Backyard cabin: dig electrical trench before or after?

After 17 years of working from home, I have decided to escape the noise of young kids and move into an office. In the backyard. It will need power of course and I believe that the trench from the main property to the cabin needs to be 600mm deep. There is no way I'll do this myself so I need to hire someone. I don't know if I should get the trench dug before or after the cabin is erected.

If the trench is dug before the cabin is built, there is a danger that it will be right in the spot where the cabin posts will go.

The cabin needs to be positioned 900mm from the boundary. If the trench is dug afterwards, is this a large enough gap for the trench person to do their work?

Any idea where to look for such a person in Sydney and what it might cost? Depending on the direction of the trench, it will be 9 to 12 meters long.

If you dig the trench before, how long will it sit open for? Will an open trench be a safety hazard for those building the cabin? Any reason the trench can't be hand dug its only 9-12 metres?

Nearly forgot...comms cabling for phone and data-will it be needed? Also alarm cabling. Whilst you have the trench open may as well throw the conduit in for these services if you think you may need them. When I wired my shed up I run 6mm2 power cable in 32mm conduit, three CAT5E data cables and two 3 pair security cables in 25mm conduit and another 25mm conduit with two RG6 coaxes and one 0.75mm2 two core cable for 12 volts which switches the security lighting.

It will sit open for a while, which is more likely to be a hazard for the kids rather then the builders. I had assumed it would be dug by hand, but there's no way I have the time or energy to do this. What's the alternative? A bobcat? I wondered about that, but figured it would be overkill, messy and access could be a challenge.

I will throw in data and an antenna cable. I hadn't thought about security, but if I need something later, I'm vaguely hoping that it will be possible to pull-through stuff later. Not sure how realistic that is considering there will probably be a couple of bends.

So do I just find someone with a trenching spade and lots of energy?

Hi clever d!ck
for your trench, find someone that operates a dingo or hire one yourself. It's much smaller than a bobcat but for your purpose should be more than enough.

When laying other services in your trench, to be compliant with eg. comms regs there's minimum separation from the power cables. I'm not exactly sure what this distance is off the top of my head but maybe someone who works with comms can chime in about that.

If laying conduit with the intent of pulling through cables at a later date, try to use sweeping bends instead of elbow joints and pull through a decent draw wire which isn't going to break halfway.

hth