I would like to reply to the response of Mr Drewery in the June edition of EMC

Mr Drewery thinks a residual-current device (RCD) needs an earth to trip, but if he looks at the causes of tripping it can be caused by a sudden inrush of current like a lamp blowing and taking out a miniature circuit-breaker (MCB).

It is regulation to fit them on TT systems where the provider does not supply an earth and we have to provide a stake.

However, I have been to many installations where the stake has been removed or the earth cable broken, leaving the property with no earth, but the RCD has still activated.

Paul Knowles, RJ Engineering, Folkestone, Kent