Surge Protection Device

[atm84]

Can anyone tell me if its a requirement to install a surge protection device to a sub Distribution Board if it serves external equipment ie a roof mounted extract fan even though a SPD is located on the Main Panel?


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[Richard Burns]

Your risk assessment will tell you whether surge protection is required and at what level.
A SPD at a main incomer will be rated differently than one at a final distribution point.
If you need accurate surge protection at an accessory then the overvoltage protection would operate at a significantly lower voltage than for a main incomer.

If you are protecting against lightning side strikes then this is not required in the UK as the risk is deemed to be low, however if equipment or services need resilience then it may be that SPD are needed.

 

[atm84]

If lightning side strikes was low then why would a Lightning Protection System be installed


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[Richard Burns]

The UK has <25 thunderstorm days per year and with the calculations in section 443 this equates to no requirement for SPD.
however if there is for example a key public service, bank server, medical system that requires continuous operation and must be protected from being be destroyed by a strike then it may be required to have spd protection.