Feature Surge Protection


As Steve Dyson, marketing manager for Hager explains, there still remains some confusion surrounding the installation of surge protection, despite becoming more common as a result of Amendment 1


any people will presume that a lightning protection system employing type 1 surge protection devices is


good enough. However, this is simply not the case as they offer no effective protection against the failure of sen- sitive electrical and electronic equip- ment or systems. To achieve this, additional co-ordinated devices will need installing.


in diagram 1) is ideally less than 0.5m but certainly no more than one metre. For type 1 devices the cross section area of the conductor must not be less than 16mm2


copper.


Some devices will have dual line and neutral terminals. This connec- tion method reduces any additional voltage drop in the connecting cables and will therefore obtain the best Up to the installation. There are how- ever, conditions to this connection.


The selection process


Surge protection needs to be selected so that the voltage protection level (Up


) is


lower than the impulse withstand capa- bility to be protected. For sensitive and critical equipment the regulations state that you should consider reducing this value to that required for Category 1 equipment - 1.5kV.


Achieving this may require several surge protection devices to be combined or cascaded into one installation. This process utilises the best features of each device and as such, improves the pro- tection level for the equipment. A high surge current capacity device could be used to divert the bulk of the transient over voltage at the origin of the installation. For a Class 1 or 2 device this would be either the spark gap arrester or a high current capacity MOV. Should finer protection be needed then a Class 3 device near the terminal equip- ment would need to be installed. Cascading increases the current diverting capacity of the SPD system whilst maintaining a low voltage (Up


)


to ensure the best protection for valu- able equipment.


Short connections


When installing the devices the con- ducting connectors need to be kept as short as possible.


The connecting conductors of the SPD need to have a cross sectional area of at least 4mm2


copper and that the total connecting lead length (a+b


Right: the whole area of surge protection has caused some debate. Not only about whether it is required, but what exactly is required and importantly how to install it


Avoiding installation confusion M


Testing, testing


For instance with Hager devices it is suitable for installations having a maximum demand up to 125A. Also if the distance between the SPD and the sensitive equipment to be protected is greater than ten metres, then oscillations could lead to higher voltages appearing at the equipment. For this reason you should consider using coordinated devices closer to the equipment. The SPD device also needs to be protected against short circuits by using an over current protective device such as a circuit breaker, which needs to allow the flow of surge current through it without operating. Manufacturers should


Above: an SPD connection diagram


After installing an SPD you will need to check that it works and include it in any future periodic inspection and test. There is usually some kind of visual sign on the SPD that the device is still operational - this is often by a green visual indicator window. If this window indicator is red then this shows that the device needs replac- ing. Depending on the product you will either need to replace the device or replace the removable cartridge. It is also worth noting that an insu- lation resistance test of 500V DC car- ried out with the SPD connected will not produce the correct readings. This is because the SPD will start to conduct as the value of Uc


may have


been exceeded. This test should be done with the SPD disconnected, or alternatively at the reduced voltage of 250V DC.


The whole area of surge protection has caused some debate. Not only about whether it is required, but what exactly is required and impor- tantly, how to install it to ensure that it operates effectively in protecting sensitive electronic equipment.


Hager www.hager.co.uk T: 01952 677 899


advise you on which device to use. In certain circumstances this sec- ondary over current device can be omitted if the upstream over current device meets certain conditions. Most modern installations also have RCD protection and the SPD needs to be installed upstream of them. If this cannot be avoided, then you should install a time delayed or S type RCD.


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JUNE 2013 Electrical Engineering


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