Electric Shower tripping RCD

[dangie]

My electric shower, a Mira Sprint 9.5kw is approximately 10 years old. It’s worked perfectly, until now. Today it tripped out the RCD. On resetting and retrying it tripped again. Note: It tripped as soon as the pull-cord switch to the shower was pulled. The shower was not flowing.

I’m assuming it’s time for a new shower. Is there anything I can check to see what is causing the trip?

 

[Trackman]

My electric shower, a Mira Sprint 9.5kw is approximately 10 years old. It’s worked perfectly, until now. Today it tripped out the RCD. On resetting and retrying it tripped again. Note: It tripped as soon as the pull-cord switch to the shower was pulled. The shower was not flowing.

I’m assuming it’s time for a new shower. Is there anything I can check to see what is causing the trip?

Well, the same thing happened to me and I bought a new shower. The thing tripped again.
The electrician checked the consumer unit and found out the MCB (circuit breaker) for the shower was shot, so it might be worth getting that checked out before shelling out on a new shower.
Edit: It actually had burn marks on the MCB

 

[D365]

Edit: It actually had burn marks on the MCB

Burn marks on the MCB and/or pullcord switch are the first thing to look out for. It’s an indication that the binding screws have loosened and will result in arcing, overheating and consequential charring of the cable and binding terminal.

 

[AndrewE]

I was wondering whether an ageing shower pump might be starting to bind, making it harder to start (increasing the inrush current?) and causing the whole thing to exceed the MCB rating.

 

[dangie]

I was wondering whether an ageing shower pump might be starting to bind, making it harder to start (increasing the inrush current?) and causing the whole thing to exceed the MCB rating.

I see that, but it tripped as soon as the pull-switch power cord was pulled. The shower start button hadn’t been pressed.

Note: It is not a Power Shower, simply mains water pressure.

 

[Trackman]

I see that, but it tripped as soon as the pull-switch power cord was pulled. The shower start button hadn’t been pressed.

Note: It is not a Power Shower, simply mains water pressure.

Same thing happened to me, you didnt need to press the start button.
I needed a new shower anyway so I wasnt that bothered when I found out there was no fault with the shower.

Burn marks on the MCB and/or pullcord switch are the first thing to look out for. It’s an indication that the binding screws have loosened and will result in arcing, overheating and consequential charging of the cable and binding terminal.

The burn marks were on the business side of the MCB on mine, looked liked arcing to me by the pattern.

 

[Enthusiast]

You mentioned an RCD tripping. Post #2 mentioned an MCB and subsequent answers concentrate on possible causes of over current. Which is it? An RCD does not protect against over current

 

[dangie]

You mentioned an RCD tripping. Post #2 mentioned an MCB and subsequent answers concentrate on possible causes of over current. Which is it? An RCD does not protect against over current

With respect, can you explain this in layman’s terms. I’m not very electrically knowledgeable.

 

[Enthusiast]

An MCB (Miniature Circuit Breaker) is like the old bare wire "fuses". If too much current flows through a circuit, the fuse blows (or the MCB trips). The excess current may be caused by a "short circuit" within a device (or even within the circuit itself) or by plugging in a device that draws more current than the circuit is designed for.

An RCD (Residual Current Device) protects principally against Earth leakage. So if you have (say) a faulty kettle which has become "live", someone touching it may face electric shock as the electricity travels from the kettle, through their body, to Earth. An RCD detects this and cuts the juice before too much harm is done.

Faults which cause an RCD to trip are usually fundamentally different to those which cause and MCB to trip. You can identify an RCD because it will have a push button with "T" (for test) on the outside. An MCB does not.

 

[Energy]

Try turning off every MCB apart from the shower. Devices typically have a little bit of earth leakage, it isn't a problem but across multiple circuits it can add up to 30mA and be enough to false trip the RCD.

 

[dangie]

Thank you everyone for the replies.
I shall investigate more today checking on exactly when the RCD trips. My initial post said it was when the pull-cord was pulled. On speaking with the wife (who was about to use the shower), it could have been when she pressed the shower ON/OFF button. I’d guess if it was the latter this would point to a shower fault.

 

[John Webb]

Most likely cause of an RCD tripping in a shower or other water-heating device is a fault in the element (most likely corrosion of the element sheath) allowing water into contact with the actual live element and giving a path to earth where there shouldn't be one, thus operating the RCD.

 

[OscarH]

An MCB (Miniature Circuit Breaker) is like the old bare wire "fuses". If too much current flows through a circuit, the fuse blows (or the MCB trips). The excess current may be caused by a "short circuit" within a device (or even within the circuit itself) or by plugging in a device that draws more current than the circuit is designed for.

An RCD (Residual Current Device) protects principally against Earth leakage. So if you have (say) a faulty kettle which has become "live", someone touching it may face electric shock as the electricity travels from the kettle, through their body, to Earth. An RCD detects this and cuts the juice before too much harm is done.

Faults which cause an RCD to trip are usually fundamentally different to those which cause and MCB to trip. You can identify an RCD because it will have a push button with "T" (for test) on the outside. An MCB does not.

Of course, this is further confused by RCBOs which do both jobs and have a test button (though these are easy to identify because RCDs will typically cover a group of MCBs, whereas RCBOs are individual)

 

[dangie]

Hello again. Did another test.
With power on and RCD reset, on pulling shower power cord RCD trips straightaway.
The top of the heating element is quite corroded. I don’t know if that is causing the problem but I’m sure it’s not helping. Have tried to attach image.

