Shower electric feed, and junction box

[garethg]

Ok, my bad definitely for somehow doing the sums and ending up around a quarter of the value I should have had. I don't know how.

I am reasonably competent with electrics, DIY etc. (although those of you reading this will probably not agree with this, I was being stupid today). I do not want to touch the RCD box/main breakout box. (plug in/plug out fuse/RCD that is all). There is no isolator between the mains supply and this box for a start.

The situation is as follows. I replaced the shower in the bathroom with a slightly lower powered one, 10.5 > 9.5 KW. That went OK.
I have later on changed the radiator and changed it to a towel rail with an electric element. The element is 300W.

I came to the point where I want to wire this in. The previous situation was: The wire runs up the outside of the bathroom from the RCD box, to the loft, to the double-pole isolator, ceiling mounted well away from the (neon+physical sign), then to the shower through the loft/wall. The RCD was rated at 32A (this was where I should have realised what was wrong).

So I thought, as the two items were in the bathroom, they could sit on the same circuit (the original ciruit would have enough lee-way for a start). The wire for the towel rail could be run, uphill through the wall, isolating any switches/joins to be outside of the bathroom/wetzone. The RCD was 32A, so I could use a 32A junction box, and take a feed to the wall, fuse plate this on a pattress box, and through to the towel rail.

I turned off the RCD, and cut the cable. It is at this point, that I realised, this is not 6mm/32A cable.

The run from the RCD to the isolator is somewhere between 5-8m (That is measured horizontal/vertical, so the difference would be the pythagoras blah-de-blah). It is more that 5m, hence the 10mm cable.

So my question is

A) do you think I can suitably use a 60A junction box to re-join this cable? I would move the join to under the floor (between ground and 1st), It would be around 3.5M from RCD, junction/join then ~3.5M to isolator.
The junction can be nicely fitted to the floor joist quite close to where the cable currently runs. The downside to this, it is around 30cm from where a hot water pipe for the central heating runs. If I can situate further away from this pipe does it make it more suitable (even if it means a longer cable run, the pipes do run close to the cable to start with).

B) If A is acceptable, is the heated rail acceptable? Or should I hard wire this (with the fuse plate) to the ring mains? This doesn't sound good to me, however, I don't like the idea of a plug/socket.

Thanks in advance. (just as well I have the bath/hot water working now!)

 

[holmslaw]

..

 

[garethg]

Hey this is one for rockenroll they speak the same lingo.

Can't decide whether that is good or not....

 

[electronicsuk]

You should not run an electrically heated towel rail from the same circuit as an electrically heated shower. Mount a Fused Connection Unit somewhere outside the bathroom and then feed via a spur from a nearby socket.

Take a 3-core flex from the load side of the FCU and bring it out into the bathroom through a flex outlet plate and straight into the towel rail, and be sure to take the zones into account.

EDIT: Remember to bond the earths for the towel rail, electric shower, batrhoom lighting and any other electrical appliances in the bathroom if you're working to 16th Ed.

 

[garethg]

Thanks, finding a socket will be difficult, there are none within 2m of the wall that the radiator is on (the other side), and all of these traverse the hall and doors. I shall think on this further as to where I could possibly position one.

My immediate concern though, is whether it would be considered safe enough to use the 60A junction to re-connect the 10mm cables. It is outside of the bathroom, and would be positioned under the floor.

 

[electronicsuk]

My immediate concern though, is whether it would be considered safe enough to use the 60A junction to re-connect the 10mm cables. It is outside of the bathroom, and would be positioned under the floor.

Mounting a JB under the floor with screw connections wouldn't really be classed as being in an 'accessible' location, therefore this is not the way to go if you want to comply with the regulations.

You would need to bring the cable into an adaptable box and then crimp the connections with a proper ratchet crimp tool if you want to do the job properly.

To answer your actual question, in my personal opinion (and please remember this is my opinion only, not my advice) it would not be unsafe to use a 60A screw terminal JB under the floor. It isn't good working practice but unaccessible junction boxes seem all too common in the real world, you wouldn't be the first or the last to do it.

 

[garethg]

>> It isn't good working practice but unaccessible junction boxes seem all too common in the real world, you wouldn't be the first or the last to do it.

Ok, thank you.

Then I think that leaves me with two workable solutions.
1) Get the electrician in immediately to replace the cable from the consumer unit to the shower isolator. (I don't want to mess with the CU).

or

2) Mount the 60A JB (from TLC) at the point where I cut the cable. This is around 6 inches from the floor, on the outside wall of the bathroom (different wall from the shower, can't be splashed. This would be 'safer' (in my opinion as it is further away from any heat source), but unsightly as it can be seen on the wall (cable was in trunking, which would need to be cut). This will be a temporary measure until I get a full list of things for an electrician to do.

Thank you for all your help. In the house, all but 1 (and there must be more than 10 including those for lights) of the junction boxes outside of the consumer unit area are either in the floor between ground and first, or in the loft underneath boarding.

