Trystan Casey
Electrical bonding is the practice of connecting equipment cases or metallic structures to the ground to prevent electric shock and protect individuals who may come in contact with the equipment. Proper electrical bonding techniques are crucial as they provide a return path for any stray voltage, preventing electric shocks and potential fires. Testing electrical bonds is essential to ensure the safety and reliability of electrical systems. While specialised earth-ground meters are ideal, digital multimeters can also be used for practical bonding tests. This involves inserting the multimeter probes into the receptacle and measuring the voltage, which should read 0.0 volts or a few millivolts.
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What You'll Learn
Using a multimeter
A multimeter is an essential tool for anyone working with electricity. It is a device that can measure voltage, current, and resistance in electrical circuits. A digital multimeter (DMM) has two probes, usually red and black, which are used to make contact with electrical components to measure their properties. The multimeter also has a dial that allows you to set the range of measurements you want it to take.
- Turn off the power supply: Before starting, ensure that you turn off the power supply to the circuit you want to test. This is an important safety precaution.
- Set the multimeter: Set the multimeter to measure resistance (Ohms) and select the lowest range for resistance. It is important to ensure that your multimeter is also set to measure voltage.
- Connect the probes: Connect the black probe (often referred to as the "common" or "COM" probe) to the common socket on the multimeter. Then, connect the red probe to the socket marked for resistance (Ohms).
- Touch the probes together: Touch the tips of the probes together to ensure that the multimeter is functioning correctly. If the multimeter displays zero resistance, it is working as expected.
- Touch the ground: Touch the black probe to a known ground, such as the metal chassis of the equipment you are testing.
- Touch the wire: With the black probe still on the known ground, use the red probe to touch the wire that you want to test for grounding.
- Observe the ground reading: The multimeter will display a resistance reading. If the wire is properly grounded, the reading should be low. If the reading is high, it indicates that the wire is not grounded properly.
- Test other wires: Repeat the above steps to test other wires in the circuit for proper grounding.
- Turn on the power supply: After completing the testing, remember to turn on the power supply to the circuit.
It is important to note that testing for grounding or working with electrical wiring can be dangerous if you are inexperienced. If you are not comfortable performing these tests, it is recommended to contact a licensed electrician for assistance.
Additionally, while a digital multimeter can be useful for practical bonding tests, it is not a substitute for a specialised earth-ground meter. In electrical systems, the ground and neutral leads should only be bonded at one point, which is the main service panel. Improper bonding at any other point can create safety hazards. By performing tests with a multimeter, you can ensure that the ground and neutral are correctly bonded only where they should be.
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Proper bonding
Electrical bonding is the practice of intentionally electrically connecting all exposed metal items not designed to carry electricity in a room or building. This is done as a safety precaution to protect from electric shock. Bonding is also used to minimize electrical arcing between metal surfaces with electrical potential differences.
There are two types of electrical bonds: direct and indirect. Direct bonds are metal-to-metal joints provided by welding, riveting, or bolting. Indirect bonds are connected through a strap or jumper. Proper electrical bonding techniques are important as they protect individuals who may come in contact with the equipment.
Before testing electrical bonds, it is important to ensure that the bonding surface is properly prepared. This means that it must be cleaned to remove all grease, paint, lacquer, or any other impurities that may inhibit a good electrical connection.
When testing electrical bonds, it is essential to use the correct tools and follow the proper procedures. While a digital multimeter can be used for practical bonding tests, it is not a substitute for a specialized earth-ground meter. To test electrical bonds in a duplex receptacle, insert the multimeter probes into the receptacle: one probe into the neutral slot and the other into the ground slot. Set the multimeter to measure AC voltage and measure the voltage. If the ground and neutral are bonded correctly, you should see an increase in the millivolt reading due to the voltage drop caused by the current flowing in the neutral wire.
In addition to testing the electrical bonds, it is important to ensure that all metal objects in the building are connected to the mains earth to form an equipotential zone. This helps to ensure that all metal objects are at the same potential, preventing the possibility of electric shock.
