How to Measure Ground Rod Resistance with a Multimeter

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A ground rod is used in your home’s electrical system to ensure that unsafe and uncontrolled electrical current is safely dissipated into the earth (ground). The unsafe electricity could be from faulty electrical circuits, outlets, utility overvoltage or even from a lightning strike.

How to Use a Digital Multimeter

Using a rod is the only way to ensure there is contact between your house’s electrical system and the earth. A ground rod helps to prevent fires, damage to electrical appliances and buildings, equipment failure, downtime in electrical systems and also the risk of electric shock. Yes, you read that right, uncontrolled current can use a person as the unintended path to earth.

To ensure your home is safe, you should always test your ground rod resistance. You can do this at home using a multimeter.It is a handheld testing tool that is mostly used to take voltage readings. Advanced digital multimeters can take ampere and ohms (resistance) readings. For this step by step guide on how to measure ground rod resistance with a multimeter, we recommend that you have A digital Multimeter as we are interested in Ohms readings.

Why Should You Keep Testing Your Ground Rod With A Multimeter?

Well, your ground rod was installed, and you were told it’s safe, you are probably wondering why you should bother yourself with further tests?

For a safe electrical system, your ground rod resistance should have a very low resistance value; the lower it is, the better job it does. Unfortunately, as time goes by factors such as ground rod corrosion, soil moisture, high salt content, high temperatures and loss of contact of your wires as well as others may increase the resistance of ground rod’s hence affecting its effectiveness. It is highly recommended that ground connections get tested once a year as preventive maintenance.

That’s why you must keep monitoring the resistance levels of your home’s ground rod. Using a multimeter, you can investigate any changes to ensure a reliable connection to the earth. The best part about it is that it is very affordable and easy to use, unlike other gadgets used by electrical and telecom experts.

The value of resistance should be read using ohms on a multimeter.An Ohm is a unit of resistance in an electrical system. Zero (0) Ohms are an indication of no resistance to the passage of electrons from one point to another.

Safety Tip: If you do not have a ground rod installed – which is very unlikely – you can easily install it for your home to ensure the electrical system is safe. A lot of homes built in recent decades have fully grounded electrical outlets.

Equipment Needed for Testing a Ground Rod’s Resistance

Assuming that a ground electrode has zero voltage or zero amps is very unsafe. Below are the equipment and tools you require to test the resistance of a ground rod safely as and effectively.

  • High-voltage gloves – as a precaution wear these gloves if you have them
  • A digital Multimeter
  • A length of wire for making connections
  • Shoes with a non conductive sole.- very important for ensuring safety
  • Protective shades to keep eyes safe

Safety Tip: When taking and testing ground rods, ensure that your hands are super dry.

Steps for Taking Ground Rod Resistance Readings.

Step 1. 

Prepare your wire by stripping back its insulation from both ends. It will allow a good connection that will enable you to take accurate readings.

Step 2. 

Connect one end of the wire to a metal stake in the ground, i.e. a good earth contact such as the ground rod where your fuse box is installed. Then run the other end to where you wish to carry out the test. The preferable place is a power outlet.

Step 3. 

Completely turn off the electricity at the location you are taking the tests. Do this by switching off the breaker for the outlet you are using for the tests. Alternatively, a safer way is to switch off the main breaker for your house.

Step 4. 

Set up your digital multimeter. Please set it to take measurements in Ohms (It is shown using a Greek letter Omega). Set the Ohm settings to take readings of less than 100 Ohms

Step 5 

Touch one of your multimeter leads to the test wire from the metal rod. Touch the other lead to your test location. For an outlet, this will be the outlet’s third hole also called a ground plug, earthing, case or common ground. An American outlet has this hole at the bottom of the other two; For an Asian outlet, it’s the top hole.

Step 6 

Your multimeter will test the connection from your device’s ground connection through the house installation to the central ground and your long test wire. Note and take the resistance readings while ensuring the leads are firmly touching both parts. The resistance should be 25 Ohms or less for a properly connected system.

Safety Tip: Do not carry out these tests on a live circuit; it is very dangerous.

What Is a Good Ground Resistance Value?

Using this method, you are likely to note a higher resistance reading because you also have to account for other wire connections resistance. However, any reading below 25Ohms when using a multimeter indicates a safe resistance.

Apart from a multimeter, there are other specialized devices for measuring ground rod resistance called clamp-on meters. They take more accurate readings since they are used directly on the electrical rod. When using them, there is no standard ground resistance threshold recognized internationally by all certifying agencies. Most of these agencies recommend a ground rod resistance reading or less than 5Ohms when using a clamp-on meter.

Safety Tip: If when taking further readings e you notice an increase of more than 20% from the safe reading of 25Ohms or an increase of 20% from your last reading, It is highly recommended you

  • Investigate the source of the problem
  • Make adjustments to lower the resistance such as replacing or adding ground rods to the ground system or the soil around the rods

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