why do I always check for stray voltage?

[Frick-n-Frags]

...when I have a real puzzler on my hands.

Classic example:

These past two days, several of my old warhorse garbage corals (P grandis, shrooms, asst zoas, rics, cabbage, etc) down in the corner of the VHO tank toward the powerheads have started bleaching.

They have also not been opening up like normal.

Then I see all my Xenia don't look as fluffy as normal, like the very tips of all their tentacles were burned. They are also at that end of the tank.


OK, I rule out poison, because I have corals in my other tank that would die way before these hosses. poison takes the whole system out more evenly.

then I thought, "better check for stray voltage"...

sure enough, I measured ACV right to a solid ground and I had 18volts. I have 3 GFI's One of which has the heater and two small powerheads in the problem tank, so I killed that one and measured. 0VAC (I was praying it wasn't my main return pump, so WHEW!) The heater isn't even fully submerged and the tube is fine so I left that plugged in. I'm thinking the little RIO, so I plugged it back in, nope....

plugged in the second ph and snap! all the GFI's kicked out didn't even get a chance to measure just to double check.
I don't even remember what brand this one was. It is old, so hey..buh bye

this morning(that all was yesterday) the rhodactis are all spread out like usual and all the zoas are open, so I think we got it solved.

 

[Frick-n-Frags]

Also, if anyone wonders why the voltmeter doesn't trip the GFI when placed directly to ground during a fault condition such as mine, it is because the meter works at very high resistance( >1megohm) and only permits microamps to flow through it, just enough to get a measurement level.
so this operates below the sensitivity threshhold of the GFI circuitry.

 

[K9]

Thanks F-n-F for the electrical lesson.

So basically, to check for voltage in the tank water, I can just buy one of these, and put the two prongs in the water, and I'll get a reading if there's stray voltage? If so, what setting would I turn the dial to?

 

[Frick-n-Frags]

I'm glad you asked that question.

First one tidbit of theory: voltage is an "electrical pressure" when there is no current flowing(parallel to a faucet turned off, so the water pressure is 40# but no water flowing). your tank with the leaky powerhead is basically pressurized with electricity.

to turn the faucet on, I have to give the juice a path back to its source, which for the powergrid is the ground.

so, your question: putting both probes in the tankwater won't show you stray wallsocket voltage. you maybe could pick small induced fields from current in devices or flourescent lights, but that is trivial,.

you need to put one probe in the water and one probe to a known good ground. now you've given the juice a path to leak

when you do this, you also should make sure you are holding the plastic of the probes. human is a lot lower resistance than meter(see above) and you are in effect grabbing two metal contacts = human ground probe.

 

[Frick-n-Frags]

to answer you second question: set it to ACV err vAC on your meter there 50v range and test. If you see nothing or a twitch, up the sensitivity to the 10volt scale. you should have pretty much nothing leaking to ground

meters have certain% error so a fewmillivolts is as good as nothing

 

[K9]

Perfect, thanks.

 

[rsw686]

I'm confused on this topic. I read this web page. Heres some quotes.

http://avdil.gtri.gatech.edu/RCM/RCM/Aquarium/GroundingProbes.html
http://avdil.gtri.gatech.edu/RCM/RCM/Aquarium/GFI&TechnicalDetails.html

"Taking a volt meter and measuring a voltage in your aquarium relative to some arbitrary ground point does not indicate that there is a current flowing through the salt water (conductive medium) in your aquarium! It just means that the aquarium water is at a different potential than the ground reference point that you chose."
"
"Second example: If a GFI is used on the pumps and lights and there is a grounding probe in place, any "induced" voltage will cause a current through the water and out the ground probe. Light, heat, motion, and induced electrical currents all represent "consumed energy". The current into the "emitter" of these energies will be the same as the current going out of the emitter. The circuit is balanced and the GFI will not trip, but energy is still created in various forms which can be transmitted to the aquarium. Consider an improbable case that will illustrate this point."

For the plus side of stray voltage

"For example, if one power head's hot lead (black wire) is exposed to the water and another power head's neutral lead (white wire) is exposed to the water, then there will be a current flow between them as well as any sea life that gets in the way. Lets say that both power heads were plugged into the same GFI. Since all the current coming in the black wire is going out the white wire (some through the power heads, some through the water and fish)... there is a balance, but an unhealthy one for the tank. The GFI would not trip. Adding a ground probe would cause the GFI to trip in this example."

There seems to be no definite answer of what is better for the aquarium. I tested my tank and I have 6 volts when just the lights are on. So my thinking is there is no good way to test this and adding a grounding probe would just cause the fish more harm.

This was just with sticking the probe in the ground hole on the outlet. I'll have to take the outlet plate off later and clip the probe on to get a good solid ground with no resistance and repeat the test.

 

[rsw686]

I did some testing in a bucket of water with a powerhead and heater. With just an empty bucket of water the multimeter reads 0. If I put in the heater or power head it reads 20-23 volts. The catch here is if I check the current flowing from the water to the ground its only 3u. Thats such a small amount it won't harm anything. Its not even close to a milliamp.

So my feeling on this is that I have induced voltage from the magnetic field on the power head and induced voltage from the heating core on the heater. Adding a grounding probe provides a path for this induced voltage to flow which would could be harmful to the livestock. Without the grounding probe it just has potential.

This is not near enough to cause you harm according to this quote

"At currents as low as 60 to 100 milliamperes, low-voltage (110-220 volts), 60-hertz alternating current traveling through the chest for a split second can cause life-threatening irregular heart rhythms. About 300-500 milliamperes of direct current is needed to have the same effect."

Comparing the above 3u is .003 milliamp. My main tank has .015 milliamp of current if I ground it. Thats all induced voltage way less than anything harmful.

When checking for stray voltage you want to measure the current of stray voltage. It might just be induced voltage and nothing to worry about. From what I've read I'm against grounding probes.

Anybody else have an opinion on this.