DIY Doctor

Mira Shower Tripping Out - Cabling Melted (With Pics)

Postby FinGerS o FuDgE » Fri Jul 09, 2010 6:43 pm

Hi, just wondering if any sparkies or plumbers/shower fitters can offer me some advice?

Had my Mira Escape shower for a few years and all has been fine, but a couple of nights ago whilst I was in the shower, it tripped out and I noticed a burning smell.
I opened the shower unit up and sure enough the neutral cable has melted badly:


I checked the other end which runs into the pole switch and all is fine there with no sign of damage:


Is there anything in particular that could have caused this?
The cable runs from a 50amp rcd in the circuit board - into the pole switch - then into the shower. There aren't any signs of water seeping into the unit.

The other thing that is confusing me is that when the shower is tripping out, it's not tripping the 50amp rcd that it's connected too. Instead its tripping a different one out which has a 'test' button on it.
This other rcd with the test button is supplying power somehow? If I switch this rcd off, then pull the pole switch there is no power and vice versa, if I turn the 50amp shower rcd off and leave the test one on, there is no power on the pole switch? Both have to be on.

Hope I've explained myself ok, and hopefully get a bit of advice. I'm a chippy so know a little about electrics, but not that much. Got a few sparkies in work that could take a look, but that won't be until next week and with this scorching weather, it's killing us not having the shower :cry: :cry:

FinGerS o FuDgE
Rank: Labourer
Progress to next rank:
Posts: 1
Joined: Fri Jul 09, 2010 6:18 pm


Simply Build It

Postby ericmark » Sun Jul 11, 2010 4:44 pm

Likely the problem is due to screws in connector block being lose. Some times vibration can cause these to become slack and once a little slack they start the heating up. Once they heat up that makes them go evenly slacker so soon they burn out.

This is why all screw connections have to be accessible for maintenance. Not that I or any one else goes around testing all the screws are tight in every socket.

The shower is thrice protected two types of over current and also a current leakage device. These can be all combined into one device the RCBO and some even have two windows to show why it tripped but in your case they are two separate units.

The MCB which will be marked something like B50 will in the end trip at 51 amps but this would take a very long time. Many hours and it is there in the main to protect the cable from overheating. The second bit in same device is designed to trip at 5 x 50 or 250A and this will trip in less than 0.1 seconds. This assumes the cable resistance will allow this current and that's why when fitting a shower or any other item the ELI (Earth loop impedance) is measured really with a RCD it is the Line Neutral loop impedance which is more important.

The RCD measures the current out and the current returning and if within the ratted difference then allows current to flow. The 63A marked on them is the current they can handle and means there should be a 63A or less Fuse/MCB before or after it to protect it. For a shower at 30ma RCD is used which in most cases means somewhere between 15 and 30ma leakage to earth will trip them. Some do have LED's Green for below 15ma and yellow and red above and don't trip until 90% of 30ma is leaked but these are rare. And some even auto reset even more rare.

Looking at pictures the Green/yellow earth sleeve is missing both at isolator and shower and this makes one wonder about the rest of the installation. If fitted DIY then the meters needed to ensure the ELI is OK and to test the RCD are not likely to have been used. Maybe you can get a spark from work to test it for you.

Likely the neutral will need extending and this may be possible using a crimp but the pliers are not cheap so again spark from work seems best option.
Likely nothing wrong with shower and the neutral has touched the earth wire. But the 50A drawn by a shower can cause a fire very easy and to be safe better to get it tested can checked I am sure some one at work needs your help and you can get it tested for a drink at local pub. Different for non tradesmen they have nothing to give back.
Rank: Project Manager
Posts: 2537
Joined: Fri Oct 02, 2009 8:49 pm
Location: Llanfair Caereinion, Mid Wales.

Postby jimmy_one_ball » Sat Jul 24, 2010 11:49 pm

Judging by the state of the grey sheathing I would definitely question the installers competence! In the first pic they have used the cpc to rip through the sheathing with pliers, something which for my Yoda pain would given have me.

My immediate instinct after looking at the pics was that the neutral terminal screw was loose then ericmarks instinct just about confirmed it for me. Also the missing green/yellow cpc sheathing would suggest non skilled installer.

A 50A MCB would also suggest over 10.5kW shower - depending on the method of installation a quick cable calc throws a possible requirement of a 16mm conductor csa at me - that looks like 6mm csa judging by the width of your thumb mate (12.5mm dia?), which may offer a suggestion as to why the MCB didn't operate but that's pure speculation of course!
Rank: Tradesman
Progress to next rank:
Posts: 35
Joined: Fri Oct 19, 2007 2:14 am

Postby sparx » Sun Jul 25, 2010 7:07 pm

can only agree with others, loose terminal on installation which is as rough as a badgers bumm!
no sleeving, wires badly twisted together, and as brown / blue colours was done since 'Part P' was in force and would have been notifiable job.

This sort of poor job is the reason DIY electrics are being restricted at last.

Bet there's no cert. for the install,

if done by someone for money get them back!
BTW the reason it's tripping the main RCD instead of the MCB, is tracking from the Neutral to the bare earth, clearly visible in picture of shower.
Rank: Project Manager
Posts: 2166
Joined: Wed Mar 21, 2007 8:33 pm
Location: The fifth continent.

Display posts from previous
Sort by
Order by

  • DIY How to Project Guides
  • DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!

  • Related Topics