Triton Spellbind shower tripping RCD

[Softus]

I'll show you for a mere £900.

 

[securespark]

A 9.5Kw should be on 10mm cable with a 40A breaker or even a 32A if poss taking diversity into account.
6mm on a 50A breaker will have melted the cable as its undersized
Using that shower on a 6mm is a fire risk!
Run a new 10mm cable from your consumer unit to the shower and downgrade the breaker.

9.5kW is 39.58A @ 240V.

Show me how diversity allows a 32A breaker to be used.

Granted the cable is undersized, but how could a 41.3A shower melt 6mm² cable, rated at a maximum of 46A? (We do not know the installation method)

Even if the full 50A was flowing through 6mm², it would only be 4A over the maximum (again, we don't know the installation method).

Run a new 10mm², yes, but downgrade the breaker? Why?

 

[Softus]

Granted the cable is undersized, but how could a 41.3A shower melt 6mm² cable, rated at a maximum of 46A?

It could happen in the extreme of adverse conditions, i.e. in conduit under/behind thermal insulation.

 

[cb1980]

Softus:

That tape measure photo is at the CU.

I don't have a photo of the red switch (I'm working today), but it's a lot like this one.

If the cable is already cooked then you're too late - replacing the shower won't eliminate the fire hazard.

Yeah, I realised that last night. *sigh*

yes there is a way. If you can't see it, pay me a thousand pounds and I will show you.

I'll show you for a mere £900.

I hope these are better ideas than removing the tiles and then putting a new cable in...

The floor tiles also have heating mats under them, so I imagine we're talking about a major job to get a new cable in under the floor the way it comes in now.

The other possibility is running the new cable via a different route. Is there a way to get it to the shower unit without removing tiles? It was bad enough hanging a mirror with those tiles (I got through 2 drillbits), so the thought of trying to remove them fills me with despair.

 

[bongos]

You might be able to run it in ceiling space and then come down to the shower. Would that be any easier (you might still have to move tiles though)?

As others have said it's possible the cable has been damaged if it has been overloaded for any period of time so you might end up needing to put a new one in anyway.

 

[Softus]

Wrong drill bits then.

Trunking?

 

[cb1980]

Wrong drill bits then.

I wasn't using wood bits...

Fortunately the third one I bought (increasing in price each time) did the job.

Trunking?

Will that look horrible? It's quite a nice bathroom.

You might be able to run it in ceiling space and then come down to the shower. Would that be any easier (you might still have to move tiles though)?

It's a sloping extension roof on a Victorian terrace, I don't know if there's any "space" there to use. It's not below a loft anyway.

I'm guessing there's probably no way to avoid removing at least a couple of tiles, either from the ceiling or floor. Trunking to the shower unit sounds dangerous and probably ugly as hell.

At least it's not going to be a difficult job to get the cable to the bathroom. The existing one goes around the cellar wall, then up below the floorboards at the top of the stairs, which is right by the bathroom door.

Since it would be so easy without the tiles it makes it even more ridiculous that they didn't do it properly in the first place...

 

[Steve]

We have a length of trunking up the bathroom wall to the ceiling, then down the wall to the shower unit. Off-white tiles, so you dont notice it much. (We had to replace the cable a few years ago, since we bought a more powerful shower. The old cable was under the tiles and the bathroom is fully tiled, so trunking it had to be!)

Trunking goes into the top of the shower, sealed around it. Its not dangerous - all the cable entries are designed so that any water that enters them drains out of the bottom without going near any electrical components.

My Grandad's shower was wired to the trunking ends at the side, and the cable is visible where it goes across the bottom of the unit and enters the bottom cable entry. By an "electrician" too.

 

[tnarg999]

Hi Cb1980,
Is there any possibility that when you put the mirror up you may have caught a cable in the wall behind? Is there any correlation between the time the Mirror went up and the circuit tripping?

Softus said that the wires in the shower with the cover off (one red, one grey) look to be 2.5mm. These are likely to go back to the switch outside of the bathroom. I reckon you have 6mm T&E from the consumer unit to the bedroom switch and then 2.5mm T&E from the switch to the shower. A photo of the inside of that switch when you get home should confirm this. If it is 2.5mm from the switch to the shower, this is way to low and needs upgrading to 10mm sq. Sorry..

If the bathroom is only a few years old, the previous owner should have had an inspection, depending on the exact date of installation wrt when Part P came into effect, but then not everyone follows the rules.

