hi all ,I took a spur 2.5mm squared to a double socket in my out house ,at the double socket in the outhouse I took a 1.5mm squared wire to a fused connection switch then from the fcu to the light switch, now it all seemed to work fine for 3 years but in the summer I'm unsure if liquid like lemonade or similar was spilt onto or into the double socket ,however the double socket started to make a fizzing noise and the power would go on and off, I have taken the socket off and the N neutral where I had the black wires has totally burnt out so I'm assuming I have it wired incorrectly, I was thinking of bringing the supply in to a 13amp fused connection unit then have the load go to the double socket and the lights .help with this problem would be great thanks in advance zebb
Hi the spur is taken from a socket and fed through round plastic conduit underground about 18 - 24inches deep ,I have cut the cable burnt ends off back to good cable ,the socket had an electric oil filled heater and an extention plug with four sockets -tv -dvd palyer-music stereo-Christmas tree,I have the feeling either it has been overloaded or fluid spilt or has the neutral wire 1.5squared to the switched fcu for the lights turned live when switched ?
Any poor connection will likely produce heat. Be it a bad switch or a screw not tight the result is the same. Over heating. All screw connections can be affected by vibration in the home we do not see it very often but in industrial installation with metal or wood framed buildings just people walking can cause screws to become loose and with item like batching plants with vibrators to stop concrete sticking it is a big problem.
There are now maintenance free connectors but unless these are used then connections do need checking in the home it is recommended every 10 years or change of occupant. I could be the connection was not tight in first place not unknown for a socket to have a bad thread so it feels tight but is not. Or could have worked loose or caused by poor plug or faulty switch. What ever the cause cut back burnt cable to a point where there is no sign of burning.
As to wiring methods 2.5mm cable is rated at around 20A according to conditions and a standard ring is fused/MCB/RCBO protected to 32A so there are a host of rules when tapping onto this supply to ensure the cable can't be overloaded. This include 434.2.1 which limits spur to 3 meters and Appendix 15 which shows us how any unfused spur must feed a single fused device be it a FCU, Single Socket, or Double Socket yes I know a double socket could supply 26A but it is deemed unlikely that two plugs would draw the maximum for a long time. The 2 kW rule for fixed equipment also reduces the chance of two items being used to the maximum 13A for any length of time.
It has been debated many times is a garden shed a fixed piece of equipment if it is then it should not be feed from the ring if it draws more than 2 kW or 8.7A so it should be feed with a FCU with a 7A fuse. OK being a bit pedantic here but clearly unless supplied direct from the consumer unit there should be a FCU at the point where it draws current from the house ring.
Rules are complex and it includes things like the volt drop and earth loop impedance easy way is to use a RCD FCU at the tapping point in the house. Question is active or passive? Using an active type means if there is a power cut then the shed will not auto reconnect but also means if there is a volt drop problem the trip will still work. So where fitted DIY using an active trip is likely safest way as most DIY guys don't have a loop impedance meter to test the installation with.
As already said twin and earth is rated for in door use only and with SWA you need something to fit the gland to so a metal clad RCD FCU will give you ready made 20mm hole for the gland.
Once feed from a FCU no real point in having a consumer unit in the shed but most lighting stuff only rated at 5A so using a switched FCU with a 5A fuse as the light switch is the easy way to comply. In my shed I just used a plug with 5A fuse for lights well in fact a 3A fuse was used.
The point is it is near impossible for a DIY guy to do electrics and comply with the regulations as the tools cost too much but the active RCD FCU is your friend it does not mean it will comply but does reduce the likely hood of any mistake being fatal.
Thanks for all the replys , I have fitted a FCU between the supply and load ,I have a 13amp fuse in at present but will bring this down to 7.5amp or 10amp,it all seems to be working fine now. Cheers zebb