copper grounding probe

[AnotherGoldenTeapot]

There was an article in TFH some years ago that concluded that you get a capacitance effect in a tank. The coils in the pumps being the plates etc.

Their conclusion was that current only starts to flow once you ground the tank, and of course, you have to ground the tank to see if current is flowing and so noting that your meter shows a potential difference between the tank and ground proves very little.

The only good reason for a grouning probe is to prove an immediate ground fault for a GFI. This gives your organisms a chance of survival by turning off the power as soon as a fault occurs. When you stick your hand in the tank the GFI would probably trip anyway - the difference will be that your fish and corals will be long dead if you wait for that to happen.

You should have probes in each discrete section of water e.g. in the tank, the sump, and anywhere else where there's powered items. It's not good enough to just have a probe in the sump if you have things like powerheads in the tank since, if the return pump fails there may not be a relaible electrical connection between the tank and the sump e.g. no column of water connecting the two.

To be killed, or to lose a tank full of organisms, for the sake of an almost free accessory is just plain stupidity.

 

[AnotherGoldenTeapot]

Eyegoggler - you're right on the mark - that is exactly what happens.

Many people conclude the eletric shock is due to an equipment fault. All that is really happening is that the "capacitor" is being discharged through the person. This has been known to motivate people to go shopping for a GFI and grounding probe out of fear of electricution - a sensible purchase motivated by totally wrong reasoning.

 

[Manofathousandpolyps]

If you have any question about stry voltage in your tank, just use a multimeter. I did this two weeks ago just out of curiosity and found there was 3.5 stray volts. I putting in a GP next week. Stray voltage may not harm anything, but for 10 bucks why take the chance?

Nate

 

[Marcosreef]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Manofathousandpolyps:
<strong>If you have any question about stry voltage in your tank, just use a multimeter. I did this two weeks ago just out of curiosity and found there was 3.5 stray volts. Nate</strong><hr></blockquote>

How EXACTLY did you do this? Did you place both probes in the water or 1 probe in the tank and the other to earth ground? I had over 60 VAC in my tank, 3.5 seems way too low...

[ April 02, 2002: Message edited by: Marcosreef ]</p>

 

[ecoman001]

Holy copper wire Batman

Man sure is a good thing you posted that question.

 

[LeoR]

To test for stray voltage place one (black) probe into the ground outlet and the other (red) probe into the tank.
If you get more than 1 VAC then you need a grounding probe.

If you get more than 3 VAC then you have a serious current leak.
To find the culprit, turn off and *remove* devices away from the tank, one by one (merely turning devices off may be insufficient in some cases).

LeoR

 

[LeoR]

Red herring, AnotherGoldenTeapot.

While volt-meter (like any meter) does affect the measurement, the effect is way too small to worry about it, much less to render measurements unusable.
Otherwise, of course, volt-meter would be unusable in *every* measurement.

It is easy to confirm this with a simple test:
Measure voltage with and without the grounding probe and with devices turned on and off.
You will see a measurable difference in voltages -- and that's precisely what we are trying to measure.

LeoR

 

[AnotherGoldenTeapot]

Nope you're wrong.

Your experiment is just like measuring the voltage between the two terminals of a battery, noticing it's non-zero and then concluding that current flows between the two terminals when the battery is not in the circuit.

The whole basis of your argument hinges absolutely on the belief that the volt-meter is not altering the circuit. It's easy to see this is an invalid assumption. Think about why it is that you can't measure a potential difference between any two points internal to the circuit of anything like the magnitude you're seeing after you ground the tank with the meter?

V=IR. The maximum value for V within the circuit (so both probes in the tank) you can find defines the maximum value for I given R hasn't changed (much anyway). Why on earth do you think this changes when you connect one probe to ground?

The meter is the cause of profound experimental error in your measurements.

 

[Marcosreef]

Even if the tank has capacitance, the constant running of pumps, ballasts, bulbs, heaters, etc, provide an endless field of electromagnetism.

