Published 2026-10-22 by 247 Rapid Electrician
Granny flats and backyard studios are common across the Shire, on the big blocks in Menai, Engadine, Kirrawee and Gymea in particular. The building side gets most of the attention, but the electrical side decides whether the flat works properly, whether the main house keeps tripping, and how much it costs to fix later. Here is what is involved.
Capacity first
A granny flat has its own kitchen, hot water and air conditioning, which is a big extra load. We check whether your main switchboard and supply can handle it. That means looking at the size of the incoming supply, the main switch, the space on the board and the loads you already have, such as a pool, ducted air conditioning or an EV charger.
If the existing board is old or full, it may need replacing before the flat can be connected. If the supply to the property itself needs upgrading, that involves the network and a Level 2 provider, which we would refer out. Finding this out early avoids delays at the end of the build.
Sub-board and submains
The flat usually gets its own sub-board, fed from the main board by a cable sized for the load and distance. The longer the run from the house, the larger the cable needs to be to avoid voltage drop. The sub-board has its own circuit breakers and safety switches, so a fault in the flat does not take out the main house.
The submain is often run underground in conduit, at the depth the wiring rules require. Run data cable at the same time while the trench is open. A spare conduit costs little now and saves digging up the yard later for internet, a camera or an outdoor light.
Planning the circuits
Think about how the flat will actually be used. A typical plan includes:
- Separate circuits for lights, power points, cooktop or oven, hot water and air conditioning
- Enough power points in the kitchen bench and living area
- Outdoor lighting for the path from the house
- A hard-wired exhaust fan in the bathroom
- Spare capacity on the sub-board for future additions
Hot water and cooking
Electric hot water and an electric cooktop are the two biggest loads in most granny flats. Instantaneous electric hot water needs a lot of current at once, so storage or heat-pump units are often a better fit for the supply. We can talk through the options with you and your builder.
Smoke alarms
The granny flat needs its own compliant smoke alarms. A new build has to meet the building code, which means hardwired alarms, interconnected where there is more than one. Your certifier will check this before the flat is signed off. If you rent it out, landlord smoke alarm obligations apply.
Separate metering
Some owners want a separate meter for the flat, for example to bill a tenant. This involves your electricity retailer, the network and an accredited Level 2 provider for the meter and supply work, so it needs planning early. We can explain the options, wire the flat to suit, and refer the meter work to an accredited provider.
Paperwork
When the electrical work is finished, you receive a Certificate of Compliance for Electrical Work. Your certifier may ask for it as part of the final sign-off, so keep a copy with your build documents.
Get the electrician in early
Talk to us before the builder locks in the layout. It's cheaper to plan circuits than to change them later. We can look at your plans, check your switchboard capacity, and give you and your builder a clear scope. Call 0421 772 661.