Because electricity prefers the route of least resistance to the ground, measuring the Ohms of your grounding system will provide you with an idea of its overall safety. The National Electric Code, for example, demands no more than 25 Ohms of resistance in a ground system. Connect your wire length to a metal post in the ground. Make sure it's deep enough that you don't hit water or soil.
You should have a resistance between 3 and 6 Ohms when there are no loads connected to the wiring. If the resistance is less than 3 Ohms, something is wrong with your wiring and/or connections; if it's greater than 6 Ohms, something is wrong with your equipment (or its wiring) and needs to be fixed.
The best way to check your grounding system is to make a simple circuit with a voltmeter. With the meter set on DC volts, connect one terminal to a metal post in the ground. Connect the other terminal to the same metal post via a second conductor. You should see a reading of 0 Volts. If not, find out what's causing the problem and fix it.
Almost all electricians and electrical inspectors are acquainted with the National Electrical Code requirement in Section 250-54, which requires a single-made electrode (e.g., ground rod) to have a resistance to ground of 25 ohms or less.
The reason for this requirement is twofold: first, to provide an open circuit between the house wiring and any other conductor (such as a metal water pipe) that might be present under the surface of the soil; and second, to prevent excessive current from flowing through the ground rod itself.
The first goal can be accomplished by selecting a ground rod made of nonconductive material (such as plastic). The inspector should make sure that the ground rod is deep enough to reach solid earth, but not so deep that it becomes a stress point for the house frame. For example, a typical depth for a ground rod is 12 inches, but some houses in very cold climates may require a ground rod up to 18 inches deep.
As for the second goal, preventing excessive current flow through the ground rod, this can be done by making sure that no part of the ground rod lies inside the area covered by the bonding jumper. If any portion of the ground rod does lie within this area, then another ground rod must be used instead.
Ohmic The System of Grounding Electrodes Section 250-56 of the National Electrical Code (NEC) requires a single ground rod or ground plate to have an earth resistance of 25 ohms or less. If you connect more than one conductor to the ground rod, they all must have equal resistance to the ground.
The code specifies that the ground rod must be either 4" or 6" in diameter, but it can be buried as deep as 300 feet from any building structure. The ground rod should be placed at least 18 inches from all electrical service panels and equipment grounding points.
In addition to being a safety measure, having a low resistance between the ground rod and the surrounding soil helps prevent current from circulating through the soil and into buildings or other conductive objects via underground cables or pipes. This could happen if there's a broken wire inside your house or office building and it's not been repaired, for example.
Current flowing through a conductor loses energy due to its resistance. So, for a given amount of current, the higher the resistance, the less energy will be lost. This means that the conductor needs to be thicker or better insulated to handle the same amount of current if it has high resistance. For example, if a ground rod has a resistance of 100 ohms, then it can support a maximum current of 100 amps before exceeding its design limits.
So, ideally, an ohm test between the neutral and ground wires anyplace in the house is zero ohms. At numerous points along the electricity distribution system, neutral and ground are connected. So, zero ohms once more. But what if they're not?
The wiring diagram for your house should indicate whether or not neutral and ground are paired at each junction box. If they're not then you have some voltage on one or other of those wires. Some simple math will tell you how much voltage there is on each wire: it's equal to the current in amps times the length of the conductor in feet divided by two times the resistance of an ohm. So, if the current is 12 amps, the length is 10 feet, and the resistance is 0.5 ohms, then the voltage on the conductor is 60 volts.
Here's where it gets tricky. You need to figure out what to do with this information. The first thing you should do is contact the electric company and report that there is no ground at your house. This means that anyone who touches these wires could be injured by a low-voltage power source. The second thing you should do is replace the wiring junction boxes with ones that are designed to connect neutrals to grounds (or leave them empty). This will protect people from electrical shocks if the wires were ever reconnected.
For generating plants and large substations, IEEE 80 substation grounding values range from 1/2 to 1 ohm. Manufacturers of sensitive electrical equipment and medical diagnostic equipment use requirements ranging from 1 to 5 ohms. Added on: 5/3/2017 9:22:44 AM
Grounding is the process of connecting a conductor to earth or ground to provide an electrically common connection for two or more circuits. The term "ground" means the complete circuit between any two points in the earth's surface. The word "grounded" means that at least one circuit element is connected to the earth or ground.
IEEE 80 refers to the standard for substation grounding used by power companies for generating stations and large substations. This standard was developed by the Institute of Electrical and Electronics Engineers (IEEE) and is known as Standard 80. It specifies that all conductors involved in the grounding system must be capable of carrying equal and opposite currents. Thus, if circuit A is grounded, then circuit B must also be grounded.
IEEE 80 requires that all live parts of a generator station's circuitry be bonded to ground. This includes all terminal blocks, switchgear, motors, and other equipment with live parts. For generators operating on the split phase system, each half of the circuit must be grounded.
Grounding is crucial for electrical safety in any structure, whether it's a business facility or your house. When surplus electricity accumulates within the system and there is nowhere for it to escape, the risk of electrocution or fire increases. This is why all household circuits should be grounded to prevent accidents happening.
The ground is used as a counter-electromotive force (EMF) when an electric circuit is opened or closed. If the circuit is closed, then the ground acts as a second source of current that opposes the current flowing into or out of the device being tested. The ground must be able to carry enough current to be effective; otherwise, it will not serve its purpose of providing a path for energy to flow back into the power line if you have one or two devices plugged in. A good way to think about this is that without a good ground, you are leaving yourself open to electrical shock.
In addition to preventing accidents, grounding is required by law in some countries to prevent damage to other people's property. For example, in Canada, if you own a home and you can prove that an older home next door was the cause of your new home's wiring problems, you can apply for an electrical permit to have the old house's wiring inspected by a qualified professional and replaced if necessary.