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Advice Please - Mains cartridge fused Isolator switch or MCB and isolator Switch.
Former Community Member
I manage a residential mobile home park with homes that individually have mains supply TT coming to a meter box recessed into a breeze block shed. The tails then come from the meter into the shed and into an old style bakelite rewireable 40a fused isolator switch. There is then an outgoing 10mm SWA cable running from the isolator switch underground from the shed to the home and then into the consumer unit for the home (total run approx. 8 to 10 metres). Having had an EICR for one of the homes I have been adviced that these isolator switches will need to be replaced as the swa cable is not properly terminated (it is not glanded in to the isolator switch and the wire stranded sheathing is twisted together and connected to the earth block.) My question is can this isolator switch be replaced with an 18th edition 3 way metal enclosure with double pole isolator switch and 40a mcb or should it be replaced with a 60a (or 40a) cartridge fused double poled mains isolator switch. Additionally would it a be a good idea to put a 60a RCD into the shed and either use a five way enclosure (in place of 3 way enclosure) or a 2 way enclosure fed from the cartridge isolator switch. All the homes have a standard consumer unit containing either a 60a or 80a RCD and 3 to 5 suitable MCB's (32a, 16a, 6a).
1) TT needs a very low Z earth electrode if there is no RCD, it is not clear if you have one.
What is the armour of the SWA connected to? Where there is a pre RCD live wire inside the SWA the armour earth needs to be a good enough earth to operate some ADS of some kind if the cable is ever spiked !!
(but it does not mean you need to have a 30ma RCD at the origin, either 300mA or 100mA and in either case with time delay would do, so long as there are 30mA ones further along before you get to customers sockets)
2) The armour wires of your SWA are not glanded.
Ugly and a bit rough yes, but not really a regs issue so long as the armour wires have been properly marshalled into some sort of earth terminal.
You could make still it look nice and still retain the existing switch if it is in good order.
That could be done by peeling back the SWA outer jacket only, and glanding the SWA armour into any suitable small box somewhere beside the switches and taking a CPC from there (pirahna nut if box is plastic ) along with uncut the cores and inner' bedding insulation of the SWA straight out of the new box, and continue straight into the existing gear as before, either close butted or in plastic conduit if it needs to run in the open for a bit.
(While the inner of an unzipped SWA looks and behaves like a rather willful flex the makers do not specify if it meets the requirements of being insulated and sleeved - like T an E . A bit of conduit or plastic trunking makes up for that.)
1) TT needs a very low Z earth electrode if there is no RCD, it is not clear if you have one.
What is the armour of the SWA connected to? Where there is a pre RCD live wire inside the SWA the armour earth needs to be a good enough earth to operate some ADS of some kind if the cable is ever spiked !!
(but it does not mean you need to have a 30ma RCD at the origin, either 300mA or 100mA and in either case with time delay would do, so long as there are 30mA ones further along before you get to customers sockets)
2) The armour wires of your SWA are not glanded.
Ugly and a bit rough yes, but not really a regs issue so long as the armour wires have been properly marshalled into some sort of earth terminal.
You could make still it look nice and still retain the existing switch if it is in good order.
That could be done by peeling back the SWA outer jacket only, and glanding the SWA armour into any suitable small box somewhere beside the switches and taking a CPC from there (pirahna nut if box is plastic ) along with uncut the cores and inner' bedding insulation of the SWA straight out of the new box, and continue straight into the existing gear as before, either close butted or in plastic conduit if it needs to run in the open for a bit.
(While the inner of an unzipped SWA looks and behaves like a rather willful flex the makers do not specify if it meets the requirements of being insulated and sleeved - like T an E . A bit of conduit or plastic trunking makes up for that.)
