AJJewsbury:

Right, where you would have a double insulated tool, which is not capable of becoming live ie made of plastic.

Which is fine for indirect contact/fault protection, but 30mA RCDs also provide protection under direct contact situations - e.g. damage to the appliance's flex exposing the conductors.


It's also hard to control loop impedances where long thin extension leads are in use - it doesn't take a huge amount of 0.75mm² orange flex running down the garden to get to the point where neither the MCB nor the plug fuse will reliably provide 0.4s (let alone 0.2s) disconnection.


   - Andy.

If both parts of the double insulated flex are damaged, and no concentric screen exists around the cores, direct contact is very much possible and thus RCD is needed.


I like to think this also fits the 3 strikes rule: Both the inner cores, outer covering and RCD must fail for a lethal hazard to exist.


You are correct, long flex leads are reasonably likely, and can certainly increase R1+R2, hence why I believe double insulation on tools are best in wet locations.


This is also the same logic I have for possibly mandating that sockets be present every 2 meters in homes and some wall spaces in commercial occupancy- going by a 70*C R1+R2 assures that 2 meters of appliance or tool cord adds negligable R1+R2 on the final circuit.


Forgive my spelling btw, I can't see to get auto correct to work on this forum. That would be my fault.     

AJJewsbury:

Right, where you would have a double insulated tool, which is not capable of becoming live ie made of plastic.

Which is fine for indirect contact/fault protection, but 30mA RCDs also provide protection under direct contact situations - e.g. damage to the appliance's flex exposing the conductors.


It's also hard to control loop impedances where long thin extension leads are in use - it doesn't take a huge amount of 0.75mm² orange flex running down the garden to get to the point where neither the MCB nor the plug fuse will reliably provide 0.4s (let alone 0.2s) disconnection.


   - Andy.

If both parts of the double insulated flex are damaged, and no concentric screen exists around the cores, direct contact is very much possible and thus RCD is needed.


I like to think this also fits the 3 strikes rule: Both the inner cores, outer covering and RCD must fail for a lethal hazard to exist.


You are correct, long flex leads are reasonably likely, and can certainly increase R1+R2, hence why I believe double insulation on tools are best in wet locations.


This is also the same logic I have for possibly mandating that sockets be present every 2 meters in homes and some wall spaces in commercial occupancy- going by a 70*C R1+R2 assures that 2 meters of appliance or tool cord adds negligable R1+R2 on the final circuit.


Forgive my spelling btw, I can't see to get auto correct to work on this forum. That would be my fault.