Secondary RCD Protection?

[Demonic]

I have a Wylex (NHRL12SL)split load consumer unit and the two socket circuits are on the RCD side.

Just lately the RCD has been tripping out. It will be fine for a day and then trip three times in short succession. I have several computers on the circuits (3 downstairs and 2 upstairs) and I think that these may be causing the tripping. I was wondering if:

a) I could plug the computers in through an RCD adaptor?
b) if there is an RCD adapter with a lower rating than the 30mA that is in the consumer unit?

If the answer to b is No, what would trip first if I were to plug the computers into a normal 30mA RCD adaptor. I am guessing that the RCD in the consumer unit could be tripping due to a combined load from the two circuits and, if so, that the RCD adaptor wouldn't solve anything. Is that correct?

Is the only other option to get some RCBOs and connect the circuits to these, in an attempt to identify the suspect circuit? If so, does anyone know if the consumer unit that I have can be amended, as all non-RCD ways are used. Can I get the RCD replaced with a standard main switch and put the RCBOs in?

I apologise for all the questions and hope the above makes sense.

Thanks in advance for any replies.

 

[Chri5]

Are any of the PC newly added, some are bad with earth leaks and the older they are (the cases / PSU) the more of an issue it is.

Another alternative might be to run the PC's via an always on feeder UPS.

 

[JohnD]

It is always worth starting by unplugging your watery and heating appliances like immersion, kettle, washing machine, oven, tea urn and boiler. When I used to PAT it was usually watery appliances, or ones with a heating element, that had earth leakage on. It is rare to find it in anything else (except a computer) unless there is damage. Also look at flexes, plugs and sockets for signs of damage. If you have any outdoor accessories (lighting, socket, pool pump) isolate that. They often get rain in.

The "lawnmower RCD adaptor" is worth a try as in my experience they trip very fast, so there is a possibility you might be lucky enough to have the adaptor trip before the CU RCD. You can't count on it though.

The better makers like MEM do make 10mA RCDs and RCBOs, they are used in hospitals where there is a risk patients will have tubes and wires poked into their flesh, increasing danger of shock. They are expensive as not sold in great volume.

 

[Demonic]

Thanks gents.

The PCs all have reasonably recent PSUs made by well-respected manufacturers. That's not to say that one hasn't developed a fault but replacement could be an expensive exercise.

The immersion, oven and hob are on three separate non-RCD circuits so I think I can rule those out?

My girlfriend says that after we reset the RCD the washing machine and fridge in the utility room don't come on for a little while after the other appliances. Maybe a minute or so. I haven't validated this though.

Anyhow, I had a quick look at the CU and I seem to have 2 spare ways on the main switch so I think that I may get an electrician to pop a couple of RCBOs in there and move the circuits over. That should at least allow me to narrow down the possible suspects (unless I'm unlucky to have them both trip at the same time). Maybe I could save some cash by buying one RCBO and moving one circuit, leaving the other on the RCD, effectively isolating them that way.

Are there any "passthru" type testers that simply place between an appliance and the socket that will tell me how much earth leakage there is? I obviously don't want to be paying out for a full test meter and I am concerned that an intermittent problem such as this may be difficult (and hence expensive) for an electrician to trace.

 

[JohnD]

A PAT tester will measure earth leakage from an appliance tha you plug into it, and if you ask your electrician before he calls, he may well have or hire one. They cost some hundreds of pounds to buy new. I suppose you may be able to pick up a used one that is out of certification on Ebay.

Not all electricians will have one as it is a very tedious job to do.