Uncommon power and ground question

[James6600]

I was thinking about noise floor and RFI from the house, line and ground. If I run a separate ground rod not bonded to the main line ground and attach all my equipment ( hear me out ) then power all my equipment through my true isolation transformer ( it’s all two prong plug ) what effects in theory or experience do you think this would have ?

 

[bunangst]

I was thinking about noise floor and RFI from the house, line and ground. If I run a separate ground rod not bonded to the main line ground and attach all my equipment ( hear me out ) then power all my equipment through my true isolation transformer ( it’s all two prong plug ) what effects in theory or experience do you think this would have ?

Un-bonded ground rods create opportunity for voltage differential (and current) on the ground bus.

Your RFI is more likely from un-bonded equipment or being received by an antenna. Does the noise floor get quiet when disconnecting the antenna?

 

[James6600]

Unhooking antenna drops dbm -10. With an isolation transformer there would be no physical connection to power. The isolated ground rod would only be connected to the coax lightning arrestor, the metal case of the antenna tuner and the metal case of the tube hybrid transceiver with a 2 prong non grounded A/C cord. The ground rod would be the only physical connection to anything. The ground rod basically would just be an RFI/static ground. With an isolation transformer there is no ground or neutral per say. True ISO transformers can only shock you if you hold both leads of the A/C line. One lead, either lead will not shock you even if you’re holding the ground rod in your other hand. It’s the process used to work on live chassis tube radios. So I have a -110DBm with antenna. A -120DBm without antenna and a -130DBm with radio off. The station monitor output of the transceiver is wired to an RSP-dx-2 then USB to computer so the number values don’t mean anything only the differences in the values.

 

[K4EET]

Having an independent station ground from your electrical panel's ground is a very bad idea. There is a very high probability that the two grounds will have a significant potential difference, especially under certain conditions. That alone raises life-threatening concerns. Mind you, I am not the resident safety expert here on equipment grounds, but the following AI response is raising red flags. Now AI responses are not always spot-on, but I would caution you to at least carefully consider this Google Gemini response based on an input of "hazard of having two independent station grounds." Proceed with extreme caution in your planning and rationalization. Your life is at stake.

AI Overview

The primary hazard of maintaining two independent station grounds is the creation of large, destructive electrical potential differences between them during a lightning strike or power fault. Because dirt has electrical resistance, separate ground rods are not at the same voltage level. When they are left unbonded, any interconnected equipment bridging the two grounds effectively becomes the wire that ties them together, resulting in severe safety and operational risks. [1, 2, 3, 4]

1. High-Voltage Shock and Fire Risks

• • Voltage differentials: A nearby lightning strike can elevate the earth potential at one ground rod to thousands of volts while the other remains lower. [1, 2]
  • Lethal bridges: If a person touches two pieces of equipment connected to different grounds simultaneously, the voltage differential will drive a lethal current through the body. [1, 2]
  • Electrical fires: The extreme current seeking equilibrium between the two independent rods can easily melt data lines, coax shields, and internal chassis wiring, triggering immediate structural fires. [1, 2]

2. Destruction of Equipment via Lightning Currents

• • Alternative paths: If your radio or electrical station utilizes an isolated ground rod for antennas or RF equipment, lightning energy hitting that antenna will travel down the feedline. [1]
  • Chassis pathing: Since the independent rod is not tied to the main utility ground, the strike finds its path to the main grid directly through your radio, power supply, and computer circuitry, instantly frying your hardware. [1]

3. Ground Loops and Persistent Data Corruption

• • Circulating currents: Even under non-fault conditions, minor differences in soil resistance and utility loads create circulating AC currents between the two independent ground points. [1]
  • Signal degradation: These ground loops introduce heavy electromagnetic interference (EMI) or a constant 60Hz hum into audio lines, radio transmissions, and data networks. [1, 2, 3]
  • Component fatigue: This continuous trickle of stray voltage degrades sensitive solid-state electronics over time, causing intermittent "ghost" errors and premature hardware failure. [1]

4. Failure of Overcurrent Protection Devices

• • High-impedance loops: A dedicated, unbonded ground rod relies purely on earth resistance to complete a fault circuit.
  • Unbroken faults: Because dry or sandy soil has high electrical impedance, a short-to-ground on an isolated rod will fail to draw enough current to trip a standard circuit breaker. This leaves the entire metal housing of your equipment permanently energized and dangerous to touch. [1, 2, 3]

 

[WB5UOM]

At what frequency is the receiver tuned to when you see the -120 with no antenna. and -110 with antenna?

 

[James6600]

At what frequency is the receiver tuned to when you see the -120 with no antenna. and -110 with antenna?

20m tune at time of reading. Antenna is 10m half wave horizontal dipole. All bands between 10m through 20m 1.4 or less SWR through tuner measured with two separate meters. The DBm numbers are from SDRuno running RSPdx-2 patched in to the station monitor output on transceiver. I wouldn’t put much faith in the -120 or -110 reading as that’s what SDRuno is interpreting. But the 10DBm difference should be somewhat accurate I would think.

