A granny flat or dependent persons unit (DPU) is a separate dwelling for electrical purposes — and the Wiring Rules treat it that way. Sub-main from the main house or fresh distributor connection? Shared metering or separate? Dedicated switchboard sized for which loads? Each of these decisions is reversible only at retrofit cost, so getting them right at the planning stage saves both money and rebuilds. Millar Electrics scopes granny-flat electrical end-to-end across Melbourne's eastern suburbs — load assessment, sub-main routing or distributor coordination, the new switchboard, and the COES on completion.
Sub-main vs separate metering
The first decision. A sub-main from the main switchboard is cheaper and quicker — the granny flat becomes a sub-board of the main building, sharing supply and metering. It works well for family-occupied DPUs where electricity costs aren't being separately accounted. The cost is in the main-house switchboard and consumer mains, which now have to carry both buildings' load — sometimes that triggers an upgrade. Separate metering is more expensive upfront (a distributor application, a fresh service drop or pillar connection, a new meter installed by the network operator) but cleaner long-term, particularly for rental occupancy where the tenant is paying their own bill.
Sizing the new switchboard
The granny flat gets its own switchboard sized for its actual loads — typically a small kitchen, laundry, bathroom, lighting, GPOs, possibly an instantaneous hot water unit, possibly an EV charger. RCBO protection on every final sub-circuit per current Wiring Rules. Spare ways for future loads. Hardwired interconnected smoke alarms within the dwelling per AS 3786 + AS/NZS 3000 §7.8. The main switch sized so a future EV charger doesn't overload the board.
Coordination at build time
We come in twice if it's a new build — rough-in before plaster and fit-off after — same as a new house. For an existing-shed conversion or pre-plumbed structure we work from the existing rough-in or run new cables in surface conduit. Distributor coordination (where separate metering is the path) happens on our side: we lodge the application, manage the meter installation booking, and energise once the network has connected. The COES gets lodged with Energy Safe Victoria the day the dwelling energises.