Checking for Stray Voltage and Current

[d2mini]

I'm curious... so i whipped out my trusty Greenlee DM-20.
http://greenlee-media.precis5.com/5e98d23afe19a774d1b2dcbefd5103eb
Can anyone tell me what setting to use?
If I set it to 200v (under V~) and i put one probe in the ground of an extension cord plugged into my gfci outlet, and the other probe into my tank, I get 0.0.
If I put one probe in the hot hole of the extension cord and one probe in the tank, i get 118 volts.
For current, I have no idea.

Much appreciated!

 

[KevinJ]

Sounds to me as if your tank is grounded. When you go from your tank to ground and get 0v you do not have any stray voltage. But when you go from 110 to your tank the electrons are flowing and they gotta go someware to the ground. It could be a pump or heater perhaps chiller? Or do you have a grounding probe?

KevinJ

 

[KevinJ]

Are you getting shocked?

KevinJ

 

[uncleof6]

I'm curious... so i whipped out my trusty Greenlee DM-20.
http://greenlee-media.precis5.com/5e98d23afe19a774d1b2dcbefd5103eb
Can anyone tell me what setting to use?
If I set it to 200v (under V~) and i put one probe in the ground of an extension cord plugged into my gfci outlet, and the other probe into my tank, I get 0.0.
If I put one probe in the hot hole of the extension cord and one probe in the tank, i get 118 volts.
For current, I have no idea.

Much appreciated!

Please don't do this anymore. This is exactly how folks earn themselves Darwin Awards...also there is no such thing as 'stray voltage,' it is an induced voltage due to the highly inductive loads used in and around aquariums. As such it, it is harmless.

When you use a meter between the source hot, and the tank water, the voltage should read 0 because the salt water is not a ground plane...No volatge potential difference. You can also get a 0 volt reading if a damaged cord has an exposed hot. You should only see 118 (or 120) from Hot to neutral, or hot to ground. Unless you have done something rather silly like put a grounding probe in the DT... The only other possibility is you have a damaged cord somewhere in the DT, that has exposed either the ground or the neutral.

The proper way to test for a voltage potential is a meter between the water and a common ground plane, not just any ground will do, such as the equipment ground of a recepticle serving the circuit you are trying to test. The reading (on a low voltage setting,) will generally be ~ 12VAC if that, that is perfectly normal and nothing to be concerned with. Greater than 40VAC is something to be concerned about. I would not have a hobbyist doing this test anymore than the one connecting up to the line hot, however.

Just so you know: If there is a damaged cord, in which the neutral is exposed, and you get in the middle of the circuit, you are going to die, and the GFCI is not going to trip. Again, please do not bridge, with a meter or otherwise, between a line hot and the tank water, unless you really do want a Darwin Award.

If you have a suspicion that there is a current (voltage is meaningless, merely potential) problem with your system, have someone that is qualified to troubleshoot the issue.

 

[d2mini]

I don't have a ground probe.

have someone that is qualified to troubleshoot the issue.

Who would that be and how would they do it?

 

[uncleof6]

I don't have a ground probe.




Who would that be and how would they do it?

A licensed electrician.

 

[d2mini]

So there is no way for me to use my meter to test for stray current?

I thought it was weird that the meter was showing zero voltage when there should be voltage from the pumps in the water, regardless of whether or not there is excess current.

 

[uncleof6]

To your question, current is measured inline with the load, and it is not done with the voltage part of the meter. However, as soon as you hook up a meter inline with the load, to check for current flow, the path is completed, (if it did not already exist) and there will be current flow, even if there was not to begin with, and voltage will drop to zero. (The potential of the neutral, and equipment grounding, conductors.)

There are inductive ammeters that do not connect inline with the load, however, you can't check for current flow in the tank, with one of these, and if there is no path to ground in the tank, (a grounding probe) there is not going to be any current flow in the tank, even with an impressed voltage of 120VAC to ground. (an exposed hot wire.)

In salt water, there will always be some minute current flow, as it is an electrolyte (think battery) coupled with inductive loads, the voltage can build to 12 VAC and above. Such small voltages, even with current flow, are of no concern. A tank running, may display a zero voltage potential, and a small current flow through the metal main shaft of an external pump. Not much can be done about that.

The only time you should be concerned is if you stick your hand in the tank and you get bit. Even that does not indicate a problem, but don't stick your hand in a second time to see if you really got bit or not.

Tank water to common ground with the pumps power source, can show a voltage potential difference if one exists. Whether it is induced or impressed is a bit harder to evaluate. The main source of a voltage, with sufficient magnitude that could cause harm given a path to ground, would be from a high resistance short in a line cord, (or a broken heater,) and the way to check for that is with a mega meter. If it were a low resistance short, it would either trip the GFCI, or the main breaker, depending on where and how it was shorting.

