One of the most common mistakes when setting up a workshop shed is underestimating electrical requirements. You install a few power points, maybe upgrade to a 20-amp circuit, and assume that’s sufficient. Then you discover your table saw trips the breaker when the dust collector is running, or you can’t use multiple tools simultaneously without overloading the circuit.

Planning electrical properly starts with listing what you’ll actually run in the shed. Not just “power tools”—specific tools with their actual power consumption. A corded drill might draw 600 watts. A table saw could be 1500-2000 watts. A large dust collector might be 1000-1500 watts. Air compressor adds another 1500+ watts. The numbers add up quickly.

The critical question is what runs simultaneously. Most tools you use one at a time, but dust collection typically runs continuously while you’re working. Lighting is always on. Maybe a radio or heater. Those are your base load. Add your highest-draw tool on top of that, and you have your peak demand.

For example: 200 watts lighting + 1200 watts dust collector + 1800 watts table saw = 3200 watts peak draw. That’s roughly 13-14 amps at 240V. A standard 15-amp circuit is barely adequate with no headroom. A 20-amp circuit gives you breathing room. Two separate 15-amp circuits would also work, distributing load across circuits.

Many sheds get a single 15-amp circuit run from the house and call it done. That works fine for light usage—some hand tools, a few power points for charging batteries, general storage with lighting. It doesn’t work when you start running multiple high-draw tools or equipment.

Upgrading to 20-amp or adding a second circuit isn’t hugely expensive during initial shed setup—running an additional cable while trenching is happening costs relatively little. Retrofitting after the shed is built and trenches are filled is much more expensive. Plan ahead based on realistic usage rather than assuming you can upgrade later if needed.

For serious workshop use, a sub-panel in the shed makes sense. This gives you multiple circuits—maybe 3-4 individual 15 or 20-amp circuits—distributed to different areas. Bench tools on one circuit, dust collection on another, lighting and general outlets on a third. This prevents any single tool from overloading the entire shed’s power.

The cable run from house to shed also matters. Voltage drop increases with distance and decreases with wire gauge. A long run with undersized cable means tools at the shed receive lower voltage than they should, reducing performance and potentially damaging motors. For runs over 20-30 meters, you need heavier gauge cable than code minimum.

An electrician should calculate this properly, but as a rough guide: 20-amp circuit over 30 meters might need 6mm² cable instead of the 2.5mm² that’s adequate for shorter runs. The larger cable costs more and is harder to install, but it’s essential for maintaining proper voltage at the shed.

Three-phase power is the professional workshop option but overkill for most hobbyists. It provides more capacity and runs large motors more efficiently, but requires three-phase supply to the property (most residential properties have single-phase only) and costs significantly more to install. Unless you’re running industrial equipment, single-phase with adequate circuits is sufficient.

Circuit breaker sizing matters too. The breaker should match the circuit wiring—15-amp breaker for 2.5mm² cable, 20-amp breaker for heavier cable. Oversizing the breaker relative to the cable creates fire risk because the cable can overheat before the breaker trips. Undersizing means nuisance tripping.

RCD (residual current device) protection is required for most shed circuits—it detects current leakage and trips the circuit before electrocution occurs. This is essential for outdoor buildings where moisture and ground contact increase shock risk. Some tools, particularly older ones or those with motors, can cause nuisance RCD tripping. Using an RCD with slightly higher trip threshold (30mA instead of 10mA) reduces false trips while maintaining safety.

Lighting circuits separate from power circuits is good practice. When you trip a breaker running a tool, you don’t want to lose lighting too. A dedicated lighting circuit, maybe 10 amps, ensures you can always see what you’re doing even if something trips the power circuits.

The physical layout of outlets also requires thought. Power points low on the walls work fine for stationary tools or charging stations. For bench-mounted tools or workbench areas, outlets at bench height (maybe 1-1.2 meters) are far more convenient. Overhead power drops for tools mounted in the center of the space avoid trailing cables across the floor.

I’ve seen sheds with adequate electrical capacity but poorly placed outlets, resulting in extension cords running everywhere. That’s not just inconvenient—it’s a trip hazard and fire risk. Plan outlet locations based on actual tool placement and workflow, not just spacing them evenly around the walls.

For anyone planning a workshop shed, I’d strongly recommend getting an electrician involved early. Describe how you’ll actually use the space, what tools you’ll run, whether you might expand usage later. One firm we talked to mentioned they’re developing load forecasting tools for workshop power planning—probably more relevant for larger operations but the same principles apply. A good electrician can design a system that meets those needs without over-engineering unnecessarily.

The cost difference between adequate electrical and inadequate is usually modest when done during construction—maybe a few hundred dollars for extra circuits or heavier cable. The cost to retrofit later is significantly higher, and living with inadequate power is frustrating. It’s one of those things worth getting right the first time.

• Dave