This will not discharge, like a capacitor can, this is a constant field. True, the first measurement will discharge any excess current, but thereafter you will be able to measure with accuracy the prolonged and sustained stray voltage that is always present in the tank.

Other than placing one lead in the tank and the other to ground, how else would you get an accurate measurement of the voltage within? We are trying to determine voltage, not current OR resistance.

 

[Minh Nguyen]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by AnotherGoldenTeapot:
<strong>Nope you're wrong.


.......

V=IR. The maximum value for V within the circuit (so both probes in the tank) you can find defines the maximum value for I given R hasn't changed (much anyway). Why on earth do you think this changes when you connect one probe to ground?

The meter is the cause of profound experimental error in your measurements.</strong><hr></blockquote>
The volt meter use minimal current because it is mainly a capacitor. The resistance is very high. That is why voltmeter doesn’t alter the circuit.
When I put the leads of the voltmeter between tow battery terminals, and it show 12 volts, I conclude that the battery have 12 volts potential difference between the terminals. I don't conclude that there is a current between the two terminals.
Even if you have an open live wire in the tank without ground, he reason you get a 0 volt if you put both leads in the tank is because there is NO potential difference between the two leads. Salt water conduct electricity. It may be true that the may be at 110 volts in compare to the ground, but this is not what you are measuring. Putting a volt meter between the tank and ground will show that you have a 110 volts. This won't alter the potential much because the volt meter have very high resistance and will not allow very much current to flow through it. How expensive the volt meter is determines how much current got through.
A good volt meter determine the potential differences between two points without allow much current to escapes.

 

[Anonymous]

I and a few others believe grounding probes increase the potential danger to hobbyiests. It is the GFCI that protects you and it doesn't require a ground probe to operate properly. If you don't have a GFCI, adding a ground probe may be lethal. Here is a thread that discusses the issue. http://www.reefland.com/cgi-bin/forum/showthread.php?s=&threadid=5785
I hope this helps.

 

[pez]

A couple of points here:

I had one of my pumps fail a while ago. The pump was connected to a GFCI. When I put my hand into the tank, I got one heck of a shock. The GFCI did not trip. I don't really know why the GFCI did not trip. It does not make me feel comfortable though. FWIW, the tank is not grounded.

Second, some of you are arguing about how a multimeter affects a circuit. First, one person is talking about induced voltage and the other is talking about the current measured using a multimeter. Now, the only way to measure voltage is to have current flow. As such, the MM *has* to affect the circuit. How much it affects the circuit depends on the circuit. Modern DMMs have an input impedance of about 10Mohms. If the impedance of the circuit is no where near that value, the DMM will have a negligible affect on the circuit. If the circuit as an impedance within an order of magnitude of the DMM's input impedance, the DMM can have a very large affect on the circuit and how it operates. I can't really say what the impedance of a reef tank would be, but I would suspect the resistance is very low, given that we are talking about saltwater. But, given all the capacitance effects, the total impedance might be very large. Regardless, for the case of a reef tank, I would say the DMM does affect the circuit, as it provides a path for current to flow, where there would normally not be one.

-Tom

 

[AnotherGoldenTeapot]

You can't use a volt-meter to determine if there is stray current leaking to earth. All you can tell with this is that when the meter is connected there is current flowing. You can't say anything about whether the same is true when the meter is not connected. The latter is all you're interested in.

You need to use a measurement tool that has less impact on the circuit you're investigating.

Think of it this way. You want to measure the tempreature in a dark room. You can't read your thermometer because the room is dark. You light a really big fire in the middle of the room to produce lots of light. Then you measure the tempreature and conclude it's really hot in the room.

Relating this to the problem with a volt-meter. The meter is the fire - it fundimentally alters the "circuit" by creating an efficent earth for the tank. The voltage measuring function is the thermometer.

 

[Scottis24]

Bathrooms use GFCI IAW local building codes in my area without a grounding probe to the sink/tub whatever... Connected with PVC plumbing which is an effective insulator leaving the container ungrounded. They still work, they saved my mom's but when the curling iron she had warming up fell into the tub she was standing in..........

