RCD adaptor trips main fuseboard RCD when tested

[pappyon]

I have just recently moved to a house with a RCD fitted on the main fuseboard. I have never had experience of modern RCDs before.

I have a portable RCD adaptor which you plug into a socket just like an ordinary adaptor, and the last twice I tested it according to the manufacturer's instructions it caused the main house RCD to trip.


Surely this shouldn't happen? Is the house RCD too sensitive or what?

 

[ColJack]

with a house rcd you don't need the rcd adaptor..
by testing it you are putting a current to earth.. if the house already has a small leak on it ( from things like computers and such ) then it takes less to trip it as it's already part way there..

 

[pappyon]

I appreciate exactly what you are saying coljack!

But this RCD is for equipment outside the house!

As you may recall you participated in a thread I had running on this subject below a few days ago

The RCD adaptor is for use with a lead which is fed outside the house to charge the battery of my car which is on charge 24 hours a day and the cable will get wet occasionally with rain.

The socket on the lead and the plug to the battery charger are out of the way of the elements in the boot of the car, but I am thinking of the cable itself!

In the light of this would you still say this plug-in RCD is not needed?

PS
The PC which is upstairs gets switched off also when this happens

 

[ColJack]

you don't need a plug in RCD if the ring is already rcd protected..

 

[ban-all-sheds]

the cable will get wet occasionally with rain.

 

[rebuke]

As has been said - if the circuit is already protected by a 30mA RCD, then there is no need to put a second one on, it serves no function as such - any fault should in theory take out both RCDs anyway...

This is why when you push the test button on your plug-in RCD, it generates a small fault condition to test the RCD, since that fault condition is also seen by the RCD in your consumer unit, it also trips.

 

[pappyon]

I'm sorry ban-all-sheds but your post has completely gone over my head I'm embarrassed to say unless it's to advise me to get a car port, and I definitely don't understand French

 

[JohnD]

I don't believe it will do any harm to have an RCD adaptor on a circuit protected by an RCD. occasionally RCDs fail (especially if they have not been regularly tested) so this gives you an extra measure of reassurance.

I agree it will be tiresome to have the whole house lose power when you test your adaptor though

Does the house have a single RCD in the consumer unit protecting all the circuits? Or are some non-RCD? In the past, it used to be common for cookers and lighting circuits not to be RCD protected; in this case you may be able to plug the adaptor into a Cooker switch socket to test it.

When you have two RCDs, although it is a matter of luck which RCD trips first, or if they both trip together, I have found that the adaptors tend to trip faster using an external test that the CU ones do. I have thought this was probably because the parts were smaller and lighter, or perhaps they were electronic and the house one wasn't. However I have also found the adapators to have a shorter life, possibly because they are cheaply made, or possibly because they get thrown about. An unreliable RCD adaptor should be smashed with a hammer and thrown away so that no one trusts their life to it.

 

[pappyon]

Quote

Does the house have a single RCD in the consumer unit protecting all the circuits?

Yes a 30ma and when it trips it puts everything off in the house bar the lights. It's very annoying when the PC switches off!

There is one socket which I converted from a FSU which fed the old boiler timer switch which was replaced. Could I test it in that even although it is only 5 amps?

 

[JohnD]

You could, but I don't think that will help as you say the whole house is protected by a single 30mA RCD

BTW this was never considered good practice. If you can post a pic of your consumer unit with the door open (no need to take the cover off) and preferably also one showing the meter and the incoming supply and the cables between and around then all, especially the green and yellow ones, we may be able to comment on how to improve the installation.

 

[pappyon]

John D

Stupid of me to think the FSU I converted to a socket would not be influenced by the main RCD. As I said, everything goes phut except the lights

In relation to your request I don't have a digital camera and even if I did I wouldn't have the faintest idea of how to post a picture.

Apart from that, I don't have the technical knowledge to make any changes to wiring etc.

How often should I test this RCD adaptor, as I could always take it to a relations's house who doesn't have an RCD on his fuseboard which was installed in 1970.

 

[ban-all-sheds]

Isn't the advice to test it every time you use it?

 

[JohnD]

Each time you use it is recommended

However you should test your house CU RCD every few months, and using the adaptor will be a good way to test it

Only downside is that you may have to reset clocks and things afterwards.

It is a good idea to put a luggage-label or something on the CU with the dates of your tests. Failure-to-trip increases a lot when they are not regularly tested (I suppose they jam or something).

If you know anyone with a mobile phone that can take pictures, that might do (if it attaches to a computer). If you manage it, instructions are in my link or on the "Forum Information" page.

 

[pappyon]

Quote
Isn't the advice to test it every time you use it?

AS I have said it is in use 24 hours a day. Does that mean I should test it every day

 

[pappyon]

Sorry
I don't know anybody with a mobile phone that takes pictures