Shower cable

[wingnot71]

Hi all, replacing an old shower and I need to extend the cable slightly. The cable(10mm) runs through the loft void and down a stud wall to the isolaing switch. Can I add a junction box in the loft and run the new length down from there or do I have to run it back to the isolating switch as to do this the cost of cable would double. If I can use a junction box would a 30amp box be ok, The new shower is 9.5kw.
Many thanks...

 

[jjjinx]

wingnot, if you do ohms law you'll see that 9.5kw shower would produce up to 39.6amps this would mean that a 30amp jb would not do.

Look more towards a henly block or something suitable for 45 amps and put it in a box suitable for it, don't forget any jb must be kept inspectable.

Cable that size inevitabley comes loose through movement so be very careful to re-re-re-re tighten the cable. its better to replace but not aways profitable.

 

[pennywise]

Or use one of these bad boys.

60 Amp 3 Terminal Junction Box - White

 

[wingnot71]

Thanks for the advice. I have just noticed that the original cable is 16mm will this cause me any problems and can a 10mm be run from the junction box down to the shower?

 

[jjjinx]

16mm? thats wierd, why would someone put in a 16 for a shower, I take it its singles?

you should check that out find out if its doing something else. I would say you could connect to it but i've not done it before, large cables don't clamp well and you should check out current carrying capacities of em.

 

[pennywise]

Is the 16mm run under rock wool for a distance exceeding 400mm or a long distance from the CU they may have de-rated the cable and so had to put in the larger cable. Still trace it as far as possible just to make sure it isn't doing anything else like an immersion heater etc.

 

[wingnot71]

No the cable is doing nothing else. Theres about 10m of cable between the cu and the shower running under floorboards up a stud wall and across a loft space for about 2m before droping down into the bathroom.

 

[Des 56]

I dont think I have ever come across a 16mm on a shower in a domestic

If you are jointing this cable,I would expect the extension of that circuit to be the same size
The current carrying capacity worked out for the circuit is for the whole of the circuit,using a smaller piece on the end would not be satisfactory in my opinion (are you absolutely sure its 16mm and not 10mm with thick insulation )

If I was jointing it,I would use a cooker type pattress with cord grips,screw it to a beam and crimp the wires
Ready made junction boxes for 10mm and above are usually crap compared with your own made up variety

 

[Jason Smith]

City Electrical factors have some line connectors. Thay are brilliant, black individual connectors with an orange cap that goes over the top when done. thay even clip together, and go up to 60 amp. will easily fit into a adaptor box. About a quid each. They are screw terminals so have to be accesible, in a loft they would be. When you screw the first one in you get the impression they are never gonna come undone, ac current or not ! A bit of a relief for 16 mil and lots of KWS.

 

[DanSwift1988]

Sorry to dig up an old thread but is there anything in the regs that says not to extend/joint a 10mm cable? replacement not always practical.

 

[Flanders]

No problem as long as use use the correct ratting of joint Not sure if wagos go that large, may need to use a din rail set up, the joint will have to be accessible though for future inspection unless its a sealed joint

 

[davesparks]

You can joint any size cable if in your professional judgement it is acceptable to do so, and if the joint is suitable.

Personally I'd be looking for a crimped joint, but other methods are available.

 

[jjjinx]

Crimp em in a PVC 2G pattress with blank plate, in one side out the other. Cable tie both ends just before they go out of the box & clip outside the pattress = permanent connection. Or you can get brown elongated octagon shaped junction boxes which have cable clamps & double screw terminals. I think they're either from WF Senate or TCL.

I prefer permanent connections on hi ampage cables

 

[davesparks]

That's not a high current cable, blimey it's only a bit of 10mm.

 

[jjjinx]

I'm talking about a domestic installation, so in that environment it is.