Inspecting hand tools — the four test steps and assessment values

The inspection guide lists inspection intervals for hand tools in a table (for example 1 year for class I at low risk), but does not cover how the inspection itself is carried out. This article goes deeper into the actual test steps and the assessment values commonly applied.

The four test steps

A periodic inspection of a portable electric hand tool (drill, angle grinder, soldering iron, extension reel with an integrated appliance) follows four steps in practice, in this order:

Visual inspection — damaged housing, frayed or kinked supply cable, missing strain relief, worn plug, signs of overheating or liquid ingress. This step alone accounts for a large share of rejections in practice.
Earth continuity test (only relevant for protection class I — see the protection class guide): the resistance between the earth pin of the plug and the accessible metal parts of the tool must be low enough for the protective device to trip in time in the event of an insulation fault.
Insulation resistance measurement: a test voltage is applied between the live parts and the enclosure/earth, and the resistance is measured — see also the insulation-resistance-measurement guide for the principle of this measurement on fixed installations.
Functional test: the tool is tested under normal operation (on/off switch, any speed control, safety switches) to establish that it is not only electrically safe but also functionally correct.

Commonly used assessment values

Note: the values below are the widely used reference values for these test steps in practice (comparable to internationally common practice for periodic inspection of portable electric tools) — the exact limit value per tool type and test instrument is given in the instructions of the test equipment used and the internal inspection procedure of the inspecting organisation.

Test	Protection class	Common reference value
Insulation resistance	Class I	≥ 1 MΩ
Insulation resistance	Class II	≥ 2 MΩ
Insulation resistance	Class I, heating element > 3 kW	≥ 0.3 MΩ (lower due to the nature of the heating element)
Earth continuity	Class I	Low resistance, measured with a test current high enough to reliably detect a poor connection without damaging the tool

Protection-class II tools (double insulated, recognisable by the square-within-a-square symbol) have no earth connection and are therefore only tested on insulation resistance and function, not on earth continuity.

Practical relevance

When setting up or outsourcing a periodic hand-tool inspection, it must be established: what protection class does each tool have (this determines whether an earth continuity test is needed), what test equipment and internal rejection limits are used, and does the inspection frequency match the risk of the environment (see the interval table in the inspection guide).

Common mistakes

Testing class II tools for earth continuity anyway (or, conversely, skipping class I) — the earth continuity test is only relevant and meaningful for class I.
Only performing the insulation resistance measurement and skipping the visual inspection — a large share of real defects (damaged cable, missing strain relief) is precisely what the visual inspection catches, not the electrical measurement.
Applying one universal limit value to all tools without accounting for the difference between class I, class II and heating elements — each has its own commonly used reference value.

Inspecting hand tools — the four test steps and assessment values

The four test steps

Commonly used assessment values

Practical relevance

Common mistakes

Related

Further reading