RCD Faults & Test Meter

[eskimo39]

Evening All, have been to a customers house this evening who is having a problem with her RCD not staying in causing her to be sat with no power all day. When I got there I stripped down the full board and removed all L,N & E conductors from breakers and bars leaving the board in a 'as new' condition. Even with nothing attached the RCD would still not stay in everytime and the few times I got it to stay in to do a ramp test on, it would trip before my fluke even registered any current (0.00mA).

This lead me to believe it is the RCD at fault so I will be replacing that tomorrow. I have installed a small 2 way RCD board which I usually use to put temporary power on building sites and just given her lighting & sockets to get her through tonight. However this even tripped once so I am now thinking there is also a fault on one of these circuits as well????

Does anyone know if I buy a cheap Earth Leakage Clamp meter tomorrow : Dilog DL6507 10uA to 60A AC Leakage Clamp meter. Buy online or call is it as simple of being able to clamp it on the main earth of the installation and take a reading, then re connect each circuit one at a time whilst monitoring the earth leackage shown on the meter until I find one with a noticable increase.

If nothing shows an increase in earth leackage I would then plan on keeping someone monitoring the clamp meter whilst going around the house switching on appliances/lights etc until a noticable rise in leakage shows on the meter.

If then that still shows no increase I would then assume the fault would most likely be on a compressor or something timed, so I would have to go down the awful route of disconnecting appliances etc for periods of time to see if we could solve the fault.

Is this how others would go try to solve this or do you have any other advice you can give. Also does anyone own an earth leakage meter they can recommend???

Cheers

 

[telectrix]

your procedure sounds logical and excellent to me. i can't add anything helpful to that.

 

[eskimo39]

Cheers mate, I am winging it to be honest as I know RCD problems can be so tricky to solve. The hardest part is trying to find the right meter to buy. Whether a cheap £100 will do the job i need it to or whether need to spend £300+ on a megger etc.

 

[telectrix]

can't help you on that one mate. i've only just stopped using AVO 7

 

[s_d]

sorry if im missing something here but could you not do an IR test on each circuit?

 

[eskimo39]

I think a IR test will only show if there is a connection between 2 conductors. If however the fault lies with an appliance leaking to earth when running (eg computer, oven element) I am not sure this would show.

 

[DurhamSparky]

why don't you PAT test the equipment...! ??? may be a long shot?

 

[pushrod]

That clampmeter seems a very good spec for the price - mine was much more than that for very little more - it will also read up to 100A.
TBH i would think you may be able to isolate the problem circuit just through a process of elimination as to which circuit is causing the problem ie switch each one on individually and turning any appliances on that use that circuit. However it can be a cumulative fault ie 10mA on one and 12mA on another and maybe 7mA somewhere else for example.
I would also just clamp the tails as i have come across several properties where you get stray currents in the earth that are completely independent of the installation.


To check individual appliances if you get about 2 metres of flex and put a plug and socket on each end (like a short extension lead) and then cut away the outer sheath only in the middle section so that you can clamp around L and N excluding the cpc . Then just plug the appliances in via your extension lead and clamp L and N (or the CPC) and check for excessive earth leakage. You can then identify what is going on exactly with each bit of equipment. Be aware that it is perfectly normal for appliances with electronic equipment in them to show some leakage eg washing machines microwaves etc and computers can easily give a milliamp or two just by themselves.

edit : forgot to say it is also very useful to get the person to try and keep a log of what was switched on each time the rcd trips - can save time in identifying the culprits.

 

[Deleted member 19807]

when checking each circuit, if its not conclusive when using the mcb's to switch the circuits you may have a neutral/earth fault. you will need to remove all the neutrals and add them back in one at a time until it trips when items are turned on supplied from that circuit. neutral earth faults are a real pain to find.