Free Electrical Tool
Granny Flat Power Estimator
Building a granny flat? Estimate the extra electrical demand and find out whether your existing supply can carry it — or whether you'll need a consumer mains upgrade, new sub-mains and separate metering.
Powering a granny flat in Sydney: what's actually involved
Every granny flat needs three things electrically: enough spare capacity at the street supply, a properly sized sub-mains cable from the main switchboard, and a decision on metering — shared bill, private check-meter, or a fully separate smart meter. Get the demand numbers wrong and the flat browns out the house every time the oven and air con run together.
Long backyard runs are where budgets blow out: cable sized only for amps often fails the 5% voltage drop rule. Check yours with the voltage drop calculator, or work the full numbers in the maximum demand calculator.
Frequently asked questions
Do I need to upgrade my power for a granny flat?
Often, yes. A granny flat with electric cooking, air conditioning and hot water can add 30–50A of demand. Older Sydney homes on a 63A single-phase supply frequently need a consumer mains upgrade to 80A or 100A when a granny flat is added.
Can a granny flat have its own electricity meter?
Yes. A granny flat can be separately metered so the tenant pays their own bill — this needs a metering panel and, in some cases, a network application. Alternatively a private check-meter (sub-meter) can track usage without a separate account.
What size cable do I need to run power to a granny flat?
Sub-mains are sized for both current and voltage drop. Long runs — common for backyard granny flats — often need 10mm² or 16mm² copper even when demand alone suggests smaller cable. Our voltage drop calculator shows why.
Who does the electrical connection for a granny flat in NSW?
The sub-mains, sub-board and internal wiring is licensed electrician work; anything involving the consumer mains, service upgrade or new metering is Level 2 ASP work. Sydney Power Group is accredited for both across Ausgrid, Endeavour Energy and Essential Energy areas, so the whole connection can be handled end to end.