Shower cable

[Adam_151]

We have a 8.5kw shower on 6mm cable on a 32A type 2 Breaker, I know this is not correct, the breaker is two small and while 6mm is seen as borderline for 8.5kw, the cable run is fairly long, and does go through a bundle and some tight spots, so thats not really right either.

Soon that shower is going to be removed, and another 8.5kw shower fitted in a different bathroom (main shower is to be replaced with pumped shower), I don't think it would be right to use the existing cable for this, howwever here comes the problem

The house is a bungalow and while most of it is covered by a loft, the kitchen isn't, guess where the cu is...

so I can only see two ways to get a thicker cable to the cu

1) Twin and earth in some kind of trunking boxing in near the ceiling to a point where it can enter the loft, however this involves going around a corner and the permittable bend radius might cause problems here?

2) SWA on the outside, then into the loft, bend radius might be a problem again if its got to go through a hole in the wall, and how would it connect to the cu (plastic casing), would it have to go into some kind of box, then have twin and earth leaving the box and into the cu, and I guess the same the other end before it goes to the shower isolater?

32A type 2 breaker would have to be replaced with 40A type b one, (its already in the RCD side of the CU), so there wouldn't be a problem on that front.

Im thinking it might be better to have an electrician sort it all out, but the decision to do so does not come down to me, it comes down to my dad, and he has the opinion that it has been alright for 5 years...etc..you know the thing

Adam

 

[ban-all-sheds]

You're right about how you'd have to sort out where to terminate the SWA - one tip though - you don't need to join onto T/E, just cut back a lot of outer sheath and armour and take the inner cable out of the box and off to the CU or switch...

And you're right about the bend radius of the SWA, particularly as it will (should) be heading in a downwards direction where it goes out of the house. Another option though if you want to go outside is to use conduit with ordinary cable inside it - singles would be the easiest.

But re the trunking - if you have the T/E on its side, the bend radius for 10mm² is about 30mm. But the real answer with trunking would again be to use singles. Much easier to put in, much easier to wire in, and they have a bend radius of about 12mm.

 

[Adam_151]

Thanks for the help Ban,

Singles in trunking around the dge of the room would not be possible, as where it leaves the room through the ceiling, it would not be possible to maintain the trunking, there is no access there, and there is a bit of a bend, its sort of in the loft where the roof meets the loft floor, there is a gap, and this leads to above the kitchen ceiling where a cable could be dropped, no way to install trunking though.

singles in conduit outside seems sensible, is pvc conduit allowed outside?, or would it have to be metal, are special watertight fittings needed?, or dosen't it matter providing there are no joins in it.

All this seems like its going to be difficult, might be easier to just have two pumped showers, but then there is the issue of how fast they would empty the water tank, things are rarely simple

Adam

 

[plugwash]

use 10mm tails?

they should be much easier to get through conduit/trunking for awkward parts of the run yet being double insulated don't need to be enclosed for the entire run.

 

[mapj1]

Just in case it is possible, how is the kitchen ceiling and (flat?) roof constructed? can facia boards be removed temporarily from an end ior side to expose a joist run, or could something be done with threading tapes, bambo cane or a drain unblocking spring, to get through any existing void, or round the edge of the roof/ceiling, into the space 'indoors'. Can you pull a new cable in using the old - this is high risk if it breaks so attach it well, and make joins that dont look like a hedgehog if you try this.
Sometimes fishing cables through surprisingly small access holes is possible. I'd suggest not accepting defeat at first if at all possible. Of course if its a solid concrete slab roof then short of a suspended ceiling beneath it I suggest that all really is lost, and trunking is needed after all.
regards M.

 

[Adam_151]

I have used my impressive graphics skills (LOL) to draw some diagrams, first the general layout of the house:

next a 3d drawing of the end of the kitchen

now an end view

and a side one:

would downsizing to a 7kw make much difference?, would an electrician be able to calculate whether this ok or not from just a description of where the cable runs, or what he have to see it himself (not possible), or could he tell by measuring the cold resistance, running the load, and measuring the reistance again to work out if its heated up much (the physics seems sound to me, but i've near heard of anyone actually doing this???)

I just wish I knew what I know now before the new kitchen ceiling was fitted, it would have been so easy to put a 10mm in then, but we only had the forward thought to put some spare 1.5s and 2.5s in (one of the 2.5s did prove useful when we upgraded the dining room sockets from a mess of junction boxes and cables seemingly modeled on a spider, into a ring

sorry if this dosen't make total sense, I've had a bit to drink

 

[mildmanneredjanitor]

Do you have to go up? Can you not go down under the floor?

You could also cut a couple of holes in the ceiling and make good after?

Say one above the CU and another near the awkward access hole above the void. You may need another if there is a noggin in the way of the run between the rafters.

I've used this method before quite successfully. I used a large holesaw to create a nice neat hole, then when making good just snotted a batten across the gap and screwed the disc back in place. Voila'

 

[felix]

If you don't mind having a rather low water flow rate in winter a 7kW shower will solve all your problems. You can run it on your existing 6mm cable and a 32 amp breaker. We had one of these in 1980 when electric showers were relatively new. You don't have to have the biggest shower in the shop.

Using the old cable to pull a new one in does work in most cases though you will run into trouble if the old one is a dead fit in a small hole. the trick is to make a really strong but smooth joint between the two cables.

I join each core to its opposite number by stripping at least an inch of insulation from each one and doubling the exposed copper back on itself to form a hook. Do this in such a way that all three pairs of hooks are taking the strain. If you have a soldering iron then by all means add solder too.

Now comes the really important bit. Build up the joint with bits of outer sheath and loads of tape until you have a smooth taper from one cable to the other. When you put on the last layer of tape, wind along the cables in the direction you'll be pulling.

Hint: Pulling the cable in is a two man push and pull job.