Annoying RCD tripping problem!

[StainlessRat]

Hi,

Sorry for the long post however I have a problem with a new RC installation that I could really do with some help with.

Basically I recently moved into a rented house which had no shower so I decided to install one (yes, I am aware of part p of the building regualtions and will be getting the installation checked once it is actually working)

The CU that is installed in the house is an old fuse type Wylex one which had no spare fuses, as such I installed a new, secondary consumer unit in the follwing manner:

HB = Henley block

Initially everything seemed fine, the light on the front of the shower illuminates, however the problem is that the moment the button which actually starts the shower is pressed, the RCD trips.

In an attempt to identify the cause of the problem I have done the following:

1) Disconnected the wiring at the consumer unit which goes to the isolator switch. Then using a multimeter I have tested the resistance between all three wires, in all possible combinations. The results were that resistance was infinite, therefore leading to the conclusion that there was no damage to any of the wiring insulation.

I have also visually inspected all of the wiring and connections for any problems; none are present that I can see.

2) I considered that the shower unit itself may be faulty. To remove
this possibility I removed the plug end of an extension lead and connected it to the wiring which goes into the shower. Then I plugged a hoover (the appliance with the highest load I had to hand - 2kw) into the extension lead. The same result occured, the RCD tripped as soon as the hoover was switched on, so I assume it is unlikely to be a fault with the shower unit.

3) I tried connecting the extension lead directly into the secondary CU and to the RCD. Again, using the hoover to apply load to the circuit, the same thing happened - the RCD tripped, which again leads to the conclusion that there is no fault with the wiring between the secondary consumer unit and no fault with the shower unit.

4) With the previous tests in mind I decided that perhaps, even although it is new, there may be a fault with the RCD itself but after replacing it with another new one the fault still persists.

At this point I decided to measure the resistance between neutral and earth on the busbars inside the secondary consumer unit. Much to my surprise the multimeter started to beep, indicating a complete circuit.

The earthing connection for the secondary consumer unit is fed directly from the busbar inside the original consumer unit via a cable so I disconnected it and again tested for resistance between the earth busbar and the neutral basbar in the secondary consumer unit, this time resistance was infinite again confirming no faults between neutral and earth with the new wiring leading to the shower.

The final test that I did was to check for resistance between the neutral cable and the earth cable which feed in from the main fuse and meter which is located in a sunken box outside the house. Again the multimeter beeped indicating a complete circuit.

I appreciate some of these tests are quite crude but my test equipment is limited to pretty much just a multimeter.

My question is: Is the lack of resistance between neutral and earth that I have previously mentioned on the incoming cables causing the
RCD to trip all the time? If so, what is the best solution to correct the problem? If not, has anyone got any ideas to what is causing it to trip all the time?

The RCD which is currently installed as a 30ma one which is the rating recommended by the shower manufacturer.

Any help would be gratefuly appreciated as this is causing me a serious headache and taking up way too much time for what should have been quite a simple job.

Many thanks.

 

[Alarm]

You need to get someone qualified to do this.

 

[holmslaw]

..

 

[StainlessRat]

Thanks for the replies. I think you may be right in that I am going to have to admit defeat and get someone to look at it.

I have wired CU and RCBs before twithout any problems so I am fairly confident that everything that I have done is correct, although there is clearly something amiss and I'm absolutely out of ideas!


I'm doing work on a rented property as the landlord was fine with a shower being installed but not so fine paying for it.

Thanks again

 

[Taylortwocities]

I'm doing work on a rented property as the landlord was fine with a shower being installed but not so fine paying for it.

Thanks again

I bet you didn't tell him that you were going to do it, and not someone who was competent.

yes, I am aware of part p of the building regualtions and will be getting the installation checked once it is actually working)

It doesn't work like that.
Either you do it yourself:,
notify the local authority before starting, and have the knowledge and test equipment to demonstrate to LABC that the installation meets BS7671.
or
You have a registered electrician to do the work.

There isn't a third way. Most registered electricians won't sign off other people's work and the terms of membership of the self certifying schemes specifically prohibits them from doing so.

 

[ban-all-sheds]

I am aware of part p of the building regualtions and will be getting the installation checked once it is actually working.

Your statement about what you will do shows that although you may be aware of Part P of the Building Regulations you are either unaware of, or have no intention of complying with, Part 3.

And everything else you have written shows that although you may be aware of Part P you have absolutely no ability to comply with it or even have any idea of what's involved in complying with it.

 

[flameport]

yes, I am aware of part p of the building regualtions and will be getting the installation checked once it is actually working

Clearly you are not, since checking things 'after they are working' is far too late - they should be properly tested before any power is connected.
The work requires notification before it is started, so once again, too late in this instance - you have already broken the law.

Then using a multimeter I have tested the resistance between all three wires, in all possible combinations. The results were that resistance was infinite, therefore leading to the conclusion that there was no damage to any of the wiring insulation.

That proves nothing, since the output from that meter will only be a few volts.

I removed the plug end of an extension lead and connected it to the wiring which goes into the shower
...
Then I plugged a hoover (the appliance with the highest load I had to hand - 2kw) into the extension lead.
...
I tried connecting the extension lead directly into the secondary CU and to the RCD. Again, using the hoover to apply load to the circuit

Testing in that way is ridiculous and dangerous. First, it proves absolutely nothing about the condition of the wiring or if it is safe. Second, if that circuit had been faulty, your 'tests' could have resulted in you being seriously injured or killed.

At this point I decided to measure the resistance between neutral and earth on the busbars inside the secondary consumer unit. Much to my surprise the multimeter started to beep, indicating a complete circuit.

The final test that I did was to check for resistance between the neutral cable and the earth cable which feed in from the main fuse and meter which is located in a sunken box outside the house. Again the multimeter beeped indicating a complete circuit.

Entirely normal behaviour for many installations, and the fact this is a surprise to you indicates you really have no idea what you are doing.

I appreciate some of these tests are quite crude but my test equipment is limited to pretty much just a multimeter.

Why then attempt work when you have neither the knowledge or equipment to do it correctly?

Your only option is to switch off the power to whatever mess you have made, and contact a competent electrician to do the job properly.

 

[ban-all-sheds]

I have wired CU and RCBs before twithout any problems

How the hell would you know?