@lowrider57 said:
I’ve learned about grounding code from forums such as this. But I’ve been wondering why can’t a subpanel have it’s own grounding rod as long as the main panel has a grounding rod? This is unclear to me because the subpanel ground is tied to the main panel grounding block.
Is a grounding rod ever used on a subpanel?
You can add a ground rod to a subpanel connected to the ground bar in the panel, BUT, an equipment equipment grounding conductor still must be ran with the feeder conductors and the equipment grounding conductor shall be terminated to the equipment ground bar in the main electrical panel as well connected to the ground bar in the subpanel.
The purpose of an equipment grounding conductor is to provide a low impedance path for ground fault current to return to the source, the utility power transformer, through the service neutral conductor at the electrical service main electrical panel where all equipment grounding conductors are connected to.
If the feeder equipment grounding conductor was lifted at one end the only path for ground fault current would be the earth driven ground rod for the subpanel... The earth is a poor conductor... The ground faulted circuit, be it a branch circuit fed from the subpanel, or a faulted feeder conductor, there would never be enough current to overload the breaker and cause it to trip open.
The main purpose for a ground connection to earth is for lightning protection. I does absolutely nothing for improving the sound of an audio system. The earth does not possess some magical mystical power that sucks nasties form an audio system
So forget adding an Auxiliary grounding Electrode to a subpanel that is located in the same building structure... Lightning loves them though...
FWIW, in a separate detached building, structure where a subpanel is installed fed from a main panel ,say in a house, then by code an new grounding electrode system shall be established. An equipment grounding conductor ran with the feeder is still required, connected at both ends to the equipment ground bar.
NEC 250.54 Auxiliary Grounding Electrodes.
It is permissible provided the sub panel feeder from the main electrical panel equipment grounding conductor is connected to the equipment ground bar in the main electrical panel as well to the equipment ground bar in the sub panel. The Aux ground rod ground wire is connected to the ground bar in the sub panel.
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Grounding Myths
"Electromagnetic Compatibility Engineering" by Henry Ott
3.1.7 Grounding Myths
More myths exist relating to the field of grounding than any other area of electrical engineering. The more common of these are as follows:
1. The earth is a low-impedance path for ground current. False, the impedance of the earth is orders of magnitude greater than the impedance of a copper conductor.
2. The earth is an equipotential. False, this is clearly not true by the result of (1 above).
3. The impedance of a conductor is determined by its resistance. False, what happened to the concept of inductive reactance?
4. To operate with low noise, a circuit or system must be connected to an earth ground. False, because airplanes, satellites, cars and battery powered laptop computers all operate fine without a ground connection. As a mater of fact, an earth ground is more likely to be the cause of noise problem. More electronic system noise problems are resolved by removing (or isolating) a circuit from earth ground than by connecting it to earth ground.
5. To reduce noise, an electronic system should be connected to a separate “quiet ground” by using a separate, isolated ground rod. False, in addition to being untrue, this approach is dangerous and violates the requirements of the NEC (electrical code/rules).
6. An earth ground is unidirectional, with current only flowing into the ground. False, because current must flow in loops, any current that flows into the ground must also flow out of the ground somewhere else.
7. An isolated AC power receptacle is not grounded. False, the term “isolated” refers only to the method by which a receptacle is grounded, not if it is grounded.
8. A system designer can name ground conductors by the type of the current that they should carry (i.e., signal, power, lightning, digital, analog, quiet, noisy, etc.), and the electrons will comply and only flow in the appropriately designated conductors. Obviously false."
Henry W. Ott
Who is Henry Ott?
http://www.hottconsultants.com/bio.html
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