Stray voltage?

[garydan]

I'm not a believer in the GP theory, but always thought measuring the voltage drop across a resistor in series was the only way to be accurate.

My compromise last time was a GP on a light switch. Before you reach in the tank, ground it out in case something shorted out. Then turn it off so you aren't leaving a path to ground 24/7.
But I'm just an electrician. you guys are the ones that think it out.

Measuring a voltage drop across a resister in series is just an application of v=ir really, so in the end you're measuring current. Why not just put the meter in the mode to measure current? In the end, volt mode in the meter is still measuring current, but it's measuring after a massively large resister and has the sensitivity increased to the point where it's susceptible to electrical noise.

My concern with a ground probe is what happens if you have a faulty house ground. Grounds and commons are connected together back at the box, if the ground is poor then you could get some charge on the ground from all of the commons. In that case, it's going to do the exact opposite of what's intended. I compared my house ground to a copper water pipe a while back though, and the difference was negligible. I'm not an electrician, so I don't know how common that situation is.

 

[JiveWalker]

Keep in mind, these are just my opinions:

When using a grounding rod on a tank, it should be outside in the ground, nothing less. Your panel electrical ground most likely bonds to a neutral somewhere at the panel or transformer. I'm no electrician, just a Facilities Manager. Residential may be different. Reefergeorge correct me if I'm wrong.

Isolating and removing the faulty appliance is the proper solution.

To say a meter can't read phantom voltage is incorrect. To say a meter can not accurately read phantom voltage would be a better statement.

If you run all of your wires for your submerged appliances into the water at the same place, in a bundle so to speak, the chance of the induced voltage through capacitive coupling is there.

reefergeorge, being an electrician, probably sees this all of the time. I see it often as well. Typically in conduits that carry too many current carrying conductors, or that get submerged.

I would think a good way to test insulated aquarium equipment would be with a megohm meter or an insulation tester, one lead to the water (in a seperate container of course), testing both the hot and neutral legs.

 

[alton]

First we need to seperate stray voltage from current, stray voltage in our tanks come from open lamps to the water (add a glass top or lense and it goes away) or power heads/internal pumps. Either way no danger to human life because it has no power. Current is what kills and is what a GFCI trips upon reaching 4 to 6 milli amps. Since our tanks are insulated, if a piece of equipment shorts out it either waits for a grounding path like the human body to acheive the 4-6 MA, or it explodes when it creates too much current (like the stealth heater issues). The worse shock I ever received was from a friends tank and it had only 2 volts. It had a grounding probe but since his service ground was no good it used his tank as one. I use a grounding probe on my tanks but I make sure my service ground is adequate. Here is a test: take a bad pump that someone claims has shocked them place it in a bucket of water and plug into a GFCI, you will notice it does not trip? Drop a grounding probe in and it trips. Remember you can feel a tingle at 1 ma, and the rule is you should be able to let go at 5ma? And your GFCI should trip at 4ma but it may take 6ma? GFCI breakers trip at 5ma or less.

 

[dkeller_nc]

Can you please post a link showing the physics behind induction within a electrolytic fluid?

I'm quite familiar with induction in wires, how inductors work, the physics of electricity. I've had two years of engineering physics, and spent a significant amount of time studying electrical theory. I know of no physics that supports induction of voltage or current flow within an electrolytic fluid from magnetic fields.

Just for the sake of the discussion, Maxwell's equations require that changing magnetic fields induce electric fields in any conductive material, whether it be solid, liquid, gas or plasma.

That said, the magnitude of this effect isn't sufficient to generate a large (> than a few microamps) current in a typical saltwater tank unless someone is spinning a very large magnetically-coupled pump.

 

[garydan]

Just for the sake of the discussion, Maxwell's equations require that changing magnetic fields induce electric fields in any conductive material, whether it be solid, liquid, gas or plasma.

That said, the magnitude of this effect isn't sufficient to generate a large (> than a few microamps) current in a typical saltwater tank unless someone is spinning a very large magnetically-coupled pump.

Yes, from the perspective if I were to create a tube of saltwater I could probably use it to make a generator, using the saltwater as a wire. We always discussed surfaces of the conductors, toroids, etc. What's happening in the center of the block of material though?

