Another question about spurs

[ban-all-sheds]

To connect, I should replace the JB with an RCD because one is not elsewhere fitted.

You should.

Try striving to do the best job you can, rather than striving to falsely rationalise yourself into doing a non-compliant poor quality job.

Since I am not inclined to pay £30 for an RCD that will never be called into service (a fixed cable would be on the surface or more than 50mm below and only class 2 devices will ever be plugged in),

1. Your lack of inclination to do things properly means that you should never do any electrical work.
2. You cannot control what other people might do with that socket.
3. It is possible to come into contact with live conductors supplying Class II items.
4. If you are in England or Wales your disinclination to fit an RCD is arguably illegal.

it seems the solution is to replace the JB with a socket or FCU and run an extension lead through. Less than ideal but that seems to be the effect of inflexible rules.

Just do it properly.

 

[ericmark]

Using screwfix prices as likely you will be able to buy for less a RCD FCU costs £25.63 plus socket at £1:10 or you can have a FCU at £1:96 and a RCD Socket at £21.94 so there is just £2.83 difference in price. By time you include either the extra price of cable if using Ali-tube plus one fitted you can add as many more sockets as you want to the RCD FCU supply it really does not make sense not to use a RCD FCU.

It also means the 3 meter rule does not apply and your unlikely to exceed the loop impedance of 2.42 ohms for a 13A fuse but quite likely to exceed the 1.44 ohms for a B32 MCB even worse the 1.15 ohms for a 30A BS 1361 fuse or 0.85 for re-wire-able type if that old.

I am sure the price of a RCD FCU is peanuts compared with price of hiring a loop impedance tester and I would never rate my loved ones live that low as not to use a RCD.

Can you really say a live is not worth £25?

 

[chapeau]

(Someone is now going to quote obscure requirements on extensions now, I expect.)

Not me...

You don't need to worry about sticking to the letter of the regulations anyway, you aren't an electrician filling out a form for the council, you just have to do it safe, as that is what the law says.

You haven't fully explained (or I haven't picked it up) what this junction box is connected to?

The thing about spurs is that you need to make sure that the current going down the spur isn't so high that it starts to overheat the cable. Basicially, and this is a good rule of thumb, that means two 13Amp plugs can at max be connected. So that means, in theory at least, the cable will never carry more than 26 amps. In theory, and as long as you don't wrap the cable in insulation for several metres, a 2.5mm2 cable can take 26amps without the regulations telling it that it cannot.

So that is why you need to put a FCU on a spur if it supplies more than one double socket.

So is this junction box...

a) on a 2.5mm2 ring main?
b) on a spur from a 2.5mm2 ring main?

The 3m regulation quoted above only applies (in practice) if the cable diameter changes, so as long as you continue in 2.5mm then you are ok anyway. Otherwise you would have FCUs on your lighting circuit..... (and there are some on here would would misread the regulation and do exactly that)

So is all you want to do put a cable from a junction box on a wall, through the wall, to a socket on the other side of the wall?

Well..

If a) then as long as you use 2.5mm2 cable to spur though the wall then just do it. I wouldn't bother with an RCD, the new cable is buried all the way in the wall.

If b) then you need to find out what that spur is doing, and if it already has sockets along the length, you need to go a point of the spur where it is going to supply sockets and put an FCU on it.

Then proceed as a)

If you want to RCD the circuit then go back to the origin to do so.
If the wiring is dodgy or hasn't been properly tested in a while might be a good idea to do so.

But I wouldn't be too anal about this if it's as simple as you suggest.

Anyway, that's one way of doing it, use your common sense and don't forget to sleeve the earth!!! Otherwise you will burn the house down and electrocute the next door neighbours

Anybody who selectively quotes will not get a response

(neither will any body who posts after me who is on my ignore list as I cannot see what nonsense you are posting anyway)

 

[ban-all-sheds]

Otherwise you would have FCUs on your lighting circuit.....

Why would you?

I wouldn't bother with an RCD

Oh good - Mr "I'm not interested in excellence I just want to shave costs and do a substandard job and would like someone to tell me that's OK" OP has found someone to tell him it's OK.

So now he can go away. Will you join him, please?

If you want to RCD the circuit then go back to the origin to do so.
If the wiring is dodgy or hasn't been properly tested in a while might be a good idea to do so.

Make your mind up.

Anybody who selectively quotes will not get a response

Please try reading Rule 9.

