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Garage radial circuit

Posted by Nathan Thomas, on
I’m looking for some advice on my garage electrics. In my garage there is a consumer unit with a 6amp breaker, 16amp breaker and a 40a RCD. The 6amp breaker is supplying the lights and 16amp breaker the sockets. The lighting circuit consists of: • Two pendant lights (2x 5w led bulbs), with one switch, for the attic • A strip led batten light as the main garage light with a switch at the side-door and a switch at the main garage door (12-watt) • Three PIR led floodlights: 50-watt, 30 -watt and 10-watt (covering the front/drive, side/garden and rear of the garage where bins are kept. All of three outside lights have their own fused switch inside the garage. The lighting circuit is wired using junction boxes. Socket circuit: • Four double sockets • A fused switch that goes to an outside IP66 single outdoor socket. In the garage I have powered: • CCTV (one plug for the DVR and one plug that splits the 12v power to the four CCTV cameras) • PC monitor – for viewing CCTV locally, if needed. • Wi-Fi booster • Radio • Small drinks fridge (only switched on in the summer) • Freezer (over 10 years old) • Tumble dryer (1 month old, B rated) I need to change the main garage door and plan to fit an electric door. The door comes with a 5amp fused plug, however, to avoid trailing wires and to make a neater job I had intended on powering this door from a fused-switch, taking a spur from one of the sockets. This is where I began to worry slightly as I opened one of the sockets (to spur from) and was surprised to find only one 2.5mm twin and earth cable going into the socket. I thought this socket might have been a spur and opened the others, turns out the garage sockets are wired on a radial circuit and not a ring main. I know this is ok, but was still surprised to find this in a building that’s not yet 10 years old. From the main board in the house there is 2.5mm armoured cable running roughly 10 meters to the garage (I assumed this would have been 4mm or 6mm cable). This is fed from a 16amp breaker also covered by an RCD. I have clearly never overloaded this as the garage has never fused and neither has anything in the house. I use the garage sockets as indicated above but also for power tools, hoover and jet-wash. I use the outside plug for cutting the lawn. I obviously don’t have the dryer running whilst hoovering, jet-washing and using the lawn mower etc. so my thinking was so long as I didn’t do multiple high-powered tasks (kids aren’t old enough yet!) the current set-up is absolutely fine, and if it was overloaded it would simply trip. Would it be ok proceed as I planned and fit a fused spur off one of the sockets for the new garage door? I would also like to add another internal LED batten light, essentially run off the same cable going to the light I already have (I’ll just put a junction box to split the cable into two) Thoughts welcome, and thank you in advanced.
David Ade

David Ade

Hello, I am guessing the 40 amp RCD is the main switch? Do you know what is actually feeding the garage supply from the house? Absolutely nothing wrong with running radials for socket circuits (as long as the final installation is tested and passed) but since you are going to be having a lot more stuff onto the circuit you might as well upgrade the MCB for sockets to 20 amps as they should be anyway. You can certainly spur off one of the sockets (fcu) to feed the garage door but space permitting on the board, why not just run dedicated circuit from the fuse box off a 6 amp MCB especially just for the garage? That's the way I'll do it anyway, and that helps with 'Diversity'. Hope the above helps. Dean Wago electrical

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