RCD with two extension leads

[Vicario]

I was up my metal ladder yesterday pruning a very large bay tree. I plugged my electric clippers into an extension lead which was then plugged into a plug-in RCD socket in the kitchen. I was reminded of that poor kid who died when she touched a metal ladder just before Christmas (I think the cause was a faulty extension lead) and began to wonder if an RCD is as effective with daisy-chained leads like the ones I was using. CU will be updated this year to include RCDs but in the meantime I'll be using the system as described and want everyone to be safe. Should I use two plug-in RCDs just to be absolutely sure?

 

[bernardgreen]

RCDs do NOT prevent electrical shocks, they only limit the duration of a severe shock.

There has to be current flowing to ground to cause the RCD to trip. This can be via the person being shocked.

The short duration shock may cause the person's muscles to spasm leading to a fall and subsequent injury.

 

[Aragorn84]

That said, the extension lead doesnt affect the operation of the RCD.

So long as its functioning correctly (has it ever been tested?) it will operate just the same with the clippers plugged in directly, as it would with an extension lead.

If you consider for a moment a CU with an RCD in it, you've got many meters of household cabling (analogous with your extension lead) then an applicance plugged into a socket (just like your clippers) so the scenario is more or less the same.

 

[jon47]

If you want to be safe your options are: using a harness so if you get a shock you don't fall from height (has a double bonus that if you slip and no shock is involved you are protected from falling as well), use a non conducting ladder so you are electrical separated from earth.

 

[ericmark]

I made a silly mistake I assumed and one should never assume that wires from light switch were vertical and proceeded to cut a double line down the wall to install the cold water supply to fridge using two hacksaw blades with spacer between them.

In fact the two way switching link went horizontal and I hit it. It was enough to knock me out for a minute or so and I did have RCD protection and it had been tested and did trip at 30ma in 18ms both before and after my accident so it did work. Permitted to take up to 40ms to trip.

Likely it did reduce the shock I got in duration but cure is not to hit the wires. My house has been RCD protected on all circuits for 20 odd years but it does not mean no shock. You can get 10ma units but they still take up to 40ms to trip so will help with pond pump so damp does not trip house but cutting a cable likely you will get the same shock.

 

[jon47]

As Ericmark says an RCD will not protect you from arc flash or exploding bits of metal when you cause a short on a live circuit (or from the desire to jump backwards off the ladder).