 

[david3456]

Can you really say a live is not worth £25?

It always comes down to emotion doesn't it? This is what is so irritating about H&S these days.

What is the statistical probability a life threatening fault occuring before the RCD reaches the end of its life?

 

[david3456]

(Someone is now going to quote obscure requirements on extensions now, I expect.)

Not me...

You don't need to worry about sticking to the letter of the regulations anyway, you aren't an electrician filling out a form for the council, you just have to do it safe, as that is what the law says.

A refreshing attitude on this forum. Don't concern about my knowledge of cable capacities, circuits or wiring skills. The issue is one of understanding the regulations and whether "must" or "should" applies on certain matters. If something does not obey a "must" is it automatically deemed to be unsafe even if it is not faulty?

The JB is inside a built in cupboard (ie, it is part of the building, not fitted) and is a junction on the ring. The spur goes through the side of the cupboard to a socket in an alcove. I want to take another cable off this junction to the next bedroom. It is not practical to loop off the existing socket so no possible conflict with regs here. By wiring direct to the junction (ie, a star), cables cannot be loaded beyond capacity (*) but, if the JB was not changed, the screw terminals would hold 4 conductors. Changing the JB for a FCU means that the terminals continue to hold no more than 3 conductors.

(*) It comes across from some circles that there is this idea that people have a big hoard of 3kW heaters waiting to be plugged in to their new sockets. I suppose it is possible to plug 6kW in a double but how likely? Isn't the traditional idea of "overloading" sockets more to do with builders being stingy in the first place?

 

[chapeau]

Well it's a good idea to understand the regulations if you are going to work on your electrics but the pass mark for the 17th edition exam is probably around 60%, and it's an open book exam. so you don't need to understand them to pass....

A far better book for domestic work is the On Site Guide.

The regulations don't specifically prohibit what you plan to do. They are wooly on this sort of thing, you shouldn't overload the cable, the ring has to be balanced etc etc. The On Site Guide (and the regs book itself) gives advice on acceptable ways to satisfy the regs. What you plan to do isn't in the list of acceptable ways to satisfy the regs, but the examples given are not exhaustive.

If you stuff four cables into a junction box then it's probably safe if the manufacturer says it can take four cables. If an electrician opens that JB up (when you want to flog your house and a check is made for example) there will be a lot of tutting and he will be looking for other things he doesn't like. It will go down on a piece of paper as not ideal, some might even say it needs fixing immediately.

If somebody gets hurt and an electrician says what you did is wrong then the magistrate will think you are guilty even if the electrician cannot prove what you did is wrong.

Some electricians would stick another junction box on the wall, connect the ring through the other junction box, and spur off that.

Most decent electricians would try to extend the ring. Doesn't make it safer but it's what they would try to do. I would try to do the same.

But from an safety point of view, cannot see why what you plan to do is unsafe, if the junction box can take four 2.5mm cables. You could always put an FCU there and connect the ring to the supply, the two spurs to the load. This would protect against overloading the spurs 100%. Again, if the manufacturer says it's OK. People will say it is 'rough'

 

[david3456]

The regulations don't specifically prohibit what you plan to do. They are wooly on this sort of thing

There is a lot that seems to be in the eye of the beholder.

Some electricians would stick another junction box on the wall, connect the ring through the other junction box, and spur off that.

In a way, an extra junction is more to go wrong. I shall just replace the JB with a FCU. (I don't keep a hoard 3kW heaters.)

 

[ebee]

Am I misunderstanding some posts on here or are there some who think that an unfused spur on a ring final must be limited to 3 metres?

I`m talking 2.5/1.5 ring with same size for a single spur (single or twin socket) whether at origin or at any other point on the ring.

 

[david3456]

[*] It is possible to come into contact with live conductors supplying Class II items.

Of course it's possible. But how do you persuade 30mA to flow to earth through wood, masonry and soft furnishings?

 

[EFLImpudence]

how do you persuade 30mA to flow to earth through wood, masonry and soft furnishings?

Touch the live conductor.

 

[david3456]

how do you persuade 30mA to flow to earth through wood, masonry and soft furnishings?

Touch the live conductor.

OK, so the body is now at that potential. Then what?

 

[RF Lighting]

Try it and find out

 

[securespark]

Hook up a web cam first so we can watch!

I am not seriously suggesting he or anyone else touch a bare live conductor.

 

[david3456]

Try it and find out

I have. Ohms law wasn't broken.