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Author Topic: How much fun (shock) can we have without tripping our GFCI  (Read 10086 times)

John Roberts {JR}

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How much fun (shock) can we have without tripping our GFCI
« on: October 19, 2015, 12:34:04 pm »

I installed a GFCI to my (ungrounded) kitchen outlet next to my sink. Yesterday I was using my trusty old kitchen-aid mixer and experienced a new shock. With the mixer turned off (but still plugged in), I felt a shock between one hand touching the metal mixing bowl (grounded to the mixer), and the metal facing strip on my wood (formica?) kitchen counters.

The metal trim is not grounded or energized (it shouldn't be). Using my neon lamp probe, one lead grounded to my hand, I get dim readings on line and ground, but dark to the metal trim (so apparently it isn't energized).

But I measure 112V with my VOM between the mixer chassis and that metal trim strip.   :'(

It was enough current to be unpleasant, but not enough to trip my GFCI (5mA)...  ;D Time to take the mixer apart and inspect the mains wiring. I don't read any DC resistance, but enough capacitance to feel it.  :o

JR

PS: maybe the mixer has a stinger cap?
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Geoff Doane

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Re: How much fun (shock) can we have without tripping our GFCI
« Reply #1 on: October 19, 2015, 01:01:14 pm »

The metal trim is not grounded or energized (it shouldn't be).
JR



The strip must be grounded, isn't it?  Try measuring the resistance between it and a known ground.  Or maybe the capacitance?

GTD
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John Roberts {JR}

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Re: How much fun (shock) can we have without tripping our GFCI
« Reply #2 on: October 19, 2015, 01:16:05 pm »

I'd have to run a wire all the way to my panel to make a real measurement (sorry not going to happen). No DCR or C  to my cold water pipe under the sink... (but I haver a plastic water feed from the meter to house since my steel pipe rusted out).

I am pretty sure humans can perceive low current shocks (I have).

Counter and metal trim probably has capacitance to real ground.

JR
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David Buckley

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Re: How much fun (shock) can we have without tripping our GFCI
« Reply #3 on: October 19, 2015, 04:46:14 pm »

Yeah, pretty much any double insulated appliance I can rub the back of my hand on it and feel the presence of electricity, its not a shock, or a tingle, more like an odd surface texture.  And the current is very low, it is just capacitive leakage.

Of course, if you want to experiment, then perhaps a Big Clive tingle-tron might be what you need.....
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John Roberts {JR}

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Re: How much fun (shock) can we have without tripping our GFCI
« Reply #4 on: October 19, 2015, 05:25:53 pm »

Yeah, pretty much any double insulated appliance I can rub the back of my hand on it and feel the presence of electricity, its not a shock, or a tingle, more like an odd surface texture.  And the current is very low, it is just capacitive leakage.

Of course, if you want to experiment, then perhaps a Big Clive tingle-tron might be what you need.....
I don't want to experiment more, I want to cook without unexpected shocks... Yes it was actually the back of my hand so at first I ignored it, but after the next time I stopped ignoring it.  ???

JR

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Stephen Swaffer

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Re: How much fun (shock) can we have without tripping our GFCI
« Reply #5 on: October 19, 2015, 10:33:42 pm »

I'd have to run a wire all the way to my panel to make a real measurement (sorry not going to happen). No DCR or C  to my cold water pipe under the sink... (but I haver a plastic water feed from the meter to house since my steel pipe rusted out).

I am pretty sure humans can perceive low current shocks (I have).

Counter and metal trim probably has capacitance to real ground.

JR

FWIW, for safety metal water piping should be grounded to the panel anyway especially if you have an electric water heater.
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Steve Swaffer

Jonathan Johnson

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Re: How much fun (shock) can we have without tripping our GFCI
« Reply #6 on: October 20, 2015, 01:11:43 am »

I felt a shock between one hand touching the metal mixing bowl (grounded to the mixer), and the metal facing strip on my wood (formica?) kitchen counters.

Topic swerve: traditionally, the metal facing strip is used with linoleum as the countertop material. (I mean actual linoleum, the product made with linseed oil, wood flour, and burlap. Not vinyl flooring that some people call "linoleum.") Considering the age of your house, if the counters haven't been redone in 60 or 70 years, the countertops very likely are linoleum instead of Formica. Linoleum is making a comeback both as flooring and as a countertop material.

