Pelliott321 wrote:
Does it makes ice to measure voltage between neutral and ground?
Can one see noise with a scope between neutral and ground
Yes and yes.
If there is a subpanel, or lots of load (like a heat pump, etc.) there can be several volts between a properly connected ground and neutral. This is because of voltage drop across a conductor with resistance. Since ground remains at 0 potential, neutral voltage will actually rise above ground. So, if one were measuring voltage on a nominal 120 volt circuit, one might find that there is 122.5 volts, hot to ground, but only 120.4 volts hot to neutral. Very common.
And that's if everything is properly connected. Loose grounds or some appliance where ground and neutral are connected inside the appliance and anything can happen.
I helped Jay Bala out several years ago. He was getting odd noises from a surge protective device when he used his microwave on a completely different circuit. Everything checked out in his panel and meter socket. BUT, the utility served his house with a ground mounted transformer, down the block from his house. Landscapers had piled up soil around the transformer. Water built up inside the enclosure and corroded the connections within.
The neutral connection had failed. So his house and a couple of others were being served with 240 volts only and a floating neutral. so long as the load on each phase remained about the same, neutral remained close to ground. But when there was an imbalance, neutral shifted with respect to the phase conductors and there was marked voltage between neutral and ground.
Every time the microwave was used, there was as much as ~9 volts between ground & neutral. We've seen this innumerable times over the decades, even seen lamps and appliances explode from overvoltage. Service call: my lights get dim/bright when I use my .....(heavy current draw appliance). When there is no connection between ground & neutral (all have failed) it's entirely possible to have way over 150 volts on one circuit and under 100 on the opposing phase. And yes, incandescent bulbs can literally explode!
A great suggestion is to use an isolation transformer for your entire rig. 240 volts in, 120 volts out. Connect to a small circuit breaker panel. Then ground one "leg" of the secondary right at the building's grounding point, usually cold water at the point of service, street side of the water shutoff. Best way to start with a clean supply.
Stuart