shocked in tub?

[billdozier]

Hey guys ive got a customer who says thier kids get shocked whenever there sitting in the tub with water drawn. I know the house is not properly grounded at the meter. Theres a #8 wire coming down and pipe clamped to what looks like an old fence post. Also the service wire into the house is old 3 wire. If I drive two ground rods and connect with a piece of 8 will this eiminate the problem? Also is there a way to test and make sure the problem has been eliminated?

 

[Karl H]

Bond the cold water pipe with a conductor sized per T250.66 to the service.

 

[HEYDOG]

It sounds like you could possibly have a open neutral on the customer or utility side of service.

 

[HEYDOG]

It sounds like you could have a open or loose neutral on the utility or customer side of service.

 

[electricmanscott]

First I'd tell them to stay out of the tub. Second I'd get over there and start searching.

Could be a number of things.

 

[gar]

090117-1615 EST

Potentially very dangerous. So no one should get into this tub until problems are solved.

However, I have questions.

1. Assume the tub is metal, conductive. The water piping is conductive and electrically connected to the metal tub, meaning a low resistance connection. Also assume the water is of some nominal conductivity. This whole combination of items --- tub, piping, and water --- is at an approximately equipotential within the water and the tub under the above conditions. The whole thing could be 1,000,000 volts above earth and it would not change what was in the tub. If the person in the tub does not touch anything outside the tub, then how do they get a shock?

2. This means you need to know if all the above said components are conductive and electrically connected together (bonded).

3. Assume they are all bonded together, then my assumption is that the shock occurs when getting into the tub, or when reaching for something outside of the tub, or someone puts an electrical current into the water in the tub.

Injecting current into the water in the pipe coming to the tub is unlikely to create a potential difference within the tub water and/or relative to the tub or faucet. Assuming the piping and attached faucet are conductive. Current in the water source coming into the tub would be shunted to the metal pipe and tub before creating a field in the tub.

4. In its present state put water into the tub. Get a high impedance digital voltmeter, like a Fluke 27. Run a test lead wire from some rod, maybe a 12" screwdriver, driven in the earth near the main service entrance. This test lead is one input to your meter. Use AC volts or millivolts range as required. With the other test lead measure the voltage to different things in this bath area --- water in tub, tub, faucet, water coming out of faucet, the floor, and anything that can be touched.

In one of my bathrooms I get 5 MV AC from the water stream to the outlet EGC. Less than this from the water stream to the faucet. Quite erratic and below 3 MV. Maybe varying DC generated from dissimilar materials.

When measuring to the tub itself there may be some problems because of the baked enamel.

If shocks really are occurring in the tub, then the above measurements may lead you in some particular direction.

Quite obviously the house, its electrical system, and the grid connections must be correctly connected for the ground and neutral.

My suggested measurements are a starting point. You can also put the meter in AC MA range and see what current levels you read.

It is important to find out what the exact conditions were when shocks occurred. At any time a minor shock could become much more serious because what ever current is causing the shock is being current limited by something. This current limiter might change and in turn cause a lethal shock.

I do not test myself or anyone for shock current levels. It is my understanding that something below 1 MA is where you feel a tingle. This might be 1/10 MA or even lower.

GFCI devices are supposed to trip on anything above 5 MA, but this gives you a substantial shock.

Also you should be careful running the tests.

.

 

[Karl H]

Since you are on the Gulf Coast (where I'm from). Drive the rods,this will not

solve your problem. Ground rods are for lightining strikes,which are very

common in the South. I don't think this is a open or loose neutral.

Of course, I have been wrong a billion times,just ask my wife.

Make sure you have a properly sized cold water bond. If there is

a cold water bond (Which I doubt) make sure the connection point

isn't corroded,and made up tight,and bonded to the service neutral.

When you are sure that everything is Bonded properly. Follow Gar's

post to the letter. Gar has explained everything IMO.

 

[ptonsparky]

Do all the checks as stated by others, repair as needed, then bond the metallic drain or sewer line to the water pipe. Bonding before you find the problem will just mask it. You could have a leaking drain that has dampened old K&T or cloth covered romex along with the flooring & created a conductive path. Do the kids make to much of a mess? Is the faucet mounted on the tub or above in the wall?