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Improper bonding
In electrical systems, the ground and neutral leads should only be bonded at one point, which is the main service panel. An improper bond at any other point can create safety risks and disrupt the electrical system's operation. For instance, if the ground and neutral are incorrectly bonded within the receptacle box or nearby on the same circuit, there will be no significant voltage difference, and the current will flow through both paths. This can lead to potential issues and affect the safety and operation of the electrical system.
Corrosion is another possible consequence of improper bonding. Excessive electrical currents from hot, neutral, and ground wires can accelerate the erosion of metal pipes or buildings. It is crucial to ensure that the ground wire has a limitless path, free from the neutral wire's electrical currents, to prevent short circuits effectively.
To identify improper bonding, a digital multimeter can be used for practical bonding tests in less critical applications. While it is not a substitute for a specialized earth-ground meter, it can help determine if there is an improper bond between neutral and ground in a duplex receptacle. By inserting the probes into the neutral and ground slots and measuring the voltage, you can establish a baseline. If there is no change in voltage when a load is applied, it suggests improper bonding.
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Testing electrical bonds
While specialised earth-ground meters are ideal for comprehensive testing, digital multimeters (DMMs) can be used for practical bonding tests in less critical applications. One practical application for a DMM is checking if the ground pin in a duplex receptacle is incorrectly bonded to the neutral. Here is a step-by-step guide on how to perform this test:
- Ensure that nothing is plugged into either outlet.
- Insert the multimeter probes into the receptacle: one probe into the neutral slot (the wider slot on the left-hand side) and the other into the ground slot (the D-shaped socket).
- Set your multimeter to measure AC voltage.
- Measure the voltage. The multimeter should read 0.0 volts or a few millivolts. This establishes the baseline voltage with no load.
- Plug a hairdryer into the other socket of the same duplex receptacle. Turn the hairdryer on to its highest setting, typically placing a one-kilowatt load on the circuit.
- Measure the voltage again between the neutral and ground with the hairdryer running.
If the ground and neutral are bonded correctly only at the service panel, you should see an increase in the millivolt reading due to the voltage drop caused by the current flowing in the neutral wire. If there is no change in the voltage reading, it suggests that the ground and neutral may be incorrectly bonded within the receptacle box or somewhere nearby on the same circuit.
Another example of testing electrical bonds is in swimming pools, where any metal object (other than conductors of the power circuit) over a certain size must be bonded to ensure that all conductors are at the same potential. A simple way to test a swimming pool bonding grid is by using an alligator clip to attach one end of a wire to an exposed bonding wire at the equipment pad. Unroll the wire to reach the furthest component to be tested and connect the other end of the wire to one of the ohmmeter test leads. Use the other probe to take readings of various metallic components by touching it to them. The needle should remain close to zero. If you find readings above zero, then you know that those components are not properly bonded.
It is important to note that testing electrical bonds may require specific tools and procedures, and it is crucial to have a good understanding of electrical systems and safety precautions before attempting any tests.
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Equipotential bonding
In simple terms, equipotential bonding is the practice of installing bonding conductors or jumpers to create an equipotential zone, where all conductive parts are at the same potential. This is particularly important in locations with increased shock risk, such as bathrooms and areas near swimming pools.
According to Australian and New Zealand Standards (AS/NZS 3000: 2018 Electrical Installations), equipotential bonding is necessary for products with conductive metallic surfaces greater than 100mm in any dimension installed within arm's reach of a body of water, such as spa pools, swim spas, and pools. This includes spa accessories like cover lifters, ladders, and rails.
There are two aspects to equipotential bonding: main bonding and supplementary bonding. Main bonding interconnects incoming metallic services such as gas, water, and electricity, while supplementary bonding is required in rooms with increased shock risk, like bathrooms and pool areas. It is crucial that equipotential bonding is carried out by a licensed electrician to ensure compliance and safety.
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