In previous pages that you have read you would have seen reference to Earth continuity, but what what is it?

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There are three main classes of electrical appliance, Class I, Class II & Double Insulated. 

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Depending on the class of the electrical appliance this would dictate the need for the appliance to be earthed.

 

• Class I - Appliances with a metal casing such as a washing machine or brass bulb holder. 

• Class II - these have a plastic casing and may not be earthed. 

• Double insulated - normally low voltage plastic cased appliances such as phone chargers where the plastic casing with any live parts being insulated twice in order to protect the user from touching them. 

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Electricity is basically lightning. And as with lightning electricity's number one goal in life is to get to earth. However along the way we can force it do things like pass through a light bulb to create light or pass through an element to produce heat.

 

Electricity is also fairly lazy and prefers to take the path of least resistance.

 

This means if there is an easier route like going through a human body to get to earth it will take that route. The only problem is it could cause serious harm or death by electrocution. 

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As you'll see above appliances with a metal casing (CLASS I) must be connected to an earth circuit.

 

The earth circuit will safely direct the current away from the electrical appliance to earth.

 

This would create a sudden surge in power which would break the fuse or cause the circuit breaker to trip this would then disconnect the mains power supply to the appliance making it safe. 

 

Earth Continuity testing is a method used by PAT testers to check that portable appliances have an un-interrupted earth connection and that any metal parts of the appliance are correctly connected to earth. The earth continuity test must deliver a low OHM reading to show that there is little resistance in the earth wire connection.  

 

This means that if a fault was to develop the earth connection will enable the power supply to be automatically disconnected quickly, and avoid anyone from being injured by a faulty appliance.