Audio Signal Processing, Amplification, and Reproduction Equipment

Article 640 covers the sound system as an installed system, not a box you plug in. It deals with how the audio cabling is supported and separated from power wiring, grounding to control noise and hazard, and the powering of amplifier racks that in a big venue can be a serious load. It also recognizes portable and temporary audio for events.

Audio is where clean grounding pays off twice: it kills the hum the client complains about and it keeps the racks safe. I keep the power and signal separated, bond the racks properly, and treat a stadium PA amplifier room as the real electrical room it is, not an afterthought closet.

When it applies

Article 640 covers permanently installed sound systems, the PA in a stadium, the audio in a house of worship, a commercial studio's wiring. It deals with how the audio circuits are wired, grounded, and managed so you get clean sound without hum, and so the cabling is supported and separated from power in a way that keeps it both quiet and safe.

Common mistakes

• Running audio cable right alongside power conductors and then chasing the hum it causes.
• Creating ground loops by bonding audio grounds at multiple points.
• Leaving bundles of cable unsupported above ceilings where other trades will disturb them.

In the field

On a big install I keep the audio runs separated from power and grounded at a single clean point. Nine times out of ten a mystery buzz in the system traces back to cable routing or a ground loop, not the gear.