Section 110.27(A) provides requirements for the guarding of live parts from accidental contact, but these are sometimes implemented inadequately. A common violation is that of considering the threshold of 110.27 to be 480V, thus leaving 277V lighting and 120V branch circuits unguarded. The threshold is 50V.

Adopting a single best practice, wherever possible, can eliminate violations. That practice is to install all electrical equipment so that exposed parts are inside approved enclosures. Generally, this is possible in all applications in a typical commercial or industrial facility.

Where it isn't possible, you have four other means of guarding.

You can install the equipment:

  1. In a vault with limited access.
  2. On a mezzanine or other platform.
  3. At least 8 ft above grade.
  4. With partitions that prevent inadvertent contact .
No matter where you install the equipment, use suitably strong enclosures or guards, and arrange them in a manner designed to prevent damage to the equipment.

If you install the equipment in rooms or other guarded locations that contain exposed live parts, post conspicuous warning signs forbidding entry by unauthorized personnel. It's better to make restricted access a physical matter rather than just an administrative one. The NEC doesn't require passkeys to restrict access, but such a system is desirable from a personnel protection and plant security standpoint.