Using ground probes in aquariums

Discussion in 'Reef Aquarium Discussion' started by Brew12, Oct 20, 2016.

  1. BigJohnny

    BigJohnny Valuable Member

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    Hey brew,

    They get a reading of 28v from brand new working pumps, but obviously this wouldn't shock you. Is this because it's freshwater or something? Are they testing a different type of voltage. I'm confused now.

     

  2. BigJohnny

    BigJohnny Valuable Member

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    I tested my sump and got 34v. The multimeter was plugged into the ground on a powerstrip plugged into a gfci outlet (wasn't tripping). So would a ground probe remove the 34v? Wouldn't I be seriously shocked at 34v? I never have been and have stuck my hand in the tank many times.
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    Last edited: Jan 10, 2018
  3. BigJohnny

    BigJohnny Valuable Member

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    Also this guy said he's been shocked even with grounding probes

     
  4. jasonrusso

    jasonrusso Valuable Member Build Thread Contributor

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    Do you have an open outlet on the power strip that the pumps are plugged into? If so, I would test the ground there.
     
  5. BigJohnny

    BigJohnny Valuable Member

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    The meter won't reach that far, but I don't see why that would be better, if anything it would skew the reading with interference from the pump plug and others. I'm testing the water not the pumps connection. Am I missing something?
     
  6. alton

    alton Active Member R2R Supporter

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    The probe can get build up and stop working properly, so you need to clean it once in a while. Anytime you hear someone say he got shocked from stray voltage, click the off button. If you look at Brews signature it says voltage doesn't kill, current does. If you are getting shocked it is because something is leaking current into your tank.
     
  7. Brew12

    Brew12 Electrical Gru R2R Supporter R2R Excellence Award Reef Squad Leader Article Contributor Build Thread Contributor Partner Member 2018

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    These are some great questions! Let me address them.
    I know they said it was fresh water, but their testing wouldn't have worked if the water was "too fresh". It had to have had enough salt/contaminants in it to be fairly conductive. He also showed a lack of basic electrical knowledge a few times but not in any overly important way. Outside of his using the Birds on a Wire analogy which absolutely does not apply in a saltwater tank. And yes, not all voltage is created equal.

    What they were showing is what is referred to as "induced voltage". To induce a voltage you need to have a conductor in a magnetic field with relative motion between the two. In this case, the magnetic field is created by the current traveling in the wire and in the motor. The relative motion is created by the fact that they are using AC (alternating current). The water is the conductor which is why you can read a voltage in it. If you noticed in the first video when they pulled the coiled up cord out of the water the voltage dropped. Less length in the water (or adjacent to to the water running outside the tank) means less voltage is induced.

    This voltage is exactly what ground probes eliminate. There is almost no true power with this induced voltage since there is high impedance in the system. So, it takes very little current through the ground probe to drop the voltage of the water to very near zero. If this were faulted equipment, it would take much higher currents to drop the voltage to zero, but it would still occur.

    Its also important to note that the induced voltage draws a tiny amount of power equally from the hot and neutral wires so it will not trip a GFCI. Fault voltage will trip a GFCI immediately with a ground probe installed.

    Without a ground probe my old system used to run at around 23VAC but I used MP40's and had short runs of cables in the water for my heaters and return pumps. I haven't tested my new system without a probe but I imagine its higher now that I'm using gyres.


    He didn't provide enough information in his video to figure out what is going on. I know people have been shocked in the top part of their tanks when they turn their return pumps off because the continuity of water between them and the ground probe is broken. There was a recent case where a guy got shocked by a ground probe because the outlet he plugged it into didn't actually have a ground wire run to it. I've also seen power strips where the ground connection was failed.


    Does that help?
     
  8. BigJohnny

    BigJohnny Valuable Member

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    Yes, thanks. It's all still a bit over my head. So the ground probe will eliminate that 34v I just measured in my sump, but it's likely not an issue for me or the inhabitants because it doesn't have much power behind it?

    Basically you could have 34 induced volts from properly functioning equipment, and 34v from faulted equipment, but the 34v from the vaulted equipment generates much more current which is what would shock me or my inhabitants?
     
  9. Brew12

    Brew12 Electrical Gru R2R Supporter R2R Excellence Award Reef Squad Leader Article Contributor Build Thread Contributor Partner Member 2018

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    I guess I never answered these directly.

    Yes, the ground probe would remove the 34V.

    Odds are you won't get a severe shock from 34V even if it is from a faulted piece of equipment. With induced voltage, it needs to be in the hundreds, if not thousands of volts to be dangerous. There is a reason that OSHA sets the hazardous level of voltage at 50V. That said, I was involved in an investigation where a young man electrocuted himself with a 9V battery. So could 34V hurt you? Sure. Is it likely? Not really.
     
