How many phases is your incoming mains supply?
What are electricity phases? Why does it matter?
In simple terms, it comes down to how many live wires you have coming into the property and the voltages between them.
Generally, urban dwellings in New Zealand have a single phase supply. The incoming cable from the street has a Live, Neutral and maybe an Earth wire. The voltage between Live and Neutral is nominally about 230 Volts AC, with a frequency of 50 Hz. All the power outlets in the house are connected together.
On the other hand, rural and industrial buildings tend to have a 3-phase supply. The power line in the street will have three high-voltage conductors (one for each phase) and small groups of dwellings may share a power pole with a transformer on top which steps down the voltage to 230V, but it remains 3-phase. The cable from the street to each property will probably have 4 wires (3 phase conductors, plus neutral). Your main fuse board will usually have one main power switch (which if you look closely is three switches bridged together) and three large RCDs – one for each phase.
If you are still unable to tell what your supply is, then take a look at your power bill and/or ask your supplier.
Why does it matter?
Mainly because it affects your choice of generator and/or Transfer Switch. You probably need to replicate your existing mains supply. If you have a single-phase supply you definitely only need a single-phase generator. If you have a 3-phase main supply … you have some choices to make. Single phase generators tend to be smaller capacity and only go up to about 15 kVA (12.5kW). 3-phase generators can have much larger outputs. Part of the reason for that, is the diameter of the cable to carry the current. With single phase it all has to go down one large wire – which needs to be fat, heavy, expensive and inflexible. With 3-phase the power is split 3-ways so each wire can be smaller for a similar total load.
Despite having a 3-phase supply, many NZ rural properties simply wire different sets of outlets, lights etc, to each of the phases. So you dont have to buy special 3-phase TVs or 3-phase fridges. You just use regular single-phase equipment. But for larger industrial-type electrical equipment (pumps, motors) you might require all 3-phases to be supplied to that device.
So … if your property has at least one actual 3-phase motor which you need to use with your generator, then you need a 3-phase generator. If you have no devices that actually consume all 3-phases, then you might be able to get away with a single-phase generator.
Transfer switches can generally be wired by your electrician to temporarily connect all three phases together while you are on the generator, and then separate them again when you go back on mains supply.
Smaller capacity generators, up to about 8 kVA, are almost always single phase. Generators larger than that, tend to be 3-phase. Connecting a large single-phase generator to a dwelling on a temporary basis becomes somewhat infeasible because of the size of the cables required. There is an online calculator here that permits you to experiment with various values.