 

[ban-all-sheds]

If you have access to under the floor, why is there a problem routing cables from the socket circuit to an FCU for the towel rail?

 

[garethg]

Shrewd question. I /personally/ would not want to route any cables so that they go closer to the bath. On that wall there is a shower, and the plumbing to the bath and taps. If these were to leak (in the same way that I had last weekend, a pipe rotted through and started leaking in the downstairs bathroom, without any prompting, when I fixed that is when I think I was distracted enough to mis-calculate the shower rating), it would not be a pretty sight, but that is what RCDs are for. But that is me being too wary possibly. I would rather error on the side of caution and use an electrician where there is any doubt.

From as far as I can tell tracing cables, the main lines going past the wall that I would want to put the socket on are lighting circuits, so not suitable. There must be a ring main going right past it somewhere, but I can't find it (unless for some unexplainable reason it goes straight to the loft). The closest socket, I was going to take a spur from a few months back. I raised the floorboards, laid the cable, put in the socket etc. then I isolated the socket I thought using the RCD which does the ring main for the house. The socket went off, but, all of the cables going in that direction stayed live (I used a 'test' meter. It is useless on my walls, but seems to be OK on cables, I also used a voltmeter wrapping the test probes around the wire and there was a decent voltage observed, switching the RCD did not change the reading). I cannot work out how the power is getting to the socket. The 'test' meter shows that basically the whole wall is live, so I can't trace a cable direction.

At this point I need to bow to an experienced electrician, hopefully everyone would understand if I think that it is not wise for me to cut a cable which a test meter shows as live, leave that to someone with a big certificate
Basically I cannot be 100% sure myself that the cable in question is no longer live. I can see no other alternative, but someone with more experience would be better suited to make that call. For the explanation given above (the water risk) I would not want that particular socket to be a spur off the cable in question, junction boxes in my opinion are not waterproof enough, and would probably need to be situated close to the shower wall. (maybe I am being too paranoid here). There are two access areas cut in the floorboards on that landing, and the carpet pulls back quite easily there, however the 4-5 junction boxes on the other circuit must be radial lighting (they stay live too).

 

[ban-all-sheds]

Shrewd question. I /personally/ would not want to route any cables so that they go closer to the bath. On that wall there is a shower, and the plumbing to the bath and taps. If these were to leak (in the same way that I had last weekend, a pipe rotted through and started leaking in the downstairs bathroom, without any prompting, when I fixed that is when I think I was distracted enough to mis-calculate the shower rating), it would not be a pretty sight, but that is what RCDs are for. But that is me being too wary possibly. I would rather error on the side of caution and use an electrician where there is any doubt.

Electrician's can't do anything about dodgy plumbing (except maybe create it), and a cable installed by an electrician is no less at risk.

From as far as I can tell tracing cables, the main lines going past the wall that I would want to put the socket on are lighting circuits, so not suitable. There must be a ring main going right past it somewhere, but I can't find it (unless for some unexplainable reason it goes straight to the loft).

You need to lift more floorboards.

The closest socket, I was going to take a spur from a few months back. I raised the floorboards, laid the cable, put in the socket etc. then I isolated the socket I thought using the RCD which does the ring main for the house. The socket went off, but, all of the cables going in that direction stayed live (I used a 'test' meter. It is useless on my walls, but seems to be OK on cables,

It's probably useless on cables too.

I also used a voltmeter wrapping the test probes around the wire

¿Que?

and there was a decent voltage observed

What do you mean by "decent"? If there wasn't 230V between live and neutral or earth then there wasn't a real voltage there.

I cannot work out how the power is getting to the socket.

Down the cables connected to it..

The 'test' meter shows that basically the whole wall is live,

¿Que?

so I can't trace a cable direction.

Start at the socket - look under the floor.

At this point I need to bow to an experienced electrician,

Yup.

hopefully everyone would understand if I think that it is not wise for me to cut a cable which a test meter shows as live, leave that to someone with a big certificate

Nobody will cut into a live cable, but you don't seem to have any means of testing if a circuit is dead or not.

Basically I cannot be 100% sure myself that the cable in question is no longer live.

And nobody will cut into a cable under the floor just hoping that it's the socket circuit.

I can see no other alternative, but someone with more experience would be better suited to make that call. For the explanation given above (the water risk) I would not want that particular socket to be a spur off the cable in question, junction boxes in my opinion are not waterproof enough, and would probably need to be situated close to the shower wall. (maybe I am being too paranoid here).

The way to do it it not to use JBs anyway - find 2 adjacent sockets and replace the cable between them with one that runs from socket 1 to FCU to socket 2.

There are two access areas cut in the floorboards on that landing, and the carpet pulls back quite easily there, however the 4-5 junction boxes on the other circuit must be radial lighting

Must they?

What size cable is it? Have you traced it to any lights or switches?

(they stay live too).

You can't say that unless you test them properly. And "stay live" when? When you turn off the lighting MCB?

I am reasonably competent with electrics

I'm sorry, but you're not, you really aren't, nor do you have the right tools.