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Topic: AC Power grimlin (Read 1090 times) previous topic - next topic

AC Power grimlin

if your power savey,  help me figure out what the heck is going on here in this vid i uploaded yesterday.

I have no idea what to check next  likely because i dont think i have a tool required to check my branch circuit feeding my garage.

This is a real mystery

Re: AC Power grimlin

Reply #1
Without being in front of it, it's kind of hard to remote trouble-shoot, but that is an odd scenario.

It's highly possible that metal shelf is getting a mild ground through the concrete, which can be an electrical conductor.

One of the notes I found
Concrete on grade level, because it will absorb moisture from the earth and be a good conductor in direct contact with the earth, is always considered to be at ground potential

Probably why you were getting a mild shock with wet shoes on the slab, and why you may be seeing the minor voltage potential you are.

Insulate the shelf/rack from the concrete slab?
Long live the 4-eyes!  - '83 Tbird Turbo

Re: AC Power grimlin

Reply #2
most modern slabs **MUST** have a ufer ground rod(s) which is a cad weld to the wire mesh or rebar.
i am positive my slab is not grounded.
the following below is what i did to further troubeshoot..............and the outcome is short of an X Files moment.  I am thinking of posting this on MikeHolts forum

I killed my house main breaker feeding my garage sub panel which makes the primary feed to the garage cold.
I hooked up my 2kw inverter to my 20th cougar
i ran the same two pr0ng backfeed circuit from the inverter to the power strip.

THE PROBLEM REMAINED !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Re: AC Power grimlin

Reply #3
The power strip  power cord is unplugged from the wall socket. Your "back feeding" of the power strip is also back feeding the unplugged power strip cord..  The floating ground/bonding wire in the power strip and power cord is picking crosstalk from the other wires. It's acting like the secondary winding of a transformer.
If that power strip case is metal, it should also be connected to the ground wire.

Re: AC Power grimlin

Reply #4
this issue was present before i made up the proper 3 pr0ng cord.
The day i got shocked, i discovered this stray / transient voltage and decided i would do a vid on it when i finally got my head around what was actually happened.  turns out i am still not undersanding whats happening but i do know a couple things that might help null it out.

i get what your saying and i would not have thought of it so good point,, coupling up at the wire nuts mixed with the temp two pr0ng would / could make that sort of thing possible.

I checked again today being its day 3 of decent no rain etc and can steadily holdd around 25 to 30vac.
all is well with a 3 pr0ng chord though.

the main thing i forgot to mention on the vid is what the purpose of the vid was actually about.  I wanted people to be aware of the dangers of 2 pr0ng devices even new items of today especially when the item has any exposed metal or exposed screw heads bonded to metal covers and such.

I am considering ideas on grounding my floor with driven ground rods. 
I know with a 3pr0ng cord this is likely not going to ever be an issue but I happen to work on super old electrical things all the time and the last thing i need is some random voltage being injected into it all because its raining outside or its wet.  I believe the reason why i just found this problem is that its the first and only time i have had an actual metal workbench in the garage and since the issue showed itself, i look at it as a cup half full giving me an opportunity to at least correct it before hand.

what i need to do is see if i can use my metal detector to determine the exact location of rebar,, then make an opening, then drive a rod,, then weld the rebar to the rod,,  Id like to do this near the area where my garage door is and another towars the long wooden workbench where all my tools are.

I am doing a part 2 on this soon to demonstrate how i sourced power from a car inverter and had all power cut off going to the garage and how the problem remained.
there is something about my pad that is doing this...  thats all i know at this point.

Re: AC Power grimlin

Reply #5
I did not mean to imply that you needed the power cord attached to the power strip to create the crosstalk condition.
Your experiments and the, fact that you did not have the power strip cord attached when you got shocked, shows just the ground wire floating in the strip is enough to have the induced voltage in the ground wire.
I believe the reason the induced voltage increases with the UPS is because you have current flowing through the hot and neutral wires.
With no current flow you only have sinewave activity on the hot wire. With current flow there is sinewave activity on both hot and neutral wires.

Re: AC Power grimlin

Reply #6
You should insure there is no possibility of a difference in electrical potential between any of the metal parts of this bench.
They should all be "bonded" together, with bolts that make a good electrical connection. or ground wires if necessary.
This should include the freezer chest that is close to the bench.

The earth ground is always going to be on your concrete floor, with varying degrees of conductivity based on moisture.
You must be aware of this. As Chuck W pointed out. You might want to consider putting a rubber floor mat in front of the bench.

Re: AC Power grimlin

Reply #7
controlling the transient was not the problem, i have that under control.  I was just wondering where it was coming from even when i suppllied my very own power from a car powered inverter all the while making all wiring to the garage cold by killing the breaker in my home.

I can easilly get the pad under control and from what i have found, i see good reason to do so.  its as simple as doing a core drill into the opposite sides of the floor then get lucky and get a hold of the wire webbing or rebar, cad weld or connnet that to my copper clade rod after driving 
what i woud like to do is drive in a pilot hole with rebar into the earth after my concrete is cleared and remove the rebar then fill my hole with salt,, then set my permanent ground rod in the hole and drive it in.  tie in the floor rebar or webbing and that should do it  meaning next time i have  two pr0ng device its likely i wont see this transient voltage anymore

Re: AC Power grimlin

Reply #8
Kitchen counter experiment.
6 position power strip with a  three pr0ng cord to a 2 pr0ng receptacle adapter.
The power strip ground is isolated from the receptacle ground.

Pwr strip ground:  to neutral 35.6v, to hot 48.2v,  to a screw on the oven door 36.6v
Pwr strip ground:  thru a toaster and ammeter on 20ma scale to screw on oven door 0 ma.
Pwr strip ground:  thru ammeter on 20ma scale to oven door screw 0 ma
Pwr strip ground: thru my wet finger to oven door screw, no shock

Removed the 2 pr0ng adapter, outlet ground connected to pwr strip ground.
0v between pwr strip ground and oven door screw.

Don't know whats making the o in pr0ng come to up capital or zero?

Re: AC Power grimlin

Reply #9
interesting numbers almost if not identical to what i was getting yet you did not get shocked which i might be alble to contribute more towards the different floor conditions especially with no shock felt.  it was funny reading how you methodically safely stepped your way into a final wet finger test............ :giggle:

so i am going to carve out time to put my electronics repair bench back to the orginal problem state and see if i can capture the amps.  that part i may need to use my small buttstuffog meter to read anything.   The main reason i put so much emphisis on this is because i will be working on hot and cold chassis devices on this bench and in many cases hot components laying on this bench as well and the last thing i need is a transient screw with me.  .................... which brings me to another thread i will post in the lounge pertaining to a proper esd & soldering """HARD BOARD""" mat.  It seems this thing i have is a unicorn by 3m.