Ground Strap or Ground Wire

Discussion in 'General Technical Questions and Answers' started by STDYIN, Sep 6, 2020.

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  1. AI5DH

    AI5DH Ham Member

    Then you disagree with NEC, IEE, NLPS, MIL, TIA, and every electrical code and practice out there. You are on an island by yourself.
    OK you can use dirt as a conductor with high voltages, but completely misses the obvious basic fundamentals. Example utilities operate at very high voltages and do use earth as a conductor. A simple analysis of Ohm's Law reveals the fact. Say your transformer outside feeding your house is 13.2 KV primary with 240/120 48 KVA or a 200-amp service most homes use today. Drive a rod into the ground and you get 100 Ohms which would be excellent for single rod. Transformer has 4 amp fuse. Is your home safe and protected?

    Darn straight it is! 13200 volts / 100 Ohms = 132 amps flowing through a 4-Amp fuse drops. POP! Your lights go out and you go in the dark. Now let's say you plant a copper mine under your house and tower. You got 10 Ohms at power frequencies. No inductance taken into account, just low power frequency is 10 Ohms. Well at 120 Volts line to ground with 1-amp of current you lost 10 volts at the load already, and burning off waste heat in your wire. Draw 12 amps you are at 0-volts at the load end. Now you are burning off all your power as waste heat on the wiring, all 1200 watts. Not a single watt to a device like a toaster or antenna. With a dead short fault 120 volts / 10 ohms = 12 amps, not enough to trip a 15 amp breaker. A circuit conductor in low voltage systems are measured in micro and milli-ohms, not 10's 100's or 1000's of Ohms as it would be at higher frequencies. That is just a fact that is well known and documented.

    Couple that with the fact that a single wire circuit of any length is unusable above power frequencies as a circuit conductor in our low voltage world of 1000 volts and less. All codes prohibit earthand equipment grounds to be used as a conductor. The only thing a single wire circuit is good for is radiating energy like a heating element or an antenna at the end of a coax. Trying to push it through equipment grounds and dirt is insane and impossible.

    I agree to some extent, but ARRL points that out quite clearly the only thing that could be considers a RF ground is RF Radials aka Counterpoises but makes it quite clear it may or may not be earthed. Irrelevant anyway because that is outside the protected area. I do agree with you most hams think ground is ground. They do not know an equipment ground from earth ground, from AC/DC ground, or a ground plane, or what functions any of them perform. There is only 1 ground. Most hams put themselves between two earth grounds inside a loop.
    Last edited: Sep 7, 2020
  2. W9WQA

    W9WQA Ham Member QRZ Page

    ha, i knew it...
  3. KB0MNM

    KB0MNM Ham Member QRZ Page

    There is a lot of good information in posts #3-6, which tells you why strap is better except where movement is involved.
    What is not addressed is which would be easier to accomplish. Strap can be drilled- use gloves to avoid 'knife-edge- windmill' effects on your hands. Braid usually has one hole already drilled- yet is that the right size ( too big or small )???
    The same goes for the pipe- if you are going to drill holes in it afterward- flat spots might make it easier to keep the drill bit from 'wandering' off target.
    Washers can minimize problems seen when tightening a stranded wire down- or making a strap or wire contact a surface. Lockwashers can be an improvement, and keep nuts & bolts together in spite of any minor vibration.
  4. KA0GKT

    KA0GKT Ham Member QRZ Page

    Lightning has an impulse duration of anywhere from 0.8 to 50 microseconds. A 0.8 microsecond waveform is 1.25 MHz. so a small diameter wire may have a fair amount of reactance even at the frequency component of a lightning waveform. A lightning waveform is basically a sawtooth wave. The sawtooth wave has energy at all harmonics of the fundamental frequency, and the relative amplitude of each harmonic is proportional to the inverse of the harmonic number, e.g., 1/1, 1/2, 1/3, 1/4, etc. so a low impedance path to ground is important for lightning currents. A flat wide copper strip has a smaller impedance than a round conductor with an identical cross section.
  5. AI5DH

    AI5DH Ham Member

    You are on point with one exception. There is no significant impedance difference between a 12 AWG, 6 AWG, 2/0, and a 750 MCM single wire circuit conductor. DC and Power Frequencies a huge difference, but almost no difference in impedance above a few kilohertz. What is important is the thermal capacity of the wire to safely pass the current likely to be encountered.

    Although lightning contains all frequencies DC to light, most all of the energy is from DC up to 1 Mhz. So you are right on point. Lightning is not a voltage event, it is a fast rise-time current pulse rising from 0 amps to 10,000 amps in 1 to 50 micro-seconds. That has a characteristic waveform of a 20 Khz to 1 Mhz. The voltage is just a product of high current flowing through an impedance.

    With a single point ground you have shrunk the protected area to 1 square foot of copper plate or ground buss. All your DC Equipment Grounds, AC Equipment Grounds, Negative Battery Post, Antenna Discharge Unit, and Outdoor coax bond originate from on a potentiality ground Plane. Literally something like a 12" x 12" x 1/16 copper plate. Once a conductors enters, is bonded, and never touches earth ground again. All grounds or grounded circuit conductors cables in the shack are an open circuit once inside. So if lightning strikes, or a power line falls on your antenna there is going to be Ground Rise Potential on your Single Point Ground and be in the thousands of volts. However none of the equipment or you can feel any potential difference because there is none. Yes the GRP voltage went up with respect to earth, every piece of equipment went right up with it like a cork on a fishing line in the water. With all ground circuits originating at the SPG, there is no potential difference between any two pieces of equipment, and thus no fault current flowing despite rising thousands of volts.
  6. K7KBN

    K7KBN Ham Member QRZ Page

    And people used to call radio "wireless"!
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I call some things an "RF ground" to establish it's an earthed connection that's not intended to radiate and has no intended resonant frequency.

    A counterpoise typically will radiate and has a resonant frequency, or possibly many resonant frequencies.
    K0UO likes this.
  8. AH7I

    AH7I Ham Member QRZ Page

    Works for hams too.
  9. WN1MB

    WN1MB Ham Member QRZ Page

  10. AD5HR

    AD5HR Ham Member QRZ Page

    It must be insured, it's branded AAA.

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