Running Power to a Shed, Workshop or Granny Flat: What's Actually Involved
Category: Power · By Alex, Ultralec
If you've got acreage in the Noosa Hinterland, sooner or later you build a shed. Then you want lights in it. Then a compressor, a fridge, maybe a welder, and eventually someone says "we could put a granny flat out there."
Getting power to an outbuilding is one of the most common jobs we do, and it's also one of the most commonly under-quoted, because the price has very little to do with the shed and a lot to do with the distance.
Step One: What's Going in the Shed?
Before anything else we need to know the load. A shed with a light and two power points is a small job. A shed with a 15-amp welder, a three-phase compressor and a split system is a different job with a different cable and possibly a different supply.
Be honest about the future, too. Running a bigger sub-main now costs a bit more in cable. Digging the trench up again in three years costs a lot more.
Step Two: The Run
This is where the money is. Power to a shed means a sub-main: a cable from your main switchboard to a new sub-board in the shed. The longer the run, the thicker the cable has to be, because voltage drops over distance and the standards set a limit on how much. A 30-metre run and a 120-metre run to the same shed are not the same price, and it's not because we're charging you for walking.
Underground is what we recommend for almost every hinterland property:
- Cable goes in conduit, in a trench, typically 500mm deep, with warning tape above it.
- No poles to maintain, nothing for a tree branch to bring down, nothing to hit with the tractor.
- You can dig the trench yourself if you want to save on the job. Plenty of people do. We'll mark out where it needs to go and how deep.
- Rock, tree roots and existing services (water, septic, Telstra) can all change the route. We look before we quote.
Overhead still makes sense in some cases: crossing a gully, a creek, or a driveway you don't want to cut. It needs poles or a span between buildings, and poles on private property are the owner's responsibility to maintain. More on the trenching side at Underground Power.
Step Three: The Sub-Board
The shed gets its own small switchboard with a main switch, safety switches (RCBOs) on every circuit, and its own earth stake. From there we run the lighting, power, and any dedicated circuits for the welder or the air con. Everything labelled, everything tested, Certificate of Compliance issued.
Do You Need Three Phase?
Most homes in the hinterland are single phase and most sheds are fine on it. You start needing three phase when:
- You've got proper machinery: a big compressor, a lathe, a three-phase welder.
- You're running a large ducted air con or a commercial cool room.
- The total load is more than a single-phase supply can sensibly carry.
If your house is single phase and you need three at the shed, that's an Energex application and an upgrade to your mains, and it's a bigger conversation. We'll tell you straight whether you actually need it. Most people don't.
Granny Flats and Secondary Dwellings
A granny flat is a shed with a kitchen and a bathroom, electrically speaking, which means:
- Interconnected photoelectric smoke alarms are mandatory in a new dwelling.
- Cooktop, oven, hot water and air con all need their own circuits.
- The sub-main has to be sized for a household, not a workshop.
- Depending on how it's being approved with council, there can be metering questions. We'll advise at the quote.
What Drives the Price
In rough order of impact:
- Distance from the main board to the shed.
- Ground conditions and who's digging.
- Load: the size of the sub-main and sub-board.
- Single or three phase.
- The condition of your main switchboard: if it's full or old, it may need work before we can add a sub-main.
- Fit-out inside the shed: lights, power points, dedicated circuits.
Every shed run gets a written fixed-price quote after we've walked the route. No guessing from the road.
Get It Looked At Before You Build
The cheapest time to run power to a shed is while the slab's being poured and the ground's already open. If you're planning a shed, ring us before the concrete truck's booked. We cover Pomona, Cooroy, Cooran, Kin Kin, Federal, Ridgewood, Traveston and out to Gympie and Imbil. See Acreage & Rural Electrical.
Frequently Asked Questions
Can I run an extension lead to the shed instead?
For a light and a drill on the odd weekend, sure. As a permanent supply, no. It's not compliant, it's a trip and fire risk, and it'll never run a compressor properly.
Can I dig the trench myself?
Yes. We'll mark the route and depth, you dig, we lay the conduit and cable. It's a common way to bring the price down on a long run.
How deep does the cable need to be?
Typically 500mm in conduit with marker tape, per AS/NZS 3000. Under a driveway it may need to be deeper or in heavier conduit.
Does the shed need its own switchboard?
Yes. A sub-board with a main switch and safety switches is required so the shed can be isolated on its own and every circuit is protected.
Do you handle the Energex side if we need three phase?
Yes. We prepare and lodge the connection application and coordinate the mains upgrade.