Power and lighting in the garden or outbuildings such as summerhouses and garden offices requires careful consideration.
You may hear some unqualified folk telling you it’s just a case of running a cable outside and that’s it way you go.
Yes, this may work – will it be safe and resilient? Most definitely not. Will it cause you problems later down the line? Based on my experience of failed DIY installations – highly likely.
Some considerations any qualified Electrician should make before installing outdoor power
Imagine you have a fault on your garden or outbuilding installation – a damaged cable, water ingress or even vandalism.
If your outbuilding is piggy backing off the house supply – depending on the type of fault, you’ll potentially lose power to the entire house.
Imagine this happens while you are away from home, you may lose the contents of your fridge freezer, if you have security floodlights, Wi-Fi based CCTV or thermostatic heating controllers you may lose access to these too.
Best practice (wherever possible) is to run a separate circuit(s) with complete isolation from the home circuitry, this way any fault outside doesn’t affect the inside and vice versa.
Rain and the obvious potential for water ingress. This is achieved by selecting the correct materials but also installing them correctly.
UV light and the effect it has on breaking down certain types of cable insulation – **HINT** those not intended for outside use.
Wind – any cable suspended in free air between 2 or more points will be susceptible to movement with wind. Cabling should be attached securely to a catenary wire under tension, this will prevent excessive movement and prevent cables from being damaged and causing a short circuit or earth fault.
Wildlife – from birds perching on the suspended cable, to rodents trying to chew cable insulation, wildlife is something that must not be overlooked in the design and construction of outdoor power.
Rarely considered by the local handyman or hairy arsed builder who’ll say ‘it’s only running a cable outside luv’ and something ignored at your own peril.
Your earthing arrangement is the means in which any earth fault current returns to your local transformer/substation – this isn’t something you can change or choose, it’s determined by the DNO (Distribution Network Operator) and you will have to work with what you have. That said, I have attended properties which have no earth facility provided and they have been like that for a long time – which is rather dangerous.
Depending on your earthing arrangement and outbuilding construction type it may be necessary to install an earth rod or install a suite of protective devices to ensure electrical discrimination is achieved – electrical discrimination means that the nearest upstream device (be it a fuse, circuit breaker, RCD etc) operates first.
