Why there isn't one number
The wiring rules for Australian homes, AS/NZS 3000, set a minimum cover for underground wiring. That is the distance from the top of the cable or conduit to the finished ground level. The figure is not the same for every job. You will find confident single numbers on a lot of websites. Treat them with care, because the right depth for your trench depends on the set-up in front of you.
What decides the depth
An electrician looks at four things.
- The type of wiring. Cable laid straight in the ground, cable in conduit and cable in heavier conduit are treated differently.
- Where it runs. A garden bed, a lawn, a path, a driveway and a road crossing all carry different risks. Anywhere a vehicle can drive needs more care than a flower bed.
- How it is protected. Conduit, a concrete cover or a slab can change what is allowed. Protection does not replace correct depth, and the way it is installed matters.
- What the circuit is. The circuit's purpose and how it is protected (safety switches, for example) are part of the picture.
There is also the electricity network. If the trench carries the cable from the meter or the street to your house, the network's own requirements apply on top of the wiring rules.
Why the depth matters
Shallow cable gets hit. Spades, fence posts, garden edging, landscaping work and vehicle weight all find cable that was buried too shallow. A cable that is damaged underground can be a shock or fire risk, and it is expensive to find and dig up again.
Who can do the work
Electrical work in Queensland must be done by a licensed electrician, and DIY electrical work is illegal. That includes the cable that goes in the trench. A licensed electrician decides the depth and protection for your job and carries the responsibility for it. Whoever digs the trench, ask the electrician how deep and how wide it has to be, and when they need to see it before it is filled.
Before you dig
Whoever you call, these details help:
- What the trench is for: a shed, a granny flat, a pool pump, garden lighting, an EV charger or a gate
- The route, and whether it crosses a driveway, a path or a garden bed
- How far it runs from the switchboard or meter
- A photo of the area and the switchboard
- Whether the soil is easy to dig, or whether you have hit rock or roots before
Call before you dig, not after. Cable is much cheaper to place correctly than to lift and relay.
Dial 1100 (Before You Dig Australia) before any digging near services, so you don't hit someone else's cable or pipe.
Getting it quoted
P4 quotes every job, so we don't publish prices. Send the details above through the quote form or call, and Jamie will tell you how he would approach it. For related work, see lighting and power upgrades and home maintenance and repairs.