Pond heater...shorting out????

Master Brian · Nov 9, 2009

I have a small pond heater/de-icer. It is a disk with a coil on the bottom that gets just hot enough to keep a small opening in a garden pond in the winter. I believe this unit is supposed to be thermostatically controlled, in that it is only supposed to be on when the water temp hits around 35-40*.

Here is a link to a picture that looks like what I have.

I've had this about 3yrs, didn't use it last year as I didn't need it and wasn't sure about it's condition. This year I'd like to either throw it away or use it. The last time it was used, I lived at a different house, so different pond, different setup. There was a submersible light and a single pond pump. Not even sure if the circuit was GFCI'd or not. Don't think it was.

In any case, when I'd lean on certain rocks and stick my hand in the water, I'd feel a slight tingle. From what I recall, when I unplugged this heater in the spring, that wouldn't happen. None of my goldfish or koi seemed affected by this as they all survived the entire winter. I believe this happened 2-4 times before I finally tracked it down to possibly having something to do with this unit.

My question is, can I test this unit and how would I go about that? I have a volt/amp meter, but besides doing Ohm readings and basic ac/dc current readings, I don't use it much.

Being as I don't think the circuit was GFCI'd, is it possibly there was a bit of "bleedthrough" currrent just following the outside of the cord, causing me to pick up the shock, when I touched the rocks and water? Why wouldn't it affect the fish? All but one of those fish is still alive today at my new house and they are thriving. The one that died, died as the result of a bad hail storm this year.

The pond circuit at my new house is GFCI'd, would it be safe to plug it in there to test it somehow and is this something the GFCI should pick up? I have a small pond feeding my larger one, I could test it in, but I should note, that my dogs frequently drink from that one!! It doesn't have any fish at this point.

I guess my main goal is determining if this thing is safe or not and how would I determine that?

Thatguy · Nov 9, 2009

Master Brian said:
In any case, when I'd lean on certain rocks and stick my hand in the water, I'd feel a slight tingle. From what I recall, when I unplugged this heater in the spring, that wouldn't happen. None of my goldfish or koi seemed affected by this as they all survived the entire winter.

You might have already used up a considerable portion of your lifetime allotment of luck. At 60 Hz, for adult males, 1mA is a tingle, 10mA is painful and at 20mA you can't let go.

Measure the resistance of a 7-1/2w incand. bulb and then wire it between the water and the earth nearby the pond.
If the bulb resistance is R then a voltage more than .005R is hazardous. E.g., if R is 200 ohms then more than 1vac across the bulb is dangerous.
This test will trip an upstream GFCI if you are using one and if the water is energized.

If the pond water is not grounded there is no voltage gradient across the fish so they don't have current going through them.

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Master Brian · Nov 9, 2009

Thatguy said:
You might have already used up a considerable portion of your lifetime allotment of luck. At 60 Hz, for adult males, 1mA is a tingle, 10mA is painful and at 20mA you can't let go.

That's what I'm concerned about!!

Thatguy said:
Measure the resistance of a 7-1/2w incand. bulb and then wire it between the water and the earth nearby the pond.
If the bulb resistance is R then a voltage more than .005R is hazardous. E.g., if R is 200 ohms then more than 1vac across the bulb is dangerous.
This test will trip an upstream GFCI if you are using one and if the water is energized..

How does one go about wiring this? Sticking a bare/stripped wire into the pond and burying a bare/stripped wire into the ground with the bulb and a volt meter between? Would this be done while the heater is plugged in and placed into the pond? If I have access to an un-GFCI'd receptacle would you use that instead? ....I would think the GFCI would be safety 1st, but if this causes it to trip, then how do you record the test?

Last, but definately not least, are you serious about this test?? ...again, see your first comment here. I have no issues replacing wiring in my house, I do however, get real nervous around water and electricity....

Thatguy said:
If the pond water is not grounded there is no voltage gradient across the fish so they don't have current going through them.

Don't really have a way of knowing if the pond water was grounded. It was a rubber liner, but there were normally rocks laying on the ground outside the pond, that eventually made their way to contacting the water surface. What I don't know is if that water surface contacted the rocks when I got shocked or not. I don't even know if there would have been enough of a connection to create that hazard. There were times, there was snow that blanketed the ground and the pond. What I do seem to remember is that if I touched the water surface without leaning on the rocks, I didn't get shocked, but if I touched the rocks, I got shocked. One last thing here, wouldn't I have in theory, at least, created the ground to the water, if I was getting that shock? Maybe it just wasn't enough to harm the fish...

