Creating insulation diagrams according to 60601-1 – Part 1: Basic concepts of insulation coordination

The electrical safety of medical devices has been the subject of several articles:

• In the article Insulation diagrams in medical technology Isolation diagrams are discussed in general.
• In the article Electrical safety in medical technology describes how electrical medical devices are classified and which principles ensure the safety of electrical devices.

This article will once again explain the basic concepts of insulation coordination in connection with 60601-1. The next article will then show how we proceed when creating insulation diagrams.

Electrical safety is documented by a safety concept and insulation diagram. Although the term "insulation diagram" does not appear in 60601-1, the appendices contain some examples of insulation distances (Annex J) and simplified patient leakage current diagrams (Annex K). The insulation diagram is nevertheless required for approval, as it is part of the IEC Test Report Form (IEC TRF). For battery-operated devices, the insulation diagram can be so simple that it is sometimes omitted, or the approval body creates it itself. For more complex devices, such as those with a mains connection and multiple applied parts, it is absolutely necessary.

An insulation diagram offers many advantages:

• It represents the safety-relevant parts of the device in the form of a block diagram.
• It serves as a basis for improvements, ideas, alternatives within the project
• It serves as a basis for discussions with the admissions office.
• It shows possibilities of how separation lines can be laid in a more technically or financially advantageous manner.
• It serves as the basis for the dielectric strength tests.
• It can show at a glance potential hazards that can arise when connecting external devices. For example, if a PC is connected via USB and suddenly the patient is no longer disconnected from the power supply by two protective measures.

Basic concepts of isolation coordination

Before describing our approach to creating isolation diagrams in the next article, some terms need to be clarified:

MOOP – English: Means of Operator Protection, protective measure to protect all persons except the patient from electric shock

MOP – English: Means of Patient Protection, protective measure to protect the patient from electric shock

MOP – English: Means of Protection, protective measure within the scope of 60601-1 for protection against electric shock, each protective measure must be classified as either MOPP or MOOP.

Degree of contamination – Contamination is defined as any contamination with gases, liquids, or solids that reduces the electrical resistance or insulation capacity of an isolating gap. Four levels of contamination are distinguished, with contamination level 4 no longer being acceptable for insulation that represents a protective measure.

Air distance – The shortest distance between two conductive parts through air

Creepage distance – The shortest distance between two conductive parts along a solid material (IC package, circuit board).

Basic insulation – Insulation to protect against electric shock

Double insulation – Insulation consisting of basic insulation and additional insulation

Additional insulation – Insulation in addition to and independent of the basic insulation as a further protective measure against electric shock

Reinforced insulation – A single insulation measure, but equivalent to the protection of double insulation.

Secondary circuit – A circuit without direct connection to the mains, supplied by an isolated power supply

primary circuit (Primary) – Circuit part that is directly connected to the mains connection or another external power supply.

Comparative tracking index CTI Comparative tracking index (CTI) – The comparative tracking index is a measure of contamination sensitivity and is highly dependent on the material and surface finish. If the CTI of the material used is unknown, IIIb is used; otherwise, you can inquire with the circuit board manufacturer, for example.

Installation or overvoltage category – This provides information about the quality of the power supply, especially which overvoltage peaks must be tolerated.

Those are the basic concepts. The next section will cover the creation of the isolation diagram using an example.

If you are interested in this topic, please contact us in our Newsletter We will soon be publishing a small brochure on insulation diagrams, which covers this topic in detail and is ideal for both initial training and as a reference.