Circuit Load Chart for Church AV Racks

The continuous load rule is the only figure that matters for a rack that runs all morning. Multiply the breaker rating by 0.8, then by the voltage. Everything else on this page is compared against these numbers.

The number on an amplifier is its output rating into a load at full power, which is not a state a worship mix ever reaches. Program draw on music is roughly a fifth of rated output for a class D amplifier and a third for class AB, which is why a rack holding thousands of watts of amplification runs happily on one circuit.

Four worked racks against the 1,920 watt limit of a 20 amp circuit. The headroom column is what is left, and the honest answer for most churches is that one dedicated circuit is plenty until the amplifier count passes three.

Capacity is only half the reason to give a rack a dedicated circuit. The other half is what else is on it. An HVAC compressor, a refrigerator in the church kitchen, a lighting dimmer or a fluorescent ballast sharing a branch circuit with the sound system injects noise onto the neutral and the ground, and that noise turns up as a buzz in the loudspeakers that no amount of work at the console will remove.

Dimmers are the worst offender. A phase-angle dimmer chops the mains waveform, and the resulting harmonics couple into audio equipment through both the power and the ground. A church that installs theatrical dimming and then discovers a buzz in the sound system has not found a sound fault, it has found a power fault.

Ground loops are the other symptom. When the rack takes power from one circuit and a stage box, a projector or a camera takes power from a circuit fed by a different panel, the two grounds can sit at slightly different potentials and current flows through the audio cable shield between them. The result is mains hum. The fix is to feed all connected AV equipment from the same panel and, ideally, the same phase, which is a decision made at rough-in and is expensive afterwards.

Never lift a ground to fix a hum. Removing the safety ground pin from a plug is the traditional church workaround and it is the one thing on this page that can kill somebody. If a ground loop is genuinely the cause, isolate the audio signal with a transformer, not the chassis from earth.

It is not an electrical design. Every figure here is for specifying equipment and asking an electrician the right questions. Circuit design, conductor sizing, voltage drop over a long branch run, panel capacity and grounding are a licensed electrician’s work to your local adoption of the NEC.

Programme draw is not peak draw. The figures assume music. An amplifier driven into a sustained low frequency passage, or a system being tested at full output, draws far more, and switch-on inrush across a rack of power supplies can trip a breaker that the running load never troubles. Sequenced power-up and a conditioner with soft start exist for that reason.

Voltage is assumed to be 120. A long branch circuit under load can sag to 112 volts, which costs you nearly 7 percent of the available watts and makes amplifiers clip earlier than the arithmetic predicts. If the room is a long way from the panel, ask for the measured voltage at the outlet under load.

It ignores stage lighting entirely. LED wash fixtures are modest individually and enormous collectively, and conventional tungsten fixtures are in a different class again. Lighting belongs on its own circuits and usually its own panel, both for capacity and for the noise reason above.

Portable systems change the question. A church meeting in a school gymnasium is using whatever outlets exist, often on one shared circuit with the building’s own equipment. There the constraint is not the rack but the room, and the honest planning step is to measure before the first service rather than discover it during one. See portable church AV setup.