IEC 62353 — periodic testing of medical electrical equipment

The guide on protection class I/II/III and the guide on insulation resistance testing cover the regular NEN 3140 inspection of portable and connected equipment in general. This article covers a category of equipment for which that regular approach does not simply suffice: medical electrical equipment, which can be in electrical contact with a patient during use, and for which a separate field-testing standard exists.

Why IEC 60601-1 is not the standard for periodic testing

IEC 60601-1 is the type/design standard for medical electrical equipment: the manufacturer tests once, under controlled laboratory conditions (for example with an elevated mains voltage or an isolated test network), whether a device type meets the safety requirements. Those test conditions cannot be replicated in a hospital or maintenance workshop, and repeatedly applying the full IEC 60601-1 test sequence to the same unit can needlessly stress the device. A separate standard was therefore developed for periodic retesting in the field (at commissioning, periodically, and after repair): IEC 62353 ("Recurrent test and test after repair of medical electrical equipment").

Three methods for measuring leakage current

A distinguishing feature compared with a regular NEN 3140 inspection is that IEC 62353 allows three different methods for determining leakage current, each with its own practical trade-off:

Direct method: the same principle measurement as in IEC 60601-1 — the actual leakage current is measured via a body-model network to earth.
Differential method: the leakage current is derived from the difference between the current in the live and neutral conductor of the supply cable. This method is faster to perform, does not require interrupting the protective conductor during the measurement, and is widely used in practice for periodic field testing.
Alternative method: measurement via the applied part (the patient connection) itself, relevant for equipment with type B/BF/CF applied parts.

Why ordinary PAT tooling is not sufficient

A standard NEN 3140 leakage current tester (PAT tester) for office or workshop equipment is generally not equipped with the differential or alternative measurement method, and does not know the specific limit values that apply to applied parts (patient connections, classified as type B, BF or CF) — those limit values are considerably lower than the leakage current limits for ordinary protection class I/II equipment, precisely because an applied part can be in direct electrical contact with the patient. Medical equipment therefore needs specialised test equipment (a "medical equipment safety tester") specifically calibrated to IEC 62353.

Practical relevance

When setting up a testing regime for medical electrical equipment (infusion pumps, patient monitors, electrosurgical equipment), it must be established that the test equipment and method used comply with IEC 62353, not a generic NEN 3140 PAT procedure — and that the correct limit value is applied for the type of applied part (B/BF/CF) of the specific device.

Common mistakes

Trying to replicate IEC 60601-1 test conditions in the field — that is a type/design test under laboratory conditions, not intended for repeated periodic testing.
Using an ordinary PAT tester for medical equipment without checking whether the instrument supports the differential or alternative method and the type B/BF/CF limit values.
Failing to distinguish between the direct and the differential method when interpreting a measured value — each measures something slightly different, and a limit value belongs to the method used.
Confusing the patient leakage current limit of an applied part with the general enclosure leakage current limit of the device — these are separate measurements with separate limit values.