neutral to ground noise?

[Al3579]

This blue trace is  neutral to ground reference and the yellow is line to ground. It is present throughout the whole house. I'm thinking about flipping breakers to see if its a device in the house dumping it on the neutral. Sometimes I've heard heard audible tones at about 1khz. The pulse width of the noise is about 1.85ms. I also recorded the ground to neutral noise directly it 9th harmonic 60hz noise which is 540hz.When it actually becomes audible its comes out as a 1khz tone. Maybe I'm just worrying too much!

[Twistedsnail]

Got any dodgy lamp dimmers or badly made LED dimmers running?

[Al3579]

yeah I'm going to the panel and start flipping breakers see if I can isolate it to a circuit I'll report back. Thanks!

[David Hess]

That is hardly unusual.  Neutral and ground are bonded together at the service entrance and since neutral carries all of the return current, it deviates from ground depending on the impedance between them.

That waveform comes from the harmonic current into a rectifier-capacitor filter commonly found on a switching power supply that lacks power factor correction.

[Al3579]

Yeah I went to the panel turned off all the breakers except the one powering the oscilloscope still there just at a diminished level depending on how far the circuit is from the panel. I turned off all the breakers and powered the oscilloscope straight from the lugs of the panel and since neutral and ground are tied together at the panel I thought I wouldn't pick up a thing. I didn't float the ground on the oscilloscope just fyi. Attached is the measurement with about 10ft of extension cord from panel without anything on in the house. I'm thinking it a measurement error or some kind of signal from the service meter or stray current.  I started this investigation because I've had 2 microwaves that messed up in a relatively short period of time and some fans that I thought died prematurely and a direct box that wasn't connected to anything short out. The direct box I had was used to take high impedance unbalanced signals and convert them to low impedance balanced signal for impedance matching into a op amp. It was a simple passive design and nothing more than a transformer with adjustable pad and ground lift.

[T3sl4co1l]

Neutral voltage drop, and induced ground voltage, comes from current flow.  So, there's a lot of current drawn on those peaks, and not as much inbetween.

This is typical for rectified mains -- SMPS and such.

Tim