According to the NCBI, approximately 400 people die yearly from high voltage electric injuries caused by various electrical appliances. An improper electrical ground connection is a major cause of electrocution.
Old houses have grounding lines for circuit boxes, but the individual power outlets do not have a ground port. While power outlets in modern homes have ground connections, you should regularly test the ground and maintain them.
This is an easy guide with step-by-step instructions on how to test ground with a multimeter. A multimeter might look complicated and difficult to use with all the symbols, numbers, and probes. But, well, it is a simple and handy tool that you can easily use.
What is ‘Ground’?
In terms of electricity, the excessive electric energy from various appliances in the circuit flows to the ground or earth to prevent electrocution. Let’s explain it in detail.
When you plug a device or an appliance into a power outlet, a certain amount of electricity flows into it. However, sometimes the entire amount of electricity is not used, and the remaining is known as ‘excess power.’
This ‘excess power’ should be flown out of the connection; otherwise, it will accumulate on the appliance body and electrocute anyone who touches it.
This is where the ground connection comes into action. The ‘excess power’ will flow through the ground connection instead of staying in the circuit, thus, preventing all sorts of electrical hazards.
Note- All your house outlets should be regularly checked to see if it has a working ground or earth connection.
What is a Multimeter?
A multimeter is a device used to measure various electrical properties of a power outlet or a circuit. You can measure voltage (volts), resistance (ohms), and current (amps) using this. It can detect both direct current (DC) and alternating current (AC).
It will cost around $20 if you want an analog multimeter or $50+ for digital ones. This is an essential tool for testing the ground connection of home power outlets.
How to test ground with a multimeter- Easy Steps
This is an easy step-by-step guide written to simplify the process of testing ground with a multimeter. Follow the instructions carefully; hopefully, it will clear all your confusion about a multimeter.
Set the voltage type on your multimeter
You can use either analog or digital multimeter to check grounding in an outlet. Households use an AC power supply so you need to set your multimeter to AC voltage settings.
If you are using an analog multimeter, turn the knob to where it says VAC or V～.
If you have a digital multimeter, set the mode to AC voltage by toggling through the settings menu.
Then, set the cutoff value to the highest voltage to get more accurate results. But if your digital multimeter doesn’t come with a cutoff value, then just set it to AC mode.
Connect the probes to your multimeter correctly
This is a step you should pay attention to. Your multimeter will have two probes, a red and a black one. Attach the red probe to the port marked as V,+, or Ω. Then attach the black probe to the COM or – marked port.
If the probes are not correctly attached, it will damage your multimeter. Do not swap the probes; avoid using probes with cracks or damage in the vinyl casing. Your probes shouldn’t have any exposed wires.
Take various readings
Your power outlet has three ports, hot/live, neutral, and ground/earth port. The hot or live port is the smaller one among the two straight ports, and the neutral port is the longer one. The ground port is the U-shaped or circular one between the hot and neutral port at the top or the bottom.
You can insert the multimeter probes into the ports and take readings. Here is how you will do so.
Push the black probe into the neutral port and the red probe into the live port. Check the reading in your multimeter and note it down. The multimeter will read 120V or slightly more if the outlet works fine. This will be your R1 (Reading 1).
Then put the black probe in the ground port and the red port in the neutral port and check the voltage. Your multimeter should read approximately 0V if the outlet is connected to a ground connection. Note down the reading as R2 (Reading 2).
Keeping the black probe in your ground port, remove the red probe from the neutral port and stick it into the live port. Check the voltage reading in your multimeter and note it down as R3 (Reading 3). If your ground point is working properly, you should get a reading of around 120V between the live and earth ports.
You can check the ground on the screw of the outlet case for extra security measures. First, touch the screw with the RED probe while keeping the black probe in the ground port, and then note the reading.
If the meter reads 0V, then there is no electricity flowing or accumulating in the screw. This indicates it will not electrocute you when you touch it.
Always insert the black probe first and then the Red probe. If you do it the other way around, it could be fatal and cause death. While sticking the probes into the ports, ensure you are not touching the metallic part to avoid electrocution.
You can read Do Surge Protectors Work Without Ground?
Compare and Evaluate the readings
Your R2 should always show 0V or slightly more. But if your R3 shows 0V or your R1 and R3 are not approximately equal, your house is not properly grounded. For example, if your R1 is 120V, your R3 should be anywhere between 115V-125V.
So far, we have checked if the ground wire is working properly, but you can also check how good your grounded electrical connection is with the above readings.
Subtract R3 from R1 and add the result to your R2. This gives you the leakage. If the final voltage is more than 2V, then you have a poor ground connection.
To simplify it,
R1 – R3 + R2 ⩽ 2V
If the leakage is more than 2V, your outlet drains power and adds to your electricity bill. Immediately get it repaired by a professional.
Hopefully, this article was easy for you to understand, and now you can easily test the ground with a multimeter for any power outlet in your house. However, if you still have some confusion, watch this video.
Palash is an entrepreneur in the tech industry and the author of the Smart Home Protector. As a tech entrepreneur & reviewer of a home safety gadget store, his job helps customers remain on top of what’s coming next in our rapidly changing world.