Garage lights + sockets

[Ljoxaa]

Can someone please have a look and let me know if this will work please? If not then any suggestions? Thank you (1.5mm connected to the light in the garage)

 

[ericmark]

This would be better, the circuit you show could be overloaded.

 

[ebee]

If I understand correctly you have a 2.5 ring final in the house, connected to a 2.5 spur for the garage and that in turn feeds a 2.5 ring in the garage.
As Eric has shown that spur should be fused down using a switched/unswitched fused connection unit to prevent house ring overload.
Then the garage ring will be OK but 2.5 cable on that ring is a bit OTT, not a problem in itself and all the better for future changes of "fusing" figurations.
Is it feasible to change the that 2.5 spur to a 2.5 ring of its own for the garage or, alternatively to extend the house ring to include the garage ring? Of course ring length of cable (R1, R2 & Rn) might become an issue.
If it is deemed OK to do that by adding another radial 2.5 near to the existing one then it might be worthwhile and could bring the advantages (and disadvantages) of rings into the reckoning.
Alternatively, making a joint from the garage radial (inside the house) to a spare way in the consumer unit and say 16 or 20 amp RCBO or MCB (if compliant , ref RCD (RCCB/RCBO) protection.
It all depends on the difficulty or ease of having 2 x 2.5 cables from house to garage.

 

[SUNRAY]

 

[ericmark]

The loop impedance to trip within permitted time should be less than 1.38Ω and to be within volt drop approx no more than 0.63Ω over the incoming line - neutral reading. So line - earth better than 1.38Ω and line - neutral better than 0.98Ω better means less than.

By inquiry is valid, so you can get the original installation certificate and simply add on the impedance of the extra circuit. A ring final can have up to 106 meters of cable, and it is unlikely that is exceeded, and to be frank even if the permitted 5% for sockets is exceeded it is unlikely to cause a problem, same with the 3% volt drop allowed for lighting.

Two work, and to comply with regulations, is not the same. And with RCD protection, 200Ω is considered the limit, after that it is seen as being unstable. And some of the rules are rather antiquated, the 3% volt drop limit for lights was because a wire wound ballast on a fluorescent light was very voltage dependent, 30 volts can make the difference between using twice the rated current and not striking, and we used to have auto switching auto transformers to reduce the power used, today they are seen as snake oil.

However, as an electrician without getting my meters out of their box, I can look at an installation and have a reasonably good idea as to how close to the wind I am sailing. Not quite so easy for the DIY guy, so the loop impedance permitted with a 13 amp fuse, is around 2.42Ω, which is a lot higher than the 1.38Ω (was 1.44Ω) allowed for a B32 MCB/RCBO. So assuming the original installation was compliant, then the 13 amp FCU as I showed is also likely compliant, but to extend the ring final, you either need a loop impedance meter to measure, or a low ohm meter to measure, or the readings from the installation certificate before you started to alter it.

With a 2 up 2 down property unlikely to be a problem, with a 6-bedroom house, then likely you need the readings.