Purpose
When Wires Talk to Each Other (Unwanted)
Electromagnetic interference is the enemy of clean signals. Adjacent wires couple noise through electric and magnetic fields. Shielding and separation are the defenses. MIL-STD-461 sets the rules.
The Physics
Capacitive Crosstalk
V_coupled ~ C_mutual * L * dV/dt
Faster signals + longer parallel runs + closer wires = more coupling.
Shielding
SE(dB) = 20*log10(E_unshielded / E_shielded)
40dB = 100x noise reduction. 60dB = 1000x.
Key Insight: EMI separation rules are WHY wire harness routing matters. You can't just bundle everything together. Artifact's constraint engine checks separation distances between signal categories automatically.
Historical
Apollo 12 (1969)
Struck by lightning 36 seconds after launch. Lost all telemetry momentarily. Flight controller John Aaron saved the mission by calling "SCE to AUX" from memory. Led to comprehensive lightning/EMI protection standards.
References
Henry Ott, EMC Engineering, Ch 1-5 | MIL-STD-461G (everyspec.com) | MIL-HDBK-454 Guideline 19