Outside light spurred from socket

[cwhaley]

Hello. I want to put in a small, LED up/down light by the back door. I know how to do this and I have the equipment to do it, but I've not been able to find a clear answer on which type of cable I should use.

My current idea of the set up is this....

- There is a socket near the back door. Spur from this with 2.5mm T&E up to a switch.
- The switch will be fused with a 3A fuse.
- Wire then goes from the switch to the light, which is only LED and will not draw a great deal of current/voltage.

My question is whether or not the 2.5mm T&E is an acceptable from the switch to the light. Some have said yes, some have said use 1.5mm instead.

Can anybody advise whether or not 2.5mm cabling would be safe/acceptable at this point?

 

[PrenticeBoyofDerry]

You can take a spur from a socket outlet using 1.5mm twin and earth.
Then form the fused connection unit it can be 1.00mm twin and earth.
If the cable goes externally and exposed to the outside environment, then it is advised not to use twin and earth, as it is not designed for the outside conditions. You should use a flexible cable that is suitable for the environment it is located. This flex can be terminated to the FCU load side, instead of twin and earth. It is feasible to use 0.75mm or 0.5mm flex, a 1am fuse would be ample for the load.

There are other things to consider, with regards to safe routing of cables and RCD protection of buried cable. Is RCD protection already present and functioning, on the socket circuit to be used?
There are also so rules on spurs from ring final circuits, you can only take one spur from a socket on the ring, this means if the socket is already an unfused spur, then it should not be another spur added.

 

[Taylortwocities]

As above. Dont try and use 2.5mm² from the FCU to the light. Electrically there is no problem, but 2.5mm² will probably be physically too big for the terminals on the light.

 

[cwhaley]

Thanks for getting back with that both; that's useful advice I appreciate it. My main concern was any potential electrical issues from using 2.5mm from the switch to the light. The location of the new light will be outdoors, so on your advice I will nip by the electrical suppliers on the way home from work and get cable suitable for external use. The owner is friendly enough to let you simply reel off what you need and he'll make a price up.

With regards to the existing circuit/sockets in the house, the house itself was only re-wired in 2008 and everything is earthed and protected by an RCD. None of the sockets in the kitchen are spurs themselves either. There is a spur taken from one of the kitchen sockets, but this simply goes to a singular socket in the out-house to power the washing machine. It is earthed and the cable is inside metal conduit.

 

[winston1]

It is feasible to use 0.75mm or 0.5mm flex, a 1am fuse would be ample for the load.

The fuse is to protect the cable, not the load. 1 amp fuses are not common, so a 3 amp would be OK if 1 amp is not available.

 

[bernardgreen]

The fuse is to protect the cable, not the load.

But in the absence of a fuse in the appliance common sense suggests that a low current fuse that limits the heat produced when the appliance goes faulty and melts down is better than a higher current fuse that allows more heat to be generated.

 

[cwhaley]

I would (from my limited, ameteur skill level) agree with that. My logic dictates that by limiting the amount of current permissible to pass through the wire to the light at 3A, I would be averting the danger of any melting wire or fire should something go wrong.

It is only an LED light, but I did want to be safe.

 

[winston1]

But in the absence of a fuse in the appliance common sense suggests that a low current fuse that limits the heat produced when the appliance goes faulty and melts down is better than a higher current fuse that allows more heat to be generated.

I don't think we know that there is no fuse or protection in the appliance. It is a light, designed to go on a lighting circuit. Such circuits are usually protected at 6 amps but can be up to 16 amps (very common in other parts of the EU where FCUs are not even available or compliant.)

 

[winston1]

My logic dictates that by limiting the amount of current permissible to pass through the wire to the light at 3A, I would be averting the danger of any melting wire or fire should something go wrong.

Well a 3 amp fuse won't do that. A 3 amp fuse won't magically blow at 3.0000000000001 amps.

 

[cwhaley]

Would it not? My aim is to fit a lower-rated fuse so that any surge in current would melt the fuse first and cut the circuit, putting my mind at rest.

I am only a DIY'er, but I've always tried to be safe. I understand about excessive load on circuits, I always route cables in conduits in the wall and any new circuit or spur has an appropriate fuse.

Thanks all for the tips and knowledge.

 

[Taylortwocities]

Have a read of this
http://www.pat-testing-training.net/articles/fuse-operation-characteristics.php

You'll see that a plug fuse will never pop at it's rated current. You'd need 1.6 times the rated amount for it to eventually blow.
In the graph you'll see that even with a load of 6A, a 3A fuse could take around 10minutes to go pop.

 

[cwhaley]

Thank you for that; I'll have a read of what the site says.

As of yet I've not installed anything as I had questions over the wiring and type of fuse to be used; so appreciate the responses.

I've got plenty of 1A fuses in - shall I just put one of those in for safety?

 

[ban-all-sheds]

I know how to do this

 

[cwhaley]

Hehe... nice quote but a little misleading without the rest of the sentence, especially the bit where I state not knowing which cable to use.

In fairness I did say I'll use a 3A fuse which is something Winston1 also said "would be okay". I could still do this now with my original knowledge and the help from PrenticeBoyOfDerry and taylortwocities on the wiring and it be a fused spur, with appropriate cabling, installed cleanly and neatly onto the wall.

It seems the discussion has branched out a little more.

 

[PrenticeBoyofDerry]

with appropriate cabling, installed cleanly and neatly onto the wall.

The cable still needs to be installed in the prescribed safe zones, if buried less than 50mm in wall. Generally because of other building regulations, cable in solid walls is rarely allowed to be chased greater than 50mm.
So you need to use the safe zones, unless mechanical protections or specialised cable is used.

https://www.diynot.com/wiki/Electrics:walls