Planning power for a shed, garage or workshop

Most shed jobs are planned from one piece of paper: a list of what you'll plug in. Write down every tool and appliance, then find the rating on its nameplate or in the manual. It's usually given in amps or watts. Photos of the plates are just as good.

Then mark which ones run at the same time. A drop saw and a shop vac often run together. A compressor cycles on by itself while you're using an air tool. A heater or a split system runs underneath everything else in winter. It's the overlap, not the total, that sets the size of the supply to the shed.

Think a few years ahead as well. If you might add a welder, a second fridge, a kiln or an EV charger in the garage, put it on the list now. Spare capacity in the cable to the shed is easy to allow for at the start and hard to add once the trench is filled.

Motors draw a burst of current as they start, well above their running figure. A compressor kicking in while a saw is running on the same circuit is the classic cause of a breaker tripping mid-cut. Larger compressors and dust extractors are often happier on a circuit of their own.

Welders vary more than most tools. Smaller inverter welders may plug into an ordinary outlet, while bigger machines come with a higher-rated plug that needs a matching outlet and circuit. Never swap the plug to suit the wall. Bring the model number and we'll work out the outlet, circuit and protection it actually needs.

Heating and cooling in a workshop usually gets its own circuit too. A metal shed is hard to work in on a hot northerly afternoon or a cold July morning, and a split system is a common addition once the power is there. Energy Safe Victoria guidance says that where an air conditioner manufacturer specifies a dedicated circuit or a safety switch, that must be followed.

A garden shed with a light, a power point for the mower charger and maybe a radio usually runs on one circuit from the house switchboard. It's the smaller job, and the circuit is protected by a safety switch at the house board.

Once the shed has tools, heating or more than a couple of outlets, a sub-board makes more sense. A submain cable runs from the house to a small board in the shed, and each shed circuit gets its own breaker and safety switch there. A tripped circuit can be reset without walking back to the house, and adding a circuit later doesn't mean another trench.

Energy Safe Victoria guidance says the Wiring Rules require safety switch protection on every final sub-circuit in a home, and additional protection when an existing installation is altered. In a shed, with concrete floors, metal tools and leads that get run over, that protection earns its keep.

Distance is the part people underestimate. Voltage drops along a cable, and the further the shed sits from the switchboard, the heavier the cable has to be for motors to start cleanly and lights to stay steady. A shed at the back of a long block can need a noticeably bigger submain than one beside the house.

Underground cable runs in conduit at the depth and with the protection the Wiring Rules set for that cable, so the route needs planning around garden beds, paths, pipes and anywhere you might dig later. Where a fence line, carport or roof gives a protected path, that can be the better route, particularly where side passages are narrow.

Timing matters. If concrete, paving or synthetic turf is going down, lay the conduit first, even if the cable comes later. Take photos with a tape measure in shot and keep a sketch of the route.

A single batten in the middle of the ceiling lights the floor and leaves the bench in your own shadow. Put lights over the bench, slightly in front of where you stand, and light the car or machine area separately. LED battens give even light with little heat, which helps in an uninsulated shed under a metal roof.

Switch the lights in groups, with a switch at the door so you're not crossing a dark shed to find it. A sensor light outside the door helps when you're carrying things in after dark, and an outdoor power point beside the shed is handy for the pressure washer or hedge trimmer.

Put double power points along the back of the bench at working height, spaced so a lead never has to stretch across the cutting area. A point at each end of a long bench and one near the door covers most layouts.

Power boards and long extension leads aren't a fix for too few outlets. They load up a single outlet and get damaged on a shed floor. If you're reaching for them every Saturday, the shed needs more points or another circuit.

Three-phase makes sense when you run machines built for it, such as some larger compressors, lathes or dust extraction, or when the shed's loads are too large to share one phase comfortably with the house. If the house already has a three-phase supply, a three-phase submain can run to a sub-board in the shed.

If the house is single-phase, the upgrade involves your distributor, new consumer mains and a new main switchboard. That is prescribed work, inspected by a Licensed Electrical Inspector before it can be switched on. Weigh it against the alternatives: plenty of hobby and trade tools run on single-phase, and a heavier single-phase supply or a different machine can be the simpler answer.

A quick sketch of the block with the house, switchboard and shed marked, and the rough distance between them, saves a lot of back and forth. Add the tool list, the nameplate photos and a photo of the switchboard.

A licensed electrician must provide a Certificate of Electrical Safety for electrical installation work, and that covers circuits, power points and lights in a shed or garage. Keep it with your route photos. Together they're the record of what was done if you sell or add to the shed later.