Panelmount Surge Protection Devices (SPDs) are simply large" hardwired "surge suppressors installed at the AC electrical service entrance, branch panels and individual pieces of equipment with in a house/building. When properly installed, they safeguard against all surges originating external of the building (ie:lightning). When installed at a critical piece of equipment, they specifically protect that piece of equipment from damaging surges and transients.

Panelmount SPDs do not eliminate the need for other power protection equipment: (line cord surge protectors, UPSs) but rather, should be used in conjunction with them to provide the maximum protection against surges originating both inside and outside your building. This type od surge protection strategy is typically referred to as 'whole house/facility',multistage or cascaded.