At the same time, these types of shorts will not cause general current flow in the tank (unless from the hot of one cord to the ground/neutral of another) and any current flow there would be, would be local to the problem area, taking the path of least resistance.

Simply, if you are not having an issue, does not do much good to go looking for one.

 

[KevinJ]

Thankyou uncleof6 your answers have been very informative. Learned some new shiz. I have had 2 pumps leak voltage into my tank a maxijet and Sicce skimmer pump. I tested it "the hard way" finger in water and yank until it stopped. :hmm5: Not the best way but...

KevinJ

 

[d2mini]

To your question, current is measured inline with the load, and it is not done with the voltage part of the meter. However, as soon as you hook up a meter inline with the load, to check for current flow, the path is completed, (if it did not already exist) and there will be current flow, even if there was not to begin with, and voltage will drop to zero. (The potential of the neutral, and equipment grounding, conductors.)

There are inductive ammeters that do not connect inline with the load, however, you can't check for current flow in the tank, with one of these, and if there is no path to ground in the tank, (a grounding probe) there is not going to be any current flow in the tank, even with an impressed voltage of 120VAC to ground. (an exposed hot wire.)

In salt water, there will always be some minute current flow, as it is an electrolyte (think battery) coupled with inductive loads, the voltage can build to 12 VAC and above. Such small voltages, even with current flow, are of no concern. A tank running, may display a zero voltage potential, and a small current flow through the metal main shaft of an external pump. Not much can be done about that.

The only time you should be concerned is if you stick your hand in the tank and you get bit. Even that does not indicate a problem, but don't stick your hand in a second time to see if you really got bit or not.

Tank water to common ground with the pumps power source, can show a voltage potential difference if one exists. Whether it is induced or impressed is a bit harder to evaluate. The main source of a voltage, with sufficient magnitude that could cause harm given a path to ground, would be from a high resistance short in a line cord, (or a broken heater,) and the way to check for that is with a mega meter. If it were a low resistance short, it would either trip the GFCI, or the main breaker, depending on where and how it was shorting.

At the same time, these types of shorts will not cause general current flow in the tank (unless from the hot of one cord to the ground/neutral of another) and any current flow there would be, would be local to the problem area, taking the path of least resistance.

Simply, if you are not having an issue, does not do much good to go looking for one.

lol, I don't know why but that part made me chuckle.

ok, thanks. It was mostly just a curiosity and if you do a google search, the amount of people testing for VOLTAGE is astounding.
I'm having some sps/lps issues that I believe is caused by something else entirely, but I wanted to rule out anything electrical.
I'll leave it alone. Unless I get bit.

 

[uncleof6]

lol, I don't know why but that part made me chuckle.

ok, thanks. It was mostly just a curiosity and if you do a google search, the amount of people testing for VOLTAGE is astounding.
I'm having some sps/lps issues that I believe is caused by something else entirely, but I wanted to rule out anything electrical.
I'll leave it alone. Unless I get bit.

Absolutely. One of the battle crys fueling the fire is:

“Stray voltage is something that exists in every tank. Stray voltage can be eliminated with a simple ground probe available at most pet shops in the twenty dollar range. Elimination of stray voltage is a simple step in reducing the stress on your fish. Every marine tank should be grounded for your protection and that of your fish.”

A very clever marketing strategy. However most people don't understand the problem and consequently a huge amount of web space has been devoted to measuring voltage in the aquarium—most of which is completely useless. Voltage is not the problem, current flow is. Voltage can exist with no current flow, and current flow can exist, even if measured voltage is zero. Voltage is merely potential, current does the work, or the 'damage' such as lateral line errosion or hole-in-the-head. (If either is actually related to electrical anything at all.) Measuring voltage is not going to tell you whether there is current flow in the tank or not.

Example: Measured voltage from line hot to ground is 120VAC. Measured voltage from line neutral to ground is 0 V. With a load connected to the line, drawing 2 amps, the hot will show 120VAC, the voltage at the neutral will still be 0V, but the neutral conductor will return a 2 amp current to the source, which will flow to earth ground, through the earth back to the power station, and ultimately back to the turbine generators at Hoover Dam, or where ever your power comes from, at 0V. (San Onofre, here locally, has been offline for quite a long time,) It started out at 500,000VAC on the high voltage transmission lines.

Some of the better write ups on this topic I have seen, generated from within the hobby, have a warning at the top to the effect: "Not for liberal arts majors," followed by the suggestion that they hit the back button. (Tongue in check of course, or not.) Ironically, the authors need to hit the back button as well, especially since current actually does flow through the bird on the wire...