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, or
(ii) res­ult in in­ter­rup­tion of pub­lic ser­vices and/or dam­age to cul­tural her­it­age, or
(iii) res­ult in in­ter­rup­tion of com­mer­cial or in­dus­trial activ­ity, or
(iv) af­fect 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 over­voltages is re­quired. If the risk as­sess­ment is not per­formed, the elec­trical in­stall­a­tion shall be provided with pro­tec­tion against tran­si­ent over­voltages.

For a single dwell­ing unit it will be a de­cision for the house owner to make whether they con­sider the small ad­di­tional cost of the surge pro­tec­tion device jus­ti­fied to pro­tect their in­stall­a­tion and equip­ment against these dam­aging over­voltages


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).



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.



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. 



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Related products

Check out our product solutions for surge protection below

Pre-fitted Surge Protection Consumer Units

Commercial Surge Protection

Residential Surge Protection