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Clamping Down on Over Voltage
In modern life, the unseen hazard from both direct & indirect over voltages can often be overlooked and not given the respect it deserves. Whether it is industrial, commercial or domestic applications; the uncertainty is ever present. For engineers, electricians and technicians who are directly exposed to the hazards, exposure to products preventing electrocution, burns, fire and explosions is vital. Our electricity supply is seen as an everyday commodity, yet we can be guilty of neglecting the increased demand we pose on a daily basis. As our demand changes, our infrastructure must change too; we must ensure we acknowledge the strongly worded recommendations put forward, in order to ensure we clamp down on over voltages.
There is a wide range of variables which can contribute to electrical accidents such as faulty equipment or installation, unsafe practices and even products being used for the wrong application. To minimise these incidents, it has always been crucial to have in place the correct safety procedures to protect equipment and personnel; since 2012 it has been important to incorporate over voltage protection into the procedure, where the relevant risk assessments conclude such devices shall be installed.
These devices will limit or stop the electrical current automatically in the event of a fault, whether this is a direct or indirect overvoltage. Indeed, it has been shown that surges can account for nearly 1/3 reduction in the operating life of electrical and electronic components within an electrical system. There are essentially two different two different types of over voltage, direct (Lightning) and indirect (Grid, field induced).
Direct over voltages can account for in excess of 30KA induced into the electrical system, whilst indirect over voltages can induce in excess of 5KA. Common indirect over voltage examples include high inrush currents, faulty wiring, power utility quality issues and downed power lines.
If you are considering whether you should be installing Surge Protection Devices, here are some of the key points you need to take into consideration:
If your application falls within certain requirements, and consequences, of section 443 of the 17th Edition Wiring Regs, then lightning and surge protection against overvoltage must be provided in all cases.
Mandatory Surge Protection
Class 1 Protection
o If outside protection, in the form of a Lightning Protection System (LPS) is fitted to the structure, then a Class I device must installed at the/each Main Distribution Board, Point of Common Coupling or service entrance. (BS EN 62305-4).
o The purpose of Class l devices (equipotential bonding) is only to minimise the risk of dangerous sparking, in order to preserve life.
o Lightning Protection Systems which only employ Class I protection provide no protection against failure or electrical and electronic systems downstream.
Class 2 Protection
o If a Class I device is present, then Class II devices must be installed at the first distribution point of every circuit connected to the MDB, i.e. sub distribution boards and control panels. (BS EN 62305-4).
Optional Surge Protection
o Where an installation is supplied by a low voltage system containing no overhead lines, no additional protection against overvoltage of atmospheric origin is necessary if the impulse withstand voltage of equipment is in accordance section 443 of BS7671.
o If there are concerns with regards to internally or externally induced surges, then Class II devices can be fitted at specific points throughout the systems to arrest these damaging over voltages. If a risk assessment carried out in accordance with BS EN 62305-2 shows that structural / external LPS is not required, and the structure is supplied via underground lines, then Class II devices can be used to protect incoming electrical services entering the building.
If your building has an external LPS then, as per the 17th Edition Wiring Regs, and as the competent party, the last person working on the electrical system has a responsibility to inform the customer if his system does not meet the current regulations.
If a surge has been proven to have travelled through the grid and into your electrical system, then you are responsible for the damage caused to your systems and components therein. You can protect your system by fitting a Class II device at the incomer, if there is no LPS present.
Although they have a smaller cross sectional area than electrical supply cables, data and signal cables can still conduct up to 5 kA. In house risk assessments can be carried out to determine if specific control / instrumentation, data interface or coax cables are required.
To give your system the highest level of protection, then a Class III device may be installed directly in front of any high value or mission critical equipment, although they must have a Class II device in front of it, as they provide limited protection by themselves.
Products are available on the market which take into account the particular mains network type and voltage level. Special Type I and Type II protective devices are also available for photovoltaic applications. The advantages of these device types can include:
Flexible positioning in the control cabinet - according to IEC 62305, the distance rather than the line path from the surge protection module to the PE connection may only be 50cm. A device that you can rotate the base through 180° means that you have the highest degree of flexibility during installation, without impacting on overall visibility.
Faster assembly time – using an optimised mounting rail clip enables easy and quick assembly and removal, without the need for tools.
Secure locking into position - an arrester that can be heard and felt locking into the base means it can be trusted to comply with the exacting requirements on such things as vibration resistance.
Exceptional overview - having a large, centred status window provides highly visible information on the status of the protective function.
Rapid status messaging - a remote signalling contact with a PUSH IN connection can be quickly connected and provides reliable information regarding the status of the protective function.
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