Monday, 13 February 2012

Garden Office and Garden Studio Electrical installations

Electricity in Garden Offices and Garden Studios

There are always some questions about the electrical supply to Garden Buildings from our prospective clients.

I am a qualified domestic installer “electrician” with experience of designing and installing more than 500 electrical systems specifically for Garden Structures.

Firstly let me explain what electricity is:

  • It is sub-atomic particles (electrons) flowing in a conductive material.
  • It is invisible it has no smell and it can kill.
  • It forms the backbone of modern industrial society and probably will do for some time to come.
  • It powers our I-phones, the internet and it makes our homes comfortable with heat, light and entertainment.
  • It is used in our factories, vehicles, transport systems and hospitals in every corner of the planet and beyond.

Electricity comes in various strengths measured in volts and various volumes measured in amperes. A high number of volts can hurt a lot and kill if it flows through the heart. A high number of amps are required to create lots of heat or start a heavy motor.

At this point I propose to stop explaining electricity but ohms law can be read at:'s_law .

Noella can still recite it word for word having learned it at school!

Here are two practical examples I hope you find easy to understand:

  1. Homes use 240 volts of alternating current.
  2. Cars are started with 12 volts of direct current.


Electricity travels better down thinner wires using wavy current (AC) at high voltage than straight current (DC) at low voltage. As you are aware our cars are started with 12 volt (DC) batteries but need massive cables connected to the starter motor to turn the engine.
The 12 volt battery system used in cars is safe to touch and travels with the vehicle waiting to start it again for the return journey. The 240 volts used in our homes can provide lots of power down thin wires but needs to be safely installed because a short exposure to 240 volts flowing through your heart can be fatal.


Low voltage with heavy demand requires big wires and high voltage is dangerous.

Electricity in Garden Offices, Garden Studios and Granny Annexes

Our garden buildings Offices, Studios, Garages, Annexes etc need 240v ac to operate all our usual domestic stuff and therefore must be installed “as safe as houses”. For some years now it has been outside the law to use any 240v appliance outside the home i.e. in the garden without the appliance being protected by an RCD. This device (full name: residual current detector), switches off the current flow if any electricity flows to earth e.g. if electrical current flows through your body to ground it will switch off the current before you are badly hurt.

I, like most electricians would prefer these devices to be fitted on every domestic circuit, however 60 % of dwellings in the UK still do not have them. I am pleased to say that EVERY Garden Building installation I have made is fully RCD protected.

Safety is paramount.

Essential elements of a safe electrical system for “Garden Buildings”

  1. None of the conductors should be exposed. This means that mechanical protection must be provided (switch covers and socket plates etc.). Every electrician is responsible for ensuring that the installation passes the “British Standard Finger Test”. It must not be possible to insert anything into any enclosure and touch a live conductor.
  2. Secondly all devices lights, sockets, appliances etc. must be sufficiently protected against any external part becoming live.

Essentials of an efficient “Garden Building” electrical system.
The Garden Office or Garden Studio is normally wired in exactly the same way as a typical home as follows:

There are lighting circuits, power socket circuits and circuits for high demand items. The wires for different circuits are of different sizes. Lights use less power than heaters therefore thinner wire is adequate. To ensure a circuit cannot be overloaded a fuse / trip (referred to an over-current device) sized appropriately and certified by the installer is fitted. If the wrong size is fitted and the wire is overloaded fire could result.

So – the correct wires and over current devices must be installed to ensure total safety inside the new building. The next job is to make sure that the building has the correct feed. This feed should not affect the main house and fulfil its job providing safely a reliable supply to the new building.

Correct connection of a Garden Office or Garden Studio to the electrical supply.

By far the most common way of providing this connection is to use a “Steel Wired Armoured cable” (SWA). The size / capacity of this cable depends on two factors a) the distance it needs to carry the electricity and b) the likely demand for amperes at peak. This is an assumptive calculation made by the installer in compliance with (Building Regulations Part P) – the armoured cable must always be overload protected at source but must be sufficient in capacity to make sure that under heavy use (like fan heaters, showers and kettles are on at the same time) the supply will not trip causing disruption to the occupants.

It is very important to note that disruption and safety are not related as safety is paramount and must be assured by the installing electrician. Each electrician is legally bound to certify each and every circuit he or she works on.

The armoured cable needs to travel from the main property to the new building. As the cable is mechanically protected against contact with the conductor and earthed (the surrounding steel strands are connected to ground) an SWA cable is electrically safe on the surface, in the air or buried at any depth.

This important point is the subject of some debate amongst electricians and quoted incorrectly on many industry websites.

