What Should I Expect From My Electrician
First step would be to test the RCD itself. As I previously mentioned the chances of the RCD being faulty are very slim but it should be tested as a matter of course none the less.
To test an RCD properly you need a special RCD ramp tester (see second picture below) and it would be worth confirming in advance with the electrician that he owns one. They're generally very expensive (>R20K for a Fluke) and many electricians make do with a very basic tester shown in the first picture that is not capable of performing the full range of tests. If he doesn’t own a full ramp tester then rather find an electrician who does.
Not An RCD Tester
RCD Ramp Tester
If the RCD passes the barrage of tests a ramp tester throws at it then the fault is definitely on one or more of the circuits it's supplying. Second step is to insulation test (IR test or Megger test) each circuit and all the items that get plugged in to check for an insulation fault that would cause an earth leakage fault current to flow.
Megger Tester
The thing with insulation tests is that there's no 100% pass, every circuit has got an insulation value that's less than infinite so every circuit has an earth leakage fault current even though it might be very small. The problem with very small leakage currents is that the RCD sees the cumulative total so if you've got 5 or 6 circuits each with 5 or 6 mA earth leakage then it's already game over because the total is >30mA even though no individual circuit would fail as having an unacceptable leakage current.
This is often where the lesser sparky calls it quits. If he's tested the RCD itself and insulation tested the circuits and there's no fault large enough to peak his interest, this is all too often a good time to get the invoice made out and hope for the best and head for the hills.
In the good old days you could do the insulation tests and from the results you could calculate your expected leakage current under live conditions and the calculations would usually have been pretty accurate. Zoom forward to the 21st century and you now have electronics everywhere and every house or business has dozens of electronic power supplies (switch mode supplies) and even under normal operating conditions they have a small amount of leakage current, it's generally one or two milliamps for each power supply but the RCD unfortunately views this current as a fault and a megger tester can't give any indication of how large these currents are or whether they're large enough to be problematic.
So... the next step for me would be a live leakage test which involves another relatively expensive tester, an earth leakage clamp meter which any good electrician should also own.
Earth Leakage Clamp Mater
The megger tests/insulation tests are dead tests (power is off) and whilst they provide valuable information about the condition of the circuits and appliances they don't tell you how much leakage there is in real-life. An earth leakage clamp meter around the live and neutral on the load-side of the RCD as a live test (power on) will indicate of the difference between the current flowing in the Live and the current flowing in the Neutral. This difference in currents is leakage and it's exactly what the RCD monitors. If that difference is > than 30mA then it trips, even over 25mA it's likely to cause occasional nuisance tripping. The live leakage test needs to be done over a long duration with a tester that has a 'max hold' facility so you can see the maximum level of leakage current that took place over time.
The other advantage of doing the live leakage test during actual real-live conditions is that many modern appliances have internal components that are controlled by 2-pole switching. This means that when there's no power on the appliance, any insulation fault that may be present would not be visible. Live leakage testing will find the fault even if it takes some time.
Finally the incoming supply should be inspected and tested. The incoming supply is unlikely to be causing an earth leakage tripping problem but there are certain main supply faults that possibly could, depending on earthing arrangements etc. It’s also good practice to make supply tests any time a DB is worked on just in the interest of safety, it takes about two minutes to do the tests and it’s peace of mind the earthing is good and the installation is safe.
A good electrician should be inquisitive, he should be checking in the ceiling, he should be rummaging under and around things, he should be removing lids and covers and he should be all over the installation looking for possible problems inside and outside. There are certain faults that all the test equipment in the world won’t find, the only way you discover them is by getting down and dirty and hands on and by being methodical and persistent.
Alas, not all electricians are made of the right stuff. All too often we’ve attended a fault after several electricians have been there before, only to find a litany of bad practice and sometimes downright dangerous ‘repairs’ where the RCD has been bypassed or a faulty circuit has been removed from the RCD as a workaround rather than going to the trouble of actually repairing the root cause of the tripping. The only advice I can offer is to find an electrician who comes genuinely recommended by other people and don’t necessarily go with the guy who has the cheapest hourly rate.
The info above is to give you a better idea of what you should be expecting from your electrician. These tests are not within the realms of DIY, they're dangerous if you're not electrically competent and even with qualified electricians live testing should be done only after an appropriate risk assessment.
Good luck with your tripping faults and stay safe.
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