LIGHTNING & SURGE PROTECTION

 

The purpose of this article is to familiarise members with some of the basic concepts of surge and lightning protection. This is in no way meant to be a technical thesis.  The idea arose primarily from the common questions that are often asked on the subject and it was decided that some form of ‘layman’s guide’ would be necessary to clear up certain facts and especially myths or misnomers on the subject.

 

What is Lightning?

 

One of natures most devastating forces are lightning.  Studies have shown that more people are killed by lightning strikes that any other element of nature’s fury.  A lightning strike could carry up to 30,000,000 Volt’s with 150,000 Amp’s, this could play havoc with your electrical system.

 

When lighting strikes a particular installation, building, house or tree and enters the ground, the effect is not over yet.  Lightning can travel through the ground from the point of impact for as far as 5 km depending on the ground resistance and the amount of electricity that was grounded.

 

On Telcom lines the strike can travel for as far as 30 km.  This has a ripple effect and any cable, water pipe or conduit could then be induced, by the electromagnetic field, and this induced current could be as high as 50,000 amps.  Thus, lightning does not have to strike directly in order to damage your equipment.  This is the reason why you should protect your incoming power, distribution boxes and all buildings.  Proper protection will manage the surge or lighting strike to avoid catastrophic evens.

 

What are electrical Surges?

 

Inductions and electrical surges are caused by lighting and switching (Council opening and closing electrical circuits).  Electrical surges originating from the electrical supply, normally 220 Volt, and are termed as spikes (600 Volt) or dips (150 Volt) of the supply voltage.  Any electrical device that are working, delivering watts, will try to maintain the work rate even when the voltage drops the only way this can happen is more current are drawn and this “blow’s” the equipment.  These surges are the silent killer of electrical equipment.

 

Lightning density

 

This is a lightning density map of the world over an eight year period from 1995 to 2003. This is an ongoing research project run by NASA.  This shows a higher density and occurrence of lightning over Sub Saharan Africa than in Europe.  It is also for this reason that the products made in Europe to protect equipment are not of a strong enough protection level for us in South Africa.  For example our mains units are between 6.5kA and 10kA while their equivalent in Europe is only 1.5kA to 2.5kA.  We are highlighting this as there is sometimes the perception that the local products are inferior or not as good as the products from Europe.  This is not the case when you compare the specifications.

 

 

The Myth of Lightning season

 

Every winter we experience a drop in work as there is no lightning.  The fact is that during winter there are more items damaged than in summer.  This is due to power surges, irregularities in the mains supply, on the Highveld especially it is dry so there is an increase in static build up to discharge through sensitive electronic equipment.

 

Some reasons for the higher occurrence of Lightning damage

 

1.            More electrical equipment being used.  Computers only started to be a household product after the inception of DOS in 1981, before that only Mainframe computers was used and these had special rooms to house it.  In the RSA the inception of TV’s only started in 1975.  This should show that the powered electronic revolution started only recently thus more equipment stands a greater chance of sustaining Lightning & Surge damage.

 

2.            More sophisticated equipment being used.  The human need for more performance, smaller items, new inventions, communication etc. made the distances between tracks on the Printed Circuits less and less and the Integrated Circuits smaller and smaller.  The distances are so small that even a static buildup could damage it, with no need for Lightning, if it was connected to an external source.

 

3.            The density of the population.  In the past the Lightning struck a tree in the field and very few people even knew what happened.  But with urbanization a suburb was developed there where the tree was and now one of the houses is struck and the resultant surge of electricity destroyed all the electrical equipment in a number of houses.

 

4.            Earthing systems.  Some developers take shortcuts when installing the electrical and more specific the earthing system in new complexes.  In the old days all water-pipes where used for earthing and bonding but with Teflon pipes being used this earth is no real earth anymore.  Other problems with earthing is the theft of copper wire, in some of the buildings we found that all the copper in a lift shaft was stolen, these were never replaced due to the costs involved, this can be a real killer of humans. The earthing system could also be burned off after a big lightning transfer and never repaired.  The old proverb of No Earth = No Protection is very valid today.

 

5.            Inappropriate protection.  The general public, and some corporations, buy an inferior product and expects that adequate protection was acquired or buys a good product that needs to be installed correctly or the wrong product for the right job.  In all these instances good money was wasted and a false sense of protection was acquired.  Good products correctly installed could also fail after a severe Lightning strike and if not replaced give no protection.

 

SURGES & TRANSIENTS

 

Effectively, any voltage that exceeds a specified fixed-voltage tolerance is a surge or transient.  Transients and surges are over voltages of short duration Electromagnetic interference (or EMI, also called radio frequency interference or RFI) is a (usually undesirable) disturbance that affects an electrical circuit due to electromagnetic radiation emitted from an external source.

 

Surge voltages, transients and the like are mainly caused by switching operations, electrostatic discharges (ESDs) and lightning discharges.  All of these ‘surge’ occurrences can enter electrical and electronic equipment either galvanic-ally, inductively or capacitively via power cables, telephone lines and data transmission lines.

