In this video he demonstrates the potential that exists in every home between your neutral return and your homes safety ground. There can be several volts, and it can vary based on what is currently drawing power in your home, as well as differ at various locations in your home if you measured it at various outlets. Thought I'd post this as it shows the reason for ground loops, why people incorrectly try to circumvent problems by lifting safety grounds, and why we devise methods like the 10 ohm resistor with capacitor and
diodes that only engage if there is truly a safety fault (see the tubecad "house ground" circuit) to get a audio ground reference that is also safe. Nice short video, for a subject that mystifies.
diodes that only engage if there is truly a safety fault (see the tubecad "house ground" circuit) to get a audio ground reference that is also safe. Nice short video, for a subject that mystifies.
Neutral is never involved in a ground loop unless there is a wiring mistake - or you're using a non-isolated device, which is not safe to connect to anything else. Neutral is connected only to the power transformer, isolated from any audio circuitry.
A radio or record player which is non-isolated (no power transformer) should be safe to operate by itself; but external connections are risky - a battery-powered input device may be OK, but I would investigate the circuit first.
A radio or record player which is non-isolated (no power transformer) should be safe to operate by itself; but external connections are risky - a battery-powered input device may be OK, but I would investigate the circuit first.
My new (to me) house has this problem in the garage, along with Sylvania-Zinsco Breaker Boxes which have a known problem of failing to open under excessive load as well as breakers welding to the bus bar.
I have an Electrician contracted to replace all the breaker boxes and correct the Ground/Return faulty wiring before I occupy the house.
In the US for residential house wiring, the power line transformer is a 240V center tap secondary feeding the service entrance. The center tap is "Neutral" which is also the return for each 120V half to the wiring. So the "neutral" does carry current.
Ground today should literally be a copper coated iron rod greater than 6' long (sometimes as long as 12'' or 3.7M depending on soil type) driven into the ground at the service entrance point, and connected to the ground buss of the breaker box. In the past when iron pipe or even copper pipe was used for water lines, the ground was often connected to the water line. This poses a problem when upgrading from iron pipe or copper pipe to PVC or nowadays PEX for the main water line into the house. Now the 'ground' is connected to the upgraded insulating water line and no longer functions as a ground.
I have an Electrician contracted to replace all the breaker boxes and correct the Ground/Return faulty wiring before I occupy the house.
In the US for residential house wiring, the power line transformer is a 240V center tap secondary feeding the service entrance. The center tap is "Neutral" which is also the return for each 120V half to the wiring. So the "neutral" does carry current.
Ground today should literally be a copper coated iron rod greater than 6' long (sometimes as long as 12'' or 3.7M depending on soil type) driven into the ground at the service entrance point, and connected to the ground buss of the breaker box. In the past when iron pipe or even copper pipe was used for water lines, the ground was often connected to the water line. This poses a problem when upgrading from iron pipe or copper pipe to PVC or nowadays PEX for the main water line into the house. Now the 'ground' is connected to the upgraded insulating water line and no longer functions as a ground.
I bought a Chinese amplifier which has a bad earth loop hum.You can buy an iFi Ground Defender which is is like a power plug/socket you plug into the power input on your amplifier and then plug in the power chord into it.I was very skeptical it would work but it did.No hum any more.
Common and ground are connected at the panel. There should never be a substantial potential between those two. It would be I-R losses in the common at the most. Bad connections in the outlet string may cause large differences, but then it is a fault in your wiring.
Never run a "tech ground". That is a separate ground rod where you ground part of the AC electrical system. You can have a potential there, and a lightning strike will create a big potential difference. Your cable ground often has a potential between it and your AC power ground. I refuse to have cable in my house. Lightning strikes in the area can blow everything between cable and power ground very impressively. I service electronics for a living. Seen it many times.
Hey TheGimp,
That's really scary! I'm glad you're dealing with it properly! I once lived in a house with aluminum wiring. They should condemn any place with that wiring in it.
Never run a "tech ground". That is a separate ground rod where you ground part of the AC electrical system. You can have a potential there, and a lightning strike will create a big potential difference. Your cable ground often has a potential between it and your AC power ground. I refuse to have cable in my house. Lightning strikes in the area can blow everything between cable and power ground very impressively. I service electronics for a living. Seen it many times.
Hey TheGimp,
That's really scary! I'm glad you're dealing with it properly! I once lived in a house with aluminum wiring. They should condemn any place with that wiring in it.
I have all copper wiring including to the heat pump.
