Shed electrics with a small board of their own, fed from the house.

How a shed supply is wired

The little board gives the shed its own main switch and breakers, so you can make everything out there safe without walking back to the house.

The feed from the house is steel wire armoured cable, made to be buried or fixed outdoors. Part P's performance standard wants wiring protected against mechanical damage, and the steel armour does that on the way across the garden.

Tell me what the building is for before anything is sized. A light and a mower charger ask very little of the cable, while a workshop running a saw and a heater asks far more.

The standard job covers one building, with a single light and a single socket on its new board. If the house board is full, a new consumer unit in the house may come first.

Extension leads and outside sockets

Plenty of sheds run from an extension lead through a window, or a cable clipped along the fence. Over a winter, rain and frost get into a lead's plug and trailing socket, and a cable on a fence is one slip of the strimmer from being cut.

If the mower or a hedge trimmer only needs plugging in now and then, an outside socket fixed to the house can be enough. A heater or power tools in the shed need a dedicated circuit, with cable thick enough that the voltage at the far end holds up when something heavy starts. BS 7671 limits how far that voltage may drop.

Burying the cable to a shed or garage

Digging the trench is the one part of a shed supply that isn't in the price. You can dig it yourself or have a landscaper do it, and I'll mark the route and the depth before anyone picks up a spade.

BS 7671 doesn't give one depth for every garden. Regulation 522.8.10 asks for buried cable to sit where ordinary use of the ground will not disturb it, with its route marked by cable covers or warning tape. Ground you dig every spring needs a different answer from ground under a path.

Where the cable can follow a wall safely, it is fixed there in its armour instead. Under a patio, a duct laid beneath the slabs saves lifting them a second time.

Earthing an outbuilding

How the building is earthed depends on the house supply and on what's inside. Many sheds share the house earth through the armoured cable. If a metal water or gas pipe runs into the building, it needs bonding there too, and on some supplies the outbuilding gets an earth rod instead.

That choice is made at the survey and written into the quote, so it doesn't become an extra on the day.

Garden room and garden office electrics

A garden office usually wants more than one socket, placed where the desk will stand, and a heater or an air conditioning unit is better on a circuit of its own.

If the room is still being built, bring me in before the walls are lined. The cables are run at first fix, then the walls are boarded, and the sockets, switches and consumer unit go on at second fix.

Small garden buildings with no sleeping accommodation are often exempt from the Building Regulations under Schedule 2. The electrics are the exception. Regulation 9(3) keeps Part P in force for any such building that takes its electricity from the house.

That makes the new circuit out to it notifiable work in England, even though the building itself may need no approval.

When the testing is finished I hand you the Electrical Installation Certificate. Planning permission for the building itself is a separate matter, covered by the permitted development rules for outbuildings (Class E) or your council.

Garage electrics

A detached garage is wired the same way, with a sub-main and a small board. If an EV charger in the garage might follow, mention it when I come out, because the cable and the board can be sized for it now.

Lights over the garage door and a camera watching the drive can go in at the same time, while the board is new and the cable routes are open.

A garage that is part of a new house or self-build belongs with the new-build wiring instead, first fix through to certificate.