Power and lighting in a container on an upper-Clarence block

First decide what the power is for

There is a large difference between a light so you can find a spanner at six in the morning, and a workshop running a compressor and a welder. The question usually arrives as "power to the container", and the honest answer depends entirely on the load.

Three rough tiers, and it is worth deciding which one you are in before you ring anybody:

Light and a couple of outlets. A batten light, a double GPO for a charger and a fan. Small enough that a modest solar and battery setup handles it, and small enough that trenching a submain a couple of hundred metres from the house is usually the expensive way to do it.

Workshop. Bench tools, a compressor, a decent light level, maybe a small welder. This is a real load with real starting current, and it generally wants a proper submain off the house switchboard rather than a battery bank sized on optimism.

Pump, cool room or anything that runs continuously. Now you are in territory where the container is incidental and the electrical design is the job. Get the sparky involved before you decide where the box goes, because the cable run may decide the site.

The part that is not negotiable

In New South Wales electrical work has to be done by a licensed electrician. That is not a preference we are expressing, it is the law, and inside a shipping container it matters more than usual rather than less. The whole structure is conductive. Everything you fix a cable to, lean against or stand on is bonded steel, and a fault that would give you a fright in a timber shed is a different event in here.

What a licensed electrician will do that a weekend cannot: bond the container itself to earth, protect the circuits properly, size the cable for the run rather than for the price, and leave you with a certificate. On a rural block a long submain has voltage drop to consider as well, which is arithmetic, not opinion.

If somebody offers to "run a lead in and put a board on the wall" for cash, that is the same instinct that gets people into trouble buying containers sight unseen.

Getting the cable in without ruining the container

This is where an otherwise good job goes wrong, and it is worth understanding before anyone arrives with a hole saw.

A container's weather sealing is a shell. Every hole cut through it is a hole through the seal, and a penetration made badly is a rust start and a leak in the same stroke. Two rules cover most of it. Put the penetration high, in the end wall or up near the top rail, never low where water runs and sits. And gland it properly, with a sealed gland and the cut edge primed, not a bare hole with a bit of silicone smeared around the cable.

What not to cut: the corner posts, the top and bottom rails, and the door aperture frame. Those are the structure. A container carries its load through the corners, and cutting into them is how a box goes out of square and stops closing.

The grade you bought matters here too. Cargo-worthy units leave the yard checked wind and watertight, and a clean glanded penetration keeps that intact. As-is units are not sold watertight in the first place, so if the plan is to fit out and wire a container, buy a grade that is sealed before you start rather than after.

Off-grid, which out here is often the sensible answer

On a block where the nearest switchboard is four hundred metres away through a gully, a small standalone system frequently beats trenching. A panel or two on a frame, a charge controller, a battery and a small inverter will run lighting, charging and a fan without much drama.

Two things people underestimate. The first is that inverters and batteries hate heat, and a closed steel box on the Clarence in February gets hot enough to shorten a battery's life considerably. Put the battery somewhere shaded and ventilated, not on the sunny end wall at head height. The second is that solar sizing is done on the worst week of the year, not the average. A system that is comfortable in November is a system that runs out in a wet June.

Solar on the roof itself

It is the obvious place and it is not as simple as it looks. A container roof is thin corrugated steel and is not a working platform — it will take a person's weight in the wrong spot and remember it as a dent, and a dent on a container roof is a puddle that never drains. Ponding water is what kills container roofs, so anything that creates a low spot is a genuine problem.

The usual answer is a frame that lands on the top rails at the corners, which is where the strength is, and sits the panels clear of the roof sheet. That has the useful side effect of shading the roof, which noticeably drops the temperature inside. Fixings go through the rails with the holes sealed, and anything on a roof in this district needs to be rated for the wind it will actually see.

Generators: outside, always

A generator never runs inside a container, with the doors open or shut. Carbon monoxide is colourless, has no smell, and a steel box is exactly the kind of enclosure that concentrates it. It builds to a lethal concentration faster than people expect, and the set-up that does it is the one that looks harmless — brief job, doors open, seemed fine.

Put it outside and well clear, with the exhaust pointing away from the doorway, and store fuel somewhere that is not the same box as your gear.

Condensation, which will find your wiring

A sealed steel box breathes through its own temperature swings. Warm damp air, cold steel overnight, and by morning there is water on the underside of the roof. Everyone on this river knows the effect from a car windscreen; a container does it at scale.

For electrical work that means two habits. Mount the board and any junctions so they are not directly under the roof sheet where the drips form, and use fittings rated for damp conditions rather than the cheapest indoor ones. If you are lining the container, get the sparky in before the lining goes on, and talk to them about ventilation at the same time — vents high and low do more for a wired container than any amount of sealant.

What we can and cannot help with

We sell and hire the container, we deliver it, and we will tell you honestly which grade suits a fit-out. We do not do the electrical work and we will not recommend anyone who offers to do it unlicensed. What we can do is make sure the box you start with is sound, because there is no point wiring a unit with a soft floor or a roof that ponds.

If you want to see one before it goes on a truck, the yard is at 1a Reid St, South Grafton and you can stand inside a container with the doors pulled to, which tells you more about where the light and the outlets want to be than any drawing will. We deliver out through Coutts Crossing and Glenreagh, west along the Gwydir past Ramornie, up the Armidale Road to Nymboida, and out to the small blocks around Pillar Valley. Ring (02) 5616 9099 and tell us what you want to run in it.