Electrical Arc or Short When Testing


Hello,
Installing under cabinet lights and upgrading 30yr old switches and receptacles in the kitchen when something I've never encountered happen.
I have a neon-tester I use to make sure there is no power before doing any work. I'm not sure if this is the official name for it, but it's a very convenient tool I've had for a couple years now. For example, I can hold one metal tip to a live black wire and put the other tip to the neutral white wire and the light at the end of the tester lights up. Or, if there is not a white neutral wire like a single-pole switch, I can put the other metal tip on my finger and the light just barely lights up.
Well, when about to replace a 30 old S.P. by my kitchen sink I went to check to see if there was power running to the switch. I grabbed my neon-test, put one metal tipped needle on the black wire screw and tapped my finger on the other and the light lit up slightly for a brief second before POP! and a puff of smoke.
After I made sure I still had my eye-brows I looked and part of the screw is melted, the side of the switch is burnt black and my beloved neon-testers metal tip is melted.
What happen?
Well, I theorized the screw was loose on the side of the switch and think an arc was created and it was a one time deal.
Well, I was wrong, because in the next two days, all when working on the same wall in the kitchen (two circuits), I've had three more loud pops and a quick burst of light when trying to test.
I thought maybe my neon-tester had gone bad, but it even happen with a new tester.
Any comments/suggestions? I do plan on calling a certified electrician to come check everything out b/c in my three years of doing electrical work around the house I've never had this happen. I do though want to learn what is happening.
Thanks!
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Native wrote:

Lets see , you connected one end of a neon to a live wire and touched your finger to the other wire.
I would have thought that makes you the ground wire and you would be electrocuted .
but thats just me .
I have a multimeter but also bought a non-contact voltage tester . Its a little pen like device that beeps if the plastic end is near a live wire.
I did have a similar incident recently , where I was using a multimeter to check for power at a switch , touched one probe to the screw and poof , blew the breaker .
It seems it was an old switch with a grounded metal shell and I had accidently caused the black wire to short to ground .
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snipped-for-privacy@yahoo.com wrote:

That's not what he said. He said he touched one lead of the tester to the hot wire and held the other lead of the tester touching his hand. That's pretty standard and will light the neon tube. The NE-2 tube used in the standard tester requires a very high resistance to keep from burning out the tube; the include resistor allows very little current to pass. Pretty much like lighting a fluorescent tube by holding it close to a spark plug wire of an operating engine (no shock there either).

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[what is a S.P. ?] the spark is usually hot to common or hot to ground. the hot could be returning from a lamp circuit or an electrified metal outlet. i'm not an electrician but i used a neon tester exactly as you did for several years until i needed to chase down odd ac voltages in our 1910 wiring. your neon tester is an old friend, but let's buy a brand new one to celebrate how it saved your behind. and a new bright headlamp, digital multimeter, a kitchen GFI, and a GFI tester. hang the old burnt neon tester up by the main panel to remind you how it saved you. no more surprises. sparks can be found at old outlets, old switches, old wire insulation, poor connections, wires improperly crowded into electrical boxes, loose connections, wire broken free from a wire nut, reversed polarity, electrified outlet box, defective appliance on the circuit such as refrigerator, motorized defective appliance leaking voltage onto wet floor. when you are working in a home where the outlet is dead and you pulled the main breaker to off or removed the main cartridge fuse disconnect, you'll still want your electrician holding a flashlight and cellphone. brush up on faq at: http://www.faqs.org/faqs/electrical-wiring/part1 / and you've earned the experience to browse next at wonderful faq for Sci.Electronics.Repair: http://www.repairfaq.org/REPAIR/F_Repair.html test equipment to buy including your good neon tester at: http://www.repairfaq.org/sam/appfaq.htm#aftesteqp
Native wrote:

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If the switches or outlets are still mounted in the box while you are testing them, the screw terminals are very close to the metal edge of the box, which is grounded. If your neon tester probe bridged the gap between the outlet and the box, you would have exactly as you describe

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Tex,
If I understand you, you have a single pole switch in your kitchen that is not connected to the circuit breaker for the kitchen outlets and repeatedly blows up neon lamp circuit testers. It's time to buy a volt meter, read the instructions, measure the voltage of each wire to a good ground, and find the circuit breaker for this switch. Use the main breaker until you find the breaker for that circuit. Sorry I'm at a loss as to why a single pole switch would have enough voltage to blow neon testers. I'd find the breaker at the box and work from there.
Dave M.
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David Martel wrote:

Hmmm, Some kitchen counter duplex outlets are divided and fed by separate source. If they are opposite leg, depending on the situation there could be 240V present. There maybe two breakers involved. First I'd look at the outlet to see if link between two is missing which means this is the case.
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That seems like the most likely explanation. But first I want to know what a SP is.
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wrote:

I imagine it means "single pole [switch]".
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Doug Miller (alphageek at milmac dot com)
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Yeah, but we want to know if it was SPST or SPDT. (I know; I'm being a wiseacre.)
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Christopher A. Young
You can\'t shout down a troll.
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Thanks for everyones help. Had an electrician come out and here is the conclusion. The sparks I saw with my neon-tester were due to the switches being back-stabbed and the screw on the side was loose. When my neon-tester probe touched the side (which was grounded) it appears (based off where the probe and screw melted) it brushed against the loose screw and then sparked. This appears to be the case with both switches.
Needless to say, he also recommended to get a digitial multimeter which I did and I love it. It was great to have him say that b/c it helped ease the price with the wife! :)
Thanks again to everyone's help!
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It doesn't have to. Once side of the outlet could be switched, and on the same phase (0V between them) as the always-live one. I have seen such outlets under a sink where the switched side is meant for a garbage disposal. These may also be found in a living room where the switched side is meant for lamps.
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thanks for all the advice and the great link to the FAQ site!
used S.P. for single-pole
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wrote:

But then why did his tester go up? Presumably he put it across 240v.
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wrote:

Sounds to me like he just shorted one of the probe tips between the hot terminal and the grounded box, thus destroying the tip. The neon tester will operate fine on 240 volts.
Don Young
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wrote:

Not a good idea to put yourself in the circuit.

i think you inadvertently shorted to the side of the box. May be wrong,. but if the tip melted on the tester sounds like thats what might haev happened. the distance in between the screws and box is very small and just the width of the test lead could short it out to the box.

Did you see any black stuff on the side of the box?

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Finding the keyboard operational Native entered:

Best guess is that the little metal probe on the hot lead got near a ground (side of the box) and caused an arc that melted the tip. But 3X? Do you have a metallic backsplash? We had one made of aluminuim and copper tiles that gave us an interesting time till we found a loose wire. I don't know where you picked up the fiinger on the other lead trick but it worries me a wee bit. It seems to me that you have a current running thru the current limiting resistor in the tester, the lamp. and then you. It's kinda like testing 9V batteries with your tounge. Almost all of the time you won't get hurt. I am glad that you are getting an electrician in. Let us know what he finds. Bob
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The Other Funk wrote:

It's all in the details. When I was young & foolish I won an awful lot of bets by taping a paperclip on each of two fingers and sticking them in a hot outlet. The "trick" was wearing rubber soled shoes and making sure my free hand was in the air. The electricity went between the 2 fingers (a tingle) and not through my body. (Kids & idiots - don't try this at home!!!) I suspect the OP may have had a similar body position.
Bob
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Not sure anyone's gotten to the bottom of this. If he's touching 2nd lead it's still only 110-120 volts. I would always start by testing to ground, not my bod. Shorting out to the box makes sense, but 3x in a row? Definitely time to turn off power and check things out.
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