skin

A person with naturally hard and dry skin will offer much higher resistance to shock current than one with soft and moist skin; the skin resistance becomes very low if it has been burned, because of the presence of conducting particles of carbon.

The NIOSH states “Under dry conditions, the resistance offered by the human body may be as high as 100,000 ohms. Wet or broken skin may drop the body’s resistance to 1,000 ohms,” adding that “high-voltage electrical energy quickly breaks down human skin, reducing the human body’s resistance to 500 ohms”.

Human resistance is about 10,000 ohms on the high side and as little as 1,000 ohms if the person is wet. Remember, ohms is the unit of measure of a material’s resistance or impedance to current flow. Current flow is obviously higher as the resistance goes down.

The elements in our bodies, like sodium, potassium, calcium, and magnesium, have a specific electrical charge. Almost all of our cells can use these charged elements, called ions, to generate electricity. The flow of charges across the cell membrane is what generates electrical currents.

The Earth Resistance profile varies between 10 Ohms and 20 Ohms. Soil identifications as well as programmed intensive field measurements of soil resistivity and earthing system at selected sites proves that soil resistivity values’ depend on the type of soil.

Earth resistivity is usually measured using the Wenner method, which involves the use of four temporary earth spikes. The spikes do not need to be moved as part of the testing procedure however – their location and spacing is determined by the depth at which it is required to determine the earth resistivity.

Factors affecting on Earth resistivity

• Soil Resistivity. It is the resistance of soil to the passage of electric current.
• Soil Condition.
• Moisture.
• Dissolved salts.
• Climate Condition.
• Physical Composition.
• Location of Earth Pit.
• Effect of grain size and its distribution.

Basic Methods to Reduce the Resistance to the Ground

• Increase the Rod Thickness. Let’s assume we bury a standard ground rod with L = 300 cm, and d = 1.270 cm, in soil with ρ = 10,000 Ω·cm.
• Increase the Rod’s Length.
• Use of Multiple Rods.
• Treat the Soil to Decrease its Resistivity.

The flow of current into the grounds depends on the resistivity of the soil in which the earth electrode is placed. The resistance of the earth varies from layer to layer. The lower layer of soil has more moisture and lower resistivity.

One of the simplest grounding problems to fix is making sure that all ground connections are correct.

1. Shut off the main electrical power.
2. Find the grounding rod driven into the ground.
3. Check the ground connection clamp.
4. Check the ground wire running to the copper or galvanized water service inside the house.

Another way to lower earth resistivity is to treat the soil with a salt, such as copper sulfate, magnesium sulfate, or sodium chloride. Combined with moisture, the salts leach into the soil to reduce earth resistivity. However, this inexpensive process can also cause problems.

The simple, but somewhat unreliable method uses a long wire and a DMM. Connect one end of the wire to a known, good earth contact (maybe next to the location where your fuse box is installed). Measure the resistance from the other end of the wire to the ground connector of the outlet/device to be tested.

Without a properly grounded electrical system, you are risking any appliances you have connected to your system being fried beyond repair. In the worst-case scenario, an overload of power can even cause a fire to start, risking not just extensive property and data loss but physical injury as well.

A bad electrical ground may affect one or more electrical systems because it forces current to search for other easy paths back to battery ground. This may cause all kinds of trouble for lights, sensors, modules and other electrical and electronic components.

The best way to check your house ground is to verify that you have current flowing in the wire to your ground rod. A clamp-on probe with a DVM (Digital Volt Meter) could be used to perform the measurement. Just make sure you have enough appliances running or lights lights on to generate a measureable ground current.

A poor electrical ground can be dangerous. Grounding an electrical circuit is very important. There are often symptoms associated with a improper ground, and a professional electrician should be allowed to test the grounding wires and electrodes in a home if such symptoms arise that indicate a poor electrical ground.

A bad ground would not cause this. This is called a parastic loss. That is when there is too much current being drained from the battery with the key in the off position.

4 grounding electrode