If I take a large block of solid steel, hollow out the center of it, and spin a magnet, what's happening? Electrons are following the magnetic fields within the block? The whole block is conductive, so even if they are, what would I measure on out outside of the block? The left edge and right edge of the block are going to have a different voltage potential? Is this voltage potential something that would even be possible for us to measure?

When you say a few microamps of current, where would you measure that? What would the frequency of it be? It's not DC, it'd have to be AC. What would the voltage be? Magnetohydrodynamics looks to be investigating that, but the high level discussion (i'm an engineer not a theoretical physasist) is investigation of rivers flowing through the earths magnetic field. That's not much different than a tube of saltwater being used as a generator.

Theoretical application is interesting, but from an engineering perspective, what would the volt meter see on the edge of the block. It seems to me like it would look like electrical noise. The meter would try to interpret it, sampling it through a very large resister and measuring for microamps in order to convert that to a voltage. It would then take microamps it measured and try to detect a frequency in them in order to provide the user a voltage measurement. So from an engineering and application perspective, I refer back to http://www.nema.org/stds/eng-bulletins/upload/Bulletin-88.pdf. While this whole thing exists from a theoretical physics sort of perspective, in real application our voltage meters can't deal with it.


Granted, there is a bit more going on here than I had originally though, the concept of "stray voltage" as this hobby defines it is still a myth, an artifact of how the volt meters measure voltage. It's not something the average joe at home has the tools to measure in any meaningful form. If you were to put an oscilloscope on the tank, it'd probably look pretty interesting though.

 

[dkeller_nc]

We aren't disagreeing - note that I said that the effect would not be so large as to have any practical effect, and I think you're right that an average voltmeter wouldn't be able to accurately measure it. I was just pointing out that there is some throw-off.

To answer the question about the metal block - yeah, there would be a voltage differential when measured in reference to a ground, because you have to have a voltage differential for current to flow, and a moving/changing magnetic field by definition will induce a current in the block.

But that's academic, though interesting, at least to me. I suppose I should let on that you're conversing with another engineer - in this case, PhD CHE.

 

[geomarq]

I finally got around to testing my tank as I knew I probably had a probelm, and this is the reading I got! But I can't figure out where it's coming from as I unplugged every electrical item with water contact and the reading did not change. I must have missed something but not sure. Any thoughts?

 

[alton]

I finally got around to testing my tank as I knew I probably had a probelm, and this is the reading I got! But I can't figure out where it's coming from as I unplugged every electrical item with water contact and the reading did not change. I must have missed something but not sure. Any thoughts?

You still have your lights on don't you? Turn them off and see what happens?

 

[garydan]

I finally got around to testing my tank as I knew I probably had a probelm, and this is the reading I got! But I can't figure out where it's coming from as I unplugged every electrical item with water contact and the reading did not change. I must have missed something but not sure. Any thoughts?

Are you looking for "Stray voltage, scourge of the universe" (tm), or equipment failure? If you want to know about "Stray voltage" I'd recommend buying an oscilloscope, because your volt meter is pretty useless for quantifying it. The meter's not designed for it.

I'm going to assume you're looking for equipment failure.

On the bottom left of your meter, I see mA just under your finger, looks like your meter can measure current. Move the dial there. There may be a line drawn on the meter from that setting to a different plug on the meter, if there is then you need to use the other plug on the meter. You'll want mA AC, not mA DC.

See what you get there. If it measures > 0, then try to track down what equipment is making it read >0.

Also, looks like you might be touching the contact between the ground probe and the meter probe (can't tell from the picture, but I see the end of the probe sticking out under your finger). Make sure you aren't touching either of the contacts.

 

[geomarq]

Here's a better pic of my unit..now what do I do to test for equipment failure?

 

[fletch999]

just read this on wiki

The third most common flowmeter behind differential pressure and positive displacement flow meters, is the magnetic flow meter, also technically an electromagnetic flow meter or more commonly just called a mag meter. A magnetic field is applied to the metering tube, which results in a potential difference proportional to the flow velocity perpendicular to the flux lines. The physical principle at work is electromagnetic induction. The magnetic flow meter requires a conducting fluid, for example, water that contains ions(salt water), and an electrical insulating pipe surface, for example, a rubber-lined steel tube(all our wires in the tank).

