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The Medical Device Developer's Guide to IEC 60601-1

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Accessible Part

Part of equipment which can be touched without the use of a tool.


Accessible Metal Part

Metal part of equipment which can be touched without the use of a tool.


Air Clearance

Shortest path in air between two conductive parts.


Applied Part

A part of the equipment which in normal use:

  • necessarily comes into physical contact with the patient for the equipment to perform its function; or
  • can be brought into contact with the patient; or
  • needs to be touched by the patient


Basic Insulation

Insulation applied to live parts to provide basic protection against electric shock.


Class I Equipment

Equipment in which protection against electric shock does not rely on basic insulation only, but which includes an additional safety precaution in that means are provided for the connection of the equipment to the protective earth conductor in the fixed wiring of the installation in such a way that accessible metal parts cannot become live in the event of a failure of basic insulation.


Class II Equipment

Equipment in which protection against electric shock does not rely on basic insulation only, but which additional safety precautions such as double insulation or reinforced insulation are provided, there being no provision for protective earthing or reliance upon installation conditions.


Creepage Distance

Shortest path along the surface of insulating material between two conductive parts.


Double Insulation

Insulation comprising both basic insulation and supplementary insulation.


Earth Leakage Current

Current Flowing from the mains part through or across the insulation into the protective earth conductor.



Exterior surface of the equipment including:

  • all accessible metal parts, knobs, grips and the like;
  • accessible shafts;
  • for the purpose of tests, metal foil, with specified dimensions, applied in contact with parts of the external surface made of material with low conductivity or made on insulating material.


Enclosure Leakage Current

Current flowing from the enclosure, or parts thereof, excluding applied parts, accessible to the operator or patient in normal use, through an external conductive connection other than the protective earth conductor to earth or to another part of the enclosure.


Functional Earth Conductor

Conductor to be connected to a functional earth terminal.


Functional Earth Terminal

Terminal directly connected to a point of a measuring supply or control circuit or to a screening part which is intended to be earthed for functional purposes.


Leakage Current

Current that is not functional. The following leakage currents are defined: Earth Leakage Current, Enclosure Leakage Current, and Patient Leakage Current.



State of a part which, when connection is made to that part, can cause a current exceeding the allowable leakage current for the part concerned to flow from that part to earth or from that part to an accessible part of the same equipment.


Mains Part

Entirety of all parts of the equipment intended to have a conductive connection with the supply mains. For the purpose of this definition, the protective earth conductor is not considered as a part of the mains part.


Medical Electrical Equipment

Electrical equipment, provided with no more than one connection to a particular supply mains and intended to diagnose, treat or monitor the patient under medical supervision and which makes physical or electrical contact with the patient and/or transfers energy to or from the patient and/or detects such energy transfer to or from the patient. The equipment includes those accessories as defined by the manufacturer which are necessary to enable the normal use of the equipment.



Person handling equipment.



Living being (person or animal) undergoing medical or dental investigation or treatment.


Patient Auxiliary Current

Current flowing in the patient in normal use between part of the applied part and not intended to produce a physiological effect, for example, bias current of an amplifier, current used in impedance plethysmography.


Patient Leakage Current

Current flowing from the applied part via the patient to earth or flowing from the patient via an F-Type applied part to earth originating from the unintended appearance of a voltage from an external source on the patient.


Potential Equalization Conductor

Conductor providing a connection between equipment and the potential equalization busbar of the electrical installation.


Protective Earth Conductor

Conductor to be connected between the protective earth terminal and an external protective earthing system.


Protective Earth Terminal

Terminal connected to conductive parts of Class I equipment for safety purposes. This terminal is intended to be connected to an external earthing system by a protective earth conductor.


Reinforced Insulation

Single insulation system applied to live parts which provide a degree of protection against electric shock equivalent to double insulation under the conditions specified in IEC 60601-1.


Supplementary Insulation

In dependent insulation applied in addition to basic insulation in order to provide protection against electric shock in the event of a failure of basic insulation.


Supply Mains

Permanently installed power source which may also be used to supply electrical apparatus which is outside the scope of IEC 60601-1.



Extra-corporeal object (e.g. screwdriver) which may be used to secure or release fasteners or to make adjustments.



Authority responsible for the use and maintenance of equipment.




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The author thanks the International Electrotechnical Commission (IEC) for permission to use material from the IEC 60601-1 international standard .

All extracts are copyright © IEC, Geneva, Switzerland. All rights reserved. Further information on the IEC, its publications and its role is available from IEC takes no responsibility for and will not assume liability for damages resulting from the reader's misinterpretation of the referenced material referenced due to its placement and context in this publication. The material is reproduced or rewritten with their permission.