Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This Question of the Day, about running buried cable to a garage, is answered by Prysmian:
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| Is three-core 4mm2 SWA cable OK? |
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Question: I want to run cable out to the garage. The distance from the existing consumer unit is approximately 50m away. Connections etc, will be carried out by an electrician, but I want to lay the cable as part of some landscaping work being done in the garden.
I know that the cable needs to be buried 600mm down (but I believe can be 450mm below patio areas) with hazard warning tape 150mm above the cable.
The garage will have one ring and one lighting circuit, but thought I'd allow for a second ring, to provide for expansion in future. Usage will be domestic power tools, i.e. hedge trimmers, chop saw, drill, chargers for cordless tools etc.
I was thinking about using three-core 4mm2 SWA, but is that sufficient?
Also, understand that I should have the SWA cable terminate at a junction box at either end, and then use 2.5mm twin & earth cable to connect to the consumer unit and the new distribution unit in garage. What junction box is best, and with the garage being wooden, should I use metal or waterproof junction box and distribution unit at that end?
Answer: We can only answer your question regarding the cable size, and would point out that we do not calculate customer's requirements based on equipment. We have therefore provided maximum currents for a range of sizes, based on 2.5% voltage drop. We have assumed that the voltage is 230V:
- A 3x4mm˛ will carry 10A over 50m to maintain a maximum 2.5% voltage drop.
- A 3x6mm˛ will carry 15A over 50m to maintain a maximum 2.5% voltage drop.
- A 3x10mm˛ will carry 25A over 50m to maintain a maximum 2.5% voltage drop.
We trust this information is of use, and would suggest that you seek further clarification from your electrician.
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www.voltimum.co.uk/consult.php?universe=consult.index.questions
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