32 volts....

[Triggerjay]

so I got the all too familiar tingle today while in my tank when my arm brushed against my light mount bracket. So, I got out my trusty fluke meter, and from ground to light bracket I get 32 volts AC. From water to ground 32v ac.. from water to light bracket 32v. I started by unplugging pumps, still 32v. Then unplugged the lights (ocean revive t-247 x2). now dropped to 0v. Here's where I get confused. My light bracket is isolated from the water (screwed to the wood stand) and I have lids on my tank, yet I get 32v from water to ground when the lights are on. I am an industrial engineer and this defies all logic. Any ideas?

 

[Brew12]

so I got the all too familiar tingle today while in my tank when my arm brushed against my light mount bracket. So, I got out my trusty fluke meter, and from ground to light bracket I get 32 volts AC. From water to ground 32v ac.. from water to light bracket 32v. I started by unplugging pumps, still 32v. Then unplugged the lights (ocean revive t-247 x2). now dropped to 0v. Here's where I get confused. My light bracket is isolated from the water (screwed to the wood stand) and I have lids on my tank, yet I get 32v from water to ground when the lights are on. I am an industrial engineer and this defies all logic. Any ideas?

Yes. The reason your voltage goes to 0V when you unplug the light is because you are disconnecting the frame of the light fixture from ground. This raises the voltage on the fixture to the same as your water when you measure it with your fluke. Your light fixture is not the problem.

A few things to keep in mind. Any cords pulling current adjacent to your tank will generate voltage in your tank through induction and through capacitive coupling. This can make troubleshooting complicated. A Simpson voltmeter would be the best way to test it, but those aren't very common anymore.
You really have 2 other options. Normally I would recommend using a portable GFCI with a ground probe to troubleshoot but you don't have a ground probe.
Since you have some familiarity with flukes, there is another option. Instead of testing for voltage, test for current. Measure current between your tank water and your light fixture. You should see it quickly drop to zero amps if the faulted device isn't on. If the faulted device is on you should see at least a steady 1A+.

If I didn't explain that well enough, or if you need me to explain why that works, let me know!

 

[Triggerjay]

my first though was it must be a pump, but unplugging them all didn't resolve the problem. I checked lighting cords and they have grounding pins on them, and are plugged into a grounded power strip. I should be able to isolate the issue with a grounding probe, but would rather get to the root of the problem first. The only pumps in the main display are a gyre, and two Jeabo WP-25's. everything else is down in the sump.

 

[Triggerjay]

Yes. The reason your voltage goes to 0V when you unplug the light is because you are disconnecting the frame of the light fixture from ground. This raises the voltage on the fixture to the same as your water when you measure it with your fluke. Your light fixture is not the problem.

The water voltage to ground drops to zero as well as the fixture to ground when the lights are unplugged. Not just the lights to ground.

I used to have a Simpson analog years back, but decided it was outdated and got rid of it.

I have a PC very close to the tank, so there is a very real possibility of induction,.. and from tank devices.

I am out and about at the moment, but will test current when I get home, unplugging one thing at a time until I read 0a.

Thank you very much for the detailed reply. My second post was being typed prior to any replies, it was intended as a continuation of my first post.

 

[Triggerjay]

Oh and I don't know if it matters, but the pumps in-tank are all D.C. Not AC. I do however have AC stuff in the sump.. dosers, pumps, heaters, etc. could be any one of those... but water voltage to wall ground goes away when lights only are unplugged.

 

[Brew12]

my first though was it must be a pump, but unplugging them all didn't resolve the problem. I checked lighting cords and they have grounding pins on them, and are plugged into a grounded power strip. I should be able to isolate the issue with a grounding probe, but would rather get to the root of the problem first. The only pumps in the main display are a gyre, and two Jeabo WP-25's. everything else is down in the sump.

The problem is that by just checking for voltage you can't tell if you are seeing an induced/capacitive voltage or the fault voltage. If the voltage is induced then current will quickly drop to 0 amps when you measure it. If it is a fault voltage, you will get a fairly constant and measurable current.