So it doesn't look like we can measure it with just a multi-meter.

 

[BeanAnimal]

while I know quite a bit about electricity and the flow of electrons, there are enough people on RC saying a probe can kill you it is creating doubt.... While I disagree with them as I know electricity always seeks a ground and that if there is one provided it is not going to choose my ungrounded body over a ground probe. I still second guess it....

Electricity seeks to move from high potential to low potential. It does not follow "one" path, but instead follows all paths in proportion to their potential.

You don't have to be "grounded" to be "shocked" you merely need to be in the path of current flow, meaning touching something of lower potential and something of higher potential.

It is not that a grounding probe will kill you, it is that they can create potential hazards in an aquarium situation that would not otherwise be present, and therefore when used MUST be accompanied by GFCI protection on ALL equipment in or near the aquarium.

Well that electrician should look at the damage caused to boats in a marina by stray voltage....one boat with a bad ground will rot the anodes off the boat next to it to nothing. Even if that boat is not connected to shore power (not grounded)...

There are a lot of other things at play here, many of them associated with the galvanic reactions of the materials the boat is built out of.

 

[BeanAnimal]

Keep in mind, these are just my opinions:

When using a grounding rod on a tank, it should be outside in the ground, nothing less.

NO NO NO NO ABSOLUTELY NOT EVER NO!!!!!


ALL grounds in your home (business, whatever) need to be bonded to the SAME system. Driving an isolated ground rod and hooking it to your aquarium can (will, does) create a very deadly situation where there could (will likely) be a difference in potential between the tank ground and the house electrical ground. Not only will current flow, but something a simple as a nearby lightening strike could create (tens of) thousands of volts difference between the tank and the homes earth connection.

I don't want to drag on with examples... as the basic point of DON'T EVERY DO IT will get lost.

Your panel electrical ground most likely bonds to a neutral somewhere at the panel or transformer. I'm no electrician, just a Facilities Manager. Residential may be different. Reefergeorge correct me if I'm wrong.

Your grounding probe MUST be grounded to this system, there is no exception.

 

[dtaranath]

Is it possible for a tank to truly read 0V, even if there are multiple powerheads and other electrical devices in there? I ask, because that's what I'm getting, even when I double and triple check that I have a solid connection between the black and the ground.

I'm just trying to figure out a reason all my corals are suddenly deteriorating, when all other water parameters are perfect.

 

[BeanAnimal]

The above post should read "Your grounding probe MUST be BONDED to this system, there is no exception".

 

[garydan]

Here's a better pic of my unit..now what do I do to test for equipment failure?

Your meter won't measure AC current, just DC current. DC current should still read 0, or practically 0. You'd put the black wire on COM (common), the red wire on mA. Put the selector on the 200 DCmA setting.

The more I read about it and learn, the less convinced I am that our multimeters will even accurately work for current. It works for me, but who knows.

A GFCI compares the current on the hot wire to the current on the common, so if > ~4mA "leaks" to ground it'll detect it and trip. Combined with a ground probe, that will pretty accurately detect equipment failure, ignoring all of the electrical noise going on in the water from the spinning magnets.

 

[BeanAnimal]

A GFCI compares the current on the hot wire to the current on the common, so if > ~4mA "leaks" to ground it'll detect it and trip. Combined with a ground probe, that will pretty accurately detect equipment failure, ignoring all of the electrical noise going on in the water from the spinning magnets.

To be specific, the GFCI knows nothing about ground. It only knows hot and neutral and will trip regardless of where the current goes. It could be ground, or another circuits hot, etc.

 

[JiveWalker]

The above post should read "Your grounding probe MUST be BONDED to this system, there is no exception".

BeanAnimal,

Thanks for correcting my statement, after thinking about it, what you say makes perfect sense! If I could go back and edit, I would.

 

[BeanAnimal]

BeanAnimal,

Thanks for correcting my statement, after thinking about it, what you say makes perfect sense! If I could go back and edit, I would.

It is a rather common recommendation, as it sounds very reasonable until somebody points out the dangers. It is (in my opinion) one of the most dangerous things anybody could do to an aquarium, thus my reaction.

 

[MKsreef]

I had issues in the past, I have a ground probe. No issues since.