Joining cable in bathroom

[dabaldie]

ok. (many in this forum may already know) , i'm fitting a whirlpoolbath where the over bath shower used to be.. I now have seperate cubicle on other side of room
now the cabling for the old shower (10.5kw) is still in place. It's 6mm T+E (i know well under rated for the shower)
The cable runs from a seperate RCD unit via a 45A FCU outside the bathroom under the boards and comes up under the old bath.
Unfortunately the new bath pump is at the other end.
Can i join the cable safely under the bath with a junction box? and does it have to be something special to comply with IEE regs cos its in a bathroom?
also the pump only needs 5A max so i've been told to use a 10A MCB with 1.5mm cable. Can i safely connect the 1.5mm to the 6mm in the junction box or must it be the same size as the main (oversized) run?
I dont want to rip out the old 6mm cable cos its so neatly hidden under the boards and in the wall and would involve lifting all the ply and lino.
incidently i know the old wiring did over heat a while back cos it had melted the insulation where it joined the old (now replaced anyway) FCU. Is this wiring still safe?... the only reason it over heated actually was from a poor connection in the old FCU..
why do i get the feeling you are all gonna say the old wiring is dangerous and must be ripped out? is it likely that the only point of failure was at the FCU?

(ignore the term FCU i meant cooker type switch...long day)

 

[plugwash]

erm there is no such thing as a 45A FCU what do you mean when you say this?

also what exactly do you mean by a seperate rcd unit? are we talking a shower CU or a RCD wired off a breaker in the existing CU or what?

can you post some pictures of the existing setup?

finally there is nothing wrong with keeping the existing 6mm but doing your new wiring in a size appropriate to the load as long as its all protected by a suitable breaker.

 

[bathjobby]

Glad I'm not going to buy this house. Never thought I'd say it, but, bigining to see some point in part P.....

 

[dabaldie]

ok.
in detail.

from a 50A MCB in the main consumer unit i have run a 10mm cable to a shower consumer unit with a spare slot. In one slot is a 50A MCB which runs to the new shower. In the other slot will be the cable for the whirlpool bath. this will be protected by a 10A MCB. Within the shower consumer unit is a 30ms RCD.
the bath requires 5A at startup
the shower is a 10.8kw so i know that that requires a 50A MCB

the cable to the shower is 10mm T+E
the cable to the bath will be the old 6mm T+E

the cable to the shower connects to a switch outside the bathroom (cooker type thing... labeled shower)

the cable to the bath will connect to a switch on the other wall outside the bathroom).. that is also a cooker type thing... (my mistake i called it a FCU... its not sorry) but is rated at 45A.

i want to run the existing cable (6mm) from the switch to connect to the bath.. but it's too short. what i need to know is.... can i joint this cable (safely within the bathroom and in compliance with IEE regs)

i understand the principles of cable sizing, MCBs, RCD etc..
being honest i cant see a problem with the way it's wired up at the moment.. (in fact its the way i've been advised by an electrical engineer)except i'm stuck about the joining of the cable.

PLEASE tell me now if anything seems dangerous?

 

[ban-all-sheds]

In descending order of preference:

1) Replace the cable, or run a new one via another route.

2) Extend the cable using crimps.

3) Extend the cable using a JB.

With 2 & 3 you shouldn't really join a 1.5mm² on just in case someone later sees the 6mm² and tries to use it for something meaty, but that's a fairly picky point.

With 2 & 3, if you're concerned about water ingress you should make the joints inside a suitably IP rated box.

HOWEVER....

incidently i know the old wiring did over heat a while back cos it had melted the insulation where it joined the old (now replaced anyway) FCU. Is this wiring still safe?...

Possibly not. Probably OK, if it was just localised heating from a poor switch connection, but you should inspect as much as you can, and run, or have run, an insulation and R1+R2 test.

 

[felix]

It really would be better to get a new piece of cable from the switch to the bath pump. Is there any chance of using the old 6mm cable to pull a new length in?

I'd also be inclined to replace that old 45 amp switch with a fused one. I know there's no real need because you have a 10 amp breaker in the line but I like to think ahead. If that breaker starts tripping (faulty pump) will somebody else look at the cable in the CU and assume that they can put a 32 amp breaker in there? Or am I just paranoid?

 

[dabaldie]

2) Extend the cable using crimps.

whats that?

and whats a insulation R1+R2 test?

from what i can see of the cable it all looks ok. (not old either)
problem with replacing it is that the cable is chased into the wall from the switch down to the floor and plastered and painted over... maybe i'm being paranoid too.. but is that the area thats most likely to be dodgy too.... (cable loading calcs for within a wall seem much lower)

maybe i'll try to pull the old cable through the chase (whats the chances of it being in conduit.. ) and replace with smaller cable 1.5mm etc

 

[ban-all-sheds]

2) Extend the cable using crimps.

whats that?

http://www.tlc-direct.co.uk/Products/DVDHCR15.html

Note - this is not the same as the cheapo squeez'n'hope tools sold for cars

etc http://www.tlc-direct.co.uk/Main_Index/Cable_Accessories_Index/Crimp_Lugs_and_Tools/index.html

and whats a insulation R1+R2 test?

http://www.tlc-direct.co.uk/Book/8.5.1.htm

http://www.tlc-direct.co.uk/Book/8.4.4.htm

 

[HDRW]

2) Extend the cable using crimps.

whats that?

These: http://www.screwfix.com/app/sfd/cat/pro.jsp;jsessionid=SYSWUJIFUQWB1CJO2C3CJ0Q?id=75317&ts=15101

crimped over the cable-ends using one of these: http://www.screwfix.com/app/sfd/cat/pro.jsp;jsessionid=SYSWUJIFUQWB1CJO2C3CJ0Q?id=18475&ts=15100

and whats a insulation R1+R2 test?

Something that professional sparks (or enthusiastic amateurs!) would have the equipment to test! An insulation test applies a voltage (usually 500V) between the various conductors in the cable to measure the resistance of the insulation. If it's low it means the insulation has been compromised by the overheating (or something else) and is likely to break down and cause a short.

R1+R2 is a measure of the resistance of the conductors (there and back, hence R1+R2) to check that they are properly intact and don't have a high resistance which would cause self-heating of the cable when it's carrying current. These apply to the cabling iteself, and could be done just on your bit of suspect cable.

There's also Earth Loop Impedance which measures the ability of the earthing arrangements to carry a fault current safely - this includes the whole earthing system, not just the cable.

You could do R1+R2 with just a multimeter set to a low ohms range, but the others need special equipment which you wouldn't want to buy (think £hundreds).

from what i can see of the cable it all looks ok. (not old either)

Problem is you may not be able to see some of the damage - you can cut back the dodgy end to find out how far any melting/discolouration goes, and you may be OK, but if there is more heat damage further along you may be storing up a problem for later.

problem with replacing it is that the cable is chased into the wall from the switch down to the floor and plastered and painted over...

That's the old story - preparation is most of the problem!

maybe i'm being paranoid too.. but is that the area thats most likely to be dodgy too.... (cable loading calcs for within a wall seem much lower)

Yes, because the wall insulates the cable so reduces its ability to keep cool. If the overheat was just because of a badly-made connection at one end then you may be OK, but if it was an overload as well then the part in the wall is where it would have suffered most.

maybe i'll try to pull the old cable through the chase (whats the chances of it being in conduit.. ) and replace with smaller cable 1.5mm etc

That would be the best bet, but of course if it's plastered in without a conduit or capping, you're knackered!

Good luck...

Howard

 

[dabaldie]

out comes the cold chisel then...


thanks for the advice and also the info...