Fused spur to Garage

[caveman2]

I'm helping a relation tidy up the wiring arrangement in his garage and improve it's safety. Along with many similar installations in the area, the power feed to attached garage is via a 4mm spur off a socket outlet in his lounge. At the moment I don't know if I could just drill another hole from another socket and just extend the ring. I say that because I know his 2 rings are not just upstairs and downstairs but either N & S or E &W and maybe pose a problem doing that.
I also believe the best way on existing arrangement would have been to have a fused spur introduced into the ring before entering the garage, but as he has solid floors, I don't thing there is the slack to change it.
Assuming I have to stay with the existing spur off the rear of the socket. Introducing a fused spur immediately, what else can I do to allow him to run sockets and lighting which would also allow a tumble drier too.

 

[EFLImpudence]

If it is 4mm² then just extend the spur. You don't need any FCUs nor to extend the ring.

What has been done is the best way.

 

[ericmark]

I used LAP grid system from Screwfix, a non fused spur was made into a fused spur so I could add more sockets, and it still had a socket at the point where the spur first socket was. But if you read the appendix 12 I think it refers to 2 kW limit to non portable appliances from a ring final, so you have to decide if there may be an overload problem.

Your writing out the minor works certificate so you have to decide if you want your name on the job.

P.S. careful on cable size, I saw a whole estate with 2.5 mm² twin and earth to a junction box, and then 4 mm² SWA under ground to garage, why not a clue, but do check.

 

[caveman2]

If it is 4mm² then just extend the spur. You don't need any FCUs nor to extend the ring.

What has been done is the best way.

Thanks for the reply. To clarify (bearing in mind I said the cable was directly of the back of the socket) that the spur is OK with say 4 sockets (one providing power to a tumble drier) because it is already 4mm cabled. If yes, would FSU be an insurance or totally unnecessary. Where would you tap off the run for a lighting feed.

 

[EFLImpudence]

Yes, the 4mm² can carry the 32A of the ring circuit without down-fusing. You have to, of course, use 4mm² for the rest of the spur.
An FCU would be pointless.

A smaller lighting cable can be branched from any point using an FCU (possibly as a switch if in the right place).

 

[caveman2]

An FCU would be pointless.

A smaller lighting cable can be branched from any point using an FCU (possibly as a switch if in the right place).

Can you expand on "in the right place"

 

[winston1]

Can you expand on "in the right place"

How about by the entry/exit door.

 

[SUNRAY]

P.S. careful on cable size, I saw a whole estate with 2.5 mm² twin and earth to a junction box, and then 4 mm² SWA under ground to garage, why not a clue, but do check.

This is a very common method these days. I don't know if it's the reason but I assume it'sto allow for volt drop and rather than calculate each one and have 2 drums of cable in stock they stickwith 4mm²

 

[caveman2]

If I can impose on your knowledge once more, can you oblige. If as I understand you can have a 4mm. spur off a socket from the house ring serve the garage. Because of the regulations you can safely draw an accumulated 15A because the rating of the cable is 32A. Why then if the rating of 2.5mm. is 20A is it necessary to install a FSU at 13A before any outlets and then not then be able to draw the same 15A

 

[EFLImpudence]

If as I understand you can have a 4mm. spur off a socket from the house ring serve the garage.

Yes, a 4mm² cable spur from the socket ring circuit will allow you to draw 32A without the need for an FCU in the house.

Because of the regulations you can safely draw an accumulated 15A because the rating of the cable is 32A.

The regulations do not say that.

Why then if the rating of 2.5mm. is 20A

2.5mm² T&E - clipped to surface or buried in masonry - has a rating of 27A.

[Why] is it necessary to install a FSU at 13A before any outlets and then not then be able to draw the same 15A

Because 13A is the largest rated fuse that is made for FCUs.
That is the usual way of ensuring that no more than the 27A is drawn through the 2.5mm² cable - by limiting it to 13A. You could install a small enclosure with a 25A MCB in it instead of the FCU.

As you have discovered - using cable which can cope with the 32A is far easier.

You can still use an FCU in the garage for the lighting.


Your electrician may not be comfortable with this as most electricians do what people usually do because that is what people usually do - it doesn't involve thinking.

 

[caveman2]

Thanks again for the very informative explanation EFLI. Could you give me an example of what you call "a small enclosure with a 25A MCB in it" - and I will leave you alone.

 

[EFLImpudence]

I can't seem to find any at the moment but they are out there.

Like this on Amazon - but just one module wide:

 

[caveman2]

Thanks again. If say I installed an MCB for both power and lighting (seeing as they're cheap) would you fit single pole MCB's and connect both N & E to block connector within the enclosure or double pole MCB's and just E on a block connector. I am not sure whether it is acceptable to connect conductors to connector blocks although they are seen in light switches a lot.

 

[caveman2]

Sorry for dragging this thread on, but. What I am asking above is if you introduce an MCB in an enclosure before the first socket then since you only wire the L to the MCB. If you then connect N & E onto block connector to then extend T&E to first socket. Does the block connector not add resistance and in turn reduce current rating of circuit.

 

[EFLImpudence]

Thanks again. If say I installed an MCB for both power and lighting (seeing as they're cheap) would you fit single pole MCB's and connect both N & E to block connector within the enclosure or double pole MCB's and just E on a block connector. I am not sure whether it is acceptable to connect conductors to connector blocks although they are seen in light switches a lot.

It is pointless and not necessary.

I only mentioned it because you asked why a 27A cable is protected by a 13A fuse.

If it is 4mm² then just extend the spur. You don't need any FCUs nor to extend the ring.

What has been done is the best way.