Re: Measuring stray voltage at the slip
I'll try, what the heck, might need a good debate here too!!
"Voltage Leakage"? I not too familiar with that one.
Back in the day, we'd use a low impedance VOM to check for "ground faults" on Subs. Couldn't have our instrumentation's' power, batteries (plus or minus) etc at/"leaking" onto any part of the hull. On the bunks, we'd tie the hull to earth and do the following.......
I guess what I'm say'n is there will always 99% of time be some voltage difference (difference in electrical potential) if two major bodies are electrically isolated (not one attached to each end of the same piece of wire) from one another
BUT, the real question here I think is being asked, is there an allowable amount of "current leakage" that can flow between the bodies and not do harm?
Short of a long winded physics lesson.....
Difference in electrical potential is made by us with magnetic.......ty Nikola!!
And then there's electrostatic difference in potential.......thx Bennie.
In order for current to flow, it needs the above (difference in potential). Then, current may flow BUT, needs a "path", it can be resistive, chemical, ionic and the like.
How much current is there depends on if there is a turbine directly attached or not making the trons live there.
So we have two large bodies(earth, boat, house, ship, dock, wife), typically conductive, but not necessarily, next to one another, NOT attached to the same wire, one with more electrons than the other and current now wants to flow from one to the other, needs a path, right?
Well you're not sure if current flowing here but, need to know your safe, that's fair, so you measure for voltage cuz you know it takes a difference in potential.........
You take a meter on volts and measure between the two bodies and there ya go, 900 Million Giga Volts......Gasssp!! Is there (enough) current flowing that will kill me and my boat and otherwise infect my soul? There certainly enough potential difference for current to be flowing here!!
How do we know? Well a current meter would be nice but, what if there a thousands of paths? Wait, this is water!! Which path do you break? hmmmmmmm
********Use a low impedance VOM(Simpson type) to measure voltage of the suspect moving/floating body/ies(conductive types are usually the ones we care about) to our reference/safe body Earth,!! This will discharge [allow the electrons to move/equalize(if they can, no turbines) rapidly from one body through the meter to Earth........THE voltmeter here is used as a low resistance PATH to discharge any built up static type charges allowing any resistive paths(hazardous/direct)developing voltage due to current(hazardous)developing voltage to be detected]
This is the typically nuisance leakage current model that is caused by capacitance as the major device that will allow a difference in potential to form and be stored(a battery), one body(plate) separated but next to another body(plate) one with an excess of electrons from the other bodies absence of electrons........whalah, difference in potential. High Impedance VOM's wn't work in these cases or take days to get there.
Start with scale on highest and switch to lowest and make sure the voltage decaying off as you scale down to the lowest in range, i.e., 1-10V.
You'll see the needle jump way up initially and fall to zero IF, the difference in potential is purely of capacitive nature(this is normal as stated above with large bodies as each are moving around in space picking up differing numbers of electrons). When the needle is at zero, no potential difference exists and therefore no current flow can exist between the bodies.
This then could be said to be low level stray leakage and the best you can do is wire floating things to earth and together to minimize the potential from developing as best you can, reduce or remove electrolytes in the media separating the bodies and/or bite the bullet and use sacrificial metals limit damage to critical things
IF a voltage reading remains after a short time and at some fixed level with the LOW IMPEDANCE meter attached, there is a turbine connected to the body/ies(plate) in question somewhere with a substantial current path. This would be considered, hazardous leakage.
Now I have a headache!! But, that's how we'd/I check for the more noteworthy leakage currents in a world of the given strays.