 

[quogueelectric]

My favorite is a handrail or plumbing fixture where they used 3" deck screws to support the equipment and ran the screws right into the kitchen sabcs on the other side of the wall. Right through the plastic boxes and landed into the hot non gfi conductor of the counter in the adjascent kitchen. Customer leaned in holding the energized grab bar and when he turned the diverter valve he got hung up and couldnt let go doing the funky chicken in his birthday suit.

 

[djtazjr]

Try checking the water heater elements and the range. I ran across this problem recently and it turned out to be both. The water heater elements were cracked and leaking voltage, and the Jen Aire cooktop was shorted to ground and there was do EGC ran with the 40 amp circuit to open the OCP when they turned on the cooktop. The typical installation of a new Cooktop is to install it to the three wire system instead of pulling of installing a new four wire.

Hope this helps.

 

[monkey]

I have solved two cases of shocks received in the tub/shower.

First one, there was a sub panel fed with 3 wires, using the emt for grounding. Someone (Hack) added 2 120V circuits to this panel using the grounding bus for their neutrals. The emt became separated on the roof, and the neutral current was finding it's way back on the gas and water piping, probably through the furnace which had a grounding connection to this panel.

The second one, someone (Hack) changed a bathroom light fixture. The bathroom light box contained the home run and a 14/3 which carried the line through as well as a return for the light switch. They connected the light to the switch return, and to the neutral wire on the 14/3, and capped off the neutral on the home run. This was an older building with conduit under the slab which somehow must have been in contact with the plumbing. The neutrals in the conduit were bare #14s. So all the loads on that circuit were finding their way back on the conduit and plumbing.

My helper believes that the conduit and the plumbing pipes did not need to necessarily have a metallic path connecting the two, he believes the neutral current could travel through the damp earth below the slab and find it's way to the plumbing pipes. I do not agree, I can't see the earth conducting enough to allow the circuit to function normally without a metallic path back to the txformer. There was a lot of stuff on this circuit, all working normally. I would like to hear some opinions on this.

 

[c2500]

Gar made a comment about the enamel of the tub creating an issue with testing. If the drain assembly is brass, or chromed brass, i have seen the point where the drain connects to have a much thinner coat of enamel. Also, this connection is often times made with plumbers putty and/or a thin rubber gasket which can allow a metal to metal connection. This also applies to the overflow, though usually there is a large (thick) rubber gasket in use which can prevent a metal to metal connection. Obviously though, conductivity will depend on a metal based drain system vs a plastic based one.

c2500

 

[gar]

090118-2121 EST

The results from the following experiment are to prove what I intuitively know from theory.

The experiment consists of a 24" length of 1/2" copper pipe filled with my tap water which has a fairly high calcium content. In other words moderately conductive water.

At each end is a nylon insulator with a 10-32 screw thru it to make an electrode in the water.

The copper pipe was connected to the wall neutral. A Fluke model 27 meter was connected between the copper pipe and an electrode at one end of the pipe. An electrode at the other end of the 24" pipe was connected to 120 V (hot) thru a 250 W bulb for current limiting in case of any problem. The voltage across the bulb was about 30 V and between the hot electrode and the pipe about 90 V.

Note: the Fluke input impedance is 10 megohms and I did not use shielded wires to the Fluke.

With none of the apparatus connected to neutral or hot the meter read 0 MV. When the neutral only was connected the reading was 13 MV AC. I assume this was capacitive coupling to the meter. When current was flowing to the other electrode 24" away the voltmeter reading increased to 14 MV. This is very good proof that you will not get current flowing thru a conductive water in a copper (metallic conductive pipe) where the pipe is connected to one side of a voltage source and the other side of that voltage source connects to an electrode in the water at some distance from the point where measurement is being made for voltage. Probably a distance of 3 to 20 times the pipe diameter from the voltage injection point to the point of measuring voltage is sufficient to get to near zero volts. The voltage measurements are relative to the copper pipe.

Note the DC voltage generated between the steel bolt and the copper pipe was about 0.6 V from the dissimilar materials in an electrolyte.

Thus, a properly grounded copper plumbing system will not present a shock problem in a tub or sink from an electric heater coil that conducts into a hot water heater. This means the copper piping must be grounded after a dielectric coupling and on the copper pipe that goes to the tub, sink, or whatever.

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