 

[Ken X]

If you want to further isolate the fault and are confident with electrics you could disconnect and make safe the heating element and repeat the test. Alternatively you could check the element resistance against the specs with the power off. Looks like £96 ish for a new element/tank assembly or £134 ish for whole shower so theres not much in it although it might be easier to swap out the tank. At least you can get parts for it still. My OC Domestic would be demanding a quick fix so hope it goes well.

 

[dangie]

Looks like £96 ish for a new element/tank assembly or £134 ish for whole shower so theres not much in it although it might be easier to swap out the tank. At least you can get parts for it still. My OC Domestic would be demanding a quick fix so hope it goes well.

Have checked for new replacement shower, as you say £134 from Screwfix. Unfortunately, as makers tend to do, the latest Mira Sprint shower is slightly larger than the one I have so will the mounting holes be in the same place? Also the cable entry is different (not really a problem), but the water entry is not the same either, will require a bit of additional plumbing.

 

[Nym]

Unless you’re in Scotland a shower will be classed as being in a Special Zone under BS 7671 so this is notifiable works under Part P of the building regs as such should be done by a qualified electrician.

If you need to be asking on a railway forum what the fault looks like, maybe perhaps you shouldn’t be trying to fault find electrical equipment?

 

[JamesT]

Mira have a service for £110 plus the cost of the new unit they’ll replace your shower. https://www.mirashowers.co.uk/installation/shower-replacement
I used it a couple of years ago as mine was ancient. They identified what the correct current model would be and it was all very smooth.

 

[dangie]

Mira have a service for £110 plus the cost of the new unit they’ll replace your shower. https://www.mirashowers.co.uk/installation/shower-replacement
I used it a couple of years ago as mine was ancient. They identified what the correct current model would be and it was all very smooth.

I clicked on that, uploaded my current shower, came up with a replacement from £404.00.

 

[Trackman]

I clicked on that, uploaded my current shower, came up with a replacement from £404.00.

Did you see the shower repair service?
Just looked my Mira up.
My shower is expensive - new one fitted £510.
Repair job £200 (3 months warranty)

 

[D365]

I’m still concerned about the charring that was found inside the consumer unit. This needs to be addressed by a qualified electrician before recommissioning a shower.

 

[dangie]

I’m still concerned about the charring that was found inside the consumer unit. This needs to be addressed by a qualified electrician before recommissioning the shower.

This was given in a reply to my original post, not by me, but thanks for your reply. As far as I can see my consumer board is ok.

Note: I have an electrician coming to check my existing shower and he will connect up a new one if necessary. I will be doing the plumbing.

 

[66701GBRF]

If you need to be asking on a railway forum what the fault looks like, maybe perhaps you shouldn’t be trying to fault find electrical equipment?

People have experience and advice for things beyond the railway you know.

 

[Nym]

People have experience and advice for things beyond the railway you know.

Maybe more apt to say that anyone asking anywhere about this kind of stuff shouldn’t be working in special zones under Part P.

 

[dangie]

…If you need to be asking on a railway forum what the fault looks like, maybe perhaps you shouldn’t be trying to fault find electrical equipment?

With all respect, doing a few simple checks to see where the fault may lie, is not quite the same as attempting to rectify the fault. I haven’t poked my fingers where they shouldn’t

 

[renegademaster]

If theirs charring inside the unit it's going to be a problem with the shower unit itself and not something with your wider house electric. That said trying to fix itself isn't the best idea but replacing it whole is no worse than changing a light bulb yourself

 

[Nym]

If theirs charring inside the unit it's going to be a problem with the shower unit itself and not something with your wider house electric. That said trying to fix itself isn't the best idea but replacing it whole is no worse than changing a light bulb yourself

I'm sorry but no.

Actually, I'm not sorry. Just NO!

Changing a high power load that requires properly matched cabling and circuit protective devices (to which most people will not understand or have access to suitable training material from the on site guide or BS7671), for which proper installation methods, terminal torqueing and subsequent testing upon installation are required, is not. I repeat several times, not, the same as changing a light bulb! I'm not trying to be offensive here, but that is one of the dumbest ideas of equivalency I have ever heard, and I have worked in some companies with very enthusiastic and ill informed project managers, and this I think beats even most of them!

As I've already said, this work is in a Special Zone according to Part P of the building regulations. I strongly suspect the OP is not "sufficiently trained and licenced" to discharge notifiable works themselves, and therefore this is not work they should be carrying out.

Changing a light bulb is a socketed device designed to be changed by non-trained personnel. Changing (let alone selecting the appropriate rating of) high power devices, in a special zone, is very much not!

 

[dangie]

.…I strongly suspect the OP is not "sufficiently trained and licenced" to discharge notifiable works themselves, and therefore this is not work they should be carrying out.

To this you are correct. Without bragging, my DIY skills are pretty good, but these do not really apply to home electrics. Even though I spent 40 years in a power station making electric, how electric actually works is beyond me ).

All I have done is a bit of basic investigation to see where the problem may lie. Any electrical work will not be done by me.

 

[Nym]

So in short no. Not licensed to work in special zones.

 

[dangie]

So in short no. Not licensed to work in special zones.

Being 73 years young I don’t think I’m licensed to work anywhere apart from the kitchen & garden