National Electrical Code Top Ten Tips: Articles 670 and 675 -- Machinery
The NEC has two Articles that provide requirements for machinery:
- Article 670, Industrial Machinery.
- Article 675, Electrically Driven or Controlled Irrigation Machines
With that spread of Article numbers, there's room for adding other categories
of machinery some day. It's anybody's guess what those might be, but there are
four slots available.
It's interesting that this series comes right after Article 669, which is a
very short article providing requirements for electroplating equipment. Since
electroplating is an industrial process, it would have been more logical to
include it as Part III of Article 670 (with the existing text being divided into
Part 1 General and Part II for the remainder). Then, various subcategories of
industrial machinery could have their own Parts in Article 670 if those end up
needing specific requirements developed.
- Article 670 provides the requirements for conductors and overcurrent
protection for industrial machinery, in addition to the requirements presented
in Chapters 1 - 4.
- Article 675 provides the requirements for irrigation machines, plus their
branch circuits and controllers, in addition to the requirements presented in
Chapters 1 - 4.
- Industrial machines must have a permanently attached nameplate that provides
five specific types of information [670.3].
- The size of the supply conductor to an industrial machine must be such
that the ampacity is at least 125% of the FLC rating of all resistance heat
loads plus 125% of the FLC rating of the highest rated motor plus the sum of the
FLC of all other connected motors and apparatus that might operate at the same
- A machine is an individual unit and must have an individual disconnect
[670.4(B)]. This disconnect is not required to be lockable, but having a lockable disconnect may be a good idea fo rmaintenance or repair purposes. Since the disconnect can be supplied by a branch circuit protected by fuses or a breaker, it isn't required to have OCPD(s) of its own. You could lock out the equipment at the branch circuit, rather than at the disconnect.
- To interconnect enclosures on the structure of an irrigation machine, you
have to use cable meeting specific criteria [675.4(A)]. It's actully quite a list.
- For irrigation machines, don't count signal and control wires for the
purpose of adjusting ampacity [310.15(B)(3)(a)] based on the number of conductors
- The main controller used to start and stop the irrigation machine must have
an equivalent continuous current rating at least that which is specified in
675.7(A) or 675.22(A) and a horsepower rating at least as large as the value from
Table 430.251(A) and Table 430.251(B) [675.8]. But a listed molded switch doesn't need
a horsepower rating.
- If you have several motors on an irrigation machine, you have to meet the
three conditions in 675.10 if the machine is protected at 30A or less,
600V nominal or less.
- The grounding and bonding requirements for irrigation machines are in
675.12, 657.13, and 675.14. Lightning protection, which also requires grounding and bonding, is covered in 6745.15. Please review the definitions of grounding and
bonding in Article 100 before proceeding, and please review Article 250, Parts
I, II, III, IV, VI, and VII.