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An Insulation Diagram (sometimes called an Isolation Diagram) is a
graphic illustration of the insulation barriers required by UL 2601-1
/ UL 60601-1 / IEC 60601-1 for electrical safety. The key to a
successful Insulation Diagram is to keep it simple. It
is not a schematic and should not show greater detail than is
required to illustrate the required barriers.
The following are examples of the items that need to be graphically
illustrated in the Insulation Diagram: spacings, components,
physical insulation, protectively earthed parts (parts with a good
connection to earth ground), and protective impedances (resistors, etc).
Some of the barriers that are required include:
- Between mains circuit and accessible parts, secondary circuits,
patient circuits, the patient, etc.
- Between secondary circuits and accessible parts, patient circuits,
the patient, etc.
- Between data ports (SIP/SOPs) and secondary circuits, accessible
parts, patient circuits, the patient, etc.
The underlying philosophy of the IEC60601-1 harmonized standards is
that equipment must be safe in normal condition (NC) and single fault
condition (SFC). To understand the electrical safety
requirements that are used to create the insulation diagram, we need
to first define a few terms:
- An Applied Part is any pieces of the equipment that can
intentionally or unintentionally be brought in contact with the patient.
- Creepage is spacing along a surface (as an ant crawls).
- Clearance is spacing through the air (as a bug flies).
- LOP is a level of protection (not defined by the standard).
- Basic Insulation (BI) is a spacing or a physical insulation
barrier providing 1 LOP.
- Supplemental Insulation (SI) is also a spacing or a physical
insulation barrier providing 1 LOP.
- Double Insulation (DI) is BI + SI and provides 2 LOP.
Note that BI + BI does not result in DI
- Reinforced Insulation (RI) is a single spacing or physical
insulation barrier that provides 2 LOP.
- Protective Impedance is a component (such as a resistor)
that provides 1 LOP.
- Protective Earth (PE) is a well-grounded part that provides
1 LOP.
- Class I Equipment uses PE as 1 LOP.
- Class II Equipment (also known as Double Insulated) does not
use PE as an LOP.
For electrical safety, the standard requires 2 LOP against excessive
unintentional current, defined as leakage current, passing through
the patient or operator. |
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The following are actual Insulation Diagrams
created for products
- As you can see, they illustrate the required
barriers for each device, as in the examples
You will also notice that the format, tables, and
information provided vary between them. This is simply because
there is no formal format and every engineer has a little different
way that he or she creates them. It simply needs to illustrate
the required barriers and other electrical protection in the simplest
way. The rest depends on the artistic capability of the
engineer and the time they have to create it.
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