Thatguy · Nov 9, 2009

>>see below

Master Brian said:
Sticking a bare/stripped wire into the pond and burying a bare/stripped wire into the ground with the bulb and a volt meter between?

>>Just touching the wire to the ground is enough.
>>The voltmeter goes across the lamp. In this case the lamp is a burn-out-proof current shunt. Start on the 120v DVM scale.

Would this be done while the heater is plugged in and placed into the pond?

>Yes. I think the heater is defective and energizing the water.

If I have access to an un-GFCI'd receptacle would you use that instead? ....I would think the GFCI would be safety 1st, but if this causes it to trip, then how do you record the test?

>>If there is no GFCI upstream you can measure the leakage current. If there is, and it trips, the water was energized.

Last, but definately not least, are you serious about this test?? ...again, see your first comment here. I have no issues replacing wiring in my house, I do however, get real nervous around water and electricity....

>>Just don't put your body in series with the water and the grounded rocks or earth.

Don't really have a way of knowing if the pond water was grounded.

>>If you put a GFCI upstream of the heater and it trips, the pond water is grounded and the heater leaks current.

It was a rubber liner, but there were normally rocks laying on the ground outside the pond, that eventually made their way to contacting the water surface. What I don't know is if that water surface contacted the rocks when I got shocked or not. I don't even know if there would have been enough of a connection to create that hazard. There were times, there was snow that blanketed the ground and the pond. What I do seem to remember is that if I touched the water surface without leaning on the rocks, I didn't get shocked, but if I touched the rocks, I got shocked.

>>see below

One last thing here, wouldn't I have in theory, at least, created the ground to the water, if I was getting that shock?

>>Yes. Even if the pond water was grounded, you could have diverted some of the current that would have gone to ground through your body.

Maybe it just wasn't enough to harm the fish...

The current density in the water was highest in the straight line between the heater and the nearest best ground, but all of the water saw some current flow.
Oddly enough, salt water is so conductive that most of the current goes around a person who is in that water. I don't know about the bulk resistivity of fish flesh, so I don't know if the fish have an advantage in salt water.

Resistivities
most soil, 30k to 50M ohm-meter
rock, less than 10k ohm-meter
tap water, 1M to 100M ohm-meter
salt water 0.2 ohm-meter
fresh water, 1000 ohm-meter
concrete, 200 ohm-meter
human body, 5 ohm-meter
copper, 20 nanoohm-meter

Drick · Nov 9, 2009

Does the heater, the light or both have a transformer?? ie;
Is the heater low voltage (12 or 24 volt)?
Was the light low voltage (12 or 24 volt)?

The reason I ask is about a decade ago I had a pond and it had underwater lighting. I had installed some inexpensive low voltage underwater lights thinking that if there was a fault I wouldn't be electrocuted. Within a year a seal around one of the lights failed. The shocks I received were just as you describe.

I learned two things from that. One, you can get electrocuted at 12 volts. And two, you get what you pay for.

As for the fish (Koi) they were fine. You can probably electrocute a fish, but you would have to work at it. I also have had a 55 gal fish tank where the entire light assembly fell in the tank. The fish were fine then too.

The GFCI should trip if it is not a low voltage heater and there is a fault. However if it is low voltage in that case I'm not sure it would trip because I believe it is effectively isolated from the GFCI by the transformer.

-rick

Thatguy · Nov 10, 2009

drick said:
One, you can get electrocuted at 12 volts.

I've never gotten a shock from 12v car battery terminals even though the energy stored in this battery is enough to run an electric chair.
The lowest voltage resulting in an electrocution in the Navy was 47 volts. The lights sewer workers use run on 24v or 28v.
You can feel a tingle on the 50vdc phone line but I doubt it's hazardous.

For 12v and >20mA the source resistance plus your skin resistance would have to be less than 12/.02 = 600 ohms. I guess it's possible.

