14/09/2017
I consider these two videos from charitable organisation www.electricalsafetyfirst.org.uk/ excellent in illustrating the need for an RCD as an addition protection in the home.
This video concludes that the incident wouldn't have happened. That is not strictly true, the incident would have still happened as a garden flex was cut by the machine. It is only two core - there is no earth lead present, so the RCD would not necessarily trip when the cable was cut. However, an RCD would have likely tripped before the electrical shock was fatal.
Basically an RCD looks for an imbalance in the flow of current, therefore can detect a leak to earth and if this current exceeds the design threshold of the RCD (30mA) then the RCD will trip. When a person receives an electrical shock, they cause a leak of current to earth through their bodies. Shocks in the garden are much worse and you are in closer contact with the earth which is often damp.
Having an RCD does not mean you can take extra risks, it is an additional protective measure. I think we all owe it to our families to ensure we have this relatively inexpensive device in our homes and workplaces.
If you receive a shock when an RCD is present you will still feel a shock sensation as the current passes through you body to earth. However the RCD is designed to trip within 40 milliseconds and before the current becomes life threatening.
Worst case scenario, you may need a new consumer unit (fuse board) and some extra earth bonding cables installing. Typically priced £300 to £400 for an average sized dwelling. A far cry from the price of a loved one.
