It is important to remember that electrical equipment should be placed in an electrically safe working condition and verified per the rules and requirements in OSHA and NFPA 70E before any maintenance, servicing, or work is performed within the equipment. The addition of service barriers to panelboards reduces the likelihood of electric shock but does not reduce the severity of an arc flash incident.
The NEC requirements are found in section 408.3(A)(2) and are shown below:
408.3(A)(2) Service Panelboards, Switchboards, and Switchgear.
“Barriers shall be placed in all service panelboards, switchboards, and switchgear such that no uninsulated, ungrounded service busbar or service terminal is exposed to inadvertent contact by persons or maintenance equipment while servicing load terminations. Exception: This requirement shall not apply to service panelboards with provisions for more than one service disconnect within a single enclosure as permitted in 408.36, Exceptions 1, 2, and 3.”
Quoted from National Electric Code 2017, © NFPA 2017