ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: 1 ... 4 5 [6] 7 8 9   Go Down

Author Topic: Test your grounds regularly!  (Read 31964 times)

Steve Bradbury

  • Newbie
  • *
  • Offline Offline
  • Posts: 47
Re: Test your grounds regularly!
« Reply #50 on: December 10, 2014, 04:02:49 PM »

T = Earth (from French Terre)
N = Neutral
C = Combined
S = Separate
I = isolated
CPC = circuit protective conductor (earth wire)
PME = Protective multiple earthing
DNO = Distribution Network Operators

So TN-C-S = Earth/Neutral-combined-separate.
A TN-S would have separate earth and neutral conductors back to the substation. The earth would typically be the armoured shield of the supply cable.

The IET (formerly IEE) have a leaflet that explains it all. If you type “earthing your questions answered” into Google you should find it. When you click on the link it just downloads a pdf so I couldn’t find a direct link.
Logged

Tim McCulloch

  • SR Forums
  • Hero Member
  • *
  • Offline Offline
  • Posts: 23729
  • Wichita, Kansas USA
Re: Test your grounds regularly!
« Reply #51 on: December 10, 2014, 04:12:58 PM »

T = Earth (from French Terre)
N = Neutral
C = Combined
S = Separate
I = isolated
CPC = circuit protective conductor (earth wire)
PME = Protective multiple earthing
DNO = Distribution Network Operators

So TN-C-S = Earth/Neutral-combined-separate.
A TN-S would have separate earth and neutral conductors back to the substation. The earth would typically be the armoured shield of the supply cable.

The IET (formerly IEE) have a leaflet that explains it all. If you type “earthing your questions answered” into Google you should find it. When you click on the link it just downloads a pdf so I couldn’t find a direct link.

http://electrical.theiet.org/wiring-matters/16/earthing-questions.cfm?type=pdf
Logged
"If you're passing on your way, from Palm Springs to L.A., Give a wave to good ol' Dave, Say hello to progress and goodbye to the Moonlight Motor Inn." - Steve Spurgin, Moonlight Motor Inn

Kevin Graf

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 343
Re: Test your grounds regularly!
« Reply #52 on: December 12, 2014, 09:39:47 AM »

Jim Brown has a 3 page summary:

POWER SYSTEM ARCHITECTURES IN EUROPE AND THE AMERICAS
Five different systems are used for the distribution of electric power in public 'low voltage'
systems, and these may also be used in private systems. These systems differ primarily
in how they treat the grounded conductor (neutral) and it's relationship to the
Protective Earth (PE) conductor. ('Low voltage' in this context means, in practice, systems
with phase voltages between 100 V and 240 V.)


In his paper:

Power and Grounding for Audio and Video Systems
A White Paper for the Real World – International Version
Jim Brown
Audio Systems Group, Inc.

http://www.audiosystemsgroup.com/SurgeXPowerGround.pdf

More Jim Brown papers:

http://www.audiosystemsgroup.com/publish.htm
Logged
Speedskater

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 17172
  • Hickory, Mississippi, USA
    • Resotune
Re: Test your grounds regularly!
« Reply #53 on: December 18, 2014, 11:13:01 AM »

I don't know if this is the right thread, but I got a little tingle the other day. I was working on my RO filter under my sink and had a trouble light plugged into a GFCI outlet nearby, while that outlet has no ground connection, since my house wiring is old.

While reaching across to grab my water faucet, my arm was touching the grounded bail from my trouble light, I felt the unmistakeable tingle of electrons and holes moving through my arm. It was pretty low level but I quickly released and decided to meter between the two exposed metal parts. My high impedance VOM measured 106V, I didn't bother to test for current and ASSume it was less than 6mA required to trip a GFCI. I finished the project at hand, but a day later decided to revisit to investigate further. To my surprise a day later I only measured 3V between the same grounds.

My suspicion is that something plugged into that GFCI circuit is leaking to the ground line. I tried to recreate exactly the same conditions but a day later low voltage.  It is not unusual to measure voltage on a floating ground with high impedance meter, but it is usually too little current to feel.

I still feel safe with the GFCI in place and am not quite sure why the sink was grounded since I replaced my steel water main from the street with ABS plastic a couple years ago (maybe there's more iron in my water than I thought. The water sediment filter is usually red). The panel in my laundry room may ground the plumbing there.

I am almost tempted to ground my kitchen outlet to the cold water pipe, while I am not sure where it is getting ground. I guess I could run a ground wire from my panel, but I don't feel like rewiring my  house.

