Last edit: 17/