help with open ground

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rickl

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i hope i can explain this problem so everybody understands.
i got a call from a homeowner to change a plug ( somebody in the past replaced it with a different color)so i change the plug without checking the voltage to ground, then after i'm checking voltage and find i have 70 volts from the hot to ground &120 volts from hot to neutral. so i check my connection again there all good. here is the situation i have 3 cables coming into the box i worked on (lets label this box B )the voltage on the plugs upstream from box B are all good, so i tear apart box B again and seperate the hots and check voltage from the incoming hot to ground & have 120 volts so i hookup the incoming hot with 1 of the other cables and everything checks out, but as soon as i hookup the third cable i have an open ground in box B and all plugs downstream from this plug. this doesn't make sense to me if i have a open ground in the third cable why is it effecting some but not all of the plugs upstream from the open. also the third cable is in a area that has been remodeled acouple of times. any help or ideas would be great
 
Re: help with open ground

as soon as i hookup the third cable i have an open ground in box B and all plugs downstream from this plug.
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Is there a broken grounding conductor in that cable?
 
Re: help with open ground

try reading this with a load.Maybe a pigtailed 60 watt lamp from hot to ground. I suspect an open ground and your getting a false reading
 
Re: help with open ground

An incandescent lamp is an excellent dianostic tool.
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Right. I keep a 100W rough service bulb in a receptacle adapter and a socket with test clips in the truck. Helps solve a lot of problems.
 
Re: help with open ground

thanks but maybe i can explain better
boxA has 2 cables,the homerun and thefeed for boxB
boxB has 3 cables the incoming from boxA and the feeds for boxC and boxD
boxA checks out using a pluging tester
box B,C,D the tester says open ground ( so i'm thinking open ground between boxA & B ) open boxB 120 volts between hot and ground on the incoming cable (from boxA)so i hookup hots in boxB coming from boxA to boxC. boxes B& C now test 120 volts to ground. so i hookup the wires going to box D and i'm back with an open ground in boxesB,C,&D
i believe i have a open ground in the cable going to boxD but why would that effect boxes B &C and not boxA. i hope this helped
 
Re: help with open ground

are you using a meter or just that plug tester?Try all your readings with a meter and a load (bulb).
And try this ,pigtail all the wires and get readings before any receptacles hooked up
 
Re: help with open ground

i've used 2 fluke meters and the plug tester i'll try the light bulb test thanks
 
Re: help with open ground

There may soon be a fire, if you don't fix it quick.I can assume that the circuit is not afi protected, because if it was it would be tripping the afi breaker. I ran into a familiar situation this year at a university were i took a job as a maintenance electrician. Between semesters we were supposed to check out the different dorms offices and apartments and fix any problems that arose. I used a plug tester with a gfi tester built into it. I came to find out that the way the old master electrician would test a plug was to use a pen "induction" tester to see if it had power, as did everybody else there. any way I found an open ground, and proceeded to track it down after pulling all the lights down and removing all the plugs, I found the nm cable between the panel and the first "light/j-box"was the problem. Followed the cable in the attic and found dark pinhole. I cut open the cable "after first turning off the power" and found were the ground was almost burnt through from the hot wire.
I replaced this piece of wire and the problem was fixed. Your only problem will be if the wire is in the wall. To prove it to the home owner you may have to hook up an AFI breaker and have it trip, after it trips you can explain to the homeowner that these are the new requirements for homes and that they are to help prevent fires.

let us know how it goes .
Will Dalrymple Master Electrician
 
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