Garage and outbuilding power in Purleyfor sheds and garden offices
Armoured cable buried to depth, feeding its own small board with sockets, lighting and heating, so the garden office works like a room in the house, not a lead out of a window.
NAPIT registered and Part P certified, £2 million insured, 10/10 on Checkatrade, 320 reviews logged over the years, twelve month workmanship guarantee.
NAPIT registered
Government-approved competent person scheme
Part P registered
Domestic work certified to Building Regulations
£2 million cover
Public liability insurance on every job
1 year guarantee
Workmanship guaranteed for twelve months
10/10 on Checkatrade
320 reviews logged on the profile over the years
Service overview
Garden, garage & outbuilding power explained
A garden office needs a proper supply, not a lead out of a window. Armoured cable, buried to depth, feeding its own small board with sockets and lighting.
What it involves
A dedicated supply run from the house consumer unit to a garage, shed, summer house, workshop or garden office, terminating in a small consumer unit at the outbuilding with its own protected circuits for sockets, lighting and heating.
The work includes assessing spare capacity at the main board, calculating cable size for the load and the run length, excavating and burying steel wire armoured cable to the correct depth with warning tape, glanding at both ends, and testing and certifying the new installation.
Who it is for
Homeowners across Purley, Croydon and Surrey building a garden office for working from home. Anyone converting a garage to a workshop or gym. Owners of summer houses and studios that need more than a socket. People who need power at the end of the garden for a pond, greenhouse or hot tub supply.
When you need it
Before the building goes up if possible, or at least before landscaping, patios and turf are laid, the trench is the disruptive part, and doing it while the ground is already open saves a great deal of work.
Also when an existing outbuilding supply is failing, is fed in unsuitable cable, or cannot carry what is now plugged into it.
Why it needs a qualified electrician
Outbuilding supplies fail in ways indoor circuits never do. Cable buried at the wrong depth or without armour gets cut. Terminations without proper glands let water track along the sheath into the enclosure. Undersized cable over a long run loses voltage and runs hot.
Load calculation matters more than people expect: a garden office with a heater, a kettle and a couple of monitors can draw more than a spare way on the house board comfortably allows. It is also notifiable work under Part P, which means it must be tested, certified and notified.
What happens if it waits
The cost of leaving it
The improvised garden supply is one of the most common dangerous installations we are called out to.
Risks and escalation
- An extension lead run out of a window or under a door is unprotected against damage, weather and overload, and is a fire and shock risk in daily use.
- Non-armoured cable buried in a garden will eventually be struck by a spade, fork or fence post, potentially while someone is holding it.
- Water tracking into an unglanded enclosure corrodes conductors and trips the RCD indoors, typically taking out house circuits with it.
- Undersized cable over a long run causes voltage drop, poor performance from heaters and tools, and a cable that runs warm continuously.
- An uncertified supply is an undocumented alteration that will be coded at the next inspection and queried on sale.
Common mistakes we are called to undo
- Burying ordinary twin and earth, or armoured cable at too shallow a depth with no warning tape.
- Feeding the outbuilding from a socket circuit in the house instead of a dedicated, correctly protected circuit.
- Skipping the small consumer unit at the far end, so there is no local isolation or protection.
- Laying the trench after the landscaping is finished, which doubles the cost of the job.
Everything we install outside is specified for the load and the location, tested, certified and guaranteed for twelve months.
Our process
How the job runs, start to finish
Step 1
Survey and load assessment
Jon checks the main board's spare capacity, measures the run, discusses what the building will be used for, and calculates the cable size needed.
Step 2
Free written quote
Cable route, excavation, board specification, circuits and any main board work set out in writing, free of charge, before anything starts.
Step 3
Trenching and cable installation
Trench excavated to the correct depth, steel wire armoured cable laid with warning tape above it, then backfilled and reinstated as agreed.
Step 4
Termination and second fix
Cable glanded at both ends, small consumer unit fitted at the outbuilding, sockets, lighting and heating circuits installed and connected.
Step 5
Testing, certification and guarantee
Full testing to BS 7671, Electrical Installation Certificate issued, Part P notification through NAPIT, and twelve months' workmanship guarantee.
What's included
Garden, garage & outbuilding power with JMO
- Steel wire armoured supply installed and buried correctly
- Small consumer unit, sockets, lighting and heating circuits
- Suitable for garden offices, workshops, garages and summer houses
- Tested, certified and guaranteed for 12 months
Costs, plainly
Free quotes on planned work. £85 call-out during standard hours, which covers the first hour of work on fault-finding jobs. Evenings and weekends £140 per hour. All workmanship guaranteed for one year.
Benefits
What you get out of it
A building you can actually work in
Proper sockets, lighting and heating capacity instead of one overloaded extension lead.
Local isolation
A small board at the outbuilding means you can isolate and fault find there without walking back to the house.