I had a fuse box in my previous house (30 years ago). I upgraded it to a breaker panel myself and had a friend (certified Electrician) double check me. No problems found.
I could do this house myself, but at my age I would just as soon hire a professional to do it with all the permits, inspections etc. I have two out buildings with their own breaker boxes. I am wondering if I need additional ground rods at each box, or just the service entry point? From what I see of NEC 250, it is just at service entry, and a ground wire should go from there to each additional breaker box. I know there is no ground wire from the service entry point to the garage, and that has to be corrected. I need to double check the root cellar breaker box.
I had a fuse box in my previous house (30 years ago). I upgraded it to a breaker panel myself and had a friend (certified Electrician) double check me. No problems found.
I could do this house myself, but at my age I would just as soon hire a professional to do it with all the permits, inspections etc. I have two out buildings with their own breaker boxes. I am wondering if I need additional ground rods at each box, or just the service entry point? From what I see of NEC 250, it is just at service entry, and a ground wire should go from there to each additional breaker box. I know there is no ground wire from the service entry point to the garage, and that has to be corrected. I need to double check the root cellar breaker box.
What could be inside this device? Diodes or bridge with parallel capacitor and/or resistor?
Regards, Gerrit
Hi, yes.
The shield on cable TV is the world's largest ground loop. If you have a lightning strike, or anything that causes a large potential difference in ground away from you, then the potential in the ground near your house may be significantly different from the potential on the shield of the cable (being metallic). Ground potential can punch through the jacket even if it didn't come from another house. It will easily travel miles and have more than enough energy to arc and cause amazing damage.
They sell 75R 1:1 isolation transformers here I used to get rid of a lot of audio hum problems. That's in normal operation, no damage.
I have worked on many insurance claims where lightning laid waste to all kinds of things. The damage is distinctive. The worst is always anything connected to the cable that is plugged in, and if anything has a three wire ground - wow! So commonly a VCR plugged into an amplifier and TV, or just a TV into an audio system. Get between the cable ground and earth ground and you now have a preferred lightning path.
The shield on cable TV is the world's largest ground loop. If you have a lightning strike, or anything that causes a large potential difference in ground away from you, then the potential in the ground near your house may be significantly different from the potential on the shield of the cable (being metallic). Ground potential can punch through the jacket even if it didn't come from another house. It will easily travel miles and have more than enough energy to arc and cause amazing damage.
They sell 75R 1:1 isolation transformers here I used to get rid of a lot of audio hum problems. That's in normal operation, no damage.
I have worked on many insurance claims where lightning laid waste to all kinds of things. The damage is distinctive. The worst is always anything connected to the cable that is plugged in, and if anything has a three wire ground - wow! So commonly a VCR plugged into an amplifier and TV, or just a TV into an audio system. Get between the cable ground and earth ground and you now have a preferred lightning path.
Over here (UK), terrestrial TV was initially augmented only with satellite TV. With the roll out of fibre optic broadband, this is now superceded with streamed or on-demand content via a wi-fi router .
kind regards
Marek
kind regards
Marek
In America cable shield must be bonded to the same Earthing rod as mains power, before it can enter the house. This plus PE (Protective Earth or safety ground, the third wire) then make their own loop from equipment back and forth to the Earthing rod. A fancier mains power outlet strip that includes some lightning protection can have F-connectors for the cable built-in - shields are bonded to PE internally - which keeps that ground loop smaller and local (all at the equipment end). Always plug everything in the system into the same power strip, or at least the same outlet, to minimize the PE ground loop, for both hum and lightning damage reasons.
All good fortune,
Chris
All good fortune,
Chris
Hi Marek,
The same has happened in North America.
Hi Chris,
You're correct. They improved things over time. But installations I have seen are not solidly bonded to earth at the panel. There is sometimes so much energy involved in a closer strike, all bets are off and enough energy makes it through to toast things.
I have some of those bars. Depending on the quality, the earth bond may not be good enough, UL label aside.
When they brought my cable in, they did not bond the shield anywhere, my GF's house is the same. What should be done isn't always what the installer does. My house was a new build in 2001. Hers in the 1990's.
The same has happened in North America.
Hi Chris,
You're correct. They improved things over time. But installations I have seen are not solidly bonded to earth at the panel. There is sometimes so much energy involved in a closer strike, all bets are off and enough energy makes it through to toast things.
I have some of those bars. Depending on the quality, the earth bond may not be good enough, UL label aside.