Linoleum is softer than Formica. Linoleum can be cut with a knife; Formica cannot, though it can be scored with a sharp point.
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Frank DeWitt

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Re: How much fun (shock) can we have without tripping our GFCI
« Reply #7 on: October 20, 2015, 12:51:28 pm »

It seems that the metal mixing bowl is electrical connected to the mixer but the mixer is not grounded.  (It is not plugged into a grounded outlet and may or may not have a grounded plug)  (My Kitchen aid mixer has a three wire cord.)

Isuspect that either because it has a grounded plug, or because it is old, or both, it is not double insulated.

The metal counter trim is not grounded.

Man gets a shock between the two.

ACTION REQUIRED.

If it were me I would get a ground into that kitchen even if i had to use wire-mold.  I would put a three wire cord on the old mixer and I would ground the counter trim.  Then I would bake a cake.




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John Roberts {JR}

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Re: How much fun (shock) can we have without tripping our GFCI
« Reply #8 on: October 20, 2015, 01:11:24 pm »

It seems that the metal mixing bowl is electrical connected to the mixer but the mixer is not grounded.  (It is not plugged into a grounded outlet and may or may not have a grounded plug)  (My Kitchen aid mixer has a three wire cord.)
yes metal bowl is grounded to ground pin on outlet. Outlet wiring does not include a ground wire, so sundry appliances plugged into the same strip can have their grounds energized by the mixer's leakage. 
Quote
Isuspect that either because it has a grounded plug, or because it is old, or both, it is not double insulated.
I do not expect it to be double insulated, while I do not read any DCR between line or neutral to ground I do measure some capacitance that I suspect is the cause of shock and measured voltage into the high impedance VOM.
Quote
The metal counter trim is not grounded.

Man gets a shock between the two.

ACTION REQUIRED.

If it were me I would get a ground into that kitchen even if i had to use wire-mold.  I would put a three wire cord on the old mixer and I would ground the counter trim.  Then I would bake a cake.
My plan is to take the mixer apart and determine where it is getting the capacitance coupling to safety ground. I may just need to clean out some smutz (technical term) from inside the mixer. It is a couple decades old.

If it has an actual stinger cap to ground inside I may remove that or rewire it line to neutral.

I already have this on a GFCI outlet so I am protected from dangerous shock (>5mA), but it can still be annoying.

JR

PS: I do plan to add a real ground to the outlet in my laundry room that is literally a few feet from my fuse panel. My dishwasher also plugs into that outlet. It would not be a huge project to snake a ground wire through the dishwasher hole to add a real ground, but for now I just plan to take the mixer apart. 
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Mike Sokol

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Re: How much fun (shock) can we have without tripping our GFCI
« Reply #9 on: October 22, 2015, 09:52:34 am »

yes metal bowl is grounded to ground pin on outlet. Outlet wiring does not include a ground wire, so sundry appliances plugged into the same strip can have their grounds energized by the mixer's leakage.  I do not expect it to be double insulated, while I do not read any DCR between line or neutral to ground I do measure some capacitance that I suspect is the cause of shock and measured voltage into the high impedance VOM....

I already have this on a GFCI outlet so I am protected from dangerous shock (>5mA), but it can still be annoying.


OK, now I'm not suggesting this as a real fix until we all think it through, but can you just add a "Stinger Cap" on the back of your kitchen GFCI between the Neutral and Ground screw? Of course, you'll need to verify that the Hot and Neutral aren't swapped in the walls, but that's easy enough to do with a NCVT.

This is more than just a question for your own "mixer" issue. At the University where I teach there's a bunch of practice rooms with 2-banger "ungrounded" wall outlets, and the students are always using ground-lift adapters on their practice amp power plugs or breaking off the ground pins on the power cords. I've told the University they need to replace these outlets with GCFI's, but we still get a lot of buzzing in the practice amps since the chassis are floating. Of course, if they all used modern double-insulated practice amps it would be safe and probably not buzz, but many of my students are finding old tube guitar amps in pawn shops (because they sound great) and bringing them into school. What would an inspector think about this stinger-cap GFCI mod? I've never seen anything in the NEC about stinger caps to create a a capacitor coupled ground for buzz mitigation, but that's essentially what it would be doing.

Thoughts?
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Mike Sokol
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Re: How much fun (shock) can we have without tripping our GFCI
« Reply #9 on: October 22, 2015, 09:52:34 am »


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