Livestock building electrics for pig units, poultry sheds, dairies and stables.

What are the electrical rules for livestock buildings?

Two sets apply. BS 7671 has its own section for agricultural premises, Section 705, which covers buildings where livestock are kept, and animal welfare law adds duties for the systems the animals rely on.

In a livestock shed, the part of Section 705 that matters most is bonding the steelwork the animals touch.

The welfare regulations cover ventilation and lighting. The two overlap, because a fan circuit that trips is an electrical fault and a welfare problem at once.

Why livestock buildings need extra bonding

In a shed, an earth fault can put a voltage on a feed barrier or a water trough. Supplementary bonding ties that metalwork together and to earth, so a fault can't leave a dangerous voltage between two things an animal touches at once.

Animals on wet concrete have nothing between them and the floor, which is why the standard deals with livestock locations on their own. Supplementary bonding is part of what I check and test in every livestock building, and missing or corroded connections are coded in the report.

Ventilation, alarms and back-up power

If pigs or poultry depend on mechanical ventilation, the welfare regulations for farmed animals in England ask for two things beyond the fans. There has to be a back-up that keeps enough air moving if the system fails, and an alarm that warns of a failure and keeps working after the main electricity supply has gone.

The same regulations set how often the back-up must be inspected and the alarm tested, and say any defect is to be put right straight away.

On the electrical side, the fans and the alarm are best kept on separate circuits, so one tripped breaker can't stop the air and silence the warning together. The alarm's own battery or supply gets tested with everything else.

A standby generator for the fans has to go through a changeover switch so it can never run in parallel with the network. The Electricity Safety, Quality and Continuity Regulations require it, and it protects anyone working on the lines.

Lighting for housed livestock and poultry

Welfare law covers light as well. Animals housed indoors can't be kept in permanent darkness, and where daylight falls short of what they need, artificial lighting has to make up the difference. They also need a proper rest from artificial light.

There has to be enough light, fixed or portable, to inspect every animal thoroughly at any time. In practice that means lights on controls that give the stock their dark period, and an inspection light that doesn't depend on the main lighting circuit.

Dairy parlours and feed systems

A dairy parlour puts water and steel in one room. The vacuum pump and the bulk tank cooler are best on circuits of their own, with RCD protection and bonding to the parlour steelwork, and a washdown-proof isolator within reach of whoever is milking.

Where the fans and feed motors outgrow a single-phase supply, the next step is a three-phase board and an upgraded supply.

Working stables and riding arenas

A working yard is hard on wiring in the same ways as a cattle shed. Horses chew and kick, and hay and bedding burn easily. Stable blocks get hosed down as well.

In a stable block the lights and sockets go up out of reach, in sealed fittings with guards, and the cable runs in steel conduit or high enough that a horse can't get its teeth into it. The circuits there get RCD protection too.

Riding arena floodlights are the other big job. They have to light the surface evenly without glare in a horse's eyes, and they go up on poles or on the building, fed by armoured cable laid round the edge of the arena.

Light that spills over the hedge into a neighbour's windows can be a statutory nuisance under the Environmental Protection Act 1990, so menage lighting is aimed and shielded to keep the light on the surface.

Foaling cameras let you watch a mare from the house, and I fit CCTV in stable blocks on the same wired system as any yard cameras.

Converting an old stable block into a home or holiday cottage is a different job, wired to the rules for a new dwelling.

Inspecting livestock buildings

Livestock housing is inspected like any other farm building. A periodic farm inspection of a pig or poultry unit looks harder at corrosion and bonding than one of a dry store.

It makes sense to check the ventilation alarm and any generator changeover at the same time, because a fault there only shows itself when the fans stop.