Discuss 18th edition exam question.. in the UK Electrical Forum area at ElectriciansForums.net
Sounds about right to me.There's me thinking an RCBO protects against over-current and earth fault current?
I think it's a genuine exam question, one of perhaps a few which the 'experts' have wrong. I can remember a similar situation with the 17th exam, where I stated the obvious answer but it was 'wrong' apparently. Even the course tutor agreed. However, this time I've skipped the course and just booked the exam so I have no tutor to back me upSounds about right to me.
I think it’s just a poorly worded example question and for what it’s worth, I would’ve picked your answer too
From the BBB: "A residual current operated switching device designed to perform the functions of protection against overload and/or short circuit"It does, and IMHO it's a really bad question. I remember that one from my exam and I'm now fairly sure I got it wrong!
I don't have BBB here at home but in the definitions section at the beginning does it have "earth fault current" listed?
It might be that "earth fault current" is more associated with "prospective earth fault current" in the regs, and answer one isn't technically using correct terminology in the mind of whoever wrote the question, in which case answer 4 is the closest.
But it's a definitely a poor question!
From the BBB: "A residual current operated switching device designed to perform the functions of protection against overload and/or short circuit"
So it doesn't protect against earth fault currents??
(Tangent, but the question I got hung up on in exam related to:
463.1.2
"A single-pole switching device shall not be placed in the neutral conductor except for the connection of the control device for lighting circuits as shown in Fig 46.1"
The question was basically " when can you switch the neutral conductor in a lighting circuit" and I was sitting there thinking "never?!"
)
Basically a contactor/relay, because the switching circuit that energises the coil is not connected to the lighting itself, so switching the N of the coil doesn’t leave the lights live. Never used that fact since!I'd think the same. But I still can't work out what a 'single pole switching device' (switching neutral only) for control of lighting circuits actually is?
I was going to do that to save conductors for some relay-controlled floodlights but the guy we used for our power feed advised against it as it is so rare it is likely to bite someone else in the future who did not expect it and did not read the documentation (or documents got lost, eaten by local dog, etc).Basically a contactor/relay, because the switching circuit that energises the coil is not connected to the lighting itself, so switching the N of the coil doesn’t leave the lights live. Never used that fact since!
Does anyone else think these are real smart a**e questions put there just to catch candidates out and not necessary to be there at all?
RCD's and MCB's are designed with a purposeBooked in for my 18th edition exam, so I've been doing some mock exams online. Can anyone explain this one? There's me thinking an RCBO protects against over-current and earth fault current?
I disagree. Nothing to do with technical terms, it's just really badly put together. The question (or statement if you like) has 4 answers, 3 of which are correct: 1,2 and 4.Hi guys,
Looking at this question in detail, I would like to add my two pennyworth. I think the question was sound and correct. It is peoples mis understanding of technical terms that leads to questions being interpreted as not being correct. In part two (definitions) of the regulations it clearly states what an RCBO is designed to do. However could I deflect your attention to the table A53.1 on page 188 of the regs book. There you will see that an RCBO has functions to protect against:
Overload, Short circuits and Residual Currents
whereas an RCD (as one of the RCCB family) only protects against Residual Currents
and Residual currents are again described in Definitions part 2.
Therefore both protect against Residual Currents, but of the two only the RCBO protects against short circuits
Enjoy the Bank Holiday, I need to get out more.
Regards
JohnC
That is also a big dodgy.Another question I'd like to take issue with! Regulation 411.3.2.3 clearly states a maximum of 5 seconds. The question clearly asks for the 'maximum' What am I missing?
I chose 5 seconds, but the 'correct' answer is 0.4ms apparently...That is also a big dodgy.
For a TN supply it is 5s sub-main or 0.4s for a final circuit. But the one you ticked was 0.4ms which is not feasible for a 50Hz supply!
Well they have a mistake in the list!I chose 5 seconds, but the 'correct' answer is 0.4ms apparently...
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