Surge Protection 18th EditionSpencer Yates
What are surges and how are they produced?
Surges are short-term high voltage impulses, other names being, transients, glitches and spikes, these show themselves for a very short duration of time, typically some micro seconds.
Remember, it doesn’t need a direct lightning strike on an installation to cause damaging voltage surges – a ground strike in the near vicinity is quite sufficient. Also remember there are many other sources of voltage transients, such as the starting of large motors and the switching of large capacitive and inductive loads. Common examples of internal switching events are a lift motor in a hotel or fluorescent strip lights being turned on or off.
Where is it in the regs?
Protection against overvoltage’s of atmospheric origin or due to switching.
Devices for protection against overvoltage
443.4 – Protection against transient overvoltage’s shall be provided where the consequence caused by overvoltage…
- Results in serious injury to, or loss of, human life, or
- Public services or damage to cultural heritage, or
- Commercial or industry activity, or
- A large number of co-located individuals
For all other cases, a risk assessment according to Regulation 443.5 shall be performed in order to determine if protection against transient overvoltage is required. If the risk assessment is not performed, the electrical installation shall be provided with protection against transient overvoltage, except for single dwelling units where the total value of the installation and equipment therein does not justify such protection.