  10. Brew12

    Brew12 Electrical Gru R2R Supporter R2R Excellence Award Reef Squad Leader Article Contributor Build Thread Contributor Partner Member 2018

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    It isn't the simplest concept to grasp which is why so many people struggle with it. Yes, the 34V you measured will go away with a ground probe, no issues. Yes, you can get the 34V from properly functioning equipment or faulted equipment but the impact of either would only be felt by you, not your fish. This is where the bird on a wire analogy goes wrong. That analogy works because the air around the bird is an insulator. Marine fish live in a conductive environment. They are more resistive than the water around them so the current will flow around them, not through them. You are more conductive than the air around you, so current will flow through you, not around you. This is why electrofishing doesn't work in the ocean. If it did, this would be how marine fish were collected for this hobby.

    There is some research that shows HLLE can be caused by voltage in the water. In this case, it wouldn't matter if it is induced or fault. They are effectively the same to the fish. So, I prefer to run my system at a 0V condition. The other issue is that faulted electrical equipment can leach toxins and copper into the water. That is why I want my GFCI to trip immediately on a fault letting me know I have a problem. Otherwise, you can poison your tank for days or longer and even a GFCI may not trip until you put your hand in the tank.
     
  11. BigJohnny

    BigJohnny Valuable Member

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    OK thanks, I get it more now. Also don't some people think stray voltage can stress corals? I've also heard that stray voltage can stress fish but it sounds like besides the hlle thing that wouldn't really make sense, except for sharks or something who use electrical signals to navigate if I'm not mistaken.

    So does it matter where I plug in the ground probe? Will the GFCI that the faulted equipment is on trip when there is an issue or the GFCI that the ground probe is plugged into, or will they all trip?
     
  12. Brew12

    Brew12 Electrical Gru R2R Supporter R2R Excellence Award Reef Squad Leader Article Contributor Build Thread Contributor Partner Member 2018

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    I'm not sure if voltage can stress corals. As far as I know, the lateral lines on fish are all at least partially sensitive to voltage. I feel that voltage is more of a factor than current in a tank. But, I'm speculating there.

    You could plug the ground probe in at your neighbors house and it would still work just fine. I try not to plug them into power strips but that will work if you need it to.
     
  13. BigJohnny

    BigJohnny Valuable Member

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    K great, thanks. Can I test if a ground is properly grounded with my multimeter? It says to have an electrician do that on the package lol.
     
  14. Brew12

    Brew12 Electrical Gru R2R Supporter R2R Excellence Award Reef Squad Leader Article Contributor Build Thread Contributor Partner Member 2018

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    Take a resistance reading from the neutral prong to the ground prong on a receptacle. They should be less than 0.5 ohms. If it is you are likely ok. The warning sign would be if some of your lights get brighter when your HVAC unit or electric clothes dryer starts. Those are signs that your neutral has disconnected from ground.
    Any other test if pretty challenging.
     
  15. BigJohnny

    BigJohnny Valuable Member

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    Ok, is that a preferable method to testing the voltage between hot and ground? I Googled to see which was neutral and which was hot and saw several people testing that way.
     
  16. Brew12

    Brew12 Electrical Gru R2R Supporter R2R Excellence Award Reef Squad Leader Article Contributor Build Thread Contributor Partner Member 2018

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    I wouldn't trust that method as much but it is another way to do something similar. The idea is that if the ground is bonded to neutral then you should get the exact same voltage from hot to ground as you get from hot to neutral.
     
  17. BigJohnny

    BigJohnny Valuable Member

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    Ok, thanks for all of your help.
     
  18. Brew12

    Brew12 Electrical Gru R2R Supporter R2R Excellence Award Reef Squad Leader Article Contributor Build Thread Contributor Partner Member 2018

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    Glad to help!
     
  19. Steve1500

    Steve1500 Active Member R2R Supporter

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    Hi Brew, I read your grounding probe article and I plan on purchasing 2 for me and 2 for my grandson. We both have two tanks. Is it ok to place the ground probe in my DT Sump? For my QT and my grandson's tanks, the probes will go directly into the tanks. Thanks for the safety tip.

    BTW, you helped me out w my QT cycle the other day and I should be adding fish this weekend!

    Thanks!
    Steve
     
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  20. Brew12

    Brew12 Electrical Gru R2R Supporter R2R Excellence Award Reef Squad Leader Article Contributor Build Thread Contributor Partner Member 2018

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    Fantastic!

    And yes, they work just fine in the sump. Not to mention looking better down there.
     
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