New Meaning to Stupid

charlie b

Moderator
Staff member
Location
Seattle, WA
Occupation
Electrical Engineer
I agree with Tom. But I will put things a different way. The coin will form part of a series circuit. That circuit will include the black wire, the coin, and the white wire. In any series circuit, the current is the same throughout.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Unless someone gets a shock from touching the penny, as happened on the call I got. (see post 33)
 

DBoone

Senior Member
Location
Mississippi
Occupation
General Contractor
Well I guess we’ll be going to prongs that are insulated up to the tip where contacts are. So exposed partial prongs aren’t leaving exposed live parts for pennies or whatever to come in contact with.
Wait, isn’t the European plug already like that?


Ohhh I never thought of that! Yep, just a matter of time before we go that route 🤦🏻‍♂️
 

Coppersmith

Senior Member
Location
Tampa, FL, USA
Occupation
Electrical Contractor
This is a legitimate issue when it comes to small children dropping pennies, dimes, quarters, bobby pins, and other assorted metallic items which leads to the issue that we are not allowed to talk about. You know the one. The one where "it" goes up or down.
 

kwired

Electron manager
Location
NE Nebraska
thats a good point, not sure what current would do in the penny event, your saying the current on L1-N would be EXACTALLY the same during a fault like that? I see the concept, but in all reality you feel it would be if you stuck a clamp around a neutral to phase fault with a penny you would get an exact number on both lines ?
Well the person that is touching the coin may experience a few milliamps depending on how well they are connected to any grounded objects. If they touch the coin to the ungrounded conductor first, is possible a GFCI trips before contact with the grounded conductor occurrs, they still might get a shock from the event though.

Outside of such possible higher resistance path all remaining current flows from one circuit conductor through the coin and to the other conductor.
 
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LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I don't see how a person could get shocked from that. Burned I could see.
First, I received the service call because an employee got shocked and experienced a boom at the same time. They discovered the penny when they saw the charring on the front of a power strip (in a commercial office) Looking at the depth of the grooves, I'd say the penny had been sitting there a while, arcing away without tripping either the strip or branch circuit breaker.

Apparently, he accidentally pressed the penny into firm contact with the prongs and, theoretically, received 60 volts to whatever grounded surface his other hand was on. He actually could have received any voltage between 120 and zero, but it was enough that he went home for the day (which is why I'm guessing hand to hand current pathway), but he was otherwise okay.

My long-term solution was to tidy up the rats' nest (clic pics for bigger rats); I hear management really liked it:

Before:
B4-2s.gif B4-3s.gif B4-5s.gif B4-6s.gif


After:

After-1s.gif After-2s.gif After-3s.gif After-5s.gif
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
This is a legitimate issue when it comes to small children dropping pennies, dimes, quarters, bobby pins, and other assorted metallic items which leads to the issue that we are not allowed to talk about. You know the one. The one where "it" goes up or down.
I never thought of it before, but the "horizontal" outlet position that's common throughout the Chicago area makes this "dropping coins" a non-issue for the most part. At least a coin is not going to hang there across the prongs. Of course metal objects can still be inserted sideways to short out the prongs.

By the way, as a very young kid I remember seeing a scorched outlet very similar to the second picture on the webpage that Dennis posted.
That was after a flash startled me. Apparently I and my siblings were inserting screwdrivers for whatever reason. To avoid this my dad at first replaced the receptacles with ones where you had to partially insert the plug and twist it 90 degrees before allowing full insertion. The problem is, at least for my dad, it didn't take us long to defeat this mechanism. Eventually my dad inserted some plastic plugs that tapered to a very narrow edge and were very difficult to remove. So I think we eventually just gave up. Which is good because I'm still here. ;)
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
This is a legitimate issue when it comes to small children dropping pennies, dimes, quarters, bobby pins, and other assorted metallic items which leads to the issue that we are not allowed to talk about. You know the one. The one where "it" goes up or down.

The location issue only comes into play if the power plug has a grounded plug, in the OP case the plug was only 2 wire.
In checking the cord plugs in my own house, that the grand-kids have access to,, only one had a ground pin and it was on a power strip.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
thats a good point, not sure what current would do in the penny event, your saying the current on L1-N would be EXACTALLY the same during a fault like that? I see the concept, but in all reality you feel it would be if you stuck a clamp around a neutral to phase fault with a penny you would get an exact number on both lines ?

IMHO if the receptacle had a grounded bare metal cover (eg. stainless) then it is very likely that some of the current would go via the plate to ground and trip a GFCI. But if you just have two leads with no conductor nearby and you short them with a penny, then all current leaving one lead would have to go to the other, and the GFCI would simply see 'load current'.

-Jon
 

anthonysolino

Senior Member
IMHO if the receptacle had a grounded bare metal cover (eg. stainless) then it is very likely that some of the current would go via the plate to ground and trip a GFCI. But if you just have two leads with no conductor nearby and you short them with a penny, then all current leaving one lead would have to go to the other, and the GFCI would simply see 'load current'.

-Jon

Do you feel if a GFCI was installed the penny would cause an unequal amount of current traveling on L1 back to the N?:unsure: what is the resistance value of a penny? I wonder if they are REALLY copper or some copper clad type thing. excuse my ignorance. I just don't know 🤷‍♂️ one would thing the penny wouldn't weld it self evenly across the terminals thus having a higher or lower value on one side? pretty interesting to think about though

case in point, would the gfci OPEN thus protecting the branch circuit conductors from damage?
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Do you feel if a GFCI was installed the penny would cause an unequal amount of current traveling on L1 back to the N?:unsure: what is the resistance value of a penny?
No. In general the penny would cause _equal_ current flow on L1 and N.

It doesn't matter what the load is or how linear (or not) it is. If the load is connected only to L and N, then any current flowing to the load on L _must_ return on N.

What would cause _unequal_ current on L and N is if current somehow found a path elsewhere, as I suggested via a grounded metal outlet plate, for example...or by plasma arcing to the ground pin.

-Jon
 

anthonysolino

Senior Member
No. In general the penny would cause _equal_ current flow on L1 and N.

It doesn't matter what the load is or how linear (or not) it is. If the load is connected only to L and N, then any current flowing to the load on L _must_ return on N.

What would cause _unequal_ current on L and N is if current somehow found a path elsewhere, as I suggested via a grounded metal outlet plate, for example...or by plasma arcing to the ground pin.

-Jon
ahhhhh thats all it took, "if current somehow found a path elsewhere" I get what your trying to say, I agree 100% idk why I wasn't seeing it in that way, that makes sense.
 

StarCat

Industrial Engineering Tech
Location
Moab, UT USA
Occupation
Imdustrial Engineering Technician - HVACR Electrical and Mechanical Systems
An EE friend of mine told me years later than a guy by name of Tom had built up these devices that consisted of a coffee can with a coil made out of a metal coat hanger. I do not recall what else may have been included in the build, but when they went round the junior high and plugged these things in under the water fountains. Apparently they created this notable hum, and drew loads of power. I always wondered about the bare coil wire being hot plugged......
 

kwired

Electron manager
Location
NE Nebraska
An EE friend of mine told me years later than a guy by name of Tom had built up these devices that consisted of a coffee can with a coil made out of a metal coat hanger. I do not recall what else may have been included in the build, but when they went round the junior high and plugged these things in under the water fountains. Apparently they created this notable hum, and drew loads of power. I always wondered about the bare coil wire being hot plugged......
Assume using the coffee can as the core and the coat hanger as the coil. Coat hangers are typically coated, maybe not with exact same coating as magnet wire, but you do need to insulate so you don't get turn to turn shorts.
 
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