PLC"s and NEC

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roc1

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I amcurios why the NEC does not have much on PLC"s?I program PLC andwe are contractors also.Since we build PLC and industrial controls just wondering why more is not covered in the code?
Thanks for info
roc1
 
Each device is not identified in the NEC, but the related items are in the NEC. For example, wiring for the PLC is covered by Article 720, 725, 727, 800 and 830.
My garbage disposal is not listed in the NEC, but the wiring for it is.
 
At this point in time the NEC is still a construction standard, in particular "premises wiring", not a manufacturing standard. There are relatively few areas in the NEC that deal specifically with the internal wiring of control panels (other than grounding and the incoming wiring). But the NEC does suggest that control wiring be done per NFPA79.
 
You have almost an entire article on PLCs, Article 725.
Do you know and understand what Class PLC wiring is?

Also there are two important documents that relate to PLCs NFPA 79 and UL508A
The NEC is far more concerned with the wiring external to the PLC control cabinet. Its all covered by the NEC...the rules that apply depend your answer to the first question.
 
In addition to the NFPA-79 and UL508, look at Article 409 in the NEC. It covers industrial control panels, which should generally cover PLC's and their wiring.
 
Article 409 is of only limited use in the construction of industrial machine control panels. It is primarily concerned with the power supply to the panel and the grounding of the installation. 409.1 suggests using UL508A as a reference and 409.3 refers us to other code articles such as 670.

Article 725 is also of little use internal to these panels. 725.1 specifically says it only covers circuits which are not an integral part of a device or appliance. It can be argued that an industrial control panel may be considered a device for the purposes of this article (see definition of Controller).

670.2 says the "associated electrical equipment, including logic controllers...are considered part of the industrial machine."

For control systems, my preference is to use NFPA 79 which deferes to the NEC for external connections and topics not specifically addressed (NFPA791.4.1 and 1.5).
 
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