Overload Protection: What You Need To Know

During the countdown to the 18th Edition of the IET Wiring Regulations becoming mandatory in January 2019, Hager’s team of experts has been out meeting electrical contractors across the UK as part of the company’s ‘Regs Live’ campaign.

One of the key areas of discussion as a result of the new regulations are the changes to overload protection. Here Steve York, residential market manager from Hager, sets out the background to the changes and highlights methods electrical professionals can employ on installations to ensure they remain compliant.

What has changed in the 18th Edition regarding the overload protection of devices?

The 18th Edition regulations state that devices such as RCCBs and switches provide no protection against overload, therefore they shall be protected by an overcurrent protective device (OCPD). In addition, a separate regulation states that overload protection of these devices shall not solely be based on diversity factors of downstream devices.

Why have the changes been made?

Devices such as switches and RCCBs in distribution boards and consumer units may have historically had their rated current determined after having taken diversity into account, but without having considered overload protection of the devices.

Where RCCBs or switches do not have the correct overload protection, there is a risk of overheating which can affect the functional characteristics of devices and in extreme cases result in fire.

How can I achieve the protection required in the new regulations?

There are a number of methods which can be implemented to achieve overload protection for RCCBs and switches. These include:

Method 1 – ensure that the sum of the rated current of the downstream MCBs does not exceed the rated current of the switch or RCCB. This method would need to consider the consequences of any spare ways and later additions.

Method 2 – ensure that the rated current of a switch or RCCB stated by the assembly manufacturer is not less than the rating of the upstream OCPD. In a domestic installation, this could be a 60A, 80A or 100A cut-out fuse.

Method 3 – select a consumer unit or distribution assembly that only utilises RCBOs on outgoing circuits. Consideration will still need to be given as to the rated current of the main switch.

What is Hager’s recommendation?

Hager feels that the easiest and most flexible solution for installers is to use a consumer unit which is 100A rated, with 100A RCCBs fitted as standard.

This enables the installer/designer to be confident that the consumer unit allows conformity to the overload protection requirements for RCCBs and switches regardless of the size of the upstream cut-out fuse fitted or the configuration of the downstream MCBs.

For more information on the 18th Edition and how Hager is on hand to support electrical contractors visit hager.co.uk/18thEdition.

  • Show Comments

  • Matt Cash

    There are several options so, lets not dismiss the most BS7671 compliant option (which is to use an individual RCBO on each outgoing way) Dual RCD boards will switch off 50% of the circuits in an installation when there’s a fault on just one circuit.

    Cant see how that would comply with 314.1? & 531.3.2?

    How can a Dual RCD type of arrangement avoid unwanted tripping of RCDs? Or retain power continuity on healthy circuits?

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