Ground Rod Theory

[ggunn]

In a possibly related story...

When I was a young man I used to listen to KAAY AM in Little Rock, AR, late at night (Bleaker Street with DJ Clyde Clifford). I lived in south Louisiana, so although KAAY was a clear channel station at night, reception could be iffy. One night when I was parked with my GF, we wanted to listen to Clyde, but someone had broken off the antenna on my 1962 Chevy and KAAY wouldn't come in. On a whim I pulled a length of uninsulated wire and my tire iron out of my trunk; I drove the tire iron into the ground and ran the wire to it from the stump of my antenna mast. KAAY came in like gangbusters as if it were a local station.

 

[electrofelon]

...... One night when I was parked with my GF......

Ok you got the radio working, continue the story, details details!

 

[ggunn]

Ok you got the radio working, continue the story, details details!

A gentleman doesn't kiss and tell.

 

[GoldDigger]

A gentleman doesn't kiss and tell.

But what about you?

 

[GoldDigger]

In a possibly related story...

When I was a young man I used to listen to KAAY AM in Little Rock, AR, late at night (Bleaker Street with DJ Clyde Clifford). I lived in south Louisiana, so although KAAY was a clear channel station at night, reception could be iffy. One night when I was parked with my GF, we wanted to listen to Clyde, but someone had broken off the antenna on my 1962 Chevy and KAAY wouldn't come in. On a whim I pulled a length of uninsulated wire and my tire iron out of my trunk; I drove the tire iron into the ground and ran the wire to it from the stump of my antenna mast. KAAY came in like gangbusters as if it were a local station.

In a nice role reversal, you made the entire car become the antenna!

 

[drcampbell]

In a possibly related story...

When I was a young man I used to listen to KAAY AM in Little Rock, AR, late at night (Bleaker Street with DJ Clyde Clifford). I lived in south Louisiana, so although KAAY was a clear channel station at night, reception could be iffy. One night when I was parked with my GF, we wanted to listen to Clyde, but someone had broken off the antenna on my 1962 Chevy and KAAY wouldn't come in. On a whim I pulled a length of uninsulated wire and my tire iron out of my trunk; I drove the tire iron into the ground and ran the wire to it from the stump of my antenna mast. KAAY came in like gangbusters as if it were a local station.

I had similar luck hacking a 27-MHz walkie-talkie when I was a teenager.

One end of the final output transformer went to the antenna; the other end to a piece of foil-faced cardboard lining the plastic housing. I connected that other end to a "good" ground (the cast-iron radiator in my 2nd-floor bedroom) and about tripled its effectiveness. No telling what difference an actual ground plane would have made.

I also made 11-meter and 5.5-meter wire dipoles. Interesting results -- because it was horizontally polarized, I could contact only a very few users, and because it couldn't be turned, I could only contact people north or south of me. But I was able to talk to people hundreds of miles away on 100 mW.

Nobody's debating the utility of good grounds for radio-frequency work.

 

[GoldDigger]

I had similar luck hacking a 27-MHz walkie-talkie when I was a teenager.

One end of the final output transformer went to the antenna; the other end to a piece of foil-faced cardboard lining the plastic housing. I connected that other end to a "good" ground (the cast-iron radiator in my 2nd-floor bedroom) and about tripled its effectiveness. No telling what difference an actual ground plane would have made.

I also made 11-meter and 5.5-meter wire dipoles. Interesting results -- because it was horizontally polarized, I could contact only a very few users, and because it couldn't be turned, I could only contact people north or south of me. But I was able to talk to people hundreds of miles away on 100 mW.

Nobody's debating the utility of good grounds for radio-frequency work.

One of the things that the foil based cardboard did was couple to your hand to provide a more effective counterpoise.
Producing a hand-held radio that did not receive as well if you just set it down.
Opposite problem with cell phone antennas where, with no external radiator, your hand could just shield the internal antenna.

 

[ggunn]

In a nice role reversal, you made the entire car become the antenna!

No, I think I made the planet the antenna; the antenna circuit is insulated from the car body, which is "grounded" to the negative side of the 12V electrical system.

 

[LarryFine]

No, I think I made the planet the antenna; the antenna circuit is insulated from the car body, which is "grounded" to the negative side of the 12V electrical system.

The received signal normally develops a voltage between the antenna lead and the car body.

Your setup created a voltage between the earth and the car body.

Since the earth is ground, your car's body became the receiving antenna element.

If it was DC, you could say you inadvertently flipped the polarity.


To add, yes, to the car, the earth seemed to be the source of the signal.

But, to the earth, the car's body seemed to be the source of the signal.

 

[Speedskater]

at AM broadcast band frequencies, often Planet Earth is half of the transmitting antenna. But depending on topography, the ground wave is only good for maybe 30 miles.

 

[kwired]

Safest system is ungrounded - with caveat that it is monitored so disconnect or warning flasher if one side gets grounded.

