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Electrical Safety Switches – Life Saving Devices!

  • What are they?
  • How do they work?
  • Should I have them installed?

Electrical safety switches, also referred to as “Residual Current Devices” (RCD’s) or “Earth Leakage Circuit Breakers “ (ELCB’s) have been mandatory on all lighting and power circuits in all new houses for some years now. They are also required to be installed to part or all of a power circuit when any additional points are being installed to an existing house.

 

Safety switches are designed to operate virtually instantaneously when a current imbalance is detected between potential earth and an active conductor. For example, a typical real-life scenario could be as follows: Say a child is kneeling on a wet stainless steel kitchen sink (which is earthed via the water pipes and earth bond). The child leans into the toaster with a steel fork or similar to retrieve some burnt toast. In this example, the toaster handle is pushed down and is still on. The child touches the live toaster elements with the fork. There is now an electrical potential travelling across their body from the fork in one hand, and out their knees on the wet sink. So what happens now? Well, if there is a safety switch installed, it senses the current imbalance and trips the circuit very quickly, usually before 30 milli amps (mA) of current has been reached. (At 240 volts AC, exposure of more than 30mA can be fatal). All you notice is the power is tripped, and an embarrassed child with a fork in their hand.

 

On the other hand, if there is no safety switch installed, then the circuit breaker or fuse will probably not trip! How come? Well, this is because there would be enough resistance in your body to allow the power circuit to happily continue providing power as long as you don’t draw more than 16Amps (or 20Amps depending on how old your power circuit is). In the example above, the human body with wet skin can have a resistance as low as 500 to 1000 Ohms. Using the Ohms Law formula for a resistance of 1000 Ohms being exposed to a voltage of 240 Volts, this equates to a current of 0.24 Amps (i.e 240 mA). So this could prove to be a fatal shock.

 

Should you have safety switches installed? As a father and an electrician, I say absolutely.