Power to sheds, studios and outbuildings
The job where cheap quotes are cheap because the cable is too small. Here's how to tell before you pay.
Voltage drop: the worked examples
Every quote you get for running power to a shed is, underneath, a cable-sizing decision. Here is the maths that decision is based on, so you can ask the right question.
The limit is 5% voltage drop from the point of supply to the furthest point of use — about 11.5V on a 230V single phase supply. For a 20 amp submain:
- 40 metres — 6mm² is comfortable. This is a garage at the end of a suburban driveway.
- 80 metres — 6mm² no longer complies. You're into 10mm², often 16mm² if you want headroom for a future load.
- 150 metres — 16mm² is marginal and 25mm² is the honest answer. This is an ordinary house-to-back-shed distance on five acres.
The cost difference between 6mm² and 25mm² over 150 metres is thousands of dollars in copper alone. That is the entire reason quotes for this job vary so wildly, and it is why the cheapest one is so often the one that gives you a shed where the welder won't run.
The question to ask every quote: what cable size have you allowed, and what voltage drop did you calculate at full load? Anyone who has done the work answers instantly.
Sub-board or single circuit?
A single circuit to an outbuilding is cheaper and occasionally the right answer — a garden shed with a light and a couple of outlets, close to the house.
For anything you'll actually use, a sub-board at the far end is better and usually not much more, because the submain cable dominates the cost either way. A sub-board gives you:
- Local isolation — you can kill power at the shed without walking back to the house
- Separate circuits for lights, general power and machinery, so a tripped welder doesn't kill the lights while you're under something
- RCD protection at the point of use
- Room to add circuits later without another trench
If there's any chance of a workshop, a studio, a pool, or a second dwelling out there in future, the sub-board is the decision you won't regret.
What outbuilding power costs
Sydney and Hills acreage, 2026. Cable and trenching dominate — the distance is the price.
| The job | Price |
|---|---|
| Single circuit to a nearby garage or shedShort run, existing board has a spare way | $600 – $1,400 |
| Submain and sub-board, up to 40mCorrectly sized cable, sub-board with RCD protection | $1,800 – $3,500 |
| Submain and sub-board, 40–100mCable up-sized for voltage drop | $3,000 – $6,500 |
| Submain and sub-board, 100m+Acreage distances. Cable size drives this more than anything else | $5,000 – $12,000+ |
| Trenching and conduitPer metre. Rock, tree roots and existing services all push it up | $40 – $90 / metre |
| Overhead catenary run instead of trenchingSometimes far cheaper where the span allows it | ask |
| Granny flat or secondary dwelling supplyUsually needs its own metering arrangement, not just a submain | quote required |
These are indicative market ranges for Sydney in 2026, not a quote. What you pay depends on your switchboard, access and what we find. We confirm a fixed price before starting, and it doesn't move.
Signs your existing shed supply is undersized
Lights dim noticeably when a machine starts
Textbook voltage drop. The supply can't hold voltage under load, which means the cable is too small for the distance.
Call 0422 253 379Motors run hot or have short lives
An induction motor fed low voltage draws more current to make the same power. It runs hotter and it dies earlier. Expensive, and easy to misdiagnose as bad luck with equipment.
Call 0422 253 379A welder or compressor trips protection every time
Starting current on top of an already marginal supply. Fitting a bigger breaker is the wrong fix and a dangerous one — the cable is the limit, not the breaker.
Call 0422 253 379The cable enters the shed with no isolation or protection
Common on owner-built or older installations. There should be a means of isolation and RCD protection at the outbuilding. Not having it is both a compliance and a safety problem.
Call 0422 253 379Buried cable with no conduit or marking tape
Direct-buried unprotected cable is a hazard for whoever next digs — often you. Worth knowing about before it becomes a discovery.
Turn it off at the board and call 0422 253 379Shed and outbuilding power questions
How much does it cost to run power to a shed?
$600–$1,400 for a single circuit to a nearby garage. A proper submain and sub-board runs $1,800–$3,500 up to 40 metres, $3,000–$6,500 out to 100 metres, and $5,000–$12,000 or more at acreage distances. Trenching adds $40–$90 per metre.
Why is my quote so much more than my neighbour's?
Almost always distance and cable size. Voltage drop means a 120 metre run needs dramatically more copper than a 40 metre one for the same load. Ask both quotes what cable size they've allowed — that's usually the whole difference.
Can I dig the trench myself to save money?
Often yes, and it's a genuine saving. It has to be the right depth with the correct conduit and marking tape, and we'll tell you the spec. Get it wrong and it has to be redone, which costs more than not helping.
Do I need a sub-board or just a circuit?
A circuit is fine for a garden shed with a light and two outlets. For anything you'll work in, a sub-board is worth it — local isolation, separate circuits, RCD protection at the point of use, and room to expand without another trench.
Can I run power to a granny flat the same way?
No — a secondary dwelling is a different thing. It generally needs its own metering arrangement and has requirements a shed submain doesn't. We'll tell you which category yours falls into before quoting.
Can I run it overhead instead of underground?
Sometimes, and where the span allows it a catenary run can be much cheaper than trenching. It needs adequate clearance and proper support. On a long open paddock run it's often the sensible answer.
What if I want to add a workshop later?
Say so now. Sizing the submain for the load you'll eventually have costs a little more today and saves the whole job being redone later. Cable is the expensive part and you only want to buy it once.
What customers say
Jason solved a really complex problem for our house with excellent professionalism and workmanship. Highly recommend, would def work with him again. On time delivery and within budget.
Jason onsite quickly and completed the work on the spot, giving us a good price and was very polite. Would highly recommend.
Excellent value and service, including follow-up.
These are Google reviews for our team at Cync Electrical & Automation — the licensed contractor behind Hills Electrician. 5.0 from 20 reviews. — see the profile
Getting power out to a shed?
Tell us the distance and what's going in it. That's enough to size it properly. Call 0422 253 379.
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