 

[cb1980]

We have a length of trunking up the bathroom wall to the ceiling, then down the wall to the shower unit. Off-white tiles, so you dont notice it much. (We had to replace the cable a few years ago, since we bought a more powerful shower. The old cable was under the tiles and the bathroom is fully tiled, so trunking it had to be!)

Trunking goes into the top of the shower, sealed around it. Its not dangerous - all the cable entries are designed so that any water that enters them drains out of the bottom without going near any electrical components.

Experienced people:

What chance do you think there is that I could get a 10mm cable up behind the tiles in the channel for the 6mm? Any chance I could pull the 6mm out bringing attached 10mm all the way through? Is this just crazy talk or can it often be done?

Is there any possibility that when you put the mirror up you may have caught a cable in the wall behind? Is there any correlation between the time the Mirror went up and the circuit tripping?

No, the shower first tripped ages before that. It's also on the opposite wall.

A photo of the inside of that switch when you get home should confirm this.

I'll get a photo of this in the next couple of days. Out for Guinnesses tonight so I won't be touching anything electrical when I get home...

If the bathroom is only a few years old, the previous owner should have had an inspection, depending on the exact date of installation wrt when Part P came into effect, but then not everyone follows the rules.

Yes, yes they should. What happened was that they didn't have it certified ("a friend fitted it"), but they "promised" to have it certified between exchange and completion (couldn't be written into the contract as dependent on a third party). Of course, they didn't. I assumed (yeah yeah, I know) that since it had been installed a couple of years ago with no problems it was fine. I should have had it checked by an electrician myself, but you live and learn...

 

[tnarg999]

Experienced people:

What chance do you think there is that I could get a 10mm cable up behind the tiles in the channel for the 6mm? Any chance I could pull the 6mm out bringing attached 10mm all the way through? Is this just crazy talk or can it often be done?

I don't think it is crazy talk, but I think you need to do some more investigating first. It sounds like from what you have said, getting a new 10mm sq cable from the consumer unit to what we think is the Double Pole (DP) isolation switch outside the bathroom is do-able. The tricky bit you are going to have is getting the new 10mm sq cable from the DP switch to the shower without ripping off them tiles...

Need to establish the route the cable takes from the shower to the isolation switch. If it goes up into the sloping roof void and then down a partition outside, you could bind the new cable to the old cable and gently pull it through. I've done this when upgrading 6mm to 10mm. You have to make sure the cables are bound tight and not too thick. Where you might come unstuck is if the existing cable is clipped to rafters or goes through them snugly - The 6mm sq cable (that you have from Consumer Unit to DP switch) is 14mm wide with the PVC coating http://i275.photobucket.com/albums/jj315/cb1980_2008/IMG_0876.jpg The 10mm sq cable I used was 18mm wide with the PVC coating... If you confirm that only 2.5mm sq T&E runs from your DP switch to the shower, you have to ask yourself why the original installer did this, when he went to the effort of installing a DP switch and 6mm sq to supply it? Perhaps access to the shower is a right g1t, and/or, he couldn't be ar*ed to use the correct size cable.

Hopefully with a bit more investigating you'll find access is more reasonable than first thought - I am sure others will divulge their secret ways of cable routing if you ask nicely!

 

[Softus]

That tape measure photo is at the CU.

I had a hunch that it was.

I don't have a photo of the red switch (I'm working today), but it's a lot like this one.

OK. That certainly appears to be a DP (double pole) switch. We really really REALLY need to know the gauge of the cable on both the supply and load sides of that switch, since there's no guarantee that the cable isn't joined somewhere between CU and DP switch.

 

[Softus]

I wasn't using wood bits...

lol - no I didn't think you were. But if, for example, you have porcelain tiles, and if, for example, you were using ordinary masonry bits, then the bits would melt without cutting the porcelain very much.

Trunking?

Will that look horrible? It's quite a nice bathroom.

Yes, and oh dear, in that order.

I'm guessing there's probably no way to avoid removing at least a couple of tiles, either from the ceiling or floor. Trunking to the shower unit sounds dangerous and probably ugly as hell.

Not at all dangerous, but as ugly as sin on a bad hair day.

Since it would be so easy without the tiles it makes it even more ridiculous that they didn't do it properly in the first place...

If I had a pound for every time I encounter that scenario, then I'd...... hang on - I do have a pound for every time.

 

[333rocky333]

Where would it go if you drilled through the back of the shower, could that be a possible route back to the switch.

 

[plugwash]

One thing I've often wondered is how you would actually do a shower with trunking coming down from the top, most showers i've seen have the hinge at the top and even those that don't I would imagine you would have a nightmare of a time getting an adequate seal.