1. Safe Voltage/Hazardous Voltage Circuits

Extra-low voltage circuit: ELV (Extra-Low Voltage) circuit

This is a secondary circuit which, under normal operating conditions, has a voltage of no more than 42.4V peak between conductors or between a power conductor and earth, and 60V DC or less. Although it is separated from hazardous voltages by basic insulation, it does not meet the requirements for SELV circuits or current-limiting circuits.

Safety Extra-Low Voltage Circuit: SELV (Safety Extra-Low Voltage)

A SELV (Safety Extra-Low Voltage) circuit is a secondary circuit in which, under normal operating conditions and under single-fault conditions, the voltage between any two accessible points does not reach a hazardous level.
For Class I equipment, it is a secondary circuit in which the voltage between any accessible part and protective earth is protected so that it does not become a hazardous voltage, and the voltage between conductors or between a conductor and earth does not exceed 42.4V peak or 60V DC.
With the exception of certain models, our power supplies comply with the requirements for SELV circuits.

Hazardous Voltage

It refers to voltages exceeding 42.4V peak for AC and 60V for DC.

2. Type of equipment

Class I Devices

This type of equipment uses basic insulation for protection against electric shock, and, in the event that the basic insulation fails, any conductive parts that may become exposed to hazardous voltage are protected by being connected to the protective earth conductor of the building’s wiring system.
Except for certain models, our enclosed-type power supplies are classified as Class I equipment.

Class II Devices

This type of equipment provides protection against electric shock not through basic insulation, but through additional safety measures such as double insulation or reinforced insulation, and does not rely on protective earthing or installation conditions.

Class III Devices

This type of equipment ensures protection against electric shock by being powered from a SELV circuit and does not contain any hazardous voltages.
Except for certain models, our DC/DC converters are classified as Class III equipment.

3. Types of insulation

Operational Insulation

This insulation is required for the proper operation of the equipment. Although it is not intended to provide protection against electric shock, it is effective in preventing ignition and fire.
In power supplies, it is applied to the rectified portion of the primary circuit.

Basic Insulation

This insulation provides basic protection against electric shock.
Although there is no specific requirement for the thickness of the insulating material, the required creepage and clearance distances vary depending on the operating voltage.
In power supplies, it is applied between the primary circuit and FG, as well as between the secondary circuit (when it exceeds ELV) and FG.

Supplementary Insulation

This is independent insulation that is provided in addition to the basic insulation in order to prevent electric shock in the event that the basic insulation fails.
The insulating material is required to have a thickness of at least 0.4mm.

Double Insulation

This insulation consists of both basic insulation and supplementary insulation.

Reinforced Insulation

This is a single insulation system that provides protection against electric shock equivalent to double insulation in both mechanical and electrical performance.
In power supplies, it is applied between the primary and secondary circuits, and in mounted components, it is used in parts such as transformers and photocouplers.

4. Insulation distance

These are the required values for each type of insulation.
The necessary insulation distances are determined based on the operating voltage within the power supply.

Clearance distances

Clearance is the shortest distance through air between two conductive parts, or between a conductive part and the accessible or grounded surface of the equipment.

Creepage distances

It refers to the shortest distance measured along the surface of an insulating material between two conductive parts, or between a conductive part and the outer surface of the equipment.

5. Other

CTI：Comparative Tracking Index

This index indicates the degree to which conductive paths are difficult to form on the surface of an insulating material.
A higher value means that conductive paths are less likely to form.
CTI is classified by material groups and PLC (Performance Level Category). Since our power supplies use multiple materials, we ensure creepage distances that comply with Material Group IIIb (100 ≤ CTI < 175).

Table 1. CTI material groups and PLCs

Flammability

These are flammability ratings determined based on the UL94 standard, which evaluates the combustion performance of plastic materials used in equipment and appliance components.
The flammability ratings, in order from most flame-resistant to least, are 5VA, 5VB, V-0, V-1, V-2, and HB.
Thin films are classified under the VTM category, with ratings, from most to least flame-resistant, of VTM-0, VTM-1, and VTM-2.
In addition, the flammability ratings for wires and insulating tubes are specified by UL224 and CSA standards, and are designated as VW-1.

Enclosure

These refer to parts that cover components or live parts where electric shock or energy hazards are present, in order to prevent accidental contact, or parts intended to contain and localize fire hazards.
Such enclosures may constitute part of a component or may form the complete cabinet of the equipment.
Since our products are designed to be integrated into end-use equipment, these enclosures are outside the scope of our safety certification.

Protective Earthing

This is intended to protect against electric shock by grounding any accessible metal parts—such as the chassis—that may become energized with a hazardous voltage in the event of a single insulation fault.
Since our products are designed for incorporation into end-use equipment, please connect the FG terminal of the power supply and the PE terminal of the noise filter to the protective earth of the customer’s equipment.
For further details, please refer to the instruction manual for each product.

Safety Interlocks

This refers to a means that prevents a person from accessing hazardous parts until the hazardous condition has been removed, or a means that automatically eliminates the hazardous condition if a person does gain access.
Since our products are designed for incorporation into end-use equipment, safety interlocks are outside the scope of our safety certification.

Power Distribution

TN-S

A system in which the neutral line and the protective earth line are kept separated throughout the entire installation.

TN-C-S

A system in which the neutral conductor and the protective earth conductor are combined into a single conductor in part of the installation.

TN-C

A system in which the neutral conductor and the protective earth conductor are combined into a single conductor throughout the entire installation.

TT

A distribution system in which one point of the power system is directly earthed, and the exposed conductive parts of the building’s wiring are connected to a separate earth electrode that is electrically independent from the power system’s earth electrode.

IT

A distribution system in which no point of the power system is directly earthed, while the exposed conductive parts of the building’s wiring are connected to an earth electrode.

Our products are intended for use in TN and IT systems.