18th Edition: Earth leakage explained

18th Edition: Earth leakage explained

Do you need to know if your cables are leaky? According to the 18th Edition, the answer is ‘yes’, as Dave Sweetman, Marketing & Business Development Director at Di-LOG Group explains.

How often have you spent hours fault-finding nuisance tripping issues for free, wishing you’d have known there was a problem before quoting for this particular DB upgrade?

There is a new 18th Edition regulation identifying the requirement for you to measure Earth Leakage, as stated in BS7671 Reg 531.33.2.

In a nutshell, each electrician must check that each install completed does not have excessive leakage to earth on each of the RCDs or RCBOs.

The maximum permitted value per RCD has been set at 30% of the nominal value, i.e. a 30mA RCD would be no more than 9mA, 100mA would be 30mA, and so on.

Nonetheless, I’m sure you’d find it useful to know if there is a potential issue on an installation before you quote for your next DB change.

The only way to indicate the presence of Earth Leakage would be to use an Earth Leakage Current Clamp Meter.

The Di-LOG DL6518 Earth Leakage Clamp is a low-cost solution that works on differential leakage measurement, which involves simultaneously clamping around the live and neutral conductors together.

You can check any installation by simply clamping around your meter tails on the supply.

The DL6518 Leakage Current Clamp measuring differential leakage on the live and neutral conductors of RCD2 indicating 5.5mA leakages, which is under the 30% threshold, as stated in BS 7671

The DL6518 has a measurement resolution of 100µA (0.1mA), making measurement very accurate when measuring minimal AC currents.

Domestic installations tend to have dual 30mA RCDs fitted or are even made up entirely of RCBOs.

If the installation shows a combined differential leakage current above 30% of each RCD/RCBO value (in this case 9mA) you may need to take action to manage the leakage to earth and minimise the likelihood of nuisance tripping.

We all know how costly call-outs are to any business to reset or investigate a tripping RCD!

Where possible, you will need to have the day-to-day electrical appliances in operation to accurately determine potential issues.

If excessive leakage is then identified on the tails, you would then need to clamp around the live and neutral conductors of each of the RCDs to determine if the leakage on that RCD is above the 30% threshold, ideally looking for a current considerably less than 9mA. You then repeat for each RCD.

Intentional or unintentional leakage

If the Earth Leakage detected on each RCD is excessive, the user will need to ask: “Is this intentional or unintentional?”

The DL6518 Leakage Current Clamp measuring differential leakage on the live and neutral conductors of RCD1 with the kitchen MCB switched off, indicating that you’d want to investigate the kitchen main ring for either ‘intentional’ or ‘unintentional’ leakage

Intentional Earth Leakage tends to be found in electrical appliances in the form of a functioning earth, where a small amount of earth leakage is required for the appliance to function.

Unintentional Earth Leakage tends to occur in poor installations where there could be a breakdown in the conductor insulation or moisture ingress, amongst many other causes.


Switching each individual circuit off, one-by-one, is a good area to start.Here you can easily identify which circuit you may need to investigate further.

Once a circuit is identified, eliminate the ‘intentional leakage’ first by switching off each individual appliance, one-by-one, to see if this changes the result.

The DL6518 Leakage Current Clamp measuring differential leakage on the live and neutral conductors of RCD1 indicating 9.5mA leakages, which is in excess of the 30% threshold, as stated in BS 7671

Every electrical appliance has a ‘Protective Earth Conductor current’ limit – you should refer to the In-Service Inspection and Testing Code of Practice for more information on these limits.

If the isolating of electrical appliances does not change the result it may well be ‘unintentional leakage’, and a check of the insulation of the conductors will be required in the form of an Insulation Test.

Leakage management

There are an array of options available to manage your Earth Leakage: balancing circuits between RCDs to fall below the 30% threshold, fitting RCBOs, testing the electrical appliances, or even a complete re-wire… all are critical when you price your next job!

Di-LOG has created a dedicated web page for readers of this article, containing all of the details you need to know about the DL6518 Earth Leakage Clamp, including special offers and technical specs. To visit the page go to: http://www.dilog.co.uk/pe-nov-2019-dl6518-earth-leakage-current-meter/

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