So, some type of ground reverence (aka ground rod) needed for reference point.

watch for it in a future code revision, the mfg need new requirements sell more 'advanced' and pricey hardware.

Still too many "dirt worshippers" that need to be converted before that will happen.

 

[LarryFine]

With a grounded system, the voltage(s) to earth is relatively fixed and known.

With an ungrounded system, the voltage(s) to earth could be much higher with, say, contact with a primary.

Is my thinking in error?

 

[drcampbell]

... With an ungrounded system, the voltage(s) to earth could be much higher with, say, contact with a primary.

Is my thinking in error?

I think a lot of people think about only their own scope of work and don't see the bigger picture.

 

[electrofelon]

With a grounded system, the voltage(s) to earth is relatively fixed and known.

With an ungrounded system, the voltage(s) to earth could be much higher with, say, contact with a primary.

Is my thinking in error?

Could you explain more specifically the situation you are envisioning?

 

[jim dungar]

With a grounded system, the voltage(s) to earth is relatively fixed and known.

With an ungrounded system, the voltage(s) to earth could be much higher with, say, contact with a primary.

Is my thinking in error?

The voltage depends on if the system is delta or wye, or center tapped.
Most of us are familiar with system where the lower Line-Neutral voltage is intentionally tied to ground, however it is possible to have the high Line-Line voltage grounded instead.

When there is a single fault an ungrounded system simply becomes a grounded system with the L-L or L-N voltage depending which conductor is faulted.

Even so-called ungrounded systems actually have some capacitive coupling to ground which produces an unstable voltage that looks like a L-N connection exists, but there are circumstances with these systems where a fault can affect the coupling capacitance can cause a voltage 2X the normal L-L voltage stressing the conductor and system insulations.

 

[drcampbell]

One of the things that the foil [faced] cardboard did was couple to your hand to provide a more effective counterpoise.
Producing a hand-held radio that did not receive as well if you just set it down.
Opposite problem with cell phone antennas where, with no external radiator, your hand could just shield the internal antenna.

That's why I specifically mentioned that piece of foil-faced cardboard and not the dozens of other components.

The frequencies cell phones operate at nowadays, I wonder if the gap between any two adjacent fingers isn't more than a wavelength.

 

[drcampbell]

Could you explain more specifically the situation you are envisioning?

Most (much? modern?) neighborhood distribution in North America is 15kV Wye.
Most user transformers use the 8kV from one phase to neutral, with a dirt rod bonding the case of the transformer to the local dirt and to the 15kV "neutral" conductor. (aka. "multiply-grounded 'neutrals' ")

If the 120/240 panel were floating, a fault from the primary to the secondary could put an 8kV potential between the household appliances and the local Earth without clearing any overcurrent protective devices. Ungrounded, double-insulated appliances could put on quite a fireworks show; they're designed to keep 120 volts isolated, not 8000. Imagine mowing dry grass with 8000 volts arcing from blade to ground -- it'd be a pyromaniac's delight.

 

[electrofelon]

Most (much? modern?) neighborhood distribution in North America is 15kV Wye.
Most user transformers use the 8kV from one phase to neutral, with a dirt rod bonding the case of the transformer to the local dirt and to the 15kV "neutral" conductor. (aka. "multiply-grounded 'neutrals' ")

If the 120/240 panel were floating, a fault from the primary to the secondary could put an 8kV potential between the household appliances and the local Earth without clearing any overcurrent protective devices. Ungrounded, double-insulated appliances could put on quite a fireworks show; they're designed to keep 120 volts isolated, not 8000. Imagine mowing dry grass with 8000 volts arcing from blade to ground -- it'd be a pyromaniac's delight.

Wouldn't a primary to secondary fault result in 8kv (or whatever) on the house conductors regardless of if the secondary was a grounded system or not? Granted the fault might clear faster on a grounded secondary system, depending on where in the winding the fault occured.

 

[Mark Bartlett]

.
Has any one watched Mike Holt video Grounding vs Bonding code 14 That explains everything about ground rods are useless he explains about how not to put a ground rod on a generator that is running a house Please watch it is so informative. Ground rod is just for the inspector so he can sign off on your inspection card. Also did you know that pouring water on a ground rod changes your readings . Here is the link Please Watch 26 minutes that make perfect sense 'I had a instructor Kevin Ritz when I was taking a marine corrosion course that turn me on to this guy this guy makes perfect sense. In the dvd he takes a 20 amp breaker hooks it to a power source and the other end and hook it to a ground rod and turn it on guess what the breaker doesnt blow. please see this video below Mark

 

[W@ttson]

So how does that translate to the 6' minimum rod spacing required by the NEC?

its "good enough" Here are some tables and a graphic that tell you the percent of resistance of an electrode:






You can see at ~6ft, you have lets say gotten away from ~90% of the resistance of the electrode.