To measure the ground resistance of an outlet, set the multimeter ohm setting to a value of fewer than 100 Ohms. Touch the two leads to the test wire and the test location. That should show the ground resistance on the display.
However, these digital multimeters use a very small DC probe voltage and current. This is nearly not enough to overcome the contact voltage between the grounding conductor and the ground around. As a result, there will be a substantially large error.
How to Measure Ground Resistance With a Multimeter
A multimeter featuring a resistance socket may sound tempting, but it is not the correct approach to measuring the ground resistance. It is only feasible when you are measuring the resistance of an outlet.
Step 1: Do a Visual Inspection
To get started, disconnect the entrance machine and disassemble one outlet. You should see an appropriate terminal to which the grounding conductor is connected. Normally, it should be in yellow-green. In that case, you can assume that the outlet is grounded.
However, sometimes you may find only two wires, brown and blue. This implies that the outlet has no protective ground. Although, the presence of a yellow-green conductor does not necessarily mean that the grounding is working properly.
Step 2: Turn off Electricity
Turn off the electricity at the place where the test is going to take place. At the switchboard, turn on the input circuit breaker. This implies that voltage must be present in the sockets. Then you have to set the voltage measurement mode on the multimeter.
Step 3: Measure the Voltage Between the Phase and the Neutral
Use the probes of the multimeter to touch the phase and the neutral contacts and measure the voltage between them. You should see a value of 220V on the display of the device.
Step 4: Measure the Voltage Between the Phase and the Grounding
Similar to the step above, use the probes to measure the voltage between the phase and the grounding contacts. You will see a slight difference from the first value. However, this indicates that there is grounding in the area.
Step 5: Measure the Resistance
Now set your multimeter to measure Ohms. Set the value to less than 100 Ohms if it has multiple Ohm settings. Touch a lead to the test wire and the other lead to the test location. If the system is connected properly, you will see a resistance reading of fewer than 25 Ohms.
When to Use a Multimeter
Although a flexible multimeter can often measure voltage, resistance, amperage, and even continuity in different circuits, it is best used in checking the outlets for proper grounding. This simply implies checking to see if there is any voltage or not.
If there is none, then that means the electrical system is faulty. Besides, you can use a multimeter to check the resistance between the ground electrode and a definite reference point.
It is already well known that electricity moves along the path of least resistance. The ground typically has the least resistance. Therefore, knowing the exact value of resistance by the simple use of a multimeter will surely give you a sense of safety.
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