BODILY EFFECT DIRECT CURRENT (DC) 60 Hz AC 10 kHz AC
---------------------------------------------------------------
Slight sensation Men = 1.0 mA 0.4 mA 7 mA
felt at hand(s) Women = 0.6 mA 0.3 mA 5 mA
---------------------------------------------------------------
Threshold of Men = 5.2 mA 1.1 mA 12 mA
perception Women = 3.5 mA 0.7 mA 8 mA
---------------------------------------------------------------
Painful, but Men = 62 mA 9 mA 55 mA
voluntary muscle Women = 41 mA 6 mA 37 mA
control maintained
---------------------------------------------------------------
Painful, unable Men = 76 mA 16 mA 75 mA
to let go of wires Women = 51 mA 10.5 mA 50 mA
---------------------------------------------------------------
Severe pain, Men = 90 mA 23 mA 94 mA
difficulty Women = 60 mA 15 mA 63 mA
breathing
---------------------------------------------------------------
Possible heart Men = 500 mA 100 mA
fibrillation Women = 500 mA 100 mA
after 3 seconds
---------------------------------------------------------------

Master Brian · Nov 10, 2009

rick,

I don't believe the heater has a transformer, if it does, it would be at the heater, not prior.

The lights are low voltage. I suppose the light is a possible source. I am not currently using that light as the bulb burned out and I haven't found the replacement. I wouldn't say it was a cheapy, but not real expensive either. Around $20 at Lowes for a single light. I've seen much cheaper units at places like harbor freight.

Would just plugging the pond heater into a standard GFCI, while out of the water tell me anything? What about an Arch Fault Protected circuit? Problem is, like I said, I think it is thermostatically controlled to come on at temps under 40*.

Master Brian · Nov 10, 2009

I am going to go back and read about this unit to see if it is indeed thermostatically controlled. I suppose if it is, I could try placing it in a bucket of room temp water to see what happens. If all goes well, I could then fill the bucket with ice to see what happens. If the GFCI doesn't trip and the ice melts quickly, would that indicate the unit is functioning properly?

Could I take a volt meter and stick the "-" probe to a grounding rod and the "+" probe into the water and take a reading to see if there is any current leakage? What setting would I start with? volts a/c? mA's? Surely I could set that up without having to do it touching anything and get the readings....

Jadnashua · Nov 10, 2009

You're playing with your life and anyone else that may approach that pond. Be very careful on any testing you do. I'd probably consider chucking that heater and investigate a new one. Maybe use an air pump - moving water will usually keep an area open of ice - bubbles from the bottom both aereate the pond and help keep the surface from freezing.

Master Brian · Nov 10, 2009

jadnashua said:
You're playing with your life and anyone else that may approach that pond. Be very careful on any testing you do. I'd probably consider chucking that heater and investigate a new one. Maybe use an air pump - moving water will usually keep an area open of ice - bubbles from the bottom both aereate the pond and help keep the surface from freezing.

I am actually contemplating throwing it away as well. Just playing through my options. If a good/safe method of testing it comes up, I'd try it, but until then....

I do have an air pump which is what I used/bought last year as I didn't trust this heater. It worked well for that setup, I redid the pond this year and it went from 1 pond of roughly 200+ gallons to two ponds just under 2000 gallons total. I am also thinking of making a pond areator, which should keep it clear of ice and well oxiginated. I just figured this heater would be a nice backup on really, really cold days....if I could determine how safe it currently is.

Thatguy · Nov 10, 2009

Master Brian said:
Could I take a volt meter and stick the "-" probe to a grounding rod and the "+" probe into the water and take a reading to see if there is any current leakage?

Yes, use the 120vac scale.
But this voltage source needs to deliver at least 10mA to be dangerous. That's where the incand. bulb/shunt comes in.

If you wear sneakers you won't be grounded, and it is a good idea not to be grounded when doing this sort of stuff. For extra protection wear dry gloves.

The resistance of a cylinder shaped volume of conducting material is R = ρL/A.

If L is 1' [0.3 m, representing the water depth], A is 0.008 sq. meters [a 4" dia. circle, representing a hand], and ρ [the Greek letter rho] is 1000 ohm-meter for fresh water, then R = 1000(0.3)/0.008 = 38k ohms.
Since the current is not confined to this cylinder the actual R would be somewhat lower.

120v/38k = 3mA. If an adult male were so risk-prone as to put his hand in this water he would probably feel this but he probably would not die from this.
Calculations aside, I would not put my hand in this water. With 24vac, I might.

