Another shower thread

[CTL]

Hi all

I know what you're probably thinking - first time forum poster, a question about an electric shower and DIY....here we go again.
I've done a lot of searching and reading so far and have learnt this is a bit of an annoyance here, so I just want to reassure everyone - I fully plan to get my local electrician in for the wiring up / turning on the power.


With that to one side, I do want to be as armed with as much information as I can be.
I recently had someone around to give me a quote for what I wanted and it was a rather bad experience. Conflicting information, a silly price (only for this to keep changing) and not being convinced he actually knew what he was on about ("Don't worry about part P mate") have caused me to read up on this a lot more.

I really just want to check that my idea is sound, before getting another guy in who has been personally recommended and has good reviews.

I have a 9.5kw shower. I can't run the power through the walls - it would need a huge amount of work doing and disruption, which just isn't an option.

Am I correct in thinking this is an acceptable solution:

A 10mm² cable from the shower straight up into the loft, with a metal shield covering the front facing side of the cable towards the room. This section will be embedded in the wall and plastered over. Space will be left around the cable for cooling.

This cable will go across the loft directly to a 50A pull cord switch that will be mounted in the same room as the shower.

A cable will then go from the isolation switch, across the loft (short distance), outside via a hole in the wall and into plastic conduit that goes down the side of the house. This will end level with where the fuse box is internally, which should allow the cable to come back through the wall and be wired up in the fuse box. Each end of this conduit would have terminators on to help keep waster and moisture out.

This entire run of cable is probably no more than 10 meters, with the isolation switch to the shower being another 3 at most.

I am aware that the cable has to be proper 10mm² for the internal wire and not the width of the sheath.

The walls are insulated, but it would only be travelling through them inside<>outside and not running within. I'd make sure the plastic conduit outside wasn't tight and the cable had some room within. With a 10mm² cable, I'm hoping overheating wouldn't be an issue here?


The consumer unit is a Memera 2000. Getting new MCBs for this seems very difficult from what I've read. I'm hoping that a 40A MCB will suffice, as I can obtain these from Ebay without too much difficulty. I worked it out as 9500/240 = ~39.6 amps.


Does this all sound fairly....sound? The last guy I had in wanted to rip out the consumer unit and replace it, even though the house is only around 8 years old.


I'd like to do most of this myself due to mass decoration going on.
Assuming everything above seems fine, I take it this is okay as long as it's never attached to the consumer unit (I wouldn't dare)?

Would the electrician want to see that the cable is a single run / anything else at all places? If so, it would mean I can't just put the cable in and plaster over it - which is fine, as long as I know.

The idea is to do as much as I possibly can, safely, before getting someone in to check and certify it and getting them to wire up the CU / turn the power on.

Thanks for any input

 

[skenk]

You need an RCD.

No need to leave space around the cable if it's going to be embedded in plaster.

No need to cover it with a metallic sheath either if it goes straight up from the shower (something of a grey area but not a problem, and you need an RCD anyway...).

Cable on the outside is not ideal. You will want a hole in the conduit at the lowest point to allow water to drain.

40A MCB is fine, the nominal voltage in the UK is 230 but shower manufacturers still use 240 becasuse it makes their showers sound more powerful.

Part p, safety, etc etc

 

[EFLImpudence]

I recently had someone around to give me a quote for what I wanted and it was a rather bad experience. Conflicting information, a silly price (only for this to keep changing) and not being convinced he actually knew what he was on about ("Don't worry about part P mate") have caused me to read up on this a lot more.

Not him, then.

A 10mm² cable from the shower straight up into the loft, with a metal shield covering the front facing side of the cable towards the room. This section will be embedded in the wall and plastered over. Space will be left around the cable for cooling.

It will cool better just buried in the plaster.
You don't need metal shield. It will be RCD protected.

A cable will then go from the isolation switch, across the loft (short distance), outside via a hole in the wall and into plastic conduit that goes down the side of the house. This will end level with where the fuse box is internally, which should allow the cable to come back through the wall and be wired up in the fuse box. Each end of this conduit would have terminators on to help keep waster and moisture out.

This entire run of cable is probably no more than 10 meters, with the isolation switch to the shower being another 3 at most.

I am aware that the cable has to be proper 10mm² for the internal wire and not the width of the sheath.

The walls are insulated, but it would only be travelling through them inside<>outside and not running within. I'd make sure the plastic conduit outside wasn't tight and the cable had some room within. With a 10mm² cable, I'm hoping overheating wouldn't be an issue here?

It will still be alright for the load of the shower.

The consumer unit is a Memera 2000. Getting new MCBs for this seems very difficult from what I've read. I'm hoping that a 40A MCB will suffice,

Yes, on an RCD, of course.

as I can obtain these from Ebay without too much difficulty. I worked it out as 9500/240 = ~39.6 amps.

Not the only outlet.
The mathematics is correct.

Does this all sound fairly....sound? The last guy I had in wanted to rip out the consumer unit and replace it, even though the house is only around 8 years old.

Not him, either. Same one?

I'd like to do most of this myself due to mass decoration going on.
Assuming everything above seems fine, I take it this is okay as long as it's never attached to the consumer unit (I wouldn't dare)?

No. You MUST discuss it with the electrician BEFORE you start.
Legally it is that or pay LABC fee BEFORE you start.
It is not up to us on a forum.

Would the electrician want to see that the cable is a single run / anything else at all places? If so, it would mean I can't just put the cable in and plaster over it - which is fine, as long as I know.

You can ask him - yes.

The idea is to do as much as I possibly can, safely, before getting someone in to check and certify it and getting them to wire up the CU / turn the power on.

No. Wrong way round. Electrician FIRST.

 

[skenk]

Got bored halfway through reading your post.... you'll want to involve whoever's signing it off before you start work, or you may run into problems.

 

[CTL]

Thank you skenk & EFLImpudence.

Understood on getting him involved from the start - I can't proceed until next week anyway so I'll give him a ring sooner than later and get his thoughts.

The guy who wanted to rip out and replace the consumer unit was the same one, yup. His story changed about 3 times. It was quite similar to what I've seen with window salesmen. A high price, only for them to slowly knock it down until they think you will commit.

His "final offer" was just above £900. Now I'm more than happy to pay a fellow man for their skills, time and knowledge, but I get the distinct feeling that's a bit more than what's reasonable for a job like this. The entire bathroom replacement has cost under a grand so far.

Anyway, I'm at the edge of my knowledge now thanks to your answers, so I hope you don't mind one final question: There is a comment about a RCD - the consumer unit has what looks like 'double switches' with "RCD Protected" printed on it in the last two slots. Am I correct in thinking that this is an RCD that protects the entire unit and anything ran off it?

If not, is the RCD a separate unit that needs to be added? I just want to make sure I don't get suckered into buying something I don't need after my last experience.

Again, thanks for your posts.

 

[bernardgreen]

Running cable on the outside of the wall is never a good idea as there are safety aspects to be considered.

If the cable is out of reach and is obvious then the risks are low.

Who has access to the wall where the cable will be located ? Just family and visitors. Or is it a public facing wall.

What are the hazards of causing damage to cable ? Is a drive way involved

You may need to consider using armoured cable as plastic conduit offers very little mechanical protection..

Will the cable and conduit be in direct sunlight. If it is then UV radiation will determine the type of conduit. Often this means black UV resistant conduit which gets hot in sunlight. This will reduce the maximum permissable currrent rating of the cable.