 

[Liem]

CGFI trips when it detects a current to gound. If one of the equipments has a crack that expose only the "hot" wire to the tank water and the tank has no grounding probe that is tied to the ground input of the CGFI circuit, the CGFI circuit will not detect any current and hence nothing will happen until you put your hand in the water.

There is a second level of protection in the form of the breakers in your garage where power is connected to your house. The difference between the breaker and the CGFI is that the breaker trips when current through it exceeds 10amps to 30amps depending on the size of the breaker. It takes only a few hundred mili-amps to kill you, so the breakers are really meant to prevent fire. CGFI circuit, on the other hand, trips on much smaller current and is more effective in preventing electrocution.

If anyone has any proof that voltmeters seriously change the voltage it suppose to measure, I would really like to know. I think I can go to court and sue the power company for charging me all this money without "good" measurement.

Liem.

 

[Anonymous]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Liem:
<strong>CGFI trips when it detects a current to gound. If one of the equipments has a crack that expose only the "hot" wire to the tank water and the tank has no grounding probe that is tied to the ground input of the CGFI circuit, the CGFI circuit will not detect any current and hence nothing will happen until you put your hand in the water.

Liem.</strong><hr></blockquote>

When you put your hand in the water, nothing will happen unless you are grounded as well. Why would anybody use a device that is ungrounded in a tank? That is the only way your example will work. Now try touching a device like a light reflector that has the same open "crack" on the hot wire and put your hand in the tank water. If the grounding probe is present you will likely die. If it is not present you will not be shocked. Which do you perfer?
If you set up a tank without a GFCI, would you ground the tank? I know I would not at it would increase my risk of shock. Now adding a GFCI to the same setup doesn't make the probe a safety feature. It just makes it safe enough to use a probe for the "supposed" health of your fish.
Put a probe in your tank if you want, but don't advertise it as a "SAFETY" feature. IT isn't!!!

 

[LeoR]

cwa

Could you help us resolve this issue once and for all, as follows:

Stick a hot wire into your bathtub, jacuzzi or pool and report your health status after each bath you take.

If we don't hear from you at all, we'll know that grounding probe is a safety feature, and not just a feel-good doohickey.

If you are afraid to do this experiment then take your sermons elsewhere.

LeoR

 

[Anonymous]

LeoR,

Sorry, I didn't mean to upset you with facts. You are free to do anything or believe anything you want, but you cannot effect me without more than your fantastic literary stab. By the way, why do you assume I bath? Is that a characteristic you attribute to people unlike yourself? Do you regulate who can post where on this thread or the whold board?

[ April 04, 2002: Message edited by: cwa46 ]</p>

 

[esmithiii]

A grounding probe in and of itself is not a safety feature. Together with a GFI it may be.

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote

When you put your hand in the water, nothing will happen unless you are grounded as well. Why would anybody use a device that is ungrounded in a tank?

Go to your tank and count the number of plugs that have the third prong (used to ground the device):

Powerheads- no
Heaters- no
fans- no
Lighting- yes
external pump- yes
Rio style pumps- no

Not having the probe could be dangerous. FWIW anyone w/ out a GFI is pushing their luck and risking their safety, IMO.

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote

Now try touching a device like a light reflector that has the same open "crack" on the hot wire and put your hand in the tank water. If the grounding probe is present you will likely die. If it is not present you will not be shocked.

Good point. This is a less likely scenario, IMO than having something fall into the tank or go bad while submerged in the tank.

 

[esmithiii]

Here is a quote from a previous thread regarding GFIs.

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr> I am here in the Dominican Republic and I spoke with the engineer for their GFI product and it turns out that the circuit checks the current flowing in and out and trips the switch if the difference is greater than 5 milliamps. An industrial GFI trips if it is greater than 30 milliamps. You can tell the difference by the color of the test button, yellow is for industrial, white is for personal use.

Ernie

<hr></blockquote>