TESTING AN RCBO AT A LIGHT SWITCH

A loop test to confirm there is an adequate earth is always required before a RCD test on circuit cable such as a twin and earth.


Andy B.

One could say, in some respects then,that testing at the remote end of a circuit has the advantage of potentially  revealing other faults and thereby improving the integrity of the circuit.

Any such problems that might affect the safety of thr circuit should have already been detected by previous tests (insulation resistance and c.p.c. continuity) before you start doing any live tests such as RCD tests.


- Andy.

Just gone 9.00 pm on a Sunday evening I have finished filing this weeks minor works certificates having been doing the relevant invoices and emailing them along with scanned copies of the MWC.


So before turning my desktop off I had a look at one of the YouTube video links posted by Zoomup and it rolled onto another one about changing a light switch.


I cannot image the consumer unit was opened for testing and actually I didn't notice any testers being taken into the building to do any testing at all, but the chances of the installed replacement switch being dangerous must be virtually nil as no shock risk is likely.


Andy

To what ends?

If you can carry out a two wire non-trip earth loop test to confirm earth continuity and a RCD test at the light switch, what is to be gained by dismantling the consumer unit?

Thanks  mapj1.

No particular fault in mind.

It just struck me that periodic testing Zs at the light switch is very convenient.

So why not, for the extra minute or so, test the RCBO.

Some colleagues have been adamant that RCBOs must be tested at the D.B.

Regards,

Mike.

What sort of fault are you testing for? - if it is to be sure the light switch is earthed, then that is a a sensible thing to verify, especially if you are working on the lihgting circuit in that room, or there is a problem with it.

However, so long as there is CPC contiuity, and the RCD trips at some point, I'd not too get hung up  on a specific accurate answer - for example if the RCD still trips at In/2, well that may just mean there is already a lot of leakage present, quite possible with a large office full of electronically ballasted lamps, and the tester pushes it over the top.

Equally a large capacitive load may make the power seem to hold up longer than expected after tripping, so it may fail the 40ms test and appear  a few tens of msec slow.

To verify the RCD functions perfectly  on its own yes it needs to be isolated from such effects, but unless you have good reason to suspect it of being faulty, this is is just a lot of extra aggro for  something that may introduce more new problems than it solves.

Of course, if the RCD never trips, even at X2 or X5 or if there is no CPC to the fitting at all, then you have found something that will need looking at, and as part of that an RCD test is then worth it.

If you are just replacing a broken light switch are you really going to dismantle the consumer unit for testing?


Andy