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Connection, Inspection & Testing


To gain maximum protection from the SPD, the connecting conductors should be kept as short as possible. This is to minimise any additive voltage drops on the connecting cables.

The connecting conductors of the SPD shall have a cross sectional area of not less than 4mm² copper and the total connecting lead length (a+b) should preferably not exceed 0.5m but shall in no case exceed 1m. Where Type 1 devices have been installed the cross section area shall be not less than 16mm² copper. Manufacturer’s instructions shall be followed. Some devices have dual line & neutral terminals.

This connection method reduces any additional voltage drop in the connecting cables thereby obtaining the best possible Up to the installation. There are conditions to this connection method however. With Hager devices it is suitable for installations having a maximum demand up to 125A.
Should the distance between the SPD and the sensitive equipment to be protected be greater than 10m, oscillations could lead to higher voltage values appearing at the equipment. Consideration should be given to additional coordinated surge protection devices closer to the equipment. Again manufacturer’s instructions should be followed Protection against SPD short circuits is often provided by an over-current protective device such as a fuse or circuit breaker.

This device must of course permit the flow of surge current through the device without operating. Manufacturers will give instructions as to which device is recommended. In certain circumstances this secondary over-current device ay be omitted if the upstream over-current device meets certain conditions.

Should RCD’s be required in the installation as additional protection or to ensure the requirements of fault protection are satisfied, then the SPD will need to be installed upstream of the RCD. Where this cannot be avoided, the RCD should be of the time-delayed or S-type.

Inspection & Testing

During the Initial Verification or as part of a periodic inspection & test, the SPD should be inspected to ensure it is operational. Any over-current protective device associated with the SPD should be intact and should be as instructed by the manufacturer. There is usually some kind of visual indication on the SPD that the device is still operational. This may be indicated by a GREEN visual indicator window. Should this window indicate RED then it is an indication that the device has reached its ‘End of Life’ and needs replacing. With some products, this will involve the replacement of the device, but on many of the products in the range, this can simply be carried out by replacing the removable cartridge. An insulation resistance test of 500V dc carried out with the SPD connected will produce incorrect readings. This is due to the SPD starting to conduct as the value of Uc may have been exceeded. This test then should be conducted without the SPD connected. Alternatively this test can be conducted at the reduced test voltage of 250V dc.