NETA, the InterNational Electrical Testing Association, publishes two documents that have become a de facto reference across much of the industry: the Acceptance Testing Specifications (ATS), for commissioning new equipment, and the Maintenance Testing Specifications (MTS), for equipment in service.
Their practical value is that, for each equipment type, they list which tests to run, how often and against what acceptance criteria, including reference value tables for insulation resistance, contact resistance and operating times. They fill the gap between what a product standard requires and what has to be decided on a specific site.
They are not mandatory standards unless a contract invokes them, but many specifications cite them directly, and modern test sets include test plans based on them.