Range shocker

[jes25]

So I go to a service call this morning and I am getting 120v between range and sink. So I shut off the breaker and pull out the range to remove wiring cover, I assumed the bonding jumper was not in cause it is a 3 wire range. To my surprise it is in and everthing seems to grounded OK. I turn the breaker back on and the short will not return, I tried everthing to get it to come back with no luck. I checked the ground on the dishwasher and the garbage disposal and everthing seems OK.

I thought maybe the sink was becoming energized somehow (its hooked up with plastic water lines) but it too seems to be grounded. I get 120V from a near by plug to the sink. From the ground on the near by plug to the sink I get approx. 2000 ohms.

So everthing seems to be grounded OK. I think it was the range that was becoming energized as it went away when I turned off the breaker. If this is true why would it not open the OCPD.

The range did appear th have some damaged wiring inside and the clock and two burners are bad. The damaged wires that I saw however did not appear to be touching the case of range but I did not take the range totally apart cause I am not a range mechanic.

So my question is if everthing is grounded why did yhe OCPD not trip, Why would the short disappear, and how can I be certain its a range problem?

 

[charlie b]

Re: Range shocker

A damaged wire might have been in contact with the exterior metal of the range, and might have moved out of contact when you moved the range. That would explain why the short disappeared and why you were not able to recreate the same short.

But if there is a short from a hot wire to the external metal parts, then this should have created a low resistance path (via the EGC) back to the source. I am not certain that I know what you mean when you say that the ?bonding jumper was in place.? Is this the connection from the metal case to the branch circuit?s EGC? If so, I have only one theory to offer: The EGC might not be continuous all the way back to the source. It might be broken or it might not be properly connected at the breaker panel.

That is as far as my thinking takes me.

 

[jes25]

Re: Range shocker

Charlie by "bonding jumper" I am talking about the piece of metal that goes from the neutral point to the case of a 3 wire range.

The neutral which doubles as a EGC in the three wire range seems OK from my tests with my meter.

Would it be possible that the short in the range is from something small ike the clock and will not open the OCPD.

I told the customer to get a new range or a range mechanic out there right away but I doubt she will as she is on a tight budget. I am worried about her getting shocked though and I feel I do not have a definitive answer as to what is happening.

Is it possible the sink was becoming energized and the grounded range was completing the circuit instead of the other way around?

 

[stew]

Re: Range shocker

I would check the entry at the clamp real close to see if you have damaged cord . I would also test from neutral to each of the hots when flexing the cord to see if there is an intermittent short . It sure seems like you have disturbed the shorted connection while moving the range. Also a grounded element may be the problem . Check from the prongs of the element to the surface of the element to see if you mite be shorted to ground at that point. anyway just my 2 c worth. The worst shock I ever got was while trying to figure out what was wrong with a dryer which is a simalar hookup. I was sitting down in a cramped space behaind the dryer when I tried to stand up I grabbed on to the top back of the dryer control panel and used the nearby water pipe to aid in standing up. The dang motor switch plate had burned at the termainal unbeknownst to me and hot was intermittently grounded to the frame . I stood up all right but it was because I was getting the shock of my friggin life. I think it rearranged some brain cells but I lived to tell about it anyway. Good luck Joe

[ June 29, 2004, 03:10 PM: Message edited by: stew ]

 

[jes25]

Re: Range shocker

Thanks for the responses

To me if the range is shorted, I simply tell the customer to get it repaired because that is not my problem. But the breaker not opening is my problem and I dont get why if its shorted to the case and its gounded properly why it wouldnt trip.

So stew when you had the similiar problem why wasnt the breaker trippin if the wire was touching the case?........ no ground?

 

[jimwalker]

Re: Range shocker

if that nutral / ground is some how open then the frame is hot but no current so ocpd would not trip.
try a temp wire from range frame to panel,i bet problem goes away

 

[charlie b]

Re: Range shocker

In a prior life, one of my tasks was to design a system to be able to survive any reasonable failure scenario. But I only had to design for a single failure. It was considered too unlikely that two or more components would independently experience failures at the same time. However, an inherent presumption in this design process is that any single failure would be discovered and repaired before there was time for another failure to take place. I think you may be looking at two failures. But the first happened a long time before the second, and it was not discovered or repaired before the second failure occurred.