When they brought my cable in, they did not bond the shield anywhere, my GF's house is the same. What should be done isn't always what the installer does. My house was a new build in 2001. Hers in the 1990's.
I’ll never forget the two times lightning struck right outside the house (but hit nothing electrical). One caused the telephone ringer to make one loud DING from induced current in the phone lines. Another caused my mom to draw an arc between her hand and the doorknob, and sent a ball of plasma down the hall. I’d hate to think what would have happened if we had (could afford) cable TV. Another one came down the service drop from the transformer, and the only things taken out were the water heater element and thermostat, and melting the insulation on the 12/2 Romex that fed the water heater. The power never even went out, but we saw the lightning hit the line at the pole with the transformer right across the street. The first clue that anything even happened was the cold bath water. Oh yeah - and the TV that was in use at the time was a tube black and white.
Hi Chris,
Yeah, you see all kinds of bad stuff out in the world. There's code, and then there's reality. It's a potential safety issue, so installers need to step up and do better. As things change over to fiber some of these issues will just age out. Hopefully.
All good fortune,
Chris
Yeah, you see all kinds of bad stuff out in the world. There's code, and then there's reality. It's a potential safety issue, so installers need to step up and do better. As things change over to fiber some of these issues will just age out. Hopefully.
All good fortune,
Chris
Hi wg_ski,
Lightning does weird stuff at times. Ball lightning seems to obey its own laws of physics. It can go places where you'd never expect and avoid places you though for sure would get nailed. I've seen a row of drawer handles vertically get melted, it had nowhere to go. It jumped off a nearby speaker wire. Don't ask about that system.
Hey Chris,
Yep. Installers pretty much do as they please. I saw telecom new installations that were horrible. When my guys did a bad job, I made them reinstall whatever wasn't up to our standards. If they did a bad job again, they were let go.
Lightning does weird stuff at times. Ball lightning seems to obey its own laws of physics. It can go places where you'd never expect and avoid places you though for sure would get nailed. I've seen a row of drawer handles vertically get melted, it had nowhere to go. It jumped off a nearby speaker wire. Don't ask about that system.
Hey Chris,
Yep. Installers pretty much do as they please. I saw telecom new installations that were horrible. When my guys did a bad job, I made them reinstall whatever wasn't up to our standards. If they did a bad job again, they were let go.
In my later life I did retail A/V install, after decades as service manager. Refused the gig as install manager because I'd had no choice in hiring the existing crew, who were very poorly paid and widely varying quality. I put myself in a First Sergeant role, in the field, lead by example and educate. Turned out to be a great job for an older guy and kept me from gaining weight. Sadly, that's no longer true.
Install is more important than it's given credit for. Plenty to go wrong and real consequences. And I found that interactions with homeowners can be very personally rewarding. It's good to meet the folk you're working for.
All good fortune,
Chris
Install is more important than it's given credit for. Plenty to go wrong and real consequences. And I found that interactions with homeowners can be very personally rewarding. It's good to meet the folk you're working for.
All good fortune,
Chris
Completely agree!
I did the same with telecom staff, and I didn't hire them either. It works.
I really loved interacting with the clients, very rewarding. And yes, it kept the weight off. lol!
I did the same with telecom staff, and I didn't hire them either. It works.
I really loved interacting with the clients, very rewarding. And yes, it kept the weight off. lol!
I use coax lightning arresters on my cable entry, along with my 2M antenna entry and my OTA cable entry.
30 plus years ago I went home at lunch to close the windows as a storm was approaching. While standing in the kitchen after closing the last window, a bolt of lightning hit a nearby power line (or ground wire for such) ball lightning came out of the light switch next to the door and floated across the kitchen and vanished. The light switch was toast (literally carbonized) along with a Satchell Carlson color TV, and my bench oscilloscope downstairs. My line transformer was later found to have an open neutral.
To plagiarize Samuel Clemens :
Thunder is good, thunder is impressive; but it is lightning that does the work.
30 plus years ago I went home at lunch to close the windows as a storm was approaching. While standing in the kitchen after closing the last window, a bolt of lightning hit a nearby power line (or ground wire for such) ball lightning came out of the light switch next to the door and floated across the kitchen and vanished. The light switch was toast (literally carbonized) along with a Satchell Carlson color TV, and my bench oscilloscope downstairs. My line transformer was later found to have an open neutral.
To plagiarize Samuel Clemens :
Thunder is good, thunder is impressive; but it is lightning that does the work.