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What is Earth Loop

earth loop Neutral - Ground connection
Each box and device in electrical system are connected to a ground wire that goes to earth.
When the Hot wire shorts against a metal box, the current enters the ground wire. The fault current is pushed through the ground wire to the ground rod.
The route the ground wire takes, from box to box to box back to the main panel and then out to the ground rod is called the ground loop, and the ground loop can offer resistance.
The less resistance, the faster the fault current can reach earth, and the less damage the fault causes. Too much impedance, and the fault will cause more damage.
Earth loop impedance testing measures resistance in the ground from the farthest point, or at a key piece of equipment.
Eartth loop testing .pdf
-Electricity is about charged electrons that are moving between unequal charges. When there is a short circuit or lightning strike, there are lots of electrons traveling on the ground wire going to the soil to equalize charge. A properly installed ground wire handles too many electrons by letting them pass freely. And so the effectiveness of ground is measured by how little resistance it offers to electrons.

-A ground is not a single ground rod. It is an array of thousands of ground rods that extend grid-wide. Just imagine how many grounds you pass each day. There is a ground rod at each pole, and each home and each business. Some installations have more than one point of grounding. All ground wires are bonded together by the Neutral wire all the way back to power company generator.

-A proper ground offers no resistance, but voltage irregularities on the grid have a background effect on ground wire resistance at each home and business. For example, if there is a lightning strike a few blocks away, even if the lightning does not strike the grid directly, it energizes the wires, causing a surge of electrons.

-The grid handles energized wires several ways, including surge protection, fuses, breakers and lightning arrestors, but the backstop that stabilizes the grid is the ground array. The excess electrons from a lightning strike are broadcast along the Neutral wire and into local ground rods. This in turn affects the resistance of the ground at your home because for a moment, the wire is crowded with electrons. The entire ground array is constantly pulsing with events that affect resistance. This acn affect the ground loop or earth loop which can cause a ground rod to have more resistance, and not work safely, especially if local soils are particularly resistant. The measurement and calculations for earth loop effect are complicated and best handled by specialized tool called earth ground clamp meter. Buy earth ground clamp meter

-If ground resistance is too high, because of earth loop or improper grounding, that can cause breakers to fail over time, and makes circuit beakers and appliances more vulnerable to surge events such as nearby lightning strike. Therefore the ground is responsible for assisting the circuit breaker, and ultimately the effect of earth loop impacts breakers..
-When a short circuit occurs, the overload should move rapidly through an unobstructed ground path and be absorbed in the earth via the ground rod. At the same moment, the breaker also senses heat on the wire caused by the overload and trips. During lightning strike, the ground array will redirect electrons to earth. If the overload exceeds capacity of ground, the subpanel breaker trips to minimize damage. If the resistance is too high on the ground wire, that affects heat on the breaker and wire. This demonstrates that the ground wire assists the breaker. And so adverse earth loop conditions impact the breaker. More ground rods or ground array can be added in vulnerable areas.

-This introduces the next point: the earth itself offers resistance to the free flow of electrons: damp-dense-warm soils conduct better than dry-rocky-cold soils, with frozen soil offering almost no conductivity. As a result, local codes for grounding vary by type of soil and local conditions, as does the need to test for earth loop effect.
-When power poles are run across rocky terrain, the local soil may be non-conductive, for example running power poles in the mountains where that surfaces might be cold and the surface made of rock. In this case ground wires are run parallel with the power poles, with one wire on each side, that bond together ground wires on multiple poles until conductive soils are reached and adequate grounding can be accomplished.

"Values adopted by one national electrical power-supply authority, on its 20 kV distribution systems, are as follows:
Maximum earth-fault current in the neutral connection on overhead line distribution systems, or mixed (O/H line and U/G cable) systems, is 300 A
Maximum earth-fault current in the neutral connection on underground systems is 1,000 A" See page B10
Measure earth loop resistance

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Fluke 1630
The Neutral and ground array
In the US: The Neutral wire runs from pole to pole across the electric grid.
When the Neutral is installed on top of the pole above the other wires (commonly found on transmission and subtransmission poles coming from power plant or traveling between substations), it's called the static line, and it's location protects the grid from direct lightning strikes by redistributing voltage to the earth through ground connections at each pole.
When the Neutral is installed below the hot wires (commonly found on distribution poles traveling from local substation to end user), it is simply called the Neutral or System Neutral.
The Neutral is connected to the ground wire at each pole.
The Neutral is bonded to all other Neutrals, and bonded to all ground wires to form a single large ground array or earthing array.

