Most machine builders are familiar with the requirement to design electrical equipment in accordance with EN 60204-1:2018. Fewer give the same attention to Section 18 — the verification and testing requirements that sit at the end of the standard.
That gap matters. Section 18 is not optional. For machines without a dedicated product standard, several of the verification activities it describes are mandatory. And even where some tests are discretionary, failing to carry them out leaves a machine without the documented evidence that its electrical protection arrangements actually work.
This article explains what Section 18 requires, when that testing is triggered, and what each test is looking for.
Why Section 18 Matters
A machine can be designed entirely in accordance with EN 60204-1:2018 and still present a risk if the installation has not been verified. Wiring errors, poor connections, damaged insulation, and inadequate earthing continuity do not always produce visible symptoms. They produce fault conditions.
Section 18 exists to confirm that the protective measures built into the electrical design — automatic disconnection of supply, protective bonding, insulation integrity — actually function as intended on the physical machine. And a test that is not recorded cannot be relied upon as evidence.
For CE and UKCA marking purposes, the technical file must demonstrate that the machine meets the relevant essential health and safety requirements. Section 18 verification is part of that evidential picture. It is also specifically referenced in the context of supply, assembly, and installation of machinery — meaning it is relevant not just at the point of manufacture but at the point of commissioning.
When Section 18 Testing Is Triggered
The standard identifies several circumstances where verification and testing applies.
The primary trigger is the supply of a new machine. Where there is no dedicated product standard applicable to the machine type, Section 18 specifies that verification shall always include documentation compliance, continuity of the protective bonding circuit, and functional testing. Insulation resistance, voltage, and residual voltage tests are additionally required or recommended depending on the machine.
Section 18 also applies to installation. Table 9 of the standard sets out how the testing requirement varies depending on the machine’s status at the point of erection. A machine assembled and connected on site, where continuity of the protective bonding circuit has not previously been confirmed, requires both Test 1 (continuity) and Test 2 (fault loop impedance) to be carried out on site.
The standard notes clearly that machines must be re-tested after installation where the earth fault loop impedance could not be verified against final site conditions at the time of manufacture.
Section 18.7 adds a further trigger: modification. Where any portion of the electrical equipment is changed, the need for re-verification shall be considered. This is relevant for any machine that has been retrofitted, upgraded, or had its control system altered.
What the Section 18 Tests Involve
The following covers the tests most commonly required and, where applicable, the criteria against which results are assessed.
1. Compliance with Technical Documentation
The first step is not an electrical test in the measuring sense. It is a verification that the electrical equipment as built corresponds to the technical documentation — that switchgear components, cable terminations, nameplates, and markings are legible, durable, and consistent with what the documentation describes.
This matters because downstream tests are only meaningful if the equipment being tested is what it is supposed to be. A fault found during loop impedance testing is significantly harder to investigate if the installed equipment does not match the schematic.
2. Visual Examination
A physical inspection of the equipment covering housing condition, cable entries and strain reliefs, plugs and connectors, signs of leakage, noise, cooling adequacy, and pollution or corrosion. This establishes a baseline condition before electrical testing begins.
3. Basic Protection Measures (Section 6.3)
Verification that measures for basic protection against direct contact are in place — covers, barriers, enclosures, and insulation. Section 6.3 of the standard sets out the requirements; the verification confirms they have been correctly implemented.
4. Test 1 — Continuity of the Protective Bonding Circuit (Section 18.2.2)
This test verifies that the protective bonding circuit — the network of protective conductors connecting all exposed conductive parts back to the PE terminal — is continuous and of appropriate resistance.
The standard requires measurement at each relevant point using a current of between 0.2 A and approximately 10 A, derived from a separated supply with a maximum no-load voltage of 24 V AC or DC. Earthed PELV supplies must not be used, as they can produce misleading results.
The resistance measured at each point should be consistent with the expected value calculated from the length, cross-sectional area, and material of the protective conductors. There is no single pass/fail threshold stated in the standard — the result is assessed against what the conductor configuration should produce. In practice, low values in the range of a few milliohms to low tens of milliohms are expected for well-bonded machine structures. Higher readings at peripheral points, such as bowl feeder frames or outfeed structures connected via longer runs, are normal and should be assessed in context.
The standard requires this test to be carried out before Test 2. A discontinuity in the protective bonding circuit can create a hazardous situation for the tester if loop impedance testing is performed first.
5. Test 2 — Earth Fault Loop Impedance (Section 18.2.3 and Annex A4.2)
This test verifies that in the event of a fault, the automatic disconnection of the supply will occur within the required time. It does this by confirming that the total earth fault loop impedance — from the supply source, through the line conductor, across the fault, and back through the protective conductor — is low enough for the associated overcurrent protective device to operate as required.