JR
   
Logged
Cancel the "cancel culture". Do not participate in mob hatred.

Stephen Swaffer

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2671
Re: Test your grounds regularly!
« Reply #54 on: December 18, 2014, 12:47:11 PM »

If you have metallic plumbing in the house it should be grounded to the panel-which should have an grounding electrode/ground rods-might not hurt to make sure they didn't just rely on a metallic water supply pipe that no longer exists.  If the water system is grounded, it wouldn't be  an entirely bad idea to ground the GFCI receptacle there-since no ground is acceptable, any ground should be OK.

Another interesting test would be with a NCTV to see which part was hot (might show both)-which would help diagnosis.

Another thought, is a poor neutral connection in your panel can potentially energize anything that should be grounded-depending on grounding electrode/soil conditions and loads turned on in the house. 
« Last Edit: December 18, 2014, 12:51:34 PM by Stephen Swaffer »
Logged
Steve Swaffer

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 17172
  • Hickory, Mississippi, USA
    • Resotune
Re: Test your grounds regularly!
« Reply #55 on: December 18, 2014, 01:53:07 PM »

If you have metallic plumbing in the house it should be grounded to the panel-which should have an grounding electrode/ground rods-might not hurt to make sure they didn't just rely on a metallic water supply pipe that no longer exists.  If the water system is grounded, it wouldn't be  an entirely bad idea to ground the GFCI receptacle there-since no ground is acceptable, any ground should be OK.

Another interesting test would be with a NCTV to see which part was hot (might show both)-which would help diagnosis.

Another thought, is a poor neutral connection in your panel can potentially energize anything that should be grounded-depending on grounding electrode/soil conditions and loads turned on in the house.

I will look into this further... but a day later the voltage was only 3V so kind of odd...

JR
Logged
Cancel the "cancel culture". Do not participate in mob hatred.

Jonathan Johnson

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3209
  • Southwest Washington (state, not DC)
Re: Test your grounds regularly!
« Reply #56 on: December 18, 2014, 01:57:24 PM »

I don't know if this is the right thread, but I got a little tingle the other day. I was working on my RO filter under my sink and had a trouble light plugged into a GFCI outlet nearby, while that outlet has no ground connection, since my house wiring is old.

While reaching across to grab my water faucet, my arm was touching the grounded bail from my trouble light, I felt the unmistakeable tingle of electrons and holes moving through my arm. It was pretty low level but I quickly released and decided to meter between the two exposed metal parts. My high impedance VOM measured 106V, I didn't bother to test for current and ASSume it was less than 6mA required to trip a GFCI. I finished the project at hand, but a day later decided to revisit to investigate further. To my surprise a day later I only measured 3V between the same grounds.

My suspicion is that something plugged into that GFCI circuit is leaking to the ground line. I tried to recreate exactly the same conditions but a day later low voltage.  It is not unusual to measure voltage on a floating ground with high impedance meter, but it is usually too little current to feel.

Possible scenario (don't have time to draw a diagram):

Upstream outlet is fed with a 2-wire cable, no ground.

There is a 3-wire cable (hot/neutral/ground) from the upstream outlet to the GFCI. The ground wire is connected to both the upstream outlet and the GFCI. (Maybe there isn't a 3-wire cable between the two outlets in your home, in which case the rest of this scenario is bunk.)

A device plugged into the upstream outlet with a three-prong cord has a hot-to-chassis fault, energizing the "ground" wire that runs between the upstream outlet and the GFCI. Because this ground wire has no connection to the neutral in the main panel or elsewhere, there is no path for the return current so the breaker does not trip, until...

You plug in your trouble light with a 3-wire cord into the GFCI, and the ground wire is bonded to the metal shell. You touch the shell and the faucet at the same time, and receive an electric shock. The GFCI does not trip, because the fault is upstream of the GFCI, and there is no imbalance measured between hot and neutral by the GFCI, and the GFCI does not monitor for current or voltage in the ground wire.

A day later, you unplugged whatever was upstream, or maybe it (the refrigerator?) wasn't operating at the time so the fault was not energized, resulting in only a 3V reading.
Logged
Stop confusing the issue with facts and logic!

Jonathan Johnson

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3209
  • Southwest Washington (state, not DC)
Re: Test your grounds regularly!
« Reply #57 on: December 18, 2014, 02:05:11 PM »

A day later, you unplugged whatever was upstream, or maybe it (the refrigerator?) wasn't operating at the time so the fault was not energized, resulting in only a 3V reading.

