Bill,
maybe you can help me , my neighbor called the other day complaining that she got a shock while she was working on her pond pumps.
I ran over there and checked some things out for her.
I shoved one lead into the ground and dropped the other lead into the sump….I read 3 volts, I checked the ground of the GFI for the pumps to the same earth probe and read 2mV.
the ground at the sump was damp, she had to kneel down, and had a rash on her arm from pruning some junipers earlier.
I also tested the GFI with an adjustable tester ..it tripped .
Do you think 3 volts is enough to get a tingle?
I will megger the pumps this Fall
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Replies
This is pure speculation, but I suspect that it has not to do with electricity.
More than once I have felt a "tingle" and after checking found a small metal splinter in my finger, or a sliver on a piece of metal, or a pinched nerve.
Sometime I could find evidence of the cause, other times just my guess. But I have observed this when I have not been anywhere near any electricity.
My speculation would be that water hit an sore from the rash and that is what she felt.
I think that 3 volts can be felt, but that would only be with two probes that are directly into flesh. But I don't know where or why I think that and don't know if I ever read anything specific.
But I think that you would have too high resistance to feel it under the conditons that you describe.
That and 99c will get you a cup of coffee at QT.
that rash making the skin more sensitive is what I thought too.
I wasn't sure about the 3 volts though.it was most likely the moist ground,rash,and submersion of her arm that gave her the tinglingKnow I wonder if that leakage, if there is any, will wear out the pump bearings?thanks"
3 volts is too high. There shouldn't be that sort of potential. Remember that ####probe shoved into the ground doesn't present much in the way of surface area.
It is good that he circuit is on a GFI but remember that a GFI will not trip if contact is made between hot and neutral, or hot to hot in a 240v GFI. GFI, as the name implies, only 'sees' Ground faults.
Also "one lead into the ground and dropped the other lead into the sump" is not the critical reading. The sump is, by contact with the earth and through the pipes and/or water to the pond which are pretty much guaranteed to be in contact with the earth, grounded. That there is 3v between the sump and the ground at the box is a warning.
One way of tracking this would be to put a ammeter on the ground lead coming from the box. This shouldn't, in an ideal situation, be carrying any current at all. Any detectable current is a red flag. But no current doesn't mean there isn't a fault.
Given the water, damp ground and voltages your going to need some skill, knowledge and care to troubleshoot this without getting shocked. So don't overestimate your abilities. A proper set of insulated gloves, protectors and boots would be a good a good thing to have. Don't leave home without them.
I have them but, other than the insulation of my boots don't use them in these cases but I have a lot of experience in similar cases. I will break them out if I feel I can't operate safely without them. Being able to 'get away' from the circuit is important. If I'm forced to lay in the mud, work in a confined space or work in water the protection comes out. Be careful. Remember this is not a video game. You only get one life, one shot. There is no reset button.
After I identified a fault, I think you have shown there is one but one that is being disguised by the ground doing exactly what it is designed to do, I would start by disconnecting the ground. This will expose the fault in all its glory.
Then it is just a matter of lifting connections to track where the fault is. Don't forget that an underground fault in a cable can be mistaken for power coming From a faulted motor when, in fact, the voltage is coming from the cable underground and traveling to the motor frame or box and on the panel by way of the ground conductor.
Of course this could be an overly sensitive lady mistaking something else for an actual shock. The voltage differential could be an artifact of a digital meter. Don't forget the variables. Test everything with the pumps both on and off. With the float calling and not. Soil moisture, the exact position she was standing and a dozen other factors could change the readings. Cover the bases.
Always keep the consequences and responsibilities in mind. You certainly don't want her to get hurt. If her body is found at the pump and the ME finds she died of electrical shock you want to be able to honestly look the jury in the eye and say that you took her concern seriously and that you made every reasonable effort to identify a fault.
I assumed that the pond is insulated from earth since the whole thing is essentially a pool (there is about a three foot lip of liner around the whole pond) I thought that is why I could read a difference of potential of 3v, ..... the reading between the soil probe and the ground at the recep was about 3mV , my meter is an old Simpson bench tester that I have used for about 18 years , and I agree that I could pickup some junk readings , but she did feel something.No floats in the setup, just 24 hr circ. pumps, puliing the plug would ......... make the problem go away !!"
One critical thing to remember, NEVER let your body be the conductor between the hot, neutral or a lifted ground and the actual earth ground. All of the conductors need to be checked and if they aren't in conduit rated for direct burial, change them.
This circuit is 117V, right? By any chance, is this pump on a three-way switch? If the neutral is being switched(like the one on my parent's garage), the ground becomes hot in one position(non-conductive conduit, garage was wired by an Electrical Engineer). My dad never believed the lawn care people when they said they got shocked whenever they touched the garage while holding onto the mower. When I sold their house, I checked all of the circuits and found that the 3 way was wired incorrectly. Since the switch in the garage was almost never used anyway, I removed it so the one in the house would be the only way to turn the light on at the alley. Problem solved.
"I cut this piece four times and it's still too short."
Edited 9/3/2005 7:58 pm ET by highfigh
the wiring is in PVC, continous to a LB at the house then EMT,ground is #10, circuit is a little low at 112v but only about 80' from the panel, I don't not want to unplug the pumps as they have replaced one of them three times in two years (mfrs. defect) and the temps were in the 90s,I don't know about you guys,but I hate 2pm shutdowns, changeovers, and weekend service calls .It would be my luck they would decide to quit"that three-way in your garage was I think called a california three-way, and when I was an appprentice my JW showed it to me with the explanation that it was used were romex was installed, it was at that moment that I decided that romex was s##t ...that was in ..'72
Edited 9/4/2005 3:51 pm ET by maddog3