The standard requires both measurement of the fault loop impedance and confirmation that the overcurrent protective device settings and characteristics are appropriate. Measurement is carried out at the machine’s incoming supply terminals. The result is assessed against Table 10 of the standard, which sets out the maximum cable lengths and minimum protective device ratings for different configurations. Where the measured impedance is below the maximum permitted value for the protective device in use, the condition for automatic disconnection is satisfied.
Where RCDs are installed, their operation must also be verified. The standard requires this to be carried out in accordance with the RCD manufacturer’s instructions, with the test procedure and test interval specified in the machine’s maintenance documentation.
This test is particularly sensitive to site conditions. Where a machine is tested at the manufacturer’s premises using a temporary supply, the earth fault loop impedance at the final installation point may differ. This is why the standard requires re-testing after installation where site supply conditions have not been confirmed against the design calculations.
6. Insulation Resistance Test (Section 18.3)
The insulation resistance test applies a DC test voltage of 500 V between the power circuit conductors and the protective bonding circuit. The minimum acceptable insulation resistance is 1 MΩ.
The test is applied across the full electrical installation, or on individual sections where the complete installation cannot be tested as a whole. Where surge protection devices are fitted that could operate at 500 V DC, they should either be disconnected or the test voltage reduced to below their protection level, provided the reduced voltage still exceeds the peak of the upper limit of the supply phase-to-neutral voltage.
Results significantly above 1 MΩ — typically in the range of hundreds of megaohms to gigaohms on a clean, dry machine — indicate good insulation integrity. A result at or just above the 1 MΩ threshold warrants investigation before the machine is commissioned.
7. Residual Voltage Test (Section 18.5 and 6.2.4)
Where appropriate, the standard requires verification that residual voltages at accessible conductive parts fall to safe levels within 5 seconds of the supply being disconnected. The requirement in Section 6.2.4 is that residual voltage shall not exceed 60 V within that period.
In practice, this test is most relevant for machines with significant capacitive energy storage in power circuits. The measurement is made at accessible points after supply disconnection and the voltage decay recorded against time. A residual voltage of 26.7 V reached within 0.2 seconds, as shown in the example test record, is well within the limit.
8. Functional Tests (Section 18.6)
The standard requires that the functions of the electrical equipment are tested. This covers the operation of control circuits, safety-related functions, interlocks, emergency stop, and any other functional behaviour that the machine is designed to perform.
In practice, functional testing is often carried out by the machine builder or integrator and documented separately, with the electrical tester confirming that such testing has taken place and the results recorded. The test record should identify who carried out functional testing and where the results are documented.
Where the Testing Requirement Is Often Misunderstood
Several misconceptions arise regularly in practice.
The first is that a test certificate issued at the manufacturer’s premises satisfies the installation requirement. It does not, where the supply conditions on site have not been confirmed. The standard is explicit: machines must be re-tested when installed if earth fault loop impedance compliance cannot be confirmed from the manufacturer’s test data in conjunction with site supply information.
The second is that the CE or UKCA declaration of conformity covers the verification. The declaration attests to the design. Section 18 verification attests to the physical implementation. Both are needed.
A third area of confusion concerns modifications. Where electrical equipment is changed, the standard requires that the need for re-verification is considered. In practice, any modification that affects protective conductors, overcurrent protection, or insulation should trigger at least partial re-testing.
How Knox Thomas Can Help
Knox Thomas provides Section 18 electrical verification and testing as a standalone service and as part of CE and UKCA marking assessments for machinery.
For clients going through conformity assessment, Section 18 testing forms part of the technical evidence that supports the declaration. We can carry out the testing, produce the documented test record, and integrate it into the technical file alongside the risk assessment, design review, and other compliance documentation.
For clients who need testing independently of a broader conformity assessment — for example, where a machine is being commissioned on site, where a machine has been modified, or where testing records are required for an existing installation — we can provide this as a separate service.
Our testing covers:
- Documentation compliance verification
- Visual examination
- Protective bonding continuity (Test 1)
- Earth fault loop impedance measurement and overcurrent device verification (Test 2)
- RCD testing where fitted
- Insulation resistance testing at 500 V DC
- Residual voltage testing
- Functional test coordination and recording
We issue a formal test report referenced against EN 60204-1:2018, with measurements recorded at each test point. That record is available for inclusion in the technical file or for use as a standalone compliance document.
If you have a machine that needs Section 18 verification — whether at manufacture, on installation, or following modification — get in touch.
We can assess what testing is required for your specific situation, carry it out against the standard, and provide a documented record that supports your compliance position.
