Periodical and service testing of electrical equipment and power tools based on current standards

Testing the safety of electrical equipment and power tools is essential in order to prevent accidents at the workplace, public utility facilities and at home. In case of failure, user’s health or even life could be at risk. From the perspective of companies, occupational health and safety regulations increasingly require the equipment in the company to be inspected on a regular basis and inspection results to be archived. This is directly correlated with criminal liability in case of accident at the workplace. The certainty of test performance with due diligence and in a correct manner is ensured by the knowledge and observation of the applicable standards.

Periodical tests are described in EN 50699:2021-07. The document defines the requirements for the periodical testing of the electrical equipment in order to check the efficiency of the protection measures. EN 50678:2020-11 defines the requirements for post-repair testing of the safety of electrical equipment in order to check if the service works had no impact on the basic protection measures. The above-mentioned standards are applicable to the equipment connected at the workplace to branch circuits with the rated voltage in the range of 25…1000 V AC and 60…1500 V DC and with the currents up to 63 A.

Whether the tests are performed periodically or post-repair, the tests must be performed by personnel with the required qualifications and training. In addition, the measurement equipment must be properly selected. The tests should be performed in the conditions corresponding to the operating conditions of the equipment (temperature, humidity, air pressure). If the equipment to test is soiled, it must be cleaned and left to dry, if necessary. The order of test performed should follow the order specified in the standards. Each individual measurement must be completed with a positive result. If the result is negative, the next testing stage must not be pursued.

If a certain test type is not possible, the measurement technician, must decide based on their knowledge if the safety of the inspected equipment may be confirmed without that step, without the measurement that cannot be performed, or if it may be replaced with another test type. The decision must be justified and included in the report.

Table 1. Equipment protection classification

Protection class	Symbol	Description
Class I		The equipment features basic insulation, which provides protection against indirect contact, and a protective earth terminal (PE)
Class II		The equipment features double or reinforced insulation
Class III		The equipment is powered with reduced voltage, which does not exceed the permitted touch voltage

Visual test

The test is intended to check the equipment for any visible damage that could have an impact on safety and to confirm the completeness of its components. The standards recommend checking the following points:

legibility and completeness of the markings, labels and symbols,
no mechanical damage or contamination that could have an impact on proper operation or safety,
proper connection of wires and their marking, no phase sequence shifting, no polarity shifting and proper connection of the earthing conductor,
mechanical check of switches, circuit breakers etc.,
condition of the mains plug, connectors and power cords,
condition of wire attachment,
condition and type of the fuse or fuses (if the components in use meet the requirements of the manufacturer),
passability of ventilation ducts,
signs of overloading or overheating of equipment, which could contribute to its significant deterioration,
signs of corrosion that could have an impact on safety,
condition of the oil,
condition of accessories (if they meet safety requirements),
condition of the insulation (no cuts or abrasions are acceptable!).

Protective conductor resistance and continuity measurement

This measurement is intended to check the proper implementation of the earthing connections protecting the user. During the measurement, the conductors cannot be straightened. They must be bent as in the natural operating conditions of the test object, in particular the ends on the equipment side and on the mains connection side. The measurement must be performed with an instrument that generates the test current of at least 200 mA as per EN 50699:2021-07 and EN 50678:2020-11.

Table 2. Maximum resistance of the PE conductor

Standard	Test current	Permitted R_PE for the protective conductor with the length of up to 5 m and the cross-section of 1.5 mm²
PN-EN 50699	≥200 mA	0.3 mΩ
PN-EN 50678	≥200 mA	0.3 mΩ

For a cross-section other than 1.5 mm2, the maximum resistance of the conductor must be calculated from the formula:

or:

where:
R – resistance (Ω)
p – electric conductivity of the metal used for the PE conductor (m/Ωmm²)
l – conductor length (in metres)
γ – conductivity (S/m)
A – cross-section of the PE conductor (mm²)

For conductors longer than 7.5 m, the resistance limit must be increased by 1 mΩ for every subsequent 5 m of the power cord. However, the total resistance should not exceed 1 Ω.