Under each substation is an array of ground rods that interconnect all the equipment in the substation, and connect with the incoming and outgoing Neutral wire. At the power plant, the generator is bonded to ground array through the Neutral wire connection.
The Neutral wire and 3 Hot wires come off the power plant generator. Only the Neutral wire is connected to ground wire array. The Hot wires are always separated from any source of ground by non-conductive insulators.

Both Neutral and ground are necessary for safety and reliability, to absorb overvoltages, surges, lightning strikes etc by providing direct pathway to earth.
The system is further protected by circuit breakers at each substation and lightning arrestors. If lightning hits the static line at a transmission tower or power pole, and the voltage is greater than the grounding can absorb, the overvoltage jumps to the hot wires, travels to the substation or power plant, causing a circuit breaker to trip at the substation.

At the end user location, the Neutral connects to the transformer neutral connection, depending on the service requirement.
For example a residential service is typically 120-240 volt single phase. The Neutral and 1 hot wire connect to the primary side of the transformer. At the same time, the Neutral is bonded to the ground wire that travels down the pole to earth. The ground wire also connects to the steel transformer can at the point where the Neutral goes to the house. The transformer is grounded by the ground wire.
Inside each transformer are two coils of wire: the primary and the secondary. The Neutral from the power company connects to the primary coil, and the secondary coil. The secondary coil on a residential transformer is actually composed of two coils, with a connection in the middle that gives rise to the Neutral wire that goes into the house, and is bonded to ground. Therefore the transformer creates it's own Neutral. The Neutral from the pole connects to the Neutral going to the house. Therefore the Neutral going into the house is connected to the metal can, thus giving continuous Neutral-Ground back to the power company generator.
The Neutral wire connects inside the home's circuit breaker panel, and the Neutral busbar is bonded to the ground busbar, and the ground busbar is connected to the outdoor ground rod.
Another example is a 3-phase service with 3 transformers and 6 coils. In some applications, the Neutral is directed connected to the Neutral going into the end-user location, assuming a Neutral is part of the wiring configuration.
The ground and circuit breaker
Ground wires, like all wires, have resistance to electricity that can slow the flow of electricity. This resistance can be measured.
The ground wire must have sufficiently low resistance, or a short circuit might cause overload on circuit breaker and wire. An overload can damage the service panel and create hazardous wiring conditions.
Each breaker has a rating for amps, but also a rating for ground resistance beyond which it will burn out. That's an extreme example of too much voltage, but the earthing or ground system plays a role for protecting circuit breakers.

When a short circuit occurs, the overload should move instantly through an unobstructed ground path and be absorbed in the earth via the ground rod. At the same moment, the breaker also sense heat from electrons filling the wire on their way to the location of the short circuit. Heat on the wire causes the breaker to trips. If the resistance is too high on the ground wire, that affects heat on the breaker and wire. This demonstrates that the ground wire assists the breaker. And of course the breaker is essential for protecting the grounding as well.

The overall grounding at each location (home or business) can be tested for earth loop impedance (resistance). Impedance measures how much the ground is impeded or slowed by poor earthing.
If the loop resistance is too high, the business or home may require more ground rods or better location of ground rod so that the ground functions correctly and can correctly protect the circuit breaker, wire and electric appliances.
Generator Neutral-Ground at generator
Illustration shows AC generator with electromagnet located in center, surrounded by 3 coils of wire.
The magnet has a north and south pole. As the north pole rotates past the coil of wire, it causes electrons to come free from their normal orbits around atoms on the wire. This starts an accelerating cascade of electrons jumping from atom to atom going down the wire. When the north and south poles are equidistant from the coil, the atoms slow to a stop and voltage on wire drops to zero. The atoms began to accelerate again as the south pole approaches the coil, except now the atoms are going the opposite direction on the wire than they were when the north pole passed. As the generator magnet spins at 60 times per second, the electrons oscillate back and forth at high speed. The back and forth action of electrons on the wire are called alternating current. Since the electrons only stop momentarily, the average voltage on each wire is always above 0 volts.
Electricity from Generator to end user
Difference between surge and ground
Difference between single and 3-phase
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