My suspicion is that the first failure is an open neutral in the branch circuit to the range. The neutral might never have been properly connected, or it may have worked loose in the circuit panel, or it might have been damaged or disconnected by some other means. Many times the only circuit on a range that uses the neutral is the clock, and you have mentioned that it is not operating. I see that as a possible clue. It explains why the failure was not discovered earlier. Many homeowners would simply ignore the broken clock (cost too much to fix), and not suspect it of indicating a more serious problem.

The second failure is a damaged wire coming into contact with the frame, as has already been mentioned. The wire being able to move about would explain why the short was intermittent. The open neutral would explain why the OCPD did not trip.

 

[jes25]

Re: Range shocker

I agree with what you guys are saying....except that the neutral is not open. The terminations are good at both ends and I can read 120v between the hots and the neutral at the range plug and at the range cord connection point.

That what led me to believe maybe the sink was getting energized.

 

[stew]

Re: Range shocker

old dryer 3 wire no egc.I became the egc!!!

 

[hurk27]

Re: Range shocker

I know you probly have checked this , But have you check for 240 volts between the hots? And have you checked if this house might have a weak neutral or grounding? the other question is what are you using to mesure this voltage? try putting a load like a lamp between the dryer and the sink to see if the current is high enough to light it. if it does then back track it to the panel with a amp probe to see which conductor has to current from the lamp on it. If every thing is off on the range then only the lamp will show the current path.

Also you said that the sink has plastic pipes feeding it. So how is it being grounded? water will not do this alone so maybe someone ran a wire on the back side of it up under the sink to hide it. Look real close as somthing must be grounding or heating up the sink.

 

[jimwalker]

Re: Range shocker

about 15 years ago on a new house i had a new surface mount range receptacle with weak nutral contact.I would not rule out an open nutral.You might be getting false readings.

 

[steve66]

Re: Range shocker

I agree with Hurk.

Check the sink and the disposal. Also be sure to check the disposal receptacle. 2000 ohms to ground implies something is wrong there. Also, all the vibration and water makes the disposal a prime canidate for a problem.

The short may have been at the sink, and the range is just providing the ground for your 120V measurement.

Steve

 

[jes25]

Re: Range shocker

Ok I am with you guys I think somehow the sink getting heated up. I messed around with my own sink and found that its not grounded at all even though its hooked with steel water lines (plastic in the faucet)

If the sink has 2000 ohms to ground combined with your bodys resistance, that is probaly too much resistance to sustain much of a shock even if the range case was energized? just a thought?

Anyhow back to the sink. The customer says this started about 2 weeks ago and about 1 month ago she got a new dishwasher. I thought that sounded very suscpicous but I checked the dishwasher hot to the frame of dw and got 120v with a digital meter (i checked everything with an ideal digital meter). So I assumed it was probaly grounded. Also the gnd wire was hooked properly so I figured that could not be it.

The garbage disposal has a plastic case with a factory whip on it. The only metal I saw was the splice cover which reading 120v between the hot wire and the metallic splice box/cover on the garbage disposal.

My question is how can check if the garbage disposal or DW is heating up the sink, All the connections in panel and appliances seem OK. The other question or idea I had was If I cant find any thing wrong with any of the appliances (as I said before the short cleared itself making it practically impossible to trouble shoot) would it be a good idea to run a gnd wire from the sink to the copper water pipe to be sure its grounded good then if the problem returns no one will die.

 

[jimwalker]

Re: Range shocker

are the drain pipes plastic or cast iron ?
Yes bond the sink to the copper water lines,but make sure that line is bonded to the service.Any chance there is some break in the water lines ? like a repair with cpvc ? Some times they forget to use a jumper

 

[jes25]

Re: Range shocker

Jim no breaks in the water line and the drain is platic as well.

So would you guys agree if I am positive the EGC/neutral on the range is good and I bond the sink and there does not seem to be any problems with the wiring of DP and DW that I have done my job as the electrcian?

 

[jimwalker]

Re: Range shocker

would rather see you find the reason but at least the hazard be gone

 

[jes25]

Re: Range shocker

Me too! But money and time is a factor as always.