1. Home
  2. Electronics Repair
  3. A tiny metal sliver on the inside of my index finger

A tiny metal sliver on the inside of my index finger

could have saved my life.

I was in my workshed which is about 60 ft from the house drilling some aluminum. I got a faint tingle in my hand, I touched the case of my drill a couple times and didn't feel any thing, so I started to drill again. I noticed the tingle again, I went through this a few times until I decided there's a problem. The tingle was at a tiny red spot on my finger, I later removed a small metalic sliver. If not for the sliver I probably would not have noticed the missing ground, for I don't know how long. The drill motor is a 3 wire system, hot, neutral and ground. I had it plugged into a GFCI. I unplugged the drill and pushed the test button. The GFCI didn't pop. I retrieved my DVM and tested from the drill case the the dirt outside the door, it was about 80v. I then tested from the Hot to the ground at the receptacle, that was about 20 v. I moved to another Receptacle closer to the house, same thing no ground connection. I moved up to a receptacle on the outside of the house on the same line, again no ground connection. Inside the garage, no ground connection. I opened the circuit breaker box and checked the ground wire, it is good. So, in my attic between the CB box and the garage there must be a connection box where the ground has opened up. Followup tomorrow evening. Mikek

Reply to
amdx
Loading thread data ...

Good catch.

The "test" button on the GFCI should work even if there is no ground to the GFCI. So you may have more than one problem here.

Don't discount the idea that the ground is open at one of the receptacles. In three houses I've worked on (one from 1965, two from

1969), if two or more NM cables come into a receptacle box, the ground wires are just twisted around each other for an inch or two, with no wire nut. Usually the contact between wires is OK but sometimes the twist is not very strong. One of the ground wires is longer than the others, and it goes to the green screw on the receptacle. When I swap a receptacle in a box like this, I usually add a green wire nut with a hole in the top for the long ground wire (Ideal "Greenie" or equal), to help make sure the ground stays connected.

Besides, checking the receptacles is probably easier than fooling around in the attic. :)

A good tool for quickly checking grounds is a 100 W incandescent lamp in a socket that has insulated wire leads. Connect the wires live to neutral to calibrate your eyes, then go from live to ground. If the brightness drops off a lot, the ground has high resistance. (If there is a GFCI in the circuit, going from live to ground should also pop the GFCI.)

Matt Roberds

Reply to
mroberds

"amdx"

** FYI:

GFCIs work independently of the safety ground in a 3 wire system - so will still trip if a few mA of current is passing to any local ground like soil, wet concrete or metal plumbing.

However, a missing safety earth conductor is never good as the metal cases of 3 wire appliances can become live and nothing blows.

BTW:

I have not seen a 3 wire, hand held drill in quite a while.

... Phil

Reply to
Phil Allison

Buy one (or two) and walk it around to every outlet in the house. Also check power strips which I've seen miswired.

The life you save may be your own.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558
Reply to
Jeff Liebermann

Re: checking in receptacle boxes, I thing I have it somewhat isolated. The CB box and the garage are on opposite ends of the house, and as far as I know, the garage is on a breaker by it's self. But it also looks like there is a connection box between the CB box and the garage, or at least a break in the ground wire. It seems a little odd, I'll figure it out this afternoon. Mikek

--
This email is free from viruses and malware because avast! Antivirus protection is active. 
http://www.avast.com
Reply to
amdx

Yes, good reminder, I knew it was a difference between the hot and neutral, but when I was missing ground my mind went elsewhere.

It is old, scares me now! Mikek

--
This email is free from viruses and malware because avast! Antivirus protection is active. 
http://www.avast.com
Reply to
amdx

Depending on the grounding arrangements, this can sometimes still happen even if there isn't a complete disconnection or any serious leakage current.

The sensation of electrical shock is entirely dependent on the current density in the susceptible tissues, rather than the voltage applied. Human tissues are very conductive, but dry skin usually acts as a partial insulator so low voltages don't create enough current to cause any sensation.

With a sliver of metal puncturing the skin and leading directly into the underlying tissue, probably quite close to nerve endings, a very low voltage would develop enough current to be easily detectable. Tests have suggested that A.C. voltages below the 2v level can be detected by the tongue when the feet are in a wet, conductive environment.

This is a particular problem where the neutral and earth conductors are bonded ("P.M.E." in the UK) because the small voltage dropped along the neutral will apear on any bonded "earthed" metalwork. In farms and other wet environments, this can lead to animals receiving shocks from licking handrails, feeding troughs - and from milking machines through the milk lines directly to their teats.

--
~ Adrian Tuddenham ~ 
(Remove the ".invalid"s and add ".co.uk" to reply) 
www.poppyrecords.co.uk
Reply to
Adrian Tuddenham

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.