The surge protection device (SPD) shall be compatible with the system it is protected and shall provide phase-to-neutral, phase-to-earth and neutral-to earth protection for either single phase or three phase power supply system. The normal operating voltage of the SPD for phase-to-neutral connection shall be 240V and the maximum operating voltage is 275V. SPD for phase-to-earth and neutral-to-earth connections shall be rated at 415V and the maximum operating voltage of 475V. The leakage current shall not exceed 3.5 mA. Unless otherwise specified, the type of SPD to be installed with respect to the location of switchboard shall be as in Table 1 below:


The peak transient let-through voltage or voltage protection level for all modes (phase-to-neutral, phase-to-earth and neutral-to-earth) shall be as in Table 1 above. Unless otherwise specified, the SPD shall be of the type complying with BS 6651 and/or IEC 61024-1 and IEC 61312-1. The surge protection device shall incorporate continuous indication of its protection status, viz. full protection present, reduced protection – replacement required and no protection – failure of protection.
The connecting leads shall be as short as possible and not more than 1000 mm in length, and shall be tightly bound together over throughout the whole length. Unless otherwise specified, four-pole moulded case circuit breaker or fuses of rating as recommended by the SPD manufacturer shall be provided to enable full isolation of SPD from the system for maintenance.


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