Safe by design
Armoured cable at the correct depth with warning tape protects the supply against spades, posts and future digging.
Built for the load
Cable sized for the run and the intended use, so heaters and tools perform and nothing runs hot.
Weather-tight terminations
Correct glanding and IP-rated enclosures stop water tracking into the installation.
Certified and documented
Certification and Part P notification for insurers, inspections and future buyers.
In detail
Garden, garage & outbuilding power: the detail that matters
Cable, depth and materials
Supplies to outbuildings are run in steel wire armoured cable, sized according to the design current, the length of the run and the installation method. A long run to the end of a garden usually needs a larger conductor than the load alone would suggest, because voltage drop has to stay within limits.
Cable is buried at an appropriate depth for the location, deeper under a drive or a cultivated bed than under a path, with warning tape laid above it. Entries into buildings and enclosures are glanded with the armour correctly terminated, which is both the earth path and the mechanical protection.
- Steel wire armoured supply from the house board to the outbuilding
- Small consumer unit with RCBO-protected circuits at the far end
- Socket circuits, internal and external lighting, and heating supplies
- Supplies for workshops, garden offices, gyms, studios, garages and summer houses
- Greenhouse, pond and hot tub supplies on correctly protected circuits
- Main consumer unit upgrade where the existing board has no spare capacity
Garden offices and working from home
A garden office has a specific load pattern: continuous low draw from IT, plus intermittent high draw from heating and a kettle. That combination is what catches out undersized supplies, particularly in winter when a heater runs all day.
We size the supply around realistic usage, split circuits so lighting stays on if a socket circuit trips, and provide enough socket positions that nothing ends up on a trailing lead. Note that JMO does not install smart home or automation systems, controls here are conventional switching, sensors and timers.
Garages, workshops and higher loads
Workshops introduce machinery with motor loads and inrush currents, which affects both protective device selection and supply sizing. Welding equipment, compressors and larger machines may need dedicated circuits.
Garages also frequently combine with EV charging, and where both are wanted it is far more economical to plan the supply for both at once rather than trenching twice.
Excavation, reinstatement and coordination
The trench is normally the biggest variable in cost. Soft ground across a lawn is straightforward; crossing a concrete drive, block paving or mature planting is not. Jon walks the route and prices the realistic option rather than the optimistic one.
Reinstatement is agreed in writing: turf relaid, paving reset, or the trench left for your landscaper. Where a builder is on site we coordinate so the cable goes in at the right stage of the build.
Areas covered
Outbuilding, garage and garden office supplies across Purley, Croydon, Caterham, Coulsdon, Sanderstead, Warlingham, Kenley, Sutton and London.
Reviews
What customers say
10/10
“Communications and arranging the date was excellent. Standard of work to a high standard and all to the agreed quotation.”
10/10
“Jon and his team turned up promptly as agreed, completed all works to a high standard and at a reasonable price.”
10/10
“Quickly turned up and safely dealt with cut cable to external garage. Great communication throughout.”
FAQs
Garden, garage & outbuilding power: common questions
How much does it cost to run power to a garden office?
The main variables are the length of the run, the ground being crossed and the load the building needs. Jon walks the route and gives you a free written quote covering cable, excavation, the board and the circuits.
How long does the work take?
A typical garden office supply is usually a day or two depending on the trench. Hard surfaces and long runs extend that, and the programme is agreed before we start.
Do you dig the trench?
Yes, excavation and backfilling are part of the job unless you would rather your own groundworker or landscaper does it, either way it is stated on the quote.
Can I just run an extension lead instead?
Not safely for anything permanent. An extension lead is unprotected against weather, damage and overload, and is one of the more dangerous arrangements we get called out to.
Do I need a consumer unit in the outbuilding?
For anything beyond a single light, yes. A small board gives local isolation and protection for each circuit, which makes the building safer and faults quicker to deal with.
Will my existing fuse box cope?
Often, but not always. Jon checks spare capacity and protection at the main board first, and if an upgrade is needed it is priced in the same quote rather than raised later.
Is the work certified?
Yes: tested to BS 7671, certified, and notified under Part P through our NAPIT registration, with a twelve month workmanship guarantee.
How long will the supply last?
Armoured cable correctly installed and buried is a permanent installation designed to last the life of the building. Include it in your periodic inspections along with the rest of the property.
Can you install an EV charger at the same time?
Yes, and it is far cheaper to plan both together than to trench twice. Jon will assess whether the supply can carry both.
Areas covered
Garden, garage & outbuilding power across Surrey and south London
Related services
New here? Start on the JMO Electrical home page, browse all services, or get in touch with Jon.
Get a free quote for power to your outbuilding
Jon walks the route, sizes the supply for how you will actually use the building, and prices the trench, board and circuits in writing.