Last edit: 17/07/2023
On 8th January 2021 the new edition of Industrial Machinery NFPA 79, the electrical standard for industrial machineries in the USA, was published. That will be valid for the next three years
Although the standard has many parts in common with IEC 60204-1 (alignment started with 2002 edition), there are still several differences.
Unlike IEC 60204-1, NFPA 79 does not recognize the advantage of class 2 insulated conductors, so the criteria for bonding metal parts is different. An excellent standard for bonding criteria is C22.2 No. 0.4 of 2017: Bonding of electrical equipment. Although it is a Canadian standard, the approach is the same in the USA.
Thanks to NFPA 79 it is possible to use Recognized cables in the machine control panel, as long as they do not come into contact with building elements, which follow NFPA 70. An exception exists for protected areas, such as inside a robot cell.
Even UL 508A, from paragraph 65, deals with Industrial Machinery, but unfortunately it is not always aligned with NFPA 79 and this can be misleading, even among insiders. The UL 508A working group expressed its own willingness to align as much as possible with NFPA 79, however being in compliance with a series of product safety criteria, which are missing in NFPA 79 that is a standard for electrical installation
The title of Chapter 5 changed from "Incoming supply circuit conductor terminations and devices for disconnecting and removing power" to "Disconnecting means". It should be clearer that this section deals with the disconnection of all power supplies of the machine electrical equipment. It would be a good idea also to change the title of Chapter 5 of IEC 60204-1 "Incoming supply conductor terminations and devices for disconnecting and switching off". But this will not be discussed before the next 5 years.
Regarding the need for a door interlock, here what the standard requires:
18.104.22.168 Enclosure Interlocking. When required by 22.214.171.124, each disconnecting means mounted within or adjacent to a control enclosure that contains live parts operating at 50 volts ac (rms value) or 60 volts dc or more shall be mechanically or electrically interlocked, or both, with the control enclosure doors so that none of the doors open unless the power is disconnected. Interlocking shall be reactivated automatically when all the doors are closed.
Still regarding main disconnection of the control panel, it has been clarified that, if the main disconnector is outside the control panel, its position must be indicated.
The necessary distances (Chapter 11) in front of a control panel are also aligned with those required by NEC edition 2020.