Joining 1.5mm cable to 2.5mm?

[SJRSJR]

So in tacking the job in my other post, I’m wondering if I could potentially solve another problem.

The garden shed, garage and outdoor light no longer work and the faulty cable was taken out of the CU. New 1.5mm armoured cable has already been run from the shed to the house but to get it to the CU, chipboard flooring would need to come up, and that hasn’t progressed.

However, where the armoured cable comes into the house is a 32A ring which is only for the sockets of one bedroom.

I’m wondering if it would be possible to break into the 2.5mm ring and join the 1.5mm cable to it?

There is an FCU where the armoured cable enters the shed, which then runs on to the shed light, outside light and garage. There’s also a socket in the garage, which is never used. The CU is RCD protected.

Not sure if a) it’s good practice or b) I’d need an electrician to do it. Thought I’d ask as it would avoid the hassle of getting a chipboard floor up.
Thanks.

 

[ETAF]

i'm no expert here ,
how far away is the shed from the house - total run of cable -
this is running both the shed and your garage
any reason you choose to lay 1.5mm cable ,
what are you planning to run in the shed - / garage
as i say no expert , so i'm sure a expert will be along here soon

did you lay the cable or an electrician

 

[ericmark]

One would normally have one FCU at the origin with 13 amp fuse, and one in the shed switched with 3 amp fuse for the lights. It does however depend on how far around the ring final, from the centre no problem, but getting near either end, and it could with other things on the ring final cause an overload.

 

[Murdochcat]

You have to fuse down for the SWA ...........

 

[SJRSJR]

Run from the house 3m. From shed to garage and an outside light another 4m.

Electrician was fine with me running the cable, there’s a lot going on and he comes in when things become certifiable. 1.5 mm was deemed okay because, if I recall correctly, it had a higher capacity that would exceed the potential load. But that was when it was to go back to the CU.

The break in point would be about 7m from the end of a 22m ring.

But if it needs to be switched to 2.5mm so be it.

 

[EFLImpudence]

Run from the house 3m. From shed to garage and an outside light another 4m.

Ok.

Electrician was fine with me running the cable, there’s a lot going on and he comes in when things become certifiable. 1.5 mm was deemed okay because, if I recall correctly, it had a higher capacity that would exceed the potential load. But that was when it was to go back to the CU.

Well that depends how much load you wanted.

The break in point would be about 7m from the end of a 22m ring.

Doesn't really matter with 13A fuse limiting the load.

But if it needs to be switched to 2.5mm so be it.

That would make no difference and could be worse with more load.

 

[SJRSJR]

Thanks for the replies.

Well that depends how much load you wanted.

The load will be three low voltage lights plus the socket in the garage. It doesn't have anything plugged in there permanently, a pressure washer is the the heaviest load that might get plugged in. If that's too much, it could just as easily run from the house.

So is the existing 13A FCU in the shed (which is before all the outlets) the only one needed? I would be really pleased if I didn't have to break up that chipboard!

 

[EFLImpudence]

The load will be three low voltage lights plus the socket in the garage. It doesn't have anything plugged in there permanently, a pressure washer is the the heaviest load that might get plugged in. If that's too much, it could just as easily run from the house.

No, that's fine.

So is the existing 13A FCU in the shed (which is before all the outlets) the only one needed? I would be really pleased if I didn't have to break up that chipboard!

If you are sure it is before all the outlets then that is a bit unusual.

Normally, which you could do, is have a 13A FCU in the house where it joins the socket circuit - a switch is desirable anyway to isolate the outside circuit.
Then that will cover the socket in the garage where you would also have a 3A FCU for the lights - not really necessary but the UK likes it that way.

 

[SJRSJR]

As far as I know the original cable came direct from the CU, would that make a difference?

How much difference does it make having the FCU in the house rather than in the shed? If you wanted to isolate or work on any of the sockets or switches you would just switch off the FCU. Anything before would have to be switched off at the CU, but I’d rather that than start chasing out plaster in a bedroom cupboard which isn’t an obvious place to control the shed etc.

I will have a look to see if there’s a separate FCU for the lights - with no power and rubbish weather I’ve not yet had a proper rummage. Thanks

 

[Murdochcat]

Having a FCU at the house end is best practice because it means you can isolate the supply to the shed AND the shed easily.

 

[SJRSJR]

Thanks. I’m beginning to think it’s a job for the electrician as I’m not clear on how I would deal with earthing the armour.

One end would terminate in an FCU on the T&G ceiling of the shed (the previous owner called it a summerhouse), the other end would join to a junction box inside under the floor.