 

[James6600]

Having an independent station ground from your electrical panel's ground is a very bad idea. There is a very high probability that the two grounds will have a significant potential difference, especially under certain conditions. That alone raises life-threatening concerns. Mind you, I am not the resident safety expert here on equipment grounds, but the following AI response is raising red flags. Now AI responses are not always spot-on, but I would caution you to at least carefully consider this Google Gemini response based on an input of "hazard of having two independent station grounds." Proceed with extreme caution in your planning and rationalization. Your life is at stake.

There wouldn’t be two grounds as there would be no connection to house mains or line in. With an ISO transformer you have to think of it as a Tesla coil or a 120v A/C battery or WiFi powering the radio. There is an insulated air gap powering the radio via magnetic fields from a coil hooked to house mains, then an air gap, then another coil converts the magnetic fields back to power to radio. The radio is not connected physically to the electric grid. Like holding a fluorescent lightbulb under high tension wires and it lights up.

 

[K4EET]

There wouldn’t be two grounds as there would be no connection to house mains or line in. With an ISO transformer you have to think of it as a Tesla coil or a 120v A/C battery or WiFi powering the radio. There is an insulated air gap powering the radio via magnetic fields from a coil hooked to house mains, then an air gap, then another coil converts the magnetic fields back to power to radio. The radio is not connected physically to the electric grid. Like holding a fluorescent lightbulb under high tension wires and it lights up.

It sounds like you have your mind made up about carrying out your plan. The equipment may be isolated but that is exactly the problem which causes a potentially lethal voltage difference. The first time you touch two isolated pieces of equipment at the same time you'll find out what I mean (if you survive). Reference point #1 bullet #2 in my post #4 above.

 

[prcguy]

In the late 1970s when I didn't know any better I had a separate ground rod for my antenna/station at the far end of the house from the main AC entry point. It put about 90VAC on my antenna shield compared to the third prong ground in my room outlets due to the extra ground rod being closer to my neighbors AC entry panel and ground rod, fed from a different transformer on the block that was at a different ground potential. It would shock the crap out of me when disconnecting an antenna and even shocked an FCC field engineer who was inspecting my station for a violation.

At your house AC entry point your ground rod or water pipe ground or UFER ground will be connected to the neutral line coming from the power company. The ground rod ground is mainly a safety device prescribed by the NEC and using an isolation transformer and a separate ground rod would circumvent the common neutral/ground and NEC rules.

Before embarking on a wild goose chase for noise that will probably not be related to your ground I would recommend powering your radios from a battery to see if that has a lower noise floor, which it probably wont. You can even turn off breakers in the house to see of any circuits have something generating RFI, which is way more likely than some noise brought in by your power company.

 

[MUTNAV]

In addition to PRCGUY s idea, I would do a real thorough inspection of your current Ground / Neutral system. I've seen far to many "solutions" to problems that were just trying to correct for other problems that were undiagnosed / needed to be fixed.

Sometimes great to think outside of the box, good call to ask and talk about it before implementing.

Thanks
Joel

 

[prcguy]

In addition to PRCGUY s idea, I would do a real thorough inspection of your current Ground / Neutral system. I've seen far to many "solutions" to problems that were just trying to correct for other problems that were undiagnosed / needed to be fixed.

Sometimes great to think outside of the box, good call to ask and talk about it before implementing.

Thanks
Joel

In addition to MUTNAVs comments it would be good to test the existing ground rod resistance to ground using an appropriate meter. I found my home ground rod was about 24 ohms if I remember right and after replacing the old loose 5/8" 8ft rod with a 3/4" 10ft my ground resistance went down below 5 ohms which is the goal.

 

[WB5UOM]

You dont say if you are living in town or out in the country, but why do you think -110dbm is a bad thing ? its like S3. and is your measurement at noon or at night? you did say 20m.
Im having trouble seeing the serious problem.

 

[James6600]

MUTNAV PRCGUY thanks for the reply’s. This is all in theory. I don’t have a ground problem or a noise or RFI problem. I run a 10 amp variac to a 2kva transformer that I use for tube radio repair. If needed I can explain the schematic and operation of this system but it’s lengthy. Hooking to a battery is an excellent idea and in doing so would isolate a radio from the grid. The antenna system would still be grounded by ground plane if used, lightning arrester that should be used and the coax shield would ground the radio equipment. But the ground lugs on the radio equipment should also run back to the same point as the lightning arrestor. Unless I missed something this is the system used on most off grid battery powered radio systems. In practice this should have a really low noise floor so I’ve read. My radio is a hybrid transistor with tube finals and cannot be hooked directly to a battery. Hence my theoretical question if I isolated my A/C power and my ground rod from the grid what might be the effect on noise floor with everything being LED and switching power supplies that are really cheap and dirty and feed noise through the neutral back to the breaker box, jumper to the ground and down to the ground rod. Again I don’t have a problem I was curious if any of the more experienced guys that still have this equipment have tried it or if someone more intelligent than me had a theory they would share.

