Existing split load 17th Install RCD question

[John-]

Customer has a large metal caravan with three phase supply feeding 3 metal Consumer units with split load RCD outlets contained within - all circuits originate form a RCD. The Boards are then fed from a TP isolate a few feet away, the earth is disconnected on eth SWA and a rod installed near by. ZS ifs pretty good around 30ohms or so.

There are is no RCD in line with the supply to the boards. These are MK Sentry CUs, and the internal wiring is only single insulated and as i read the OSG p21, there should be an RCD in series with the supply offering protection from internal shorts within the CU - a TT system.

I just checked and it seem that MK do not offer an S type RCD.

They do offer a 100mA RCD. As all final circuits are covered with 30mA RCDs, i was planning to use the 100mA RCD and replace the isolator module in each of these boards with one, thus covering the internal Bus Bar and cabling.

Why is it 100mA and not less mA? I tried to find in the regs but could not see.
Would i still get issues with nuisance tripping seeing as it is not timed?

Do i just cut my losses and install a separate 100mA timed RCD?

Thanks

John

 

[i=p/u]

So not needed at all if if final circuits 30mA protected and meet the installation methods mentioned .. learning day

 

[John-]

So not needed at all if if final circuits 30mA protected and meet the installation methods mentioned .. learning day

Unfortunately whilst i have RCDs and RCBOs in these boards, bus bars are not insulated and interconnecting cables are standard MK single insulation, so i will need to fit an RCD in series with the supply.

 

[Deleted account]

I still fitted And would continue to fit plastic enclosures for up front RCDs In Domestic TT systems. normally a 100mA s type.

possibly this is a deviation from the regs, but if it is I’m making the installation just as safe if not safer.

 

[loz2754]

I still fitted And would continue to fit plastic enclosures for up front RCDs In Domestic TT systems. normally a 100mA s type.

possibly this is a deviation from the regs, but if it is I’m making the installation just as safe if not safer.

I do the same. I do not classify a simple enclosure as "similar switchgear".