For example, lets say the problem is a heater. If your return pump is running that fault voltage is available everywhere in the tank. If the return pump is off, the fault voltage is only impacting the sump. Your powerheads in the DT could be inducing the 32V you are seeing when they are running but it won't cause a tingle. However, if your return pump is running and the faulted heater is on, you may still only read about 32V in your DT but now you can get shocked.
Troubleshooting with a ground plug and portable GFCI is simple. You can plug your equipment into the GFCI one by one. If your ground probe is in the sump and your return pump is running, the faulted equipment will trip the GFCI. Anything inducing a voltage in the tank will not.

 

[Brew12]

The water voltage to ground drops to zero as well as the fixture to ground when the lights are unplugged. Not just the lights to ground.

I used to have a Simpson analog years back, but decided it was outdated and got rid of it.

I have a PC very close to the tank, so there is a very real possibility of induction,.. and from tank devices.

I am out and about at the moment, but will test current when I get home, unplugging one thing at a time until I read 0a.

Thank you very much for the detailed reply. My second post was being typed prior to any replies, it was intended as a continuation of my first post.

Those old Simpsons are wonderful. I keep one at work specifically to check for induced voltages. The old Wiggins voltage testers work well, too.

Just keep in mind that an induced voltage will not cause a tingle, you definitely have a faulted piece of equipment.

 

[Brew12]

Oh and I don't know if it matters, but the pumps in-tank are all D.C. Not AC. I do however have AC stuff in the sump.. dosers, pumps, heaters, etc. could be any one of those... but water voltage to wall ground goes away when lights only are unplugged.

DC pumps work by converting the 120V AC into DC then back to a variable frequency AC.
The light issue does have me baffled. Does your light have a 3 prong plug or 2?

 

[Triggerjay]

3. It has grounding pins on both plugs, plugged in to a three pin power strip.

 

[Triggerjay]

I need to test continuity on the el-cheapie power strip and make sure it has a true ground.. I have heard that some of them do not have the grounds tied together.

 

[Brew12]

3. It has grounding pins on both plugs, plugged in to a three pin power strip.

I miss read your original post. Now I understand your confusion...

Salt tracking can cause some interesting conditions. In theory, if you have a 3 prong plug the ground should be connected to the metal housing of the light fixture, which should be connected to the mounting arm. This should prevent your mounting arm from rising above ground potential. If you get 32V from the light fixture case to the wall ground that is a pretty serious condition. I would try taking a resistance reading from a non painted surface (such as a screw) from the light fixture to a wall ground on a different outlet. Something in your ground path may have corroded or become disconnected.

 

[Brew12]

I need to test continuity on the el-cheapie power strip and make sure it has a true ground.. I have heard that some of them do not have the grounds tied together.

You've got this. You don't need help, you just needed a few minutes to think this through!

 

[Triggerjay]

Just got home. Tested current from water to light bracket. Snapped a couple pics. Showing zero current, but still showing the V.

 

[Triggerjay]

Good thing I was standing on carpet!

 

[Brew12]

Just got home. Tested current from water to light bracket. Snapped a couple pics. Showing zero current, but still showing the V.

Can you take those readings from light bracket to a wall ground? Something still isn't right.

 

[Triggerjay]

Actually, I don't remember if this meter will read amperage with the probes.. may only work with the loop at the top.. ugh! Time to call it a night and think on it. I'll pick up a portable GFCI and go that route. It may be a couple days but I'll post the results here,... and buy a grounding probe.

 

[Triggerjay]

Can you take those readings from light bracket to a wall ground? Something still isn't right.

Yes.

 

[Brew12]

Actually, I don't remember if this meter will read amperage with the probes.. may only work with the loop at the top.. ugh! Time to call it a night and think on it. I'll pick up a portable GFCI and go that route. It may be a couple days but I'll post the results here,... and buy a grounding probe.

Nope, you are correct, you can' test it with the leads. That is unfortunate. Get a good nights sleep. If you are anything like me what is going on will be much clearer in the morning.

 

[Triggerjay]

From wall ground to light bracket, v and a.

 

[Triggerjay]

From water to ground on outlet