As with previous posts, I'm always somewhat ginger about posting questions like this, because there may be something obvious I'm overlooking which could make me look foolish. But as the old adage goes, 'there are no stupid questions' (well, not completely true, but anyway), and if it helps with my learning then I'm willing to accept some embarrassment.
This is a slightly convoluted question too, and I partly, perhaps, answer it myself here, but it doesn't matter if people are minded not to reply, and I'm always interested to read what replies, if any, contain in response to my posts. (As an aside, tbh that is one of the things I really like and value about this website, there's clearly a massive knowledge base, and when for various reasons I've not been able to get satisfactory answers from other professionals I know, these forums have repeatedly been a source of very interesting, useful and helpful feedback. Anyway enough waffle.)
I'm studying for my 18th edition exam, and in section 740 of Part 7, which relates to Temporary Electrical Installations (Structures, Amusement Devices etc) under the heading 'Protection for Safety', nowhere does it mention OCPDs. It just talks about RCDs. My understanding is, say if you had a fault within the machine, a fairground ride for example, and the load started drawing a huge current, as long as that same current was also going back down the neutral, surely the RCD would not trip? Because it is only looking at the comparison of current between line and neutral. So the cables could start to melt or catch fire.
Later in the section, under Isolation and Switching, it does state "Every electrical installation of a booth, stand or amusement device shall have its own means of isolation, switching and overcurrent protection, which shall be readily accessible". So it is mentioned, but I would have expected to see that mentioned under Protection for Safety (specifically, there are subsections therein called 'Protective Measure: Automatic Disconnection of Supply' and 'Protection Against Thermal Effects', surely you'd expect to see something in either of those two subsections about OCPD's?), and in keeping with earlier chapters, I would have expected to see OCPD's mentioned before considerations about RCDs.
There are other sections of Part 7 where this has occurred to me as well, there didn't seem to be mention of OCPDs.
This is a slightly convoluted question too, and I partly, perhaps, answer it myself here, but it doesn't matter if people are minded not to reply, and I'm always interested to read what replies, if any, contain in response to my posts. (As an aside, tbh that is one of the things I really like and value about this website, there's clearly a massive knowledge base, and when for various reasons I've not been able to get satisfactory answers from other professionals I know, these forums have repeatedly been a source of very interesting, useful and helpful feedback. Anyway enough waffle.)
I'm studying for my 18th edition exam, and in section 740 of Part 7, which relates to Temporary Electrical Installations (Structures, Amusement Devices etc) under the heading 'Protection for Safety', nowhere does it mention OCPDs. It just talks about RCDs. My understanding is, say if you had a fault within the machine, a fairground ride for example, and the load started drawing a huge current, as long as that same current was also going back down the neutral, surely the RCD would not trip? Because it is only looking at the comparison of current between line and neutral. So the cables could start to melt or catch fire.
Later in the section, under Isolation and Switching, it does state "Every electrical installation of a booth, stand or amusement device shall have its own means of isolation, switching and overcurrent protection, which shall be readily accessible". So it is mentioned, but I would have expected to see that mentioned under Protection for Safety (specifically, there are subsections therein called 'Protective Measure: Automatic Disconnection of Supply' and 'Protection Against Thermal Effects', surely you'd expect to see something in either of those two subsections about OCPD's?), and in keeping with earlier chapters, I would have expected to see OCPD's mentioned before considerations about RCDs.
There are other sections of Part 7 where this has occurred to me as well, there didn't seem to be mention of OCPDs.
