Safety question

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Shower blew yesterday when I was showering! Massive sparks , black water etc.

After isolating it via the double pole isolator and turning water supply off I went to check the 40 amp MCB and found it hadn't tripped.

I took the the shower off today to find an absolute mess inside, Live wire/s fused to block connector etc. The supply looks like 6mm to me which is fine for the shower that was on there but not for the new 9.8kw Mira Sport I've just bought.

Obviously I'll have to run some 10mm from the board to the shower which is fine, I've done it before and used to have Part P limited scope for what thats worth!. However I'm concerned the MCB didn't trip and would like to get a fully qualified spark in to check things out. Also I may as well get them to put in a consumer unit to replace the fuse board. I have a few questions though as its an old house.

I think my incoming supply is TT, in fact virtually certain it is. Will this affect anything? I also want to run a 40amp supply to an outside workshop I'm building, will I need a separate unit for this?

O also, should the the shower circuit be on an RCD or is MCB ok?

Just want to be informed when the eletrician turns up really. Thanks

 

[EFLImpudence]

6mm² is fine for 9.8kW as long as it is cliped direct to surface or buried in masonry - not in or under thermal insulation or in conduit.

It should have an RCD.

If you have TT you must have RCDs on everything.

 

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Thanks for the reply. I'd assumed it needed 10mm as the Mira site had a table showing any of their showers at or above 8.5 kw needed 10mm. I will have another look at their site I may have read it wrong.

The last bit of run to the shower the cable is buried under the plaster,(I assume this is OK?) I'll check the rest of the run.

I can't get RCDs to plug into an old fuse box so I'm still going to get a CU installed for safety reasons.

 

[EFLImpudence]

Yes, buried in plaster is fine.

If your installation is TT you should have RCDs already.

Do you have an obselete Earth Leakage Circuit Breaker near the supply or CU?
There are various types -
https://www.flameport.com/electric_museum/old_elcb/index.cs4

 

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Thanks. I'll check the rest of the run and if it pans out at least that has saved me some money to go towards the new CU!

there is still a wylex fuse box on there, hence my concern about safety and having to use the pull cord on the double pole isolating switch when it happened. When doing some work on the house when I first moved in the earthing rod was dug up .The earth wires to the earthing rod were upgraded then.. There is no Earth Leackage Circuit Breaker on there.

 

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6mm² is fine for 9.8kW as long as it is cliped direct to surface or buried in masonry - not in or under thermal insulation or in conduit.

It should have an RCD.

If you have TT you must have RCDs on everything.

Hi , I've checked the Mira wiring guide (https://www.mirashowers.co.uk/media/1453/miras-guide-to-electric-showers.pdf) and it says 10mm for this and even lower Kw showers. I've also followed links to IEE wiring reg tables and as you said 6mm surfacce clipped is rated high enough for the current drawn by this shower. Whats going on ? Is it just an ACE with Mira? or have they got it wrong?

 

[EFLImpudence]

A bit wrong I think.

Had a quick look - the tables are for maximum lengths of cables aren't they - would be slightly shorter for smaller cable.
Also not sure what the crucifix cross symbol refers to.

Also 40A circuit breaker is adequate.

It appears they must be using maximum values for the Earth Fault Loop and other things but which may not apply to your premises.
A worst case scenario which must be satisfatory no matter what.


As I frequently say, 10mm² is often used to supply whole flats where there is a shower, heaters, oven and all the other usual things.

 

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Yes, either that or a management Arse Covering Exercise!

 

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Since I'm getting a CU installed I thought I'd go the whole hog and get a Hager with RCBOs. I've got 6 circuits on muy current fuse box and am going to need a 40A to supply an outside workshop so I'm thinking a 10 bay box would be enough and give me scope for expansion. I've seen various places selling them with included MCBs and 2 RCDs but since I won't need these can I get them empty and therefore cheaper?

 

[JohnW2]

It appears they must be using maximum values for the Earth Fault Loop and other things but which may not apply to your premises. .... A worst case scenario which must be satisfactory no matter what.

Am I missing something? Are they seriously suggesting a maximum of 4 metres of 10mm² T+E (for both 45A and 50A MCBs) with TN-S? Quite apart from the fact that I think one would struggle to arrive at such a figure, even taking all 'worst case' possibilities into account, but they are effectively saying that the shower is not suitable (at least, with 10mm² T+E) in a TN-S installation unless the CU is in (or perhaps immediately below) the bathroom (and not necessarily even then)!!

Kind Regards, John

 

[EFLImpudence]

can I get them empty and therefore cheaper?

Yes, you can get them with just a main switch.
http://www.discount-electrical.co.uk/section.php/109058/1/hager-switch-isolator-consumer-units

 

[winston1]

Hi , I've checked the Mira wiring guide (https://www.mirashowers.co.uk/media/1453/miras-guide-to-electric-showers.pdf) and it says 10mm for this and even lower Kw showers.

Manufacturers instructions are guidance only and don't have to be followed ESPECIALLY WHEN THEY ARE WRONG as in this case.

 

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I've had an electrician round today, hes done work for a plumber mate of mine and comes recommended. I've booked him but am sourcing my own CU. I'm getting a Hager design 10 from sparksdirect. I also want to have the old part of my house(has its own power and lighting circuit) and Shower on RCBOs. I can get RCBOs from sparks direct but I'm a bit confused about which type I need, type A,B or C? They have the reduced height ones which I assume would be a better fit, but not in the 45A needed for my shower

 

[ban-all-sheds]

I've had an electrician round today, hes done work for a plumber mate of mine and comes recommended. I've booked him but am sourcing my own CU.

So no warranty, then.

And probably paying more for it than the electrician would.

I can get RCBOs from sparks direct but I'm a bit confused about which type I need, type A,B or C? They have the reduced height ones which I assume would be a better fit, but not in the 45A needed for my shower

So as well as not providing materials, this electrician is not doing any design.

Not sure what you expect to happen when it comes time for an EIC to be issued, or for Building Control to be notified.

 

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Sorry, why wouldn't it have a warranty? I'm getting it from an sparksdirect , cost for a hager 10way is about £84 which seemed a reasonable price to me.

The electrician has been to look at the job and we've had a discussion about what I need and whats there(ie:earthing,circuits, new feeds I want) so why wouldn't I get an EIC or notification done?