(updated 11/12/2015) "Don't need to change anything here electrons are still electrons and safety is still the main thing" There have been a few challenges from electricians wanting to bury SWA  Armour (steel wired armoured cable) at high cost to the client but I assume by now no-one else wants to challenge me on this. SWA is safe above ground or below ground that is all. I think the comments are good enough - it's still a boring subject but safety sometimes is - it doesn't make it less important because safety remains VITAL.

What is the difference between Earth and Neutral (blue and green)?

Both go to the same place but earthing is done for the protection of humans and neutral takes back the electron count. So when you switch on a light the electrons used are is counted by the meter so you must pay. If you send it back down the earth the light will still come on but you may may pay with your life as correct earthing is a life saver.

Earthing is provided to an outbuilding in the swa armour by the outer steel sheathing and sometimes an inner core as well. Earth rods are not necessary if good connection to earth is made at the main property. The armour can be on the surface or underground it is a safe cable protected by steel connected to earth.

This post written by Richard Grace Project Director Garden Structures Ltd

Comments and links to this post welcome:


  1. It's the armoured cable that is always the issue. Should it be underground? And please explain why!


  2. In cabling garden a little bit risky but in side i just call a Electrical Sydney to do the work.

  3. Nice Post..enjoyed visiting here and also did get lots of good information from here. thanks for sharing such post.
    Office fitout

  4. Seems to attract attention - next month I will dismiss the myths on plumbing. In particular our wast pumping system which reduces the cost of installing a toilet in Garden Buildings.

    1. Do you mean saniflo Richard ��

    2. Sort of but if the waste has to go long way or uphill use saniflo to get waste to tank then dirty water pump to get it through 25mm smallbore to main drain. I have this working at 100m distance and 23m rise to exit. It works read full description published on this blog.

  5. We are providing structure of garden office, garden studio, planning permission for garden offices, granny annexes or garden studios and outdoor kitchens.

  6. A really nice article provided a nice balance between educating about electrical science and safety. I do think you could mention a little earlier, and in a little more detail that there are specific standards that electrical installations need to be carried out to, BS 7671:2008 Requirements for Electrical Installations and Part-P of the Building Regulations.

    All works involving special locations, kitchens, bathrooms, saunas, jacuzzi's, require work to be carried out by a licenced electrician, Part-P approved and able to design, install, inspect and test, then certify to the local authority building control.

    If works are being carried out by non licenced electrical contractors, at best you risk troubles selling your property, at worst you run the dangers of electrocution.

    Really enjoy the blog, keep it up!

  7. Hi there! Thank you so much for sharing this blog post. I'll be looking forward for your other posts as well. You have such a nice page. I'll try to visit this page again some other time. Before electricians are allowed to work without supervision, they are usually required to serve an apprenticeship lasting from 3 to 5 years under the general supervision of a Master Electrician and usually the direct supervision of a Journeyman Electrician. Schooling in electrical theory and electrical building codes are required to complete the apprenticeship program. Many apprenticeship programs provide a salary to the apprentice during training. A Journeyman electrician is a well rounded craftsman who has met the experience requirements for on the job training (usually 4080 to 6120 hrs) and classroom hours (about 144 hrs.); they may also have a two year relevant degree and another two to three years of apprenticeship training and have passed a licensing exam for their jurisdiction, be it state, county or city. They are trained in all phases of electrical construction installation in various building styles (residential, commercial, industrial, basic electronics) and maintenance of equipment after installation. All of their time is well documented under the jurisdiction of the state government in order for their time to be credited. A Journeyman is usually permitted to perform all types of electrical work except the design of electrical systems, although in some jurisdictions a Journeyman may design systems within certain limits. By contrast, a residential electrician is only permitted to work on residential projects with limitations (for example under 4 stories), and apprenticeship is typically four to five years. In certain states like Michigan, to go on to be a Master Electrician and then an electrical contractor, a journeyman has to work another two years past his passing of the extensive exam given and then apply to take the Master's exam which is another very rigid exam. Then they can apply for an electrical contractors license according to the guidelines of that government. Welcome to McCurdy Electric, where you'll find more than your average list of electrical services. Our trained and certified team of North Reading electricians brings several years of experience to every project and continues to keep up with all of the latest developments in the industry.
    Electrician North Reading MA

  8. I have been looking the World Wide Web for this information and I want to thank you for this post. It’s not easy to find such perfectly written information on this topic. Thanks for sharing such valuable information Electrician North Sydney

  9. Thank you for sharing excellent information. Your web-site is so cool. I’m impressed by the details that you have on this website. It reveals how nicely you understand this subject. Bookmarked this website page, will come back for more blogs.

  10. I am going to update this soon with bit of a re-write. It has been a few years and done well. It is still valid and all my installations are still perfect there have been no faults whatsoever in any at all.



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Richard is an experienced business consultant specialising in garden structures design and planning + The UK's leading expert in using Pinterest for business marketing web traffic generation at lowest cost.