 

An example here of how unprotected equipment generally is, was when the US conducted a ‘post mortem’ on equipment that went to the scrap yard after the Gulf War.  They experienced malfunctions in their guidance systems, computers failed and died, etc.  Their findings were that, because of the energy radiated by all the explosions in the region there were numerous surges, transients and ionising energy in the air generated, which blew the equipment.  In this situation one cannot afford to have downtime.

 

In the business world can you afford to have downtime on your administration or your production while your competitors are running?  It is not just the issue of downtime here, but also if you look at the effects this could have on emergency services in a hospital and operating theatres.  From the business angle then, what is the real cost of bringing everything online again.

 

Electrostatic Discharges (ESD)

 

ESD is the major cause of equipment failure.  In most instances it slowly degrades and shortens the life of electronic circuitry.  An ESD occurs when a static electrical charge is transferred between two bodies – between cables, circuit boards or objects.  This transfer takes place in a very short time, having a very high peak voltage and current level.  The immense energy of a lightning strike is discharged in a few microseconds.  On the other hand, the lower levels of ESD found in office and industrial environments can strike a hundred times faster.

 

For example walking across a synthetic carpet on a dry day (<40% relative humidity) may generate a charge potential of 20,000 volts on a human body.  When suddenly discharged through touching a switch or an object, the shock felt is caused by a discharge lasting around 10 nanoseconds and having a peak of up to 40 amperes.  It is therefore not difficult to imagine what levels of electrostatic energy can build up during winter times in telephone, power and data lines.

 

After the NASA programme involving the Apollo and Gemini series had wound down, there was a great deal of research and testing conducted for failures.  It was estimated that 70% of the failures were due to ESD damage.  In electronic equipment, ESD damage occurs in two ways:

 

  • The first is where a conductor such as the track on a PC board or inside an integrated circuit is damaged, like blowing a fuse, so that the equipment immediately ceases to function.

  • The second is where it causes latent damage leading to gradual degradation resulting in eventual failure.  ESD damage costs millions each year and is one of the main culprits of equipment failure.

 

Myths

 

There are numerous myths and a lack of awareness with regard to this subject, which could be why we are faced with so much scepticism.  The questions always asked at this point by sceptics and technical people alike, are

 

  • What do I need?  The old saying of horses for courses is very appropriate here talk to a professional in the field.

  • Does it really work?  Where appropriate the insurance watchdog SAIA, SABS & Telkom approved our products.  If it is good enough for them it’s good enough for you.

  • What guarantee is offered?  No guarantee can be given seeing that lightning travels for kilometres through a non conductor, the best that we could do is to try and manage the strike.

 

Some common myths include the following:

 

  • Circuit breakers and a fuse will protect electronic equipment.

 

The fact is that circuit breakers and fuses are slow reacting devices.  They cannot detect fast transient and surges induced by lightning or ESD.  They also cannot filter dangerous spikes and high frequency noise.  In fact lightning can pass through a 500 mA glass fuse without it being blown, the duration is so short that it starts to cool off before it can burn-off.

 

  • Lightning protectors are only needed in summer when it rains and when there is lightning.

 

The truth is that, in winter when it is dry, very high levels of ESD are present and there are induced surges due to the high peak usages on the mains power.

 

  • Our product will work and protect with a direct lightning strike.

 

It does happen that a unit is protected with a direct strike and saves the equipment, but it will very seldom survive and needs to be tested & replaced if necessary.

 

Benefits of installing Surge protection

 

  • Decreased cost on equipment repair or replacement.

  • Lengthens the equipment lifespan.

  • Creates a safer working environment.

  • Prevents data loss on servers.

  • Maintains product efficiency even in hazardous environments.

  • Reduce downtime.

 

Protection Measures

 

What must be realised from the outset is that surge protectors are preventative devices and can not prevent a strike.  They are there to manage voltage discharges by leading them to a good earth and thus preventing damage.

 

Outside.  If a structure is often hit by a direct strike a Faraday cage must be erected for the structure and earth lattices installed.  In some instances a Lightning conductor could be sufficient protection.

 

Inside.  Normal protection inside of a structure will be a three part process:

 

1.            Filter.  All external feeds to the structure must be filtered, this entails:

 

a.    Supplied Power.  The main electricity feed to the structure (main DB) needs to be filtered & protected and all subsequent DB’s protected to prevented surges from entering the structure.

 

b.    Telephone lines.  This is the most common carrier of surges and a vital item to be filtered. (Crone blocks, Alarm communication etc.)

 

c.    Antenna’s & LAN connections.  All cabling on the outside can transfer a static induction into the structure.

 

2.            Protect sensitive equipment.  After all the external feeds are filtered & protected the sensitive equipment must be individually protected.  A surge or transient could be induced through a water pipe or other equipment on the system.  An electrical device that blows spectacular could send a spike through the system.

 

3.            Ensure good earth.  This is the most important part of the protection process.  The SABS guideline of below 10 Ω is followed religiously and this ensure that no surprises, of protection not working, happen.

 

Latest Lightning Density charts