Listening to this a few months late but thought I'd ask a question anyway.
You mentioned that aircraft and automobile structures aren't truly grounded (aircraft chassis are usually connected to earth during ground maintenance, autos aren't).
With the proliferation of 12 VDC-to-115 VAC inverters, some of them built-in to new SUVs, has safety become a concern because of possible high voltage differences in potential between the auto's chassis and earth?
@bicyclebill: The current is a steady state. The configuration is as follows: 115VAC to EMI line filter to switch to system entry point. I tend to agree with the effect of caps in the line filter. should I get a line filter with lower cap value?
Jojo--if it not a miswired outlet or switch (or defective switch--could be) then probe with a voltmeter looking for potential difference (aka voltage)--since that is what drives the current you are seeing.
jojo--wow, that's nasty. You'll have go go through things connector, wire, and chassis inch by inch, look for intentionmal or unintentional contact points. That's a lot of current to be leaking through. Whatever you do, use an isolated (battery powered) meter--not a plug-in.
jojo--current can't come from nowhere, of course. But first--is that 2A steady state or a transient? If a transient, it may be from caps in the line filter. In general, caps anywhere in a system are a potential source of unexpected current flow (and voltage sparks) even after primary power is shut off. Old TVs for famous for this, with their high voltage supplies--you get get a lethal spark 30-60 minutes after shutting it off.
@bicyclebill: I have 115VAC supplying power to my system. This 115VAC is going through an EMI line filter prior to entering the system. When I turn off the 115VAC switch to my system I measure approximately 2A flowing in my ground wire. Can you please explain why I am measuring 2A flowing in my ground wire?
I can see why you'd put the instrumentation electronics behind an isolation transformer, but I guess I don't really see why you would need to isolate your shunt... I'm just trying to think of a scenerio.
cmeadows6959: most test transducers are pretty stable-unless there are dramatic shifts in ambient temp, or their dissipation, or they have been overloaded. But if they are "moved" they may need recal due to ambient magnetic fields, for example.
NLS22--it depends--one side of a single-phase AC line is called common, usually also connected to earth ground. Three phase not so. But most AC line measurements use an isolated coil, so high/low side is not an issue. And it's safer, too.
Check out our Model 2802 Power Analyzer, it has the ability to be connected to External Shunts, Rogowski Coils, Hall Effects or with use with our built in Shunts, we are used for Energy Star Compliance, IEC62301 and high power applications.
Energiman--you need a scope or equivalent to see what you have, and there are power meters for non-sine rms situations. It depends on what you are trying to see: power factor, waveform shape, transients, or just power used.
Mr E: to verify isolation, I suggest two things: look at the drawings--assumng you have them, and measure with an ohmmeter, just to be extra sure (and be sure all power is off, first). You should see infinite resistance. If you don't--find out why--where is that current flowing? But also be sure nothing changes state when you turn power on (such as a relay) which chnages the isolation situation.
When lookinmg at Test Equipment verify if the unit is electrically isolated, for Sensors, we calibrate and or verfiy the Sensor with known currents flowing through them and can then characterize the performance with in our Power Analyzer.
Thank you for the classes. I wish Digikey / Design news does a class or two on stepper and dc motors and controls. Many people and I mentioned this pont here earlier. I hope they are trying to bring in some motor experts.
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Noting that we now live in an era of “confusion and ill-conceived stuff,” Ammunition design studio founder Robert Brunner, speaking at Gigaom Roadmap, said that by adding connectivity to everything and its mother, we aren't necessarily doing ourselves any favors, with many ‘things’ just fine in their unconnected state.
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