How a sub-board connects
A breaker on the main switchboard, sometimes with a safety switch, feeds a heavier cable called a sub-main. The sub-main runs to the sub-board, which usually has its own main switch, circuit breakers and safety switches for the circuits in that building or area. It saves running every circuit back to the main board and gives the outbuilding its own point to switch everything off.
Where to find one
Look in the garage, the shed or workshop, a laundry or hallway in an extension, or near the entry of a granny flat. Pool and spa equipment sometimes has a small board of its own. Units and townhouses often have the meters grouped together, with a board inside each home fed from the main switchboard.
Why both boards need checking after a trip
A fault on a circuit in the sub-board can trip its own safety switch or breaker, the protection for the sub-main back on the main board, or both, depending on how the two were set up. So if an outbuilding loses power, check both boards before deciding nothing has tripped. Reset one device at a time, once, and if anything trips again, leave it off. Energy Safe Victoria's advice is to call a licensed electrician if a safety switch won't reset.
Sub-boards matter when you plan work too. A new main switchboard, an extension or a big new appliance in the outbuilding can mean the sub-main, the sub-board's protection or both need upgrading, so include every board when you send photos with an enquiry.
What you can safely do now
- Check the main switchboard and any sub-board for tripped devices, without removing covers.
- Unplug what was running in the area that lost power, then reset one device at a time, once.
- If a device trips again or won't reset, leave it off.
- Once you know which breaker on the main board feeds the sub-board, note it on the board's label chart.
Services that can help
Read more in our guides
Related questions
- Is my meter box the same as my switchboard?Not quite, though they are often in the same place.
- Why is there no power to my shed or garage?Start at the switchboards.
- How do I tell which switch has tripped on my switchboard?Open the switchboard door and look along the rows of switches.
- Do I need to be home for a switchboard upgrade?Someone should be there at the start and at the end, and the electrician needs access to the switchboard and to the rooms inside for testing.
Sources for this answer
1 source, with the date each was checked
- 1.Energy Safe Victoria: Locate your electricity box outside your home and check whether the safety switch has tripped. If it has tripped, reset the switch. If the switch won’t reset, call a licensed electrician. Accessed 30 September 2026.
General information for homes in Victoria. Every installation is different, so treat this as a starting point. Where this answer refers to Victorian safety or rental rules, the sources above have the current requirements.