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Electrical Testing Types
Electrical test of light switch

Types of Electrical Testing UK

Many types of electrical testing can be performed on industrial, commercial, and residential equipment and installations. In this article, we discuss the most common ones and why they are important.

To ensure the safety and reliability of your electrical installations, it is important to understand the different types of electrical testing available.

What Is the Purpose of an Electrical Test?

Electrical tests ensure that the wiring in a home, commercial building, or other property types is entirely safe and functioning correctly.


These tests detect problems such as shorts, leaks, or faulty connections. They can also be used to determine the size of the fuse or circuit breaker needed to protect the wiring.

Tests can be performed on the electrical system as a whole or on individual components, such as outlets, switches, and specific fixtures.

The most common electrical tests include:

  • Supply test: This measures the voltage of the electrical supply. The voltage must be within the acceptable range for the appliances and equipment being used.

  • Circuit test: This measures the current flowing throughout the circuit. It determines if the circuit is overloaded or if there is a short circuit.

  • RCD test: This measures the resistance of the circuit. It can determine if there is an insulation problem or if there is a ground fault.


Each type of test has its purpose and can be used to detect different problems. If you are unsure which test is suitable for your situation, consult a qualified electrician. They will be able to assess your system and recommend the best course of action.

Electrical Testing in the UK

On June 1, 2020, the UK government mandated that all private landlords must get electrical installations in their properties inspected by qualified and competent electricians at least every five years. Electrical safety reports must be furnished to tenants and local authorities.

Exact timelines and frequency for electrical testing in commercial properties are varied. However, it is an employer’s responsibility to ensure that all equipment is safe for use. And all business premises open to the public must not cause harm to anyone.

Here are a few common tests that ensure the safety of everyone on the property, whether it’s commercial or residential: 

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The Zs Test

A Zs test ensures that the property’s grounding system is effective. It also measures the electrical resistance of this grounding system.

This value must be within the parameters set for the property’s grounding system.


The greatest Zs value measured shall not exceed 0.8 of the applicable BS 7671 value for each circuit. This test is important because an effective grounding system is crucial for ensuring the safety of the overall electrical system.

The short-circuit resistance (resistance between live and neutral wires) and earth fault (resistance between the live wire and the earth) are measured for each circuit. If it is safe to do so, the Ze and R1+R2 measurements can be used to estimate these values for each circuit.

These measurements determine how big of a fuse or circuit breaker is needed to isolate a malfunctioning circuit within a predetermined amount of time in case of a failure. This prevents overloading of the circuitry before the fault can be isolated. The circuit rating and kind of protection determine the acceptable Zs values (Electrical Supply Council, 2011).

The Ze Test

The external ground fault loop impedance, or Ze, is a measure of the resistance in the wiring connecting the circuit breaker box (also called fuse board) and the transformer that supplies electricity to the property.

The impedance must be low enough that protective devices (fuse and circuit breaker) will break the current if a high-current fault occurs.

The Ze test measures the impedance of a grounding electrode relative to a remote reference electrode, usually the general mass of the ground around the installation. A low impedance reading indicates a good connection to the grounding unit, which is essential for the effective operation of the grounding system.

The maximum value for external earth loop impedance (Ze) is typically 0.8 Ω for the TN-S system and 0.35 Ω for a TN-C-S system (Sparky Facts UK, NA).

The actual value measured may differ due to factors, such as Zs values. Therefore, it is crucial to regularly test external ground fault loop systems to ensure they are functioning correctly and providing adequate protection.

The Purpose Of Testing Electics
Electrical Testing In The UK
Zs Testing
Ze Testing
Testing A Electric Cooker Switch

R1 + R2 & Insulation Resistance

The resistance of each wire back to the source is measured for live and earth wires in a circuit. The resistance in a radial circuit increases with increasing distance from the source. This test will uncover any errors in cabling or connectors.

Because the resistance of R1+R2 is consistent along a ring circuit, it's easier to determine whether or not an appliance has been connected in parallel with another.

This test is repeated to measure the combined resistance of a live conductor (R1) and its neutral counterpart. Because it is easier to run test wires across a property than pair-wise, conductors are frequently examined in groups.

The earth's resistance (R2) can be calculated directly from the source to the output.

This test can detect polarity difficulties, such as when one live wire is accidentally swapped with another. It can also identify when a high resistance has built up in an outlet due to a defective connection or terminal damage. These must be replaced immediately to ensure the safety of whoever will use them.

Thorough testing prevents fires, shocks, and other hazards if an electrical system is not maintained correctly.

The fully qualified, accredited, insured, and highly trained electrical inspectors at Obtain Electrical Services will provide all your legal electrical certificate needs.


Testing your electronic installations allows for the detection of issues long before they cause an unexpected loss of power or worse.

If you need an EICR report, fire alarm testing, PAT testing, or an emergency lighting report for your residential or commercial property, contact us for a free, no-obligation quote!


Fuse Board Main Switch
Insulation Reistance Testing
R1 + R2 Testing
Hire An Electrical Inspector
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