An impedance tester is an electronic device that qualified technicians use to

  1. Measure the level of resistance in the earth return circuit and
  2. Make sure it is low enough to allow enough current to flow through the circuit and operate a protective device when a fault is detected.

This procedure is called a loop impedance test. Loop impedance needs to be measured to ensure the functionality of your protective devices. When the earth return circuit is functioning at an optimal level, your circuit protection (MCB or miniature circuit breaker) can effectively disrupt the flow of electricity when an abnormality is detected. This protects your circuit from unnecessary damage.

In simple terms: your circuit breaker will not be able to protect the system unless your resistance is at a certain level. That’s where the testing comes in. You need to employ a qualified technician to inspect your circuit and make sure everything is as it should be.

What is an earth return circuit?

When we talk about the earth or ground in terms of electrical circuits, we mean the direct physical connection a circuit may have with the earth, or the common return path for the electrical current. Electrical circuits are connected to the ground for a variety of reasons including the following:

  • Protection – if your building suffers a surge in electricity, the earth can absorb the excess instead of overloading your circuit. When excess electricity is present, it always takes the path of least resistance.
  • Exposed metal parts (of electrical equipment) can be grounded to prevent human contact
  • Earth is a good conductor
  • Generally, earthing provides an alternative path for dangerous current to flow and limit the occurrence of electrical shock.

An impedance system connects the distribution system and the ground to limit the flow of current that can go into the earth. Our technicians use an impedance tester to check that the flow is at the right level.

How does this electrical testing procedure work?

External earth fault loop impedance is measured in a value called ‘Ze’. This is a measured resistance of the wiring between the supply unit (for example, the fuse board), the transformer, and the earth return path.

Total system loop impedance is called ‘Zs’. This type of resistance has to be measured at each individual circuit at the location that is at the most distance away from the point of supply. This may be measured in a power socket or with an external earth probe.

A test & tag technician will plug an impedance tester into the socket or attach it to the supply unit. The testing machine must operate with a low electrical current so that it does not activate the residual current device that is protecting the circuit. After collecting a reading from the circuit, the technician will compare the results to the recommended impedance level guides and record the reading in a report.

After receiving these results, you will know whether your circuits will allow a functional MCB to trip the system when required.

Why is it important?

As a nation, we need to make a concentrated effort to protect our employees from injury. Circuit damage can result in electrical fires that can harm your staff. You can prevent injury and death in your workplace by investing in regular testing.

You have a duty to ensure a safe working environment for yourself and those around you.

Choose Jim’s Test & Tag for Impedance Testing

If you care about safety in your business, contact us today. We are experts in electrical risk assessment. We use the best industry equipment – our earth loop tester devices are checked for accuracy and provide reliable results for all of our clients.

Our services are completely mobile and available across New Zealand. Simply call us and we will put you in touch with your local team member. One of our friendly electrical experts will visit your property and measure the external and total system resistance (subject to your requirements).

For all of your impedance tester requirements, there’s no better option. Take advantage of our safety testing services today. Your safety is our business.