All installations should utilize surge protection devices (SPDs), to provide maximum protection
regardless of the source of the surge. The three zones include:
• The rst zone is at the service entrance where the most robust SPD is placed to divert surges
coming from external sources such as lightning. SPDs installed here are listed as Type-1, SPD
devices.
• The second zone of protection is within the facility at locations identied as susceptible to surg-
es. SPDs at these locations are listed as Type-2, SPD devices and are installed on equipment such
as switchboards, panel-boards, motor-control centers.
• The third zone of protection is at the outlet or point of use. SPDs installed here are listed as
Type-3, SPD devices.
It is required that a professional engineer, experienced with surge suppression
technology, be retained to design the protection system for your facility to ensure all SPDs are
properly sized and coordinated.
Third zone
First zone
Second zone
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