Electricity + Control October 2016

EARTHING + LIGHTNING PROTECTION

OPINION

depending on their location in relation to the point of the lightning strike, thereby creating potential differences in voltage between earth points. This will cause voltage to find any path from the highest voltage earth point to equalise the other earth points via any cable it finds e.g. data lines, communication lines etc. To stop this phenomenon, make sure that all earth points are bonded together and in turn bonded back to the mains earth • There are reputable companies in South Africa that specialise in the checking and installation of earth systems Important to know! Lightning and surge protection cannot be used for protection against extended over or under voltage conditions. These devices are used to protect against short duration interferences in the pico to micro second range which may be induced into and / or carried by electri- cal circuits. Conclusion Much time and money has been spent to understand the dynamics of lightning and switching transients. With this in mind, repu- table manufacturers of lightning and surge protection de-

• Type 2 (Class II) – Medium protection. These devices are used for protection against Other Surges i.e. switching transients. Normally situated in the secondary DBs supplied from a main DB which would consist Type 1 devices. Should there be only one DB servicing a facility with no secondary DBs, a combination Type 1 and 2 device should be installed in the DB • Type 3 (Class III) – Fine protection. These devices are used for protection against Low Energy Surges which can damage sensi- tive equipment. These devices are normally situated as close as possible to the equipment to be protected. Type 3 devices may be used in all areas of electrical / electronic applications including: • Mains power supply ac and dc • MCR (Measurement, Control and Regulation) • Information technology and Telecommunications • Transceiver systems.

Type 3 devices should also be used in conjunction with Type 2 devices.

When do we use protection devices? Around the world all electrical and electronic equipment will be exposed to some form of damaging transient activity. The cost of protection is almost always less than the cost caused by the consequences of surges.

vices are effectively able to protect equipment against damaging transients when the correct installation and earth procedures are adhered to. Use a reputable manufacturer or supplier of lightning and surge protection to advise on what type of products should be used for required ap- plications.

It is therefore obvious that the use of SPDs (Surge Protection Devices) is an imperative and should always be considered in any facility.

What else? It is also important to note that an effective structural earth system is not an option and must be part of a com- plete Lightning and Surge protection solution. • Most protection devices rely on an effective earth system to divert excess energy away from protected equipment • No earth systemmeans no protection. A poor earth systemmeans poor or no protection • Beware of potential differences. A potential difference in an earth system is when you have two or more separate earth points con- nected to the same electrical system. At the time of a lightning strike the voltage rise in the earth will differ at each earth point

Tony Rayner joined Phoenix Contact South Africa in 2006 as the national product manager for surge and lightning protection products. He continues to support the industry with seminars, technical support and training. Enquiries: Email tonyr@phoenixcontact.co.za

• Lightning is a natural phenomenon…occurring around the world. • Surges are manmade, mostly generated by electrical switching operations. • A reputable manufacturer should be consulted for advice on lightning and surge protection.

take note

Electricity+Control October ‘16

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