Whole-House Surge Protector (SPD)
A panel-mounted device that clamps voltage spikes from lightning, utility switching and large motors before they reach your electronics. Required in new panels by recent code cycles.
Surges are short, violent voltage spikes, and the damaging ones mostly come from outside (lightning down the street, utility grid switching) or from your own big motors cycling. A whole-house SPD at the panel diverts spike energy to ground for everything downstream at once: HVAC boards, appliances with electronics (which is now all of them), EV chargers, the lot. Plug-in strips then serve as a second, finer layer for sensitive gear.
Two facts set expectations: SPDs are sacrificial, with indicator lights that report when they have absorbed their last surge, and they need a healthy grounding system to divert into. The 2020 NEC made them standard equipment in new and replaced panels, which says what the industry concluded about their value.
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- Ground Wire (Equipment Ground) : The bare or green wire that carries no current in normal use.
- Bonding : Connecting all the metal parts that could become energized (panels, pipes, pool equipment, gas lines) so they sit at the same voltage and faults trip breakers instead of waiting for a person.
- Ungrounded (Two-Wire) Circuits : Pre-1960s circuits with only hot and neutral, no ground conductor.
- Bootleg Ground : A jumper from the neutral screw to the ground screw inside an outlet box, installed to fool testers into showing "grounded.