Stray votlage

[mike31154]

Originally Posted by Seafan

I'm confused by this. I had a small powerhead that was causing me to get a small shock every time I put my hands in the water, it was plugged into a gfci as was everything else in the tank, yet the gfci was not tripping. At the time I did not know which device was causing the shock. We picked up a grounding probe and it instantly tripped the circuit. Had to use a process of elimination to determine the faulty device. So until the grounding probe was in the tank the gfci wasn't ever going to trip to warn of an issue or possible harm. So my question is how do you know when a gfci is going to function properly to possibly save your life? For now I will trust my probe.

There are no absolute foolproof guarantees, even GFCI devices can fail or be faulty and everyone's wiring situation is a little different. You say you received a small shock, perhaps it was insufficient to trip the device. Not really sure why or how in your situation, adding the grounding probe suddenly caused the GFCI to trip. They are sensitive devices designed to operate on a very low amperage current differential between line and neutral.

I've had the GFCI trip on occasion simply from plugging in a small powerhead or air pump. Once the device is plugged in and I reset the GFCI, it's fine. I also have a T5HO set up on a digital timer power bar consistently tripping my GFCI. I have two of these set ups that are identical, same power bar, same ballast, same lamps. One trips the GFCI, the other doesn't. I simply don't use the set that trips the device any longer even though there's no indication of a safety issue.

[Seafan]

Originally Posted by mike31154

There are no absolute foolproof guarantees, even GFCI devices can fail or be faulty and everyone's wiring situation is a little different. You say you received a small shock, perhaps it was insufficient to trip the device. Not really sure why or how in your situation, adding the grounding probe suddenly caused the GFCI to trip. They are sensitive devices designed to operate on a very low amperage current differential between line and neutral.

I've had the GFCI trip on occasion simply from plugging in a small powerhead or air pump. Once the device is plugged in and I reset the GFCI, it's fine. I also have a T5HO set up on a digital timer power bar consistently tripping my GFCI. I have two of these set ups that are identical, same power bar, same ballast, same lamps. One trips the GFCI, the other doesn't. I simply don't use the set that trips the device any longer even though there's no indication of a safety issue.

No this was not the case at all, actually The G in gfci stands for ground which most of our equipment in our tanks does not have a ground in the plug-in therefore gfci is quite useless in half of the equipment we run, I was merely pointing out that this is why I would not run without a ground probe.

[wingedfish]

your right in that it stands for ground, and also right in that most of the equipment doesn't have a ground.

A little off topic but a gfci monitors current in and out on hot and neutral (simplistic terms, there is no in and out etc) if more goes out then comes back on neutral, usually do to a short to ground, then it trips. This explain why a gfci would trip upon the addition of a ground rod. but the problem existed before it. The more grounds the safer.

[mike31154]

Originally Posted by Seafan

No this was not the case at all, actually The G in gfci stands for ground which most of our equipment in our tanks does not have a ground in the plug-in therefore gfci is quite useless in half of the equipment we run, I was merely pointing out that this is why I would not run without a ground probe.

The F in GFCI stands for 'Fault'. GFCIs are designed to keep you safe irregardless of whether the equipment plugged into them has a ground prong on the plug or not. GFCIs are required by code in bathrooms and most electric shavers, hair dryers etc., only have two prong plugs. As mentioned, they monitor the current coming in and going out of the circuit they are installed in. As long as the device sees the same current on both the hot and neutral, all is well. If there is a differential of a few mA, not sure what the number is off hand, the device is designed to trip before serious harm comes to the individual using the appliance.

Just my speculation here and I could be totally wrong, but it's the only explanation that makes sense to me. I suspect that in the case of your powerhead there was some degree of deterioration of the insulation waiting to find a path to a lower potential (ground if you wish). Although you felt a shock, your body resistance was likely too high to cause enough current to flow to trip the device, i.e. it was not enough to harm you. By introducing the grounding probe (much less resistance to ground than your body), sufficient current was able to flow from the faulty powerhead to ground tripping the GFCI. It's great that you were able to isolate the faulty device by installing the ground probe before it became bad enough to trip the GFCI with your hand in the water.