NFPA 79 - 2021, Chapter 6: Protection from Electrical Hazards
This is the chapter that was most changed, compared with the 2018 edition.
Here the language from the 2018 edition (220.127.116.11 Enclosure Interlocking).
Here the new language:
18.104.22.168 Enclosure Access.
Opening an enclosure (e.g. doors, lid, cover) that contains live parts operating at or above 50 volts rms ac or 60 volts dc shall be permitted only under one or more of the following conditions:
- The use of a key or tool is necessary for access to live parts operating at or above 50 volts rms ac or 60 volts dc. AII live parts mounted on the inside of doors or covers that are operating at or above 50 volts rms ac or 60 volts dc shall be protected from unintentional direct contact by the inherent design of components or the application of barriers or obstacles such that a 50 mm (2 in.) sphere cannot contact any live parts. A safety sign shall be provided in accordance with 16.2.4.
- The disconnecting means supplying the enclosure is interlocked with the enclosure door(s) in accordance with 22.214.171.124.
- Opening without the use of a key or a tool and without disconnection of live parts shall be permitted only when all live parts inside that are operating at or above 50 volts rms ac or 60 volts dc are separately enclosed or guarded such that there cannot be any contact with live parts. A safety sign shall be provided in accordance with 16.2.4.
In essence, the inside of a control panel does not required any type of protection from direct contacts (IP 0 in IEC terminology). If IP 1 is present for components mounted on the inside of the doors, than a key is enough to guarantee protection; otherwise, all the doors need to be interlocked.
That means, from 2021, that no door interlocks will be required anymore for most of the industrial control panels with destination USA or Canada.