Joining flex to t&e

[stunlawless]

Morning everyone,

Need to join a bit of flex from a mirror heater to t&e. The flex from the heater isn't long enough to draw to anywhere accessible, so I'm faced with making a joint which will be inaccessible (mirror glued to wall, tiled surround).

Is it ok to use crimps with flex ? If not, any suggestions ?

Thanks, David

 

[CortinaV8]

Flex Outlet plate?

I'm sure someone will be along to point out the finer part of the regulations regarding electrics in the bathroom.

 

[ban-all-sheds]

Or just a flex outlet plate if the mirror is switched on the light circuit and doesn't need an FCU...

 

[CortinaV8]

What a let down

 

[stunlawless]

No need for a flex outlet - the heater flex comes out of the back of the mirror, so I'd need to bring it out of the wall to get back into the flex outlet...

I'd thought about using a FCU or switch mounted on the wall high up to connect the cable & flex (heater is switched via light so doesn't need another switch) but I don't really want anything visible, hence my thoughts turned to crimps.

What do you think about using crimps with flex ? maybe if I put a bootlace ferrule over the flex first (assuming it fits in a red crimp) ?

Thanks, David

 

[Chri5]

So what happens when the heater goes pop or you decide to change the mirror.

The reason everyone is suggestion a accessable point is for that reason, and also to give an isolation point with low amp fuse protection.

As an absolute minimum take the cable in to a back box and have a blanking plate for access, better still a switched fuse spur.

 

[TheOriginalTonkaToy]

Just use an FCU then.

 

[ban-all-sheds]

Or run the mirror cable up through conduit to the loft/floor space above, than if it needs replacing it can be pulled out.

 

[stunlawless]

"what if the heater or mirror needs replacing ?" well, then the wall comes down...mirror will be glued to ply false wall (hides all the pipework) so its there for ever. Guess I could cut around it with a jigsaw if raked out the grout. This aspect was considered in the design, and the client (SWMBO !) agreed.

I guess raking out & cutting with a jigsaw doesn't count as accessible ?

More seriously, isolation & fusing is taken care with a sw FCU in the airing cupboard. If there's a problem with heater, then we accept that it will disconnected (at the FCU) and can't be replaced. As the flex is permanently fixed to the heater, then it can't be replaced, so I don't feel a pressing need to make the junction between the flex & T&E accessible, hence my quest for a maintainance free junction.

I take your points though, and I think the flex is long enough to be drawn into the attic, so I will put in a jb there (with bootlace ferrules over the flex !).

As an academic point of interest, is it normally acceptable to use crimps with fine stranded flex ? I know it's frowned upon to put flex in a jb type screwed terminal, which is why I put a bootlace ferrule on beforehand.

Can't find anything in red book or OSG to back this up. I just remember being told this - could be at college, on this forum or someone else.

Thanks, David

 

[electronicsuk]

As an academic point of interest, is it normally acceptable to use crimps with fine stranded flex ? I know it's frowned upon to put flex in a jb type screwed terminal, which is why I put a bootlace ferrule on beforehand.

I've never seen a regulation that says it shouldn't be done, nor had any problems using crimps with stranded wire. As long as the crimp is the appropriate size for the conductor, it should compress enough to provide a secure connection. For fixed installation, you wont be using any less than 1mmsq conductors anyway.

 

[aptsys]

Last time we had a visit from Tyco, the rep said that if anything, the connection on the crimps will be better with stranded cables

 

[ban-all-sheds]

As an academic point of interest, is it normally acceptable to use crimps with fine stranded flex ? I know it's frowned upon to put flex in a jb type screwed terminal, which is why I put a bootlace ferrule on beforehand.

Would that be a crimped ferrule?

Can't find anything in red book or OSG to back this up.

526.8.1?

 

[stunlawless]

Ah, obviously I didn't look hard enough...

528.6.1 "suitable terminals shall be used or the conductor ends shall be suitably treated"

Not sure what a "suitable terminal" for fine stranded wire is (one where the screw doesn't bear directly on the wire like on mcb's ?), but I'd argue that a correctly fitted bootlace ferrule is "suitably treated". Yes it's crimped, but the crimp is more like an uninsulated lug, in that it is both compressed and indented at three or four points. The result is that the wire fills the crimp completely, and the indents ensure it can never be withdrawn.

528.6.2 goes on to expressly prohibit tinning of fine wire conductors in screw terminals. Presumably this is to guard against fatigue failures at the end ofthe tinning due to thermal cycling ?

A crimp for an insulated terminal just compresses the barrel, and in my experience, I've never had a bad crimp on a bootlace ferrule, but occasional bad ones on insulated crimps.