Surge Protection

Surge Protection

The need for Surge Protection

The protection of electronic systems is often ignored, yet the damage to such systems, caused by lightning, can be catastrophic.

lightning strikes

The probability of electronic systems being damaged by lightning is many times greater than that of the building itself being struck by lightning!


Imagine a building. It’s a relatively small target for lightning to hit, yet we will spend money on installing structural protection and have it tested annually, but ignore the dangers posed by lightning induced transients or surges.

Our homes, places of work, factories, offices, hospitals, airports, etc are all interconnected by overhead and buried cables forming a huge spider’s web, that is easily affected by lightning.

Fact . . .

Lightning up to 1km away can damage electronic systems. Now, draw a 2km diameter circle around your building – that is a large target area for lightning to hit, compared to the size of the building itself.

The resultant mains borne transients from the secondary effects of lightning can be as high as 6,000 volts and have the capacity to destroy electronic systems. Smaller transients may cause degradation to electronic components and disruption of system performance.

But the threat to electronic systems does not end there. Transient voltages caused by electrical switching are common.

Surge Protection - Fact


Electronic systems have invaded our everyday lives and we now depend on them to a huge extent:

  • Business (where such systems control administration and manufacturing operations).
  • Hospitals (where our lives can depend on the functioning of electronic equipment).
  • Security services (police, fire and ambulance).
  • Leisure (when we go shopping or even to the cinema or entertainment complex).
  • Personal communications (email and phone).
operating theatre
data centre
fitness equipment


We can also see that the electronics supporting our everyday lives have become increasingly sophisticated and miniaturised. So much so that they are now more susceptible to damage or degradation.

Put this in the context of a 2km diameter target area for lightning – a spiders web of power and data cables – then we have a recipe for disaster!

Imagine what would happen if we didn’t have these systems – inconvenience, lack of service, perhaps even life threatening situations.

The consequences to operators of such systems are damage, degradation, and disruption.

All of this can be costly but the good news is that it can be prevented!

surge damage

How do lightning and electrical switching events affect my electronic systems?

Resistive Coupling

Lightning simply striking the ground injects a huge current of up to 200,000A into the ground.

This current flows away from its point of entry into the ground. It does this through the most readily available conductive medium, the ground itself (soil, rock etc). However, the earth terminations and electrical cables of electronic installations are often better conductors of current than the ground itself.

This resulting current flows through the earth, neutral and phase conductors, as well as data lines which are connected to buildings further away. It flows through the electronics and electrical systems of the buildings closest to the strike point. As it does so, devastating transient voltages appear, causing damage to sensitive electronic equipment.

Inductive (Magnetic) Coupling

The building may have structural lightning protection, but if data and power cables inside the building are routed close to a lightning down conductor, any lightning strike to the building will cause current to flow through the down conductors, resulting in an electromagnetic field that will induce transient voltages in the buildings internal power and data cables (figure SPD:3). The same can happen in an unprotected building too, the lightning current from a direct strike now finds its path to earth through the building’s structure (reinforcing bars, steel columns etc) as well as internal pipework, cables and conduits.

Similarly, cloud to cloud lightning discharges (figure SPD:4) can induce transients in overhead power, data and telephone lines. This is because lightning is a massive discharge of current. When a current flows it creates an electromagnetic field and cables passing through this field have a voltage induced on them.

Direct Strike

If an HV power line is struck directly by lightning, it will flashover to earth with one line flashing over before the others, creating a line to line transient that easily passes through supply transformers to reach electronic systems.

Electrical Switching

We have already established that when a current flows through a conductor it creates a magnetic field. This field stores energy, higher currents and long lengths of conductor create more stored energy. When the current flowing along a conductor (the power supply) is switched off, the energy in the magnetic field is released in the form of a transient which can then flow through unprotected electronic equipment.

Switching events are commonplace. Inductive loads such as motors, transformers, electrical drives, large banks of lighting, industrial process equipment and so on are all sources of switching events.

What does a lightning induced transient look like?

240 volt AC sine wave
The magnitude of the transient is what causes damage. Milliseconds in duration, with magnitudes of up to 6,000 volts.

transient sine wave

What problems will a lightning induced or electrical switching transient cause?


Depending upon the severity of the transient, damage can range from burnt-out circuit boards, to impaired operation of components on the circuit board. This latter damage is harder to pinpoint, but is often caused by lightning induced transients. IEC 60664 places this level at 15,400 volts for electronic equipment.


Long term exposure to transients, which can be from electrical switching (quite common) or the secondary effects of lightning are often unknown to the operator of the electronic systems. But these transients degrade electronic componentry, reducing the lifetime of those systems and equipment. Almost like a silent killer creeping up on you.


Here there is no physical damage, but the logic levels of the electronic system are disrupted. This can cause such things as data loss, corruption of software, loss of data, unexplained computer crashes and so forth.

The type of damage is very much influenced by a number of factors – equipment susceptibility (EN60664-1 states 1,500V as the minimum withstand voltage for electronic equipment). As the components of systems become smaller, susceptibility to damage and degradation worsen.


. . . (or the ability to use the system) is caused through inoperative systems.

Consequential loss

Consequential loss is the inability to use the electronic system – this can be extremely expensive and includes, but is not limited to:

  • Replacement hardware
  • Replacement software
  • Loss of service
  • Loss of revenue from suspended sales or manufacturing/process activity
  • Cost of labour

The loss (or cost) varies from organisation to organisation, but it is not only inconvenient to have these problems, they can be prevented.

It is vitally important to reduce the size of lightning induced transients from 6,000 volts, to below the withstand voltage of the equipment to be protected (often cited as 1,500 volts).
This is the performance of European type units and the new Kingsmill range.

Consequential loss
Translate »