P.S. -- I don't know if it was you or someone else who wired your kitchen, but the more I think about this (without enough information  :) ), the more I'm suspecting a fault in the compressor of the refrigerator. Here's why.

It's not uncommon for electricians to put the refrigerator outlet as the first in the circuit, then feed a GFCI on the countertop. You generally do not want the refrigerator on a GFCI (to prevent loss of food if it accidentally gets tripped). So maybe the electrician did that, but the home run he tapped into to energize that refrigerator receptacle happened to be a 2-wire cable. Since the new cable he installed between that and the GFCI would have been 3-wire, he dutifully connected the ground wire at both ends.

Then, your refrigerator compressor motor developed a hot-to-chassis ground fault. Because the ground wire in the circuit is not connect to neutral (at least isn't not a bootleg ground!), the fault does not trip the circuit breaker. Because the refrigerator is upstream of the GFCI, it does not trip the GFCI. And because it's a refrigerator, it cycles on and off -- giving you the varying readings from 106V to 3V.
Logged
Stop confusing the issue with facts and logic!

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 17172
  • Hickory, Mississippi, USA
    • Resotune
Re: Test your grounds regularly!
« Reply #58 on: December 18, 2014, 02:35:26 PM »

Possible scenario (don't have time to draw a diagram):

Upstream outlet is fed with a 2-wire cable, no ground.

There is a 3-wire cable (hot/neutral/ground) from the upstream outlet to the GFCI. The ground wire is connected to both the upstream outlet and the GFCI. (Maybe there isn't a 3-wire cable between the two outlets in your home, in which case the rest of this scenario is bunk.)

A device plugged into the upstream outlet with a three-prong cord has a hot-to-chassis fault, energizing the "ground" wire that runs between the upstream outlet and the GFCI. Because this ground wire has no connection to the neutral in the main panel or elsewhere, there is no path for the return current so the breaker does not trip, until...

You plug in your trouble light with a 3-wire cord into the GFCI, and the ground wire is bonded to the metal shell. You touch the shell and the faucet at the same time, and receive an electric shock. The GFCI does not trip, because the fault is upstream of the GFCI, and there is no imbalance measured between hot and neutral by the GFCI, and the GFCI does not monitor for current or voltage in the ground wire.

A day later, you unplugged whatever was upstream, or maybe it (the refrigerator?) wasn't operating at the time so the fault was not energized, resulting in only a 3V reading.
Found it..... the leakage path is a 3 wire plug electric kettle plugged directly into the GFCI outlet. I unplugged the  kettle to probe between the outlet ground and the sink...

Today with the kettle unplugged I measure 5V between grounds, with the kettle plugged in I measure 106V. Since I am on my way out to go shopping I think I will get a new kettle for Christmas.  ;D ;D ;D

Problem solved for now and hopefully if the shock was strong enough the GFCI would trip... We can stick a fork in this one... as always makes sense after the fact.

JR

Logged
Cancel the "cancel culture". Do not participate in mob hatred.

Mike Sokol

  • Moderator
  • Hero Member
  • *****
  • Offline Offline
  • Posts: 3361
  • Lead instructor for the No~Shock~Zone
    • No~Shock~Zone Electrical Safety
Re: Test your grounds regularly!
« Reply #59 on: December 18, 2014, 02:43:33 PM »

Found it..... the leakage path is a 3 wire plug electric kettle plugged directly into the GFCI outlet. I unplugged the  kettle to probe between the outlet ground and the sink...

Today with the kettle unplugged I measure 5V between grounds, with the kettle plugged in I measure 106V. Since I am on my way out to go shopping I think I will get a new kettle for Christmas.  ;D ;D ;D

Problem solved for now and hopefully if the shock was strong enough the GFCI would trip... We can stick a fork in this one... as always makes sense after the fact.

JR

This is exactly the sort of thing that can happen to an RV that has an open EGC on its shore power cord. Any inside appliance with a grounded plug can energize the RV's electrical ground plane, and feed through the entire electrical system grounds. It's what I call a Reflected Hot Skin Voltage since I like to come up with names for fails like this.

ProSoundWeb Community

Re: Test your grounds regularly!
« Reply #59 on: December 18, 2014, 02:43:33 PM »


Pages: 1 ... 4 5 [6] 7 8 9   Go Up
 



Site Hosted By Ashdown Technologies, Inc.

Page created in 0.051 seconds with 25 queries.