Surge Protection

The whole nature of how elec­trical equip­ment is used in homes and at work has evolved; with every­day activ­it­ies re­ly­ing on elec­tronic equip­ment.

Products such as com­puters, print­ers, tele­vi­sions, in­dus­trial con­trol equip­ment such as PLC’s, alarms, mi­crowaves and wash­ing ma­chines are com­mon place. These can all be vul­ner­able to tran­si­ent over­voltages, which can sig­ni­fic­antly re­duce the equip­ment’s lifespan through de­grad­a­tion and dam­age.

A tran­si­ent over­voltage or surge is a short dur­a­tion in­crease in voltage meas­ured between two or more con­duct­ors. In short, this means any­thing from mi­cro­seconds (mil­li­onths of a second) to a few mil­li­seconds (thou­sandths of a second) in dur­a­tion.

Surge Pro­tec­tion Devices (SP­D's)

SP­D’s pro­tect elec­trical and elec­tronic equip­ment against tran­si­ents, ori­gin­at­ing from light­ning, switch­ing of trans­formers, light­ing and mo­tors.


These tran­si­ents can cause pre­ma­ture age­ing of equip­ment, down­time, or com­plete de­struc­tion of elec­tronic com­pon­ents and ma­ter­i­als.

18th Edi­tion Re­quire­ments

The 18th edi­tion BS 7671 now stip­u­lates

Pro­tec­tion against tran­si­ent over­voltages shall be provided where the con­se­quences caused by an over­voltage could

(i) res­ult in ser­i­ous in­jury to, or loss of, hu­man life
(ii) failure of a safety service, as defined in Part 2
(iii) significant financial or data loss

For all other cases, protection against transient overvoltages 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.

Se­lec­tion Cri­teria

Surge pro­tec­tion devices are clas­si­fied ac­cord­ing to their func­tions:

Type 1
SPD which can dis­charge par­tial light­ning cur­rent with a typ­ical wave­form 10/350 μs. Usu­ally em­ploys spark gap tech­no­logy.This, if re­quired, will be in­stalled in the primary dis­tri­bu­tion board at the ori­gin of the elec­trical in­stall­a­tion. A Type 1 SPD does not in it­self of­fer the re­quired pro­tec­tion level and must be used in con­junc­tion with co­or­din­ated type 2 devices. An in­stall­a­tion with a light­ning pro­tec­tion sys­tem will re­quire a Type 1 SPD.

Type 2
SPD which can pre­vent the spread of over­voltages in the elec­trical in­stall­a­tions and pro­tects equip­ment con­nec­ted to it. It usu­ally em­ploys metal ox­ide varis­tor (MOV) tech­no­logy and is char­ac­ter­ised by an 8/20 μs cur­rent wave.This device would nor­mally be in sub-dis­tri­bu­tion boards and in the primary dis­tri­bu­tion board if there was no re­quire­ment for a type 1 device

Type 3
These SPDs have a low dis­charge ca­pa­city. They must there­fore only be in­stalled as a sup­ple­ment to Type 2 SPD and in the vi­cin­ity of sens­it­ive loads. Type 3 SP­D’s are char­ac­ter­ised by a com­bin­a­tion of voltage waves (1.2/50 μs) and cur­rent waves (8/20 μs).

Ter­min­o­logy

Iimp – Im­pulse cur­rent of 10/350 μs wave­form as­so­ci­ated with Type 1 SP­D’s
In – Surge cur­rent of 8/20 μs wave­form as­so­ci­ated with Type 2 SP­D’s
Up - The re­sid­ual voltage that is meas­ured across the ter­minal of the SPD when In is ap­plied
Uc - The max­imum voltage which may be con­tinu­ously ap­plied to the SPD without it con­duct­ing.

Main­ten­ance

Most SPDs have an in­dic­a­tion win­dow that they are op­er­a­tional. If the in­dic­ator is green they are provid­ing pro­tec­tion. If they are red then they have reached ‘end of life’ and will need re­pla­cing. Of­ten there is a re­place­able cart­ridge which can simply be with­drawn and re­placed with a new op­er­a­tional device.

Fre­quently Asked Ques­tions: 

What does surge pro­tec­tion do? 

A surge pro­tec­tion device is de­signed to pro­tect elec­trical devices such as com­puters and TV's from voltage spikes. The surge pro­tec­tion device (SPD) at­tempts to lessen the voltage sup­plied to an elec­trical device by either block­ing or short­ing to ground any un­wanted voltages above a safe stand­ard.

Do you really need surge pro­tec­tion?

If elec­trical equip­ment is used then a surge pro­tec­tion device is def­in­itely needed as elec­trical equip­ment comes with sens­it­ive com­pon­ents that could be dam­aged very eas­ily. A surge pro­tec­tion device will in­crease the longev­ity of elec­trical equip­ment.

How long do surge pro­tect­ors last?

This will very much de­pend on how many surges the device will have to deal with, so there is no defin­it­ive an­swer.

The product stand­ard re­quires the device to cope with a min­imum of 15 surges at its rated value. However, a surge at the rated value would be a very large surge in­deed. Most events are much smal­ler than the max­imum, but it is these events which de­grade sens­it­ive equip­ment over time. Be­cause the likely surges are smal­ler than the max­imum, it is likely the device will last for many years.

Surge pro­tec­tion devices are equipped with an in­dic­a­tion ‘win­dow’ which will turn red when the device has reached its end of life. Usu­ally, it is a simple case of re­pla­cing a cart­ridge at this time. It is re­com­men­ded this win­dow is checked from time to time es­pe­cially after a light­ning storm.

Can a power surge dam­age a TV?

Yes, elec­trical surges have the cap­ac­ity to over­load and short out any elec­trical equip­ment in a home, sig­ni­fic­antly de­grad­ing the life of the equip­ment. Any­thing that is plugged into a wall can be af­fected by elec­trical surges.