Fig. 1. Measurement of the resistance of the protective conductor with the Sonel PAT-8x tester

Insulation resistance measurement

The measurement must be performed between the live parts and each accessible conductive part (including the protective earthing). The test must be performed until the measurement results are stabilised. Attention must be paid to all activating/circuit braking/disconnecting components that could be found in the power supply system of the equipment – during the insulation resistance measurement, they must be in the activated (conducting) position. On the market, there are pieces of equipment fitted with a mechanical electrical connector, e.g. contactor. In such cases the completion of the subject test is only partial. It must be replaced with a differential leakage current measurement.

Table 3. Insulation resistance measurement requirements for equipment under periodical and post-repair testing as per EN 50699 and EN 50678

Test range		Protection class	Limit
Between live parts and touch-accessible metal parts with connection to earthing	General	I	1.,0 MΩ
	With heating elements	I	0.3 MΩ
	With elements with the power above 3.5 kW	I	0.3 MΩ
Between live parts and touch-accessible metal parts without connection to earthing		I and II	2.0 MΩ
Between live parts and metal parts insulated from live parts		I and II and III	2.0 MΩ
Between live parts with SELV/PELV protection from accessible conductive parts		III	0.25 MΩ

Fig. 2. Insulation resistance measurement of class I equipment with the Sonel PAT-8x tester

Fig. 3. Insulation resistance measurement of class II equipment with the Sonel PAT-8x tester

Leakage current measurement

Leakage current measurement is required for equipment with such protective connection that is not permanently connected to the mains. We distinguish the following leakage current types:

Equivalent current (alternative). This is a theoretical current. The tested equipment is powered from a reduced safe voltage source and the resulting current is scaled up to calculate the current that would flow with the rated power supply (which also makes this measurement the safest for the tester operator). The equivalent current measurement is not applicable to the equipment that requires the full supply voltage for start-up.

Current in the PE conductor (direct). This is the current that flows through the protective conductor, when the equipment is in operation. It must not, however, be identified with the total leakage current as other leakage routes may exist in addition to the PE conductor. Therefore during the test, the tested equipment should be separated from the ground.

Differential current. According to Kirchhoff’s first law, this is the difference of the values of the currents flowing in L and N conductors of the test object in operation. The measurement enables determining the total leakage current of the object, i.e. the sum of all leaking currents, not only the one flowing through the protective conductor (for class I equipment). The measurement is performed as a replacement of the insulation resistance measurement.

Table 4. Leakage current measurement requirements as per EN 50699 and EN 50678

	Limit as per standard
	EN 50699	EN 50678
Maximum permitted leakage current	3.5 mA	3.5 mA

Requirements for equipment with heating elements with the power of >3.5 kW 1 mA/kW, max. 10 mA

Touch current – this is the current leaking to the ground from a component insulated from the power supply circuit, when this component is shorted.

Table 5. Touch leakage current measurement requirements as per EN 50699 and EN 50678

	Limit as per standard
	EN 50699	EN 50678
Touch leakage current	0.5 mA	0.5 mA

Note: For class III equipment this measurement type is not performed.

Fig. 4. Measurement of the leakage currents with the Sonel PAT-8x tester

SELV/PELV-supplied equipment test

For SELV/PELV-supplied equipment powered from an isolation transformer, protection efficiency is checked by:

confirmation of the consistency of the transformer supply voltage with the equipment specification,
insulation resistance measurement between the primary and secondary side of the transformer,
insulation resistance measurement between the active parts and metal components without PE connection

Confirmation of efficiency of other protection measures

For equipment with additional protection measures like RCD, PRCD or other switches, the switch activation test must be performed according to its specification and characteristics. This is required by EN 50678.

Note: In addition, it is required to check the proper connection of the power cords (polarity)!

Functional test

As per EN 50678, the sequence of measurements is concluded with a functional test. The measurement values must be compared with the parameters of the nameplate of the test object, followed by the assessment of the object.

Records and reporting

After testing the equipment, a test report must be completed. It should include the information such as:

information enabling the unambiguous identification of equipment (e.g. identification number),
inspection date,
measurement results,
end result of the test (positive/negative),
recommended next test date,
test equipment information and its metrological certificate,
information of the person responsible for completing the measurements (first name, surname, licence number…),
signature of the person responsible for completing the report and measurements,
comment, if necessary.

The test results must be evaluated to answer the question if the test object is fit for further operation.

Figure 5. Sonel PAT-86 with accessories

Author:
Michał Cichoń
SONEL S.A.