Shower Tripping

[Gibbo100]

I hope someone can help me. 
Firstly I am not a electrician. But I do know a fair bit about most DIY..
Recently my mira advanced ATL thermostatic shower started tripping my separate RCD. As I was not sure that the shower was at fault I brought a like for like second hand unit and replaced it. The RCD did stop tripping for a while but the new (second hand) shower just kept shutting off and going to RESET mode!
Soon it was also tripping the RCD again..
I have a wyelex consumer unit feeding a separate RCD which was 32 amp.
I replaced it for a 40 amp fuse. 
I did the maths and it does require a 40 amp I believe. ( 9kw)
It was still tripping the RCD. 
out of desperation I changed the double pole pull switch ( it looked a bit manky)
Still no joy.
I put the old shower back, as I was now thinking that the second hand shower I brought was no good,
Still tripping. 
I tried testing the heater element within the shower with multimeter..
0.5 ohms resistance? I think i did it right. The shower doctor on the Internet said I should be getting 11 to 18 ohms!
Then I brought a brand new shower and the resistance was the same, so I think the second hand one was good, probably along with the original!
I have not fitted the brand new one as I have spent too much already and may sell it. 
I guessing all that can be left is the cabling.
I got what looks like 10mm from CU to RCD and 6mm to the pole switch and then to shower.  
Should I and how do I test the cabling? 

 

[Doc Hudson]

I hope someone can help me. 
Firstly I am not a electrician. But I do know a fair bit about most DIY..
 

Welcome to the forum Gibbo100. Unfortunately it looks like you may have suffered from the same problem as many DIY people who think they understand electrical installations. Completely missed the point of what makes an RCD trip. I would suggest that you need to have both the cable and the RCD properly tested with a calibrated Insulation resistance tester, continuity tester and RCD tester. What test equipment do you have access to? Multifunction meters to perform these tests cost typically anything from £400+ to £900+ dependent upon make. Test equipment can be hired from some tool hire shops, but it may be cheaper to get an electrician to come and do a comprehensive test for you. Was the shower installed correctly in the first place? do you have the test certificates and original readings for when the shower was first installed? 

Doc H.

 

[Gibbo100]

 Residual current?
No cert as I fitted it myself, as per sparky  friends instructions.
Worked fine for years.
Access to hand held multimeter.
Is installed as follows.....
CU to separate RCD (10mm t&e) 300mm length
Separate RCD to double pole switch (6mm t&e) 9 meters approx length
Double pole switch to shower (6mmt&e) 1 meter length
The pole switch should be un reachable while in the shower, but it isn't but appart from that I think it wired ok..?
Think I might have put this topic in the wrong place? 

 

[SLIPSHOD & SLAPDASH]

This needs checking with a insulation resistance meter and a rcd tester. A multimeter will not do but after turning off try testing resistance between all cores of cable with everything disconnected.

 

[ProDave]

As already said you don't really have the right gear to do the tests, but here's something you could try.

Disconnect the shower cable in the consumer unit.  Measure resistance with your multimeter from the L of the shower cable to E. then from N to earth.  you should get open circuit or a very high resistance on both. Come and tell us what your meter reads.

If you get a low reading, then disconnect the cable from the shower and repeat the measurements.

This will be very inaccurate as your multimeter will be measuring resistance at typically 9V, whereas a proper insulation tester will be applying anything between 240V and 1000V to make that measurement, so will find faults more reliably.

 

[Badger]

sounds to me like a earth leakage through cable, but unless an electrician meggers/insulation resistance tests it its difficult to say,

 

[Doc Hudson]

 Residual current?
No cert as I fitted it myself, as per sparky  friends instructions.
Worked fine for years.
Access to hand held multimeter.
Is installed as follows.....
CU to separate RCD (10mm t&e) 300mm length
Separate RCD to double pole switch (6mm t&e) 9 meters approx length
Double pole switch to shower (6mmt&e) 1 meter length
The pole switch should be un reachable while in the shower, but it isn't but appart from that I think it wired ok..?
Think I might have put this topic in the wrong place? 

Thread moved. From what you have said your sparky friends guidance sounds dubious if he failed to recommend you had the cable correctly IR tested. As said your situation is a common problem, someone installs an electrical items switches it on as it appears to work OK, so  assumes everything else is correct and safe. Your RCD tripping was indicating an earth leakage fault, but you have not done any tests to verify where this leakage could be occurring. Overload, fuses blowing and Earth leakage are very different types of fault. You need to test in relation to the fault symptoms experienced, not just random irrelevant tests. There could be a damaged cable, poor joint somewhere, exposed conductors inside an accessory making some contact. Swapping shower components as a first step is an expensive trial and error investigation. An electrician with appropriate test gear should be able to verify the cable integrity, polarity, earth connections, correct RCD operating times, etc. within an hour. I would suggest from what you have said you would be best to employ someone to come and carry out the correct electrical tests. this should then give you a clear picture of the probable cause.