 

[James6600]

You dont say if you are living in town or out in the country, but why do you think -110dbm is a bad thing ? its like S3. and is your measurement at noon or at night? you did say 20m.
Im having trouble seeing the serious problem.

No problem. This was just an experimental thought I had. I live in the country and I have gathered up most of the towers I need to put up a 160m full loop and have to add a larger ground system. I figured if there’s no info or thoughts on this I would swap the A/C plug from the wall outlet to the ISO transformer before I hook the new ground system to the grid ground and take a before and after noise floor reading. I was curious if anyone had experience or thoughts. I didn’t want to reinvent the wheel.

 

[prcguy]

MUTNAV PRCGUY thanks for the reply’s. This is all in theory. I don’t have a ground problem or a noise or RFI problem. I run a 10 amp variac to a 2kva transformer that I use for tube radio repair. If needed I can explain the schematic and operation of this system but it’s lengthy. Hooking to a battery is an excellent idea and in doing so would isolate a radio from the grid. The antenna system would still be grounded by ground plane if used, lightning arrester that should be used and the coax shield would ground the radio equipment. But the ground lugs on the radio equipment should also run back to the same point as the lightning arrestor. Unless I missed something this is the system used on most off grid battery powered radio systems. In practice this should have a really low noise floor so I’ve read. My radio is a hybrid transistor with tube finals and cannot be hooked directly to a battery. Hence my theoretical question if I isolated my A/C power and my ground rod from the grid what might be the effect on noise floor with everything being LED and switching power supplies that are really cheap and dirty and feed noise through the neutral back to the breaker box, jumper to the ground and down to the ground rod. Again I don’t have a problem I was curious if any of the more experienced guys that still have this equipment have tried it or if someone more intelligent than me had a theory they would share.

I was going to post a pic of my 2KVA isolation transformer with ground switch that will ground at input, output or floating and it has a 20A Corcom RFI filter at the output socket and a separate 20A variac, but I somehow misplaced the beast. If you configured your transformer with a switchable ground and tested it with a good AC line filter it could tell you some things about noise riding on your AC power ground or if severing the ground would have an useful affect.

Looking at one of my HF rigs that can display dBm it looks like my noise floor right now on 20m with an 80-10m EFHW is around -110dBm. But I don't know what RBW or VBW the Elecraft P3 display is using and that is important as changing the RBW by 2X or 10X will change the spectrum display noise floor by 3dB or 10dB.

 

[James6600]

I was going to post a pic of my 2KVA isolation transformer with ground switch that will ground at input, output or floating and it has a 20A Corcom RFI filter at the output socket and a separate 20A variac, but I somehow misplaced the beast. If you configured your transformer with a switchable ground and tested it with a good AC line filter it could tell you some things about noise riding on your AC power ground or if severing the ground would have an useful affect.

Looking at one of my HF rigs that can display dBm it looks like my noise floor right now on 20m with an 80-10m EFHW is around -110dBm. But I don't know what RBW or VBW the Elecraft P3 display is using and that is important as changing the RBW by 2X or 10X will change the spectrum display noise floor by 3dB or 10dB.

Your variac system is configured very similar to mine but my switchable ground stops at the ISO Trans metal case not the ISO output receptacle. The reason I do this is because the all the equipment under test is not grounded. If one would modify the equipment under test with a grounded power cord and safety capacitors it can still inadvertently shock you but probably won’t kill you unless the capacitors short. Without the ground on the ISO output there is no hazard unless you touch both leads of the twin lead A/C cord at the same time. But you have one you probably know this. I don’t modify my tube stuff with a grounded power cord but I typically add a polarized plug to keep the chassis from being hot. Your panadaptor readings are in line with mine. If I zoom out I can get 2000KHz VBW. I never run that, I typically zoom in to only see the entire voice area of the band. N1UGK has an article very similar to my setup. At 8am my noise floor was -105 to -107 with heat pump running. At 8:30am it’s -99 to -103 without heat pump running. My ground rod is directly below the meter, breaker box other side of wall from meter with my heat pump less than 2’ from wall under meter. So not ideal on heat pump. Our soil is highly conductive also. I need to move the heat pump.

 

[MUTNAV]

If I understand what you're saying right, you want to use an arrangement that is usually used ot just isolate test equipment (ie O'scope carts sometimes have a grounded plug that isn't grounded.) To power an entire radio bench or room?

Thanks
Joel

 

[James6600]

If I understand what you're saying right, you want to use an arrangement that is usually used ot just isolate test equipment (ie O'scope carts sometimes have a grounded plug that isn't grounded.) To power an entire radio bench or room?

Thanks
Joel

The only thing powered is the transceiver the rest is all passive with the exception of my computer that runs the pan adapter and for the temporary time it takes to get measurements I could isolate it too