stationary industrial machines run three phase motors. Many welders use two of three phases to get the 400v phase to phase voltage. If you ever plan to have a workshop with stuff like bigger lathes, mills, compressor, welder etc, then three phase power would be super handy. Means you can pick up cheap ex-industrial / ex-commercial gear cheap too.

Some bigger (really big) heat pump's are three phase only (as an example Mitsubishi electrics 22.4kW and 25kW heating PEA series dusted heat pumps are three phase only). Same deal for bigger (25kW+) swimming pool heat pumps.

Some stuff is three phase, simply because of the amount of power it draws, and is a basic resistance load that could be run off single phase of one had enough capacity. Common examples would be Clay Kiln's, Sauna's etc.

Is 60A single phase (approx 14kW) going to be enough?

Comes down to how big / power hungry the house is. A big factor to this is if your house is going to be all electric, or use other fuels like gas. And generally how much power hungry stuff you have (spa pool, swimming pool, water pump)

Note that it is the pole fuse that will blow if this is exceeded (for many minutes if only just), which means no power for a couple of hours and paying for the lines company to come out and replace it. If you want you can have a main breaker installed in your property (instead of the typical main switch) which should protect the pole fuse, but with the advantage of being self re-settable. Electrician will need to do a calculation based on a bunch of stuff and may require you to go three phase, or have a main breaker added.

My house is a 60A single phase. As an example of load that would take to exceed that (all at the same time):

Hot water 16A
Oven 16A
Lounge heat pump flat out 8A
Tumble dryer 8A
Induction cooktop (32A @50%): 16A.

That's me past my 60A limit if I did all that stuff at once. Could also use:

8A of lighting
2x 8A fan heaters
8A of misc plug in load (TV's, computers, Electronic's, chargers, rice cooker etc.)
8A EV charger
8A hair dryer

I consider my setup (all electric fairly small 3 bedroom +study house) to be about on the limits of a 60A supply, but have never blown a pole fuse. But if OP is going to have stuff like dual ovens in their kitchen (A steam oven and a normal oven looks like a sweet setup), 90cm induction cooktop (43A feed needed), spa pool, swimming pool or similar, three phase would be a good call.

Other things to consider;

Solar (/battery): In short, with current tech, single phase solar solutions are a little cheaper than thee phase solutions. Three phase battery solutions are harder to come by.

One big issue with three phase solar setups is phase balance. As an example if one had a solar setup that with current lighting conditions was generating 3.6kW, and was set up with either a thee phase inverter (or matching numbers of micro inverters on each phase), it would be making 1.2kW on each phase. Lets say everything in the house was off, except for a 3.6kW hot water cylinder connected to a single phase. Phases will be as follow's:

1.2 solar - 3.6kW load = 2.4kW Import
1.2kW Export
1.2kW Export

The issue with the above, is that power companies pay around 6c/kWh for exports, but charge 18 - 30 c/kWh for imports, and it is calculated per phase. So the above situation would result in a charge from the power company. If it was a single phase setup, net demand is zero, no import or export, so no charge from the power company...

Next issue is that many current battery products (such as tesla power wall), are single phase only. No three phase option (other than having three of them, one on each phase, great but $$$). The two phase family members house I mentioned above recently had a solar + battery setup installed. Installers recommended that the phase loading be changed from a fairly even spread, to everything (solar, battery & all load) to being on one phase. Means they could use single phase solar gear (no such thing as two phase inverters, so would have needed two separate single phase ones), they don't waste any generation to exports, that could potentially self consume, and the Battery back's up everything (5kW max draw).

Possibly pushing it, having that house all on one 60A phase (drinking water pump, electric fence machine, pool with 2x pumps, 2x bigish heatpumps, 32A EV charger etc), but they have the hot water & pool on timers so they run in the middle of the day when there is solar output, they avoid charging the EV while cooking dinner, and they have the 5kW of output from the battery to chip in unless it has gone flat. No issues so far.

Hopefully in the next decade or so there will be a polyphase battery solution, that can produce unbalanced output to match phase loading, and can move power between phases to avoid the simultaneous export & import situation. That said, a lot of north america is single phase, and a lot Europe has "Net metering" so phase balance doesn't matter, so the market for the product may be kinda small.

EV's

First thing, is that people who don't have EV's often overestimate their need for charging speed at home. As long as an overnight charge adds enough range to cover the next day's needs, you are golden. And note it is very rare to start from zero %.

A 8h overnight charge from a wall outlet (at 8A) adds about 100km of range. A 8h overnight charge from a 32A wall-box ads about 350km range.

Also note that for very rare use case situation's can be covered by spending 30mins at a fast charger if you have one nearby.

Surprising numbers of EV owners make do with the the slow 8A cord as their main charging method.

Times it is nice to have fairly faster charging ability at home:

Ability to top off quickly during the day. - Say you do 80km commuting / running errands in the morning, come home to pack bags / have lunch for say 2.5 hours in the middle of the day before heading out of town. 7.4kW charging would have replaced that 80km in that time, but charging from a wall outlet would have only replaced about 20km.
If you have a longer commute, and faster charging is either needed to cover that, or for that to fit in your power companies off peak window.
You do back to back long trips, and want the ability to be fully charged when you wake up.
You have a EV with a massive battery pack, i.e. Rivian R1T with 180kWh pack. charging that at 7kW is going to take 25 hours, faster charging would be nice...

I would recommend that any EV owner with a 40kWh battery or bigger have a wall charger installed. Kinda nice to be able to fully recharge overnight and top off fairly quickly, and the $2k cost of the setup pales in comparison to the cost of the car.

Most better EV's at the moment support charging close to maxing out a 32A single phase connection (cira 7.4kW). A decent number also support 3x16A charging (11kW). Ability to charge at 22kW (3x32A) is rare - pritty much just the zoe at the moment.

In terms of wall boxes, 3 phase ones generally cost only slightly more, Generally they all support 32A, but have jumpers inside to slow them down if your wiring can't handle that.

For dwellings that are close to maxing out their capacity, EV wall-boxes are available that do the following:

Share a set amount of power (say 32A) around multiple EV's dynamically (say 50:50 at the start, then 100:0 once one finishes)
Measure your house's total (single phase) draw, and slow down the EV charging if required to avoid overload. For example:

https://oemaudio.co.nz/electric-vehicle-charging-products/eo-mini-pro-2-wall-charger-white-active-load-management-package

But to answer the headline question, if it is a bigger house, and charging two EV's at once, three phase would definitely be nice to have.

lyndondrake

Scott3