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  #1   IP: 99.241.172.112
Old May 25th, 2008, 12:49 PM
MikeM MikeM is offline
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Default Electric shock from an electric stove

Hi,

My wife complained that she gets an electric shock from the stove every time she leans over it. I found with a screwdriver voltage indicator that the voltage is present on two front elements when they are on. On another internet board
it was suggested that most likely reason is that the stove is connected with a 3-prong plug. Mine has a 4-prong plug though... I took the back panel off and made a picture showing internal connections... Any ideas before I call an electrician? Thanks.
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  #2   IP: 76.104.172.149
Old May 25th, 2008, 01:49 PM
suemarkp suemarkp is offline
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Voltage would be expected near the coils when they are energized, so that's not a problem. The first thing I'd look at is the wall receptacle. Turn of the circuit breaker for that circuit and remove the receptacle cover. Is there actually a bare ground wire on that 4'th grounding prong? If so, does that wire go just to the metal receptacle box or to a bare wire in a cable that goes all the way back to the source breaker panel?

If all appears good, you may need to check the integrity of that ground wire on the receptacle to make sure it really fully conducts.
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  #3   IP: 209.91.39.169
Old May 25th, 2008, 02:13 PM
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Here is some helpful information posted by suemark:


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Originally Posted by suemarkp View Post
There are multiple reasons why this is bad. First, electric services are bonded to the service neutral not to the earth. Ground electrodes like rods and buried pipes are only for lightning protection. Water pipes are bonded to remove any current that accidently gets applied to them by routing it directly to the service neutral.

If you bond to a water pipe, you may be OK if the plumbing is also bonded to the service and the integrity of your plumbing is good. With all the PVC and other plastic piping used now days, you could end up with an isolated section of pipe and now your "ground" isn't bonded but floating. Should there be a fault to the chassis in the oven, the oven chassis and the bonded pipe and everything metal connected to that pipe would become energized and a shock hazard. A fault may be current limited because a wire was just barely nicked in the oven, so you may not notice the shock, or it may be a mild tingling. But lets say this happens and now you need to do some plumbing work. So you cut the pipe to add a fitting and grab around each side of the cut with your hands. Now, your plumber is most likely dead, as that nice conductive metal pipe will fry you whereas the oven only tingled you (you were poorly earthed because of the kitchen flooring and your shoes). The idea in the NEC is not to use pipes as a bonding conductor, but only to bond them in case they somehow accidently get energized by some electric and water device, like a water heater.

The ground rod idea is even worse. The earth is not a good conductor. Bonding via the earth will not trip a breaker at 120V or 240V even if you clamp it directly to a ground rod. You'd be lucky to trip a 15A breaker on a 480V circuit when using the earth as a conductor. So if you bond the oven frame to a ground rod and a fault to the chassis occurs, it won't trip the breaker. Depending on how bad the fault is, you may be flowing a few amps through the earth forever (and wonder why the power bill is so high) until one day you touch the oven and a water faucet or some grounded metal appliance at the same time. Now you become a parallel bonding wire, but it only takes .02 amps to kill you and 15 or more to trip a breaker. Touching the oven in this case may only tingle or bite you, again because of the resistance of the flooring and your shoes. But if you touch something well bonded (like metal pipes or appliances) with one hand and the range with the other, it could be lethal.

The reason a separate ground wire is preferred is because the integrity of the bonding wire is maintained better over time if it never carries current (except when/if a fault happens). In a 3-wire range circuit, the neutral is both a current carrier and a bonding wire. This is OK, but there is a voltage drop in the neutral, and this will raise the oven chassis a few volts above the earth and pipe grounding reference. While a few volts won't shock you, it can cause a spark when the chassis and something else grounded touch each other. This typically isn't a huge hazard in a home, but if you had some sort of explosive atmosphere (gas leak) or a flammable liquid near where that spark occurs, you could have a fire or explosion.

In all cases though, you want your bonding wire to get back to the service neutral with the best possible conductivity. This just can not be assured with piping, and never with an earth only path.
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  #4   IP: 209.91.39.169
Old May 25th, 2008, 02:19 PM
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Then WG (Just helful information):
Quote:
Originally Posted by Wgoodrich View Post
I suspect you have a heating element that has gone short to ground, or you are using a bare wire as a current carrying neutral that is supposed to be a whiter wire instead of a bare or green wire. To find this short to ground drive a pipe into the ground in a remot area outside and connect a jumper wire to that pipe. Run that jumper wire to the metal water piping in your home. Take a voltage tester and measure one test lead to the metal pipe and the second test lead to the jumper wire from the pipe in the ground.

When you are able to read this shocking voltage then keep reading the voltage to the noncurrent carrying metal in your house [water pipe metal of appliance etc.] Now while you are reading your voltage have someone turn off each of your breakers one at a time.
When you see the voltage disappear turn all breaker back on except that last breaker you shut off. If you have the voltage you have to start over because you have more than one leak to ground and you will have to find that second leak to ground. If you turn all the breakers back on but that one breaker and your voltage is not reading then find what is not working in the house [most likely a water heater element or someone used a bare for a neutral]. Then repair that leak to ground.

Hope this helps

Wg
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  #5   IP: 96.2.185.56
Old May 25th, 2008, 02:42 PM
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Hi,

Never seen a cord connected to a stove like that.
Is this a free standing stove?

How old is this stove?
Got a make and model number?
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  #6   IP: 209.91.39.169
Old May 25th, 2008, 05:50 PM
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I agree, I haven't seen anything like it??
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  #7   IP: 99.241.172.112
Old May 26th, 2008, 06:57 PM
MikeM MikeM is offline
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Quote:
Originally Posted by suemarkp View Post
Voltage would be expected near the coils when they are energized, so that's not a problem.
What do you mean not a problem? I am observing the voltage on the top of the elements!
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  #8   IP: 64.83.225.185
Old May 26th, 2008, 07:21 PM
junkcollector junkcollector is offline
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Quote:
Originally Posted by MikeM View Post
What do you mean not a problem? I am observing the voltage on the top of the elements!
I think He meant at the terminals of the element, not the metal casing of the element itself.

(After turning off power)
I would take a look at the connections at the receptacle. Someone may have installed a 4 prong receptacle with three wire cable.
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  #9   IP: 99.241.172.112
Old May 26th, 2008, 09:32 PM
MikeM MikeM is offline
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Quote:
Originally Posted by ApplianceJunk View Post
Hi,

Never seen a cord connected to a stove like that.
Is this a free standing stove?

How old is this stove?
Got a make and model number?
Yes it is a free standing stove and it's over 10 years old for sure and probably quite a bit more. The make is White-Westinghouse. For the model number I need to move it off the wall, which I can't do now...
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  #10   IP: 76.104.172.149
Old May 27th, 2008, 07:37 AM
suemarkp suemarkp is offline
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Quote:
Originally Posted by MikeM View Post
What do you mean not a problem? I am observing the voltage on the top of the elements!
You said a "screwdriver voltage indicator". I took this to mean a non-contact voltage tester (a plastic screwdriver looking thing which detects voltage when you're within an inch or so of it).

The coil is a big resisistor. There should not be voltage exposed on the element, but the fine wire within it will have a 120V gradient in it relative to ground (the absolute voltage of that gradient varies as you follow the coil). The non-contact testers don't tell you how much voltage is there, so it could be 50 or 100 or 120. But if it is contained within the black covering of the element, it won't hurt you.

If you're using a conductive direct contact tester, and you have voltage on the element, that would be a problem.

Does your wife get shocked regardless of whether a stove element or the oven is turned on, or only when a a specific knob or any knob is turned on?
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