Another shower electrics post!

[Rocketmen]

I am about to install a 10.8KW shower in place of a mixer unit. I have installed water supply from mains. Bought 10mm cable and have 10mm earth to bond to copper pipe just as it feeds shower. Electrical supply is from a new CU with 50A mcb that is only 8M from new shower. What size holes are needed for the floor joists that have the cable run through them? The cable rises from the floor and through a 300mm sq boxed section in the corner of the room - is this ok wrt permitted zones? After feeding a pull switch the cable will need to drop 500mm through a studded wall that is 4" wide including board and tiles. If I remove insulation from this area, can I just clip cable to the studding or does it need to be put into conduit?

Finally, is there a special tool for pulling tight the bond strap?

Many thanks from a virgin poster!

 

[automationman]

Rocketman, is the shower really 10.8KW?

At 230VAC a 10.8KW shower will draw almost 47amps which will exceed the current carrying capacity of the cable. You may be looking at 16mm cable.

If the cable is bundled with other cables or run through any thermal insulation (even for a fraction of its length) then it will not even carry 46 amps safely.

You do not need to bond the water pipe at the shower with 10mm earth cable. Equipotential bonding needs to be assessed first. In some cases it is not required at all.

I would strongly encourage you to hire a registered electrician for this work. He/She will be familiar with the regs and cable size calculations for specific conditions. you must also have RCD protection on any shower circuit. This is notifiable work.

I expect you have good reasons for swapping (what sound like) an energy efficient mixer shower (assuming you heat your DHW with gas) for a non-energy efficient electric shower.

 

[londonboy]

........

I expect you have good reasons for swapping (what sound like) an energy efficient mixer shower (assuming you heat your DHW with gas) for a non-energy efficient electric shower.

I think thats debatable.

 

[mikej2005]

Rocketman, is the shower really 10.8KW?

At 230VAC a 10.8KW shower will draw almost 47amps which will exceed the current carrying capacity of the cable. You may be looking at 16mm cable.

There are loads of threads on this forum which state that 10mm cable is normally sufficient for a 10.8kW electric shower - I only know this because I've searched for this information myself in the past, when trying to find whether the shower I inherited with my current house was installed properly.

Eg. //www.diynot.com/forums/viewtopic.php?t=132577

 

[securespark]

Auto, are you getting 10mm2 mixed up with 6mm2?

6 has a max CCC of 46A.

10 has a max of 63A.

 

[automationman]

My mistake indeed, 10mm will be OK provided the installation method is appropriate. Though I would still encourage the OP to get a registered electrician in to spec and do the work.

 

[holmslaw]

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[Rocketmen]

Many thanks for your replies. You would be amazed at the difficulty I've had trying to get a spark to come and quote for just the shower installation. Three were called, 2 turned up and none rang back with a quote. I intend to press ahead with installation but look for someone to certify before use.

Perhaps people want the whole refurb job.

Any advice on joist hole diameter for 10mm cable?

Thanks again

 

[holmslaw]

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[Rocketmen]

Thanks Holmslaw. My DHW is via gas boiler (not combi) and seems a waste to leave for work every morning with a tank full of hot water. Also, you hit the nail on the head when you mentioned poor flow - the mixer unit was very poor because I had only 2ft of head between shower outlet and the MST. The elec shower seemed to be the best way forward for both probs.