A boundary may cover an entire building, in the case of a small telecommunications installation or remote telemetry site, it may cover a single floor of a multistorey building, a single room or even a single piece of equipment. Generally the boundary will divide areas of different potential.

In the case of a multistorey building, a lightning strike to the top of that building will create a potential gradient from the top to the bottom of the building. Metallic services running from top to bottom of the building will also be subjected to this potential gradient. It is for this reason that we choose to establish boundaries at each floor.

All services crossing the boundary require protection whether they be power, data or RF signals. It may also be necessary to provide further staged protection for some services within the boundary. For example surge diverters on incoming power may be augmented with power surge filters downstream to protect selected equipment. A fax or modem is a good example where a combined power surge filter and telephone line protector would be installed directly at the fax or modem itself.
 
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