Safety Switch and UL Certification

What is UL?

UL is a specialized organization that tests and certifies whether products are safe.

Its official name is Underwriters Laboratories, and it was established in the United States.

UL is not a product manufacturing company. From a separate standpoint from manufacturers, UL actually tests and verifies whether a product is safe for human use and whether it is designed to minimize accidents.

What is a safety switch?

A safety switch is a switch that automatically stops a machine when its door is opened. Factory machines operate at very high speeds and with great force, so if they continue to operate with the door open, it can lead to serious accidents. Therefore, safety switches are strongly required:

to stop the machine reliably
not to fall into a dangerous state even if they fail

What rules does UL use to verify safety?

UL tests products based on structured safety rules (standards). Typical standards related to safety switches are:

UL 60947-1
UL 60947-5-2

What is UL 60947-1?

UL 60947-1 is a basic safety standard common to electrical switches and components.

It verifies basic safety aspects of electrical products, such as:

Is it designed to prevent electric shock?
Does it generate excessive heat?
Is it durable enough for long-term use?

What is UL 60947-5-2?

UL 60947-5-2 describes more detailed safety rules for sensors and detection switches. For safety switches, the key points for verification are:

Can it precisely detect when a door is open?
Is it resistant to malfunctions?
Does it maintain its performance regardless of repeated use?

Significance of UL certification

Only products that pass tests based on UL 60947-1 and UL 60947-5-2 can receive UL certification. UL mark is the proof that a third party has verified safety. Particularly in the United States, UL certification is essential to supply parts and products to factories and machine manufacturers.

By the way, UL 60947-1 and UL 60947-5-2 are product safety standards based on the standards defined by IEC (the International Electrotechnical Commission), such as IEC 60947-1 and IEC 60947-5-2.

IEC is an organization which establishes international rules in the electrical and electronic fields, and UL tests and certifies actual products based on the rules.

Appendix: Differences in roles between international standards and UL certification

In addition to IEC, there is ISO (the International Organization for Standardization), also an international organization that defines universally applicable safety and quality rules. Neither organization “sells products” nor “conducts tests”, but defines:

how to think to ensure safety
what mechanisms are necessary to prevent accidents

and documents safety concepts and standards.

For the safety of machines in particular,

ISO 13849-1
IEC 61508
IEC 62061

are the representative standards for the field called Functional Safety.

As a certification institute, UL can not only evaluate and certify whether actual products comply with UL standards, but also with these functional safety standards.

Therefore, it can be said that a safety switch that has received UL functional safety certification is designed according to the safety concepts considered by ISO and IEC.

Summary

UL is a specialized organization that verifies, using actual products, whether a safety switch can reliably protect people (operators). UL certification can be regarded as a mark of reliability that the product has passed the prescribed safety rules.