I was asked why the change to six months. To be honest, I couldn’t answer with confidence. I did hear that folk might be more inclined to test the RCD at the twice yearly clock change. Can anyone point me to an authoritative explanation?
All modern RCD testers are required to carry out a loop test before application of the RCD test. If the loop would cause more than 50v to be dropped due to the RCD test current then the test is required to be inhibited. Some testers have a facility to adjust this so-called touch voltage down to 25v.
Any way, it looks like none of us would have scored points for this question in the 2396 exam unless the acceptable answer was indeed related to the bi-annual clock change.
I am fielding an enquiry to the CandG external verifier.
By the way, across the nation 70% of the folk sitting the exam failed. Perhaps off the rail type questions like this didn’t help.
Oh dear, well that is the one to be "dumbed down" next as the QCA will be on the case! My experience is that very few consumers test the RCDs ever, and with RCBOs they are confused even more and don't even look. But that is life. It, therefore, matters little what the label says, six months is no worse than 3 months, and accident rates are virtually zero, so realistically does it matter? This is not a good exam question, it is not useful to most candidates, they are already scared stiff of electricity and their only thought is H&S, not the fundamentals of real designs.
All modern RCD testers are required to carry out a loop test before application of the RCD test. If the loop would cause more than 50v to be dropped due to the RCD test current then the test is required to be inhibited.
The assumption is that this is to detect a broken cpc ... but if the RCD is in an IT system (which is covered by BS EN 61557-6), that may well not be the case, as there may be no return path down the cpc at all, and the upstream/downstream method used. I think it's a general "catch all" if there's a problem detected with the test path?
In addition, where voltage detection is used, the "fault voltage" may persist for some time until the test current is disconnected (time based on Figure 1 of IEC 61010-1 ... but in general this must be DRY condition AC because 50 V exceeds the WET condition). There is no guarantee people will be protected, particularly children (although this is the case with RCDs themselves, we are introducing the hazard with the test instrument, deliberately so, and therefore this must form part of the risk assessment).
Some testers have a facility to adjust this so-called touch voltage down to 25v.
Otherwise testing in Medical Locations (Section 710) and Fuel Filling Stations (APEA/EI Blue Book) would not be possible. Depending how the test instrument does this, it may provide protection better than "DRY" condition in Figure 1 of IEC 61010-1, but there is no requirement in the product standard for this.
Any way, it looks like none of us would have scored points for this question in the 2396 exam unless the acceptable answer was indeed related to the bi-annual clock change.
Very interesting. Where would I find that in BS 7671? Or IET Guidance? As far as I know there are no references to the 6 months being related to clock changes or daylight saving etc. (although I could have missed it ... I did try a text search in the digital editions for related words to no avail).
I am fielding an enquiry to the CandG external verifier.
Excellent idea.
BTW, I have sent you a PM!
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