mikehoopes
Member
I worked as an engineer at Panamax for 16 years, and performed quite a few leakage tests. The limit for plug-in residential equipment is 0.5 mA (thought to be the limit of "sensibility") through a simple "body model" (1500 Ohm resistor || 0.22 µF cap). Leakage can also become audible as mains hum if it causes a voltage difference between grounds in earth-referenced audio equipment. That would be a LOT of leakage.
It's more likely that mains interference in audio signals is happening inside of the equipment, due to stray ac fields. Sometimes there can be electrostatic interference outside of the equipment if low-voltage (line-level) analog audio wiring is run closely adjacent to mains wiring in the wall; I've seen installers co-locate A/V cables with the ac when running in-wall wiring to video monitors, and still wondered why they could see "hum bars". In the digital world, though, the signals are more tolerant of this.
The NEC has a recommendation for <5% drop in a circuit branch, but it actually isn't a requirement. There are conductor sizes that are required per the outlet ampacity (say, 14 AWG for 15 A), but if the run is long enough, you'll need a heavier gauge to achieve the NEC recommendation. Not all electricians take voltage drop into account when speccing wire.
This is especially evident with large copy/imaging machines in the far reaches of office environments. The fuser inrush current can cause a temporary undervoltage on the line, and sometimes microcontrollers in the office machines will go into shutdown if the supply voltage sags enough.
And yes, the earth conductor is only allowed to carry "temporary" currents; its primary intention is to trip a breaker in the circuit branch if a metal enclosure is accidentally energized.
It's more likely that mains interference in audio signals is happening inside of the equipment, due to stray ac fields. Sometimes there can be electrostatic interference outside of the equipment if low-voltage (line-level) analog audio wiring is run closely adjacent to mains wiring in the wall; I've seen installers co-locate A/V cables with the ac when running in-wall wiring to video monitors, and still wondered why they could see "hum bars". In the digital world, though, the signals are more tolerant of this.
The NEC has a recommendation for <5% drop in a circuit branch, but it actually isn't a requirement. There are conductor sizes that are required per the outlet ampacity (say, 14 AWG for 15 A), but if the run is long enough, you'll need a heavier gauge to achieve the NEC recommendation. Not all electricians take voltage drop into account when speccing wire.
This is especially evident with large copy/imaging machines in the far reaches of office environments. The fuser inrush current can cause a temporary undervoltage on the line, and sometimes microcontrollers in the office machines will go into shutdown if the supply voltage sags enough.
And yes, the earth conductor is only allowed to carry "temporary" currents; its primary intention is to trip a breaker in the circuit branch if a metal enclosure is accidentally energized.