Field glossary

ZSI

Zone-selective interlocking; breakers signal each other so the upstream device trips fast only for a fault in its own zone

Used across 3 Anvilfield field guides, most in Electrical.

Also defined as

Zone-selective interlocking, a restraint signal between trip units that speeds clearing of in-zone faults
Zone-selective interlock, a restraint signal so the device nearest the fault clears first

Where this shows up