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Earth Leakage Testing

Another test that is carried out on Class I and II appliances, the earth leakage test ensures that current flowing from live parts to touchable metal is low enough to cause no harm to the user of the appliance.

It can be used as an alternative to the insulation resistance test when it can’t be performed.

When carrying out this test and using rotating machinery such as drills and grinding machines, always secure the appliance so that when the power is applied the appliance will not cause injury.

Testing Class I Appliances (Protective Conductor Test)

Another simple test – this one simply requires you to plug your class I electrical appliance directly into your PAT tester and activate the testing procedure.

This will make the appliance switch on briefly, so make sure if you’re using something like a kettle that you put some water in it (not doing this damages the element)!

It’s important that you also know the current Pass Marks.

  • Heating appliances should have a current that should be less than 0.75 milliamps per Kilowatt up to a max of 5 milliamps.
  • Portable/handheld appliances have to have earth leakage current of less than 0.75mA to be considered safe.
  • Other Class 1 appliances such as IT, movable and stationary equipment have a limit of 3.5mA
  • Class 2 appliances – 0.25milliamps
  • For Class III appliances the limit is 0.5milliamps

Notes on the above (from the IET Code of Practice):

The values for maximum protective conductor or touch current given above are to be doubled if:

  • If the appliance has no control device other than a thermal cut-out, a thermostat with an ‘off’ position or an energy regulator without an ‘off’ position or
  • All control devices have an ‘off’ position with a contract opening of at least 3mm and disconnection in each pole

Equipment with a protective conductor current designed to exceed 3.5mA should comply with the requirements of section 15.12.

The nominal test voltage is:

  • 1.06 times rated voltage, or 1.06 times the upper limit of the rated voltage range, for appliances for d.c. only, for single phase appliances and for three-phase appliances that are also suitable for single-phase supply, if the rated voltage or the upper limit of the rated voltage range does not exceed 250V.
  • 1.06 times rated line voltage divided by 1.73, or 1.06 times the upper limit of the rated voltage range divided by 1.73 for other three-phase appliances.

Testing Class II Appliances (Touch Current Test)

To perform this test, plug the appliance into a PAT tester and connect up a test lead to a metallic part of the appliance.

This, again, will power the appliance, so if you’re testing a drill or rotating machinery ensure that the appliance is secured so as not to cause harm.

To be considered safe there should be a leakage current no greater than 0.25mA.

Written by Barry Atkins