Switchgear and protection: trapped key interlocking vs LOTO

There are two potential options when considering a mechanical safety system for switchgear applications. The choice is between a trapped key interlocking system or a padlock-based lock-out / tag-out (LOTO) system. Both systems:

  • Provide a method of isolating switchgear.
  • Allow safe personnel access when maintenance of machinery is required.
  • Are available in full stainless steel or brass versions.
  • Offer a comprehensive range of products with different forms and sizes to suit the needs of the equipment concerned.
TKI Switchgear

Trapped key interlocking applied to switchgear protection.

However, in terms of safety, trapped key interlocks (TKIs) offer significantly higher levels of protection compared with LOTO.


LOTO systems don’t provide the same level of protection as trapped key interlocking.

There are four main reasons trapped key interlocking beats out LOTO:

  1. TKIs are durable with a proven track record of withstanding harsh operating environments through decades of operation.
  2. TKI’s force workers to follow a strict process which prevents them from deliberately skipping or inadvertently missing steps. The equipment is interlocked together in such a way that steps cannot be overlooked or ignored.
  3. In an environment where staff may be unfamiliar with operations and speak a range of different languages, the enforced procedure of TKIs negates miscommunication or misunderstanding of operating practice.
  4. When there is a need for full-body access, TKIs provide a personnel key that protects workers from potential danger and puts them in control of the process. Until the personnel key is returned, the switchgear cannot be returned to the live state.

By: Adam Felton, Technical Marketing, Castell Safety International Ltd.

2 Responses to “Switchgear and protection: trapped key interlocking vs LOTO”

  1. Ronald Benton says:

    In the above article you are stating that your trapped key interlock is better than lockout/tagout in protecting workers from the unexpected startup of a machine. Is your trapped key interlock an electrical control circuit type of interlock? If so, doesn’t OSHA specifically prohibit this type of protection for work that requires LOTO? I know they granted a variance to Nucor Steel, but Nucor had to put in place a number of additional safeguards and show that they were effective in protecting the worker. Are you able to market your above system as meeting all of OSHA’s 1910.147 LOTO standard requirements?


  2. Lisa Wallner says:

    Thank you for this great question!
    First, in regards to the question: Is your trapped key interlock an electrical control circuit type of interlock? Castell offers a full range of mechanical bolt and access interlocks, as well as electrical power isolation interlocks, which can be used in combination, depending on applications needs.

    In regards to your second question: If so, doesn’t OSHA specifically prohibit this type of protection for work that requires LOTO? OSHA does not make mention of key interlocks specifically in their 1910.147 standard. However, our interlocks do conform to ANSI Z244.1 standard for CONTROL OF HAZARDOUS ENERGY LOCKOUT/TAGOUT and ALTERNATIVE METHODS, and OSHA has recognized the ANSI Z244.1 standard (official letter here: https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIONS&p_id=24969).

    If you’d like to discuss how Castell can help you address your safety and standards compliance needs, I’d be happy to have an applications engineer contact you directly.

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