What if your pond pump shocks you, is it a bad pump?

So while messing around with my aquaponics setup, I put my hand in the water and got a little tingle. The fish seemed okay, so I didn’t worry about it right away. I had to go to work.

That day, my wife was feeding the fish, and SHE got an electric shock when she put her hand in the water. She called me to complain.

That night, I went to work researching what could possibly be wrong. Right away, everyone I read said that my sealed pump was no longer sealed, that water had gotten into it and electricity was being introduced into my setup. The standard answer was to purchase a new pump, and to throw away my brand new (less than a month out of the box) $300 pump that pushed 3000 GPH. A pump I looked long and hard for, and which had great ratings by everyone.

IBC setupSo I did. I went out immediately and bought a 2000 GPH pump from a different manufacturer for the system. I removed the first pump, and plugged in the second.

And I immediately got a shock from it!

So my choices were that I had unluckily purchased TWO bad sealed pond pumps in a row; or something else was going on here.

My system is made of 4 IBC containers.  (See the diagram)  Each IBC is plastic, with the top cut off.  Each container is still sitting on the original pallet / cage that is made of some sort of steel.  I’ve grinded off the tops of the cages to make them even with the tops of the plastic.

I don’t get shocked if I place my hand in the water.  A shock happens when I lean on the metal cage and THEN place my hand in the water.  At first, I thought these cages were getting a ground from somewhere, and my arm was completing the path.  But a little testing with a multimeter showed me that was not the case.

I then took the first pump, dropped it in a 5-gallon bucket filled with salt water, and used my multimeter to try to detect a short between the 3-prong plug and the salt water.  If there is a break in the sealed casing, I should read some sort of resistance.  Since I felt a shock, that resistance is most likely to be under 100K Ω.  But when I tested, every reading I took showed infinite resistance – or an “open” circuit.  There was no short to water.  The sealed pump remained sealed.

So where did that shock come from?

I didn’t get shocked when the two pumps were not plugged in.  I also didn’t get shocked when I dropped in a 10GPH pump that I used on a wooden barrel pond.  

This was all very strange. 

There’s one other thing you should know about this system.  It is way out back in my backyard.  It is powered through a 50 foot long extension cord that has a power strip plugged into it on the side of the fishery.  The other end is plugged in at the house.  And this house was built in the 1940’s, and has never had its power upgraded from the original other than to put in an upgraded breaker box.  As far as I can tell, the home lacks an Earth ground.

So here’s what I’ve figured out.

My high capacity pumps use a huge coil of wire to run the magnetically driven sealed impeller.  These coils, along with the underwater length of power cord that goes from the sealed pump to the power strip, are the problem.  

What was happening is that electromagnetic energy is being capacitivly and inductively coupled from the big coil in the motor, off of that coil and off of the power cord, and onto the steel cage that sits around each IBC.  The charge builds up on that cage, and it’s looking for a discharge path.

By creating a bridge, with my arm leaning against the wet metal cage and my hand in the water, I’m creating a discharge path for this giant capacitor that is created by this system.  Those electrons run back to the water where they belong, giving me a non-fatal shock.  (I’m sure that under the right conditions that shock could be fatal!)

So how did I fix this?  

First, I purchased a receptical tester like this one.  When I plugged it into my power strip at the fishery, it told me that the hot and ground were reversed.  This was my first clue that unnecessary energy was on the ground.

Next I purchased a 15 amp grounding adapter and a section of 1/2 inch copper ground rod.  I also picked up a 1/2 inch ground rod clamp, and some 12AWG copper stranded wire.

I plugged the grounding adapter between the power strip and the extension cord, drove the copper rod into the ground at the fishery, and connected the Earth from the grounding adapter to the ground rod clamp on the ground rod.

When I turned on the system with my first pump installed again, the shock was gone.  I then checked it with my multimeter and read zero potential between the metal and the water.  The radiating energy from the pump is not inductively or capacitively coupling to the metal cage around the IBC tank anymore. Instead, that energy now has a path to travel to ground.

Oh, and the reversal of Hot and Ground shown by the receptical tester? Yea, the house doesn’t have an Earth ground, so there is some coupling to a wire that is basically hanging there like a receive antenna.

Yea, this house needs major electrical work… but it’s a rental, and I’m moving soon.

Now for the warning.

If you are experiencing the same sort of problem, DON’T FIX IT THIS WAY!  USE THE CORRECT METHOD OF REPAIR – the correct repair tool for this job is a certified electrician.

I’m just an electrical engineer who knows just enough to be really dangerous.  As described, this method of fixing a system is not the correct way!   (Maybe you actually have a broken pump, in which case this fix method will result in large pretty sparks!) 

I’m warning you, if you try this on your own, you will get electrocuted and die, your house will burn down, and everything you hold dear WILL be destroyed!

 

The only reason why I’ve described the problem I experienced, and my temporary fix action, is so that I can point out that everyone’s assertion that, “the pump is broken!” is not always true.  Under the right conditions, which are surprisingly common with a standard IBC setup, you could be creating a sort of battery or capacitor that has the ability to give you a bad shock.  

The correct way to fix this is to have a certified electrician run electricity to your fishery professionally.  This electricty should include a Ground Fault Interruptor, and the electrician may recommend a local ground too.  Talk to them about it.

This is what I will be doing with my next fishery!

And last, if you think your sealed pump has a cracked or open case that is allowing water to the electronics inside, there IS a way to test this.  Use my 5 gallon bucket full of salt water method.  Drop the pump into a bucket of very salty water, then use an ohmmeter between the water in the bucket, and the 3 prongs at the end of the power cord.  If any of those prongs gives you a reading – ESPECIALLY if that reading is under 500,000 ohms – then yes, you have an electrical path from your pump to the water, and you should throw it away.

2 comments

  1. James’s avatar

    I don’t quite get how you’re checking between the salt water bucket and end of 3-prong cord, but it doesn’t matter – I hopefully won’t be doing this. But also wondering if you couldn’t just run a wire between the support cage and the water, to let the induced charge back into the water?

  2. calladus’s avatar

    So if you drop a pump into a bucket of impure (salty) water, and that pump has a leak, then the water will get into the pump and create a path of conduction for the electricity into the water.

    If you were to plug that motor into power, you could possibly use a multimeter, and while being VERY careful to NOT get wet, measure the potential electricity between the salty water and an Earth ground.

    If you get more than a couple of volts, then there is probably a leak in the pump that is allowing some of the water to touch a coil, and some electricity will follow the path of conduction through the water, through your meter, and to ground.

    If the socket is a Ground Fault Interrupt type, with a good Earth ground, you won’t even be able to measure a voltage because the GFI will trip and remove power from the motor – which would be a good sign of a problem.

    But doing it this way is dangerous, and if you are not VERY careful, you might get electrocuted trying to find out if your pump has a break in it.

    So leave the motor unplugged, drop it in a bucket of very salty water, and then measure the conductivity between the water and all of the prongs on the plug.

    If water has found its way into the motor housing, you should get a complete circuit (with some amount of resistance) to one or more of the plug prongs. If the motor housing is truly sealed, you should read infinite resistance.

    Why use (impure) salty water? Because it conducts electricity very well. Pure distilled water conducts poorly. (Note, Fresno water is high in conductive minerals, and may not need any salt.)

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