# EMP and Faraday Cages

**EMP** stands for electromagnetic pulse. A sufficiently strong pulse induces
currents in conductors, and small unshielded electronics with long attached leads
are the most vulnerable.

## What a Faraday cage does

A Faraday cage is a continuous conductive enclosure. Incoming fields induce
currents in the shell, which cancel the field inside. Three things determine
whether it works:

1. **Continuity.** The conductive layer must be unbroken. A seam that is taped
   rather than conductively bonded is a hole.
2. **Insulation.** Contents must not touch the conductive shell. A cardboard box
   inside a metal trash can is the classic arrangement.
3. **Closure.** The lid must make contact all the way around. Copper tape along
   the rim is a cheap fix.

A galvanized steel trash can with a tight lid, contents boxed in cardboard, is a
genuinely effective cage. It does not need to be grounded to protect its
contents — grounding matters for personnel safety, not for shielding.

## What to put in it

Spares, not primaries: a backup handheld radio, a spare charge controller, an
old laptop with offline references, a spare inverter board. Anything already
plugged into long wiring during the event is likely lost regardless.