Surge Protection Devices

28 March 2022

Regulation 443

Protection against transient overvoltages of atmospheric origin or due to switching

Regulation 443.4 Overvoltage control

This regulation covers where protection against transient overvoltages is required and has been significantly redrafted.

Regulation 443.4 has been deleted and replaced by Regulations 443.4.1 and 443.4.2.

These new regulations stipulate the separate requirements for:

  1. Transient overvoltages due to indirect lightning strokes
  2. Equipment overvoltages.

The Risk Assessment method detailed in 443.5 has now been deleted.

The new regulations are as follows:

Transient over voltages due to the effects of indirect lightning strokes

Protection against transient over voltages shall be provided where the
consequence caused by the over voltage could result in:

  • Serious injury to, or loss of human life
  • Failure of a safety service, as defined in Part 2
  • Significant financial or data loss

For all other cases, protection against transient over voltages shall be provided unless the owner of the installation declares it is not required due to any loss or damage being tolerable, and they accept the risk of damage to equipment and any consequential loss.

NOTE: Part 2 “Definitions”, defines a Safety Service, as “an electrical system for electrical equipment provided to protect or warn persons in the event of a hazard, or essential to their evacuation from a location”.


Transient over voltages caused by equipment

Protection against over voltages shall be considered in the case of equipment likely to produce switching over voltages or disturbances exceeding the applicable rated impulse voltage of equipment according to table 443.2, e.g. where inductive or capacitive equipment such as motors, transformers, capacitor banks, storage units, or high current loads are installed.


Transient overvoltages are now clearly defined as those of atmospheric origin, and those caused by equipment within the installation.

For protection against indirect lightning strokes, the installer is still required to assess whether the consequences of an overvoltage (as detailed in 443.4.1) could result in one of the three defined results, which would make protection mandatory.

443.4.1 also states that in all other cases, protection shall be provided unless the owner declares that such protection is not required due to anyloss being tolerable.
Therefore, outside of the three defined areas, SPD’s must be fitted, unless expressly excluded by the owner of the installation.
When referring to overvoltages caused by equipment, the installer must evaluate whether any equipment within the installation can produce switching overvoltages which could adversely affect other load equipment within the installation.

This has to be based upon the impulse voltage withstand capability of the equipment, as defined by its Overvoltage Category as not as detailed in 443.6, including Table 443.2.

Share on

Related news

It looks like you are browsing from outside the UK...
Would you like to browse our global Lewden Export website?
Browse Lewden Export Continue on the Lewden UK website