When people say that ground rods "anchor" your system, what do they mean? Do they mean it provides a reference point with respect to voltage measurements. I have also heard they help stabalize the system under a surge. For the life of me the only things I can see they do is disipate static electricity, lightning protection, and are used to facilitate a fault current path for HV. Is there something I'm missing.
How do ground rods "anchor your system"?
- Thread starter iowa
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- Massachusetts
iowa said:
I think you have it nailed down.
I think the other items like 'stabilizing the voltage' or 'surge protection' is bunk.
stickboy1375
Senior Member
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- Litchfield, CT
iowa said:
I suppose if you did have enough of them it very well may keep you house from blowing away.... :grin:
- Location
- Lockport, IL
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- Semi-Retired Electrical Engineer
I'll not comment on "surge protection." But "stabilizing the voltage" is a real characteristic of grounded systems, and an important one as well. I've posted my explanation of this concept before, but I don't think I kept the Word file in which I wrote it. For now, let me just make a couple observations.iwire said:
1. "Voltage" is the difference in potention between two points in space.
2. In a typical home's electrical system, the voltage between the ungrounded conductor and the center point of the transformer feeding the house is 120 volts, regardless of whether that center point is ever connected to planet Earth (i.e., by the utility or by a ground rod associatd with the home's service).
3. If that center point is not connected to planet Earth, then the voltage between that point and, let us say, a pipe that is connected to Earth can be anything. It can be zero, or 10V, or 100V, or 1000V. Also, the voltage between an ungrounded conductor and that same pipe can be anything.
4. If that center point is connected to planet Earth, then the the voltage between that point and the pipe will be zero, and the voltage between the ungrounded conductor and the pipe will be 120.
That is the sense in which the ground rod "stabilizes the voltage."
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- Massachusetts
charlie b said:
I don't believe electrodes can do that.
At best it will raise or lower the potential of the earth in the near vicinity of the electrode to meet the potential of the grounded conductor but it will not hold the grounded conductor to a particular potential as evidenced by a service conductors open neutral and the wild voltage variations that can still happen.
Bob I have covered this before, but I will offer it again.
Before giving the reasons why systems should be grounded, I will argue that all power systems are grounded. The difference is that one is planned and the other is unplanned. The unplanned system (the one we call ungrounded) really has a distributed leakage capacitance connection to ground. The leakage capacitance in the unplanned ungrounded system can cause all kinds of havoc.
Examples:
Note: when a system is purposely grounded, the leakage capacitor is shorted, nullifying its adverse effects.
Before giving the reasons why systems should be grounded, I will argue that all power systems are grounded. The difference is that one is planned and the other is unplanned. The unplanned system (the one we call ungrounded) really has a distributed leakage capacitance connection to ground. The leakage capacitance in the unplanned ungrounded system can cause all kinds of havoc.
Examples:
- In large AC ungrounded systems, if a L-G short should occur, several amps of steady state AC leakage current could flow through the leakage capacitance without causing any OCPD to operate. This leakage current represents a hazard if personnel get into the path.
- Part of th steady state leakage current flows through conductor insulation, speeding up deterioration and thus decreasing useful life.
- Under transient conditions, the leakage capacitance can resonate with an inductance in the circuit causing very high voltages both across insulation and loads; lifetime is decreased by this added stress.
Note: when a system is purposely grounded, the leakage capacitor is shorted, nullifying its adverse effects.
winnie
Senior Member
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- Springfield, MA, USA
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- Electric motor research
The stabilization of voltage with respect to earth is a real feature of ground rods, but it is limited by the ground rod resistance. To the extent that the perturbing current source is very high impedance, the ground rod will keep the electrical system voltages referenced to earth, but drop a high current source on to the electrical system, and the ground rod will act in exactly the fashion that you describe; the electrical system voltage will go someplace strange, and the ground rod will take a small patch of earth with it.
Static electricity (which you agree ground rods 'bleed off') is such a high impedance source. The capacitive coupling that causes 'phantom voltage' is also a high impedance source. Minor insulation leakage current is a high impedance source. All of these things could charge bonded metal relative to ground, but are of such high impedance (low currents) that a ground rod could actually maintain a good earth reference.
-Jon
Static electricity (which you agree ground rods 'bleed off') is such a high impedance source. The capacitive coupling that causes 'phantom voltage' is also a high impedance source. Minor insulation leakage current is a high impedance source. All of these things could charge bonded metal relative to ground, but are of such high impedance (low currents) that a ground rod could actually maintain a good earth reference.
-Jon
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