The shed electrical question is one I get asked about constantly. Owner-builders thinking about workshop conversions, hobbyists planning workspace upgrades, people converting half a shed into a home office or studio. The mistakes I see most often are made at the rough-in stage and produce expensive retrofits two or three years later.

Worth being clear: shed electrical work in Australia is licensed work. The rough-in planning is something you can think about and specify, but the actual cabling and connection work needs to be done by a licensed electrician with the relevant qualifications for any 240V work. The information here is about what to plan for, not about doing the work yourself.

What gets undersized

The single most common mistake is undersizing the supply. Sheds are commonly run from a domestic supply via a 20A or 25A circuit, which sounds adequate until you actually use the workshop properly. A welder, a dust extractor, a compressor, and the workshop lighting all running together can routinely exceed 20A. The result is nuisance tripping, the inability to run multiple tools simultaneously, and a workspace that’s frustrating to use.

The realistic shed supply for a workshop with multiple power tools is a dedicated subboard fed from the main distribution board with 32A or larger feed. The cost increase at construction time is moderate. The cost of upgrading later, after the slab is poured and the cable is buried, is substantial.

The same logic applies to circuit count. Plan for more circuits than you think you need. A workshop that’s been thought through properly typically has separate circuits for: general power on each wall, dedicated tool circuits for major equipment, lighting, any HVAC, and any specialist requirements (welding outlets, three-phase if you’re going there). Six to ten circuits in a serious workshop subboard isn’t unusual.

The cabling capacity in the conduits running to the shed needs to support the future circuit count, not just the day-one circuit count. Pulling additional circuits through the same conduits is straightforward if the conduits have spare capacity. Adding new conduits later means trenching, which means breaking up the slab or route, which is expensive.

Outlet placement that actually works

The standard Australian shed has wall outlets at random positions that nobody planned. The good shed has outlets where the work actually happens.

The principle for outlet placement: think about where the workbench will go, where the major tools will live, where the storage will be. Put outlets at workbench height (around 1.2m above the floor) directly above the work surface. Put outlets at floor level only where you specifically need floor-level outlets (compressor, vacuum). Put outlets in the ceiling for any tool that’s mounted overhead — drop-down extension reels, fluorescent lighting, ceiling-mounted air filters.

The outlet count per wall should be generous. The four-outlet wall section that seems excessive at planning time fills up faster than you think once the workshop is in use. Specify more outlets than you think you need; under-counted outlets produce extension cord chaos that defeats the purpose of having dedicated power circuits.

Group outlets by circuit deliberately. Don’t put all the outlets on one wall on one circuit; spread them across circuits so a single tripped breaker doesn’t kill the whole work area. The outlet labeling or colour coding matters in serious workshops where troubleshooting power issues is a real concern.

Lighting that doesn’t disappoint

Workshop lighting is consistently undersized in residential shed installations. The lighting that’s adequate for a storage shed is dramatically inadequate for detailed work.

The current LED panel options produce excellent results. T8 or T5 LED tubes in batten fixtures, mounted in regular spacing across the workshop ceiling, produce even illumination at moderate cost. The lumen output to specify is usually higher than retail recommendations suggest — aim for 500 to 750 lux at workbench level for serious work, which usually means more fixtures than the showroom specifications would indicate.

Task lighting at the workbench, separate from the general overhead lighting, makes a substantial difference for detailed work. Adjustable LED task lights or mounted strip lighting under shelves above the bench produce shadow-free working light that overhead lighting alone can’t achieve.

Outdoor lighting around shed entries gets forgotten and shouldn’t be. Approach lighting, motion-sensor security lighting, and useful lighting at the door for after-dark loading and unloading should all be in the rough-in spec. Adding them later means surface-mounted conduit and cable that looks rough and is more expensive than build-time integration.

Three-phase considerations

Three-phase power in a residential shed is an option that many owner-builders dismiss without thinking through whether it actually applies. For most home workshops, single-phase is genuinely adequate and the additional cost of three-phase isn’t justified.

The cases where three-phase makes sense are specific. Large stationary tools (table saws above 3HP, lathes, mills) often have three-phase motors that run more efficiently. Welders above 200A typically need three-phase supply. Dust extractor systems sized for serious workshop use sometimes do.

If you’re seriously considering tools that require three-phase, plan for it during the supply install. Retrofitting three-phase to a shed that was wired for single-phase is expensive enough that you’d usually replace tooling instead.

Subpanels and protection

The subboard in the shed should have enough breaker spaces for the planned circuits with room for expansion. The minimum sensible size for a workshop subboard is 12 breaker positions; 18 or 24 is better.

RCD protection is required by current Australian wiring regulations on most circuits, but the implementation matters. RCDs that trip on tool inrush currents or compressor starts are a constant frustration. Specifying high-quality RCDs designed for workshop loads, or zone-based RCD protection that doesn’t kill the whole workshop on a single trip, makes the difference between a workshop that works and a workshop that’s constantly being reset.

Surge protection at the subboard level is worth the cost. The big tools represent real investment, and a single power surge can damage motor electronics and tool control boards. SPD (surge protection device) at the subboard provides cheap insurance.

Communications and data

Plan for data infrastructure during rough-in. The shed that becomes a part-time office in three years’ time is much easier to convert if there’s already cat6 cable run from the house. The same applies to TV antenna or coax if relevant, security camera cabling, and any audio infrastructure.

The cost of pulling additional cables during the initial rough-in is small. The cost of adding them later is substantial. Specify more than you think you need.

What I’d tell someone building right now

Three things.

Plan for the shed you’ll have in five years, not the shed you’re building today. Workshop usage tends to expand. The capacity you build in at rough-in is the capacity you’ll be glad of later.

Get a proper electrician involved at planning stage, not just at install stage. The conversation about what you want to do with the shed and how the electrical should support it is worth having with someone who can specify the work properly.

Don’t compromise on the supply size to save money at build time. The supply is the bottleneck for everything that happens later. A 32A or 40A supply that’s overkill on day one is essential by year three. A 20A supply that seemed adequate on day one is the constraint that limits what the workshop can do, every day, for as long as you own the shed.

The shed electrical work is unglamorous and largely invisible once it’s done. It’s also the difference between a workspace that works and a workspace that frustrates. Spend the time and money on it at the right stage.