Master Brian · Nov 10, 2009

Thatguy said:
Yes, use the 120vac scale.
But this voltage source needs to deliver at least 10mA to be dangerous. That's where the incand. bulb/shunt comes in.

If you wear sneakers you won't be grounded, and it is a good idea not to be grounded when doing this sort of stuff. For extra protection wear dry gloves.

The resistance of a cylinder shaped volume of conducting material is R = ρL/A.

If L is 1' [0.3 m, representing the water depth], A is 0.008 sq. meters [a 4" dia. circle, representing a hand], and ρ [the Greek letter rho] is 1000 ohm-meter for fresh water, then R = 1000(0.3)/0.008 = 38k ohms.
Since the current is not confined to this cylinder the actual R would be somewhat lower.

120v/38k = 3mA. If an adult male were so risk-prone as to put his hand in this water he would probably feel this but he probably would not die from this.
Calculations aside, I would not put my hand in this water. With 24vac, I might.

Maybe I'm being a bit slow here, but I like to think of it as overtly cautious, you are saying to do the bulb test with the heater plugged in and in the water, correct?

What I don't understand, and hope someone can clarify, is why would I need the bulb? Re-reading as I type this....am I correct that it is what tells me, through your formula, how many vac going through the volt meter would be dangerous?

Yes, sneakers, leather gloves and energizing through the circuit panel would be the only way I'd attempt this. Standing back to get the reading!!!

It is interesting, but it does sound too risky!!! Heck, I'm even thinking of tossing away the light that burnt out, even though I used it last year without problems, it's making me think it could be a possible culprit as well!! zap, zap, zaaaappp!! isn't fun! The tingle I got originally, wasn't even as bad as what you get from a 9v battery to the tongue, but uncomfortable never the less.

Just thinking about all of this, makes me feel a bit bad for using the electric training collar on my dogs, no wonder they behave when it's on!!

Thatguy · Nov 10, 2009

Master Brian said:
you are saying to do the bulb test with the heater plugged in and in the water, correct?
>>Yes, if you're careful. Do the voltage test first. Put a long insulated wire in the water, scrape off the insulation at the wet end, and run it to a dry, ungrounded place to run your test.

The voltmeter tells you if voltage is present. Over 50v in water I would consider potentially dangerous.

The bulb/voltmeter tells you the current supplied by this voltage-through-the-water. Over 20mA is dangerous.

Current is what does the harm. Voltage just forces the current along.

If your body/skin resistance is somehow as low as 300 ohms, as little as 6vac could give you a bad shock. I think most people come in at over 3000 ohms.
http://www.easternvoltageresearch.com/datasheets/safety.pdf
see table 1

Jadnashua · Nov 10, 2009

There are so many variables here...a big metal watch band helps by being a good conductor...being very sweaty so you have more salt on your skin's surface, and numerous other things. A good path across your chest is the killer, so it's a good idea to always keep one hand in your pocket! Playing with electricity requires a wary mindset, good practices, and some knowledge or just dumb luck. Sometimes, by the time you realize you have a problem, it's too late! Watch the warning signs...it's never good to get shocked, although many times you live to tell about it...all it takes is once when all the planets align, and you won't.

Thatguy · Nov 10, 2009

this should put everyone to sleep. . .

http://bme.ccny.cuny.edu/faculty/mbikson/BiksonMSafeVoltageReview.pdf

Drick · Nov 10, 2009

jadnashua said:
You're playing with your life and anyone else that may approach that pond.

Doubtful if the heater is on a GFCI.

I assume the heater has a ground wire since its 120V and under water. Therefore it has a path back to ground if there is a fault so the GFCI should trip long before you stick you hand in with it.

If the heater appears to be in good condition and your concerned about it do the ice water in a bucket test - plugged into a GFCI obviously. Thats what I would do. If your really concerned just throw it away and buy another. Consider it a cheap price to pay for piece of mind.

From personal experience I am still leaning toward it being your low voltage light

-rick

hj · Nov 11, 2009

telephone

I was working in the basement of the Bell System terminal. When one of the technicians saw me working by a bus bar, he mentioned, that even though it was only 24 volts, there was enough amperage there to melt my aluminum ladder.

Pond heater...shorting out????

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