Doc H.

 

[SPECIAL LOCATION]

Maybe lose connection at one of the terminations, causing overheating of the cable while the shower is running....

(very few DIYers know how to correctly tighten connections or dress cables in an accessory)

....Softening the insulation till 'N' makes partial contact with 'CPC'

Thus RCD trips after shower installed for a while??

OR..

Mice chewing the cables in the loft???

opcorn   

 

[Gibbo100]

Checked cables in loft and visibly that are ok..

could have chewed some under floorboards. 

Forgot to mention, that shower runs on cold, but as soon as you turn the heat up, and the switches in the shower start switching, it trips the RCD..

Those resistance test, as I'm not to confident I'm getting the wires back in to the consumer unit, can I just do it at the shower end? 

 

[Doc Hudson]

Checked cables in loft and visibly that are ok..

could have chewed some under floorboards. 

Forgot to mention, that shower runs on cold, but as soon as you turn the heat up, and the switches in the shower start switching, it trips the RCD..

Those resistance test, as I'm not to confident I'm getting the wires back in to the consumer unit, can I just do it at the shower end? 

No.  You will get false readings if the cables are still connected at the consumer unit. Pro Dave's description is post#5 is correct. If you are not confident removing and re terminating cables at the consumer unit, then now is probably the time to get professional help in with the correct test gear. 

Doc H.

 

[Gibbo100]

I know, I'm trying. Can't get hold of my mate. 

I could do it.  Just a lot of wires. 

Can I disconnect from RCD? Instead of the CU, and test at shower end? 

What I have just done is with RCD switched off, put my probes from multi meter in pole switch.

L to E and N to E and then in shower, the same.

getting an infinity reading ( a 1)

then I switched on the RCD, and did it again in the shower L to E, and it tripped the RCD.

Does that mean anything? 

Ok. With power on probes in N And E getting readings Of 0.06 to 0.13 

multimeter on ohm 200

no tripping.

 

[Evans Electric]

Hi  Gibbo,   the test you did between L-E  would trip the RCD  in any case  as that is it's function .

If ,as you say, the RCD trips when you change from cold to hot , it indicates ( without testing) that the cable is probably OK  and if both showers tripped the RCD ...then the RCD may be tripping prematurely .   DO NOT BE TEMPTED TO TAKE IT OUT OF THE CIRCUIT.  That can be checked by a Sparky with the right tester.   Or you could replace the RCD if you feel confident .

It may have been cheaper to get a Sparks in at the begining

May I point out that earthing on a shower is the most important thing in the galaxy ,when you put it back into service.     

 

[ProDave]

If it trips when the heater comes on, then very likely a failed heating element. That can only be tested inside the shower.

Best to call an electrician I think.

 

[Gibbo100]

Ok. That was my thinking ( heating element) and that's what I tested. I went on you tube and watched a video by the shower doctor. 

PICK tested the resistance and was getting low readings. He said I should be getting 11-18 ohms. I was getting 0.5 ohms. On both the original one and the second hand replacement. Which led me to believe that the second hand one was faulty too!

thats why I brought a new one.

which I tested as soon as I got it, and got the same readings,,!

couldnt believe it. 

Anyways I just fitted the brand new one, and all seems fine

i now think that the first and second one had PCB faults. 

Either ways it seems that buying a second had replacement cause me a lot of bother!

but thanks for all the help and advise. 

Really appreciate it 

 

[ProDave]

What you needed to check on the heating elements was not the resistance between one terminal and the other, but the insulation between either terminal and earth. that should read infinity or very close to.  but it's unlikely your multimeter would show up the fault anyway.

I would never buy a second hand shower. you can get them new for under £50 so why bother?

 

[Gibbo100]

£300 new. 

£60 second hand. 

Managed to. Get new with damaged box for £180. 

 

[ProDave]

I wouldn't pay that much. 6 times as much as a cheap triton. 

It won't heat the water any better. Just looks nicer, and with lots of fancy controls to go wrong and cost money to fix.

 

[Evans Electric]

I agree with PD on that one .   I fitted a Redring (specified by Social Services for an elderly disabled lady)  The ones with the Anti -Scald circuitry but it was nothing but trouble.  Cost about £280.00 .   Handed it over to Redring Engineer as it kept cutting out .   

Nice & simple Triton with as few special features as possible to go wrong.

 

[steptoe]

I agree with PD on that one .   I fitted a Redring (specified by Social Services for an elderly disabled lady)  The ones with the Anti -Scald circuitry but it was nothing but trouble.  Cost about £280.00 .   Handed it over to Redring Engineer as it kept cutting out .   

Nice & simple Triton with as few special features as possible to go wrong.

I have one of those redrings on my house Deke,

brilliant shower, when they work, we had loads of callbacks to them also, I deffo wouldnt pay full price for one,

it really does seem to be pot luck if you get a good one or not, mine been in 5years now and still never a problem,

but, the anti scald thing is good for the little one, esp as he can now reach it.,!