Supply Isolator required to be metal on TT

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I have installed this arrangement many times over the years and never had an issue with accumulated leakage on a domestic installation to that level.
I have however come across this issue on dairy installations where the vacuum pumps have been upgraded and changed to vfd driven. The vfd's were causing the milking shed to trip and shut the whole lot down!

Single pole rcbos with a N+E fault can take out the upfront S type.
I also came across where next doors' induction hob was tripping the up front s type in the other house.

 

[SparkySy]

Single pole rcbos with a N+E fault can take out the upfront S type.
I also came across where next doors' induction hob was tripping the up front s type in the other house.

That they can but that is not accumulated leakage, that is a fault.
Having double pole RCD's downstream of the main switch RCD limits that to a few circuits, now with double pole RCBO's this is much less of a problem.

 

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That they can but that is not accumulated leakage, that is a fault.
Having double pole RCD's downstream of the main switch RCD limits that to a few circuits, now with double pole RCBO's this is much less of a problem.

The point being whether it’s a fault or accumulated leakage you can’t guarantee total selectivity using a up front rcd on a tt supply.

 

[nicebutdim]

I've seen an upfront 30mA/100ms upfront RCD taken out when testing downstream RCBOs, although I'd consider that a fairly unusual situation. In the majority of domestic TT installations, any upfront Type S RCD would generally be 100mA - I doubt most wholesalers would stock any other single phase Type S RCD.

 

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I've seen an upfront 30mA/100ms upfront RCD taken out when testing downstream RCBOs, although I'd consider that a fairly unusual situation. In the majority of domestic TT installations, any upfront Type S RCD would generally be 100mA - I doubt most wholesalers would stock any other single phase Type S RCD.

I agree but in most domestic situations they wouldn't be on a TT and if they are then they probably wouldn't have vfd driven borehole pumps, dual EV charging points, Solar, Wind, and battery storage