I went to the Elex show at Coventry today and spoke to various people regarding how and when BS7288 RCD devices can and should be installed and used, only one person seemed to have formed a clear and definite opinion; and it's not a opinion that everyone else would readily accept as being the definitive answer.
I would describe the general level of understanding regarding the requirements of BS7661 and if BS7288 RCD devices meet those requirements as confused.
Yesterday I bought the new IET Guide to temporary power systems practitioners guide, published this year 2019.
I may be about to get involved with a Santa's sleigh mounted on a trailer with a generator, lights and sound system, so I was looking through my new reference book and spotted an anomaly.
I have read all of the above and am confused I do not have the relevant BS standards apart from 7671 and being retired I have no time to try and understand the detail. Don't criticise lack of time in retirement until you have tried it :)
While semi retired the odd friend gets through my defences. So when Mike the farmer asks me to install an outside socket on the back of his barn to occasionally run a fan to air the corn stored in his second metal hand tower purchased cheaply at auction what are the options? He has a three phase TN-C-S incomer to his calf shed with a concrete floor covered in Part P, he usually puts some straw down in front of the incomer if I am going to work at the board, with a submain (no RCD protection) to a second three phase board, now obsolete, in an open front barn cum workshop with a sandstone floor again with no RCD protection.
So from what I have read above, if I do the job according to the regs I have to TT the installation or at least the second board which would require a new TP board with single phase RCBOs and TP RCBO for a submain to third board that has been wired underground in concentric and put in rods to the sandstone. Then I can put a double outside socket fed by SWA. Cost £700 plus.
OR I put in a small SP RCD TT board adjacent the second board along with rods into sandstone and feed the socket from that. Cost £200 ish.
OR I could ignore the regulations and do what many of have done for years: put a RCD protected waterproof double socket fed in SWA from an existing MCB. Cost £70 ish,
OR he knocks a few bricks out of the back wall and runs an extension lead from an existing non RCD protected socket and stuffs the socket and plug in a plastic bag. Cost £15.
I have his safety as a concern as does he but while he is prepared to spend a little to be safe he does not have the money to go mad.
He has a three phase TN-C-S incomer to his calf shed with a concrete floor covered in Part P
Certainly doesn't seem ideal for a PME supply (although I'd be a lot less worried if it was PNB).
So from what I have read above, if I do the job according to the regs I have to TT the installation or at least the second board which would require a new TP board with single phase RCBOs and TP RCBO for a submain to third board that has been wired underground in concentric and put in rods to the sandstone. Then I can put a double outside socket fed by SWA. Cost £700 plus.
Or stick in a say 4-pole 300mA S-type in an insulating enclosure (REC 4 kind of thing) in the tails upstream of the first DB and a rod - and leave all the existing switchgear as is? Then just add some DP 30mA RCDs downstream as and where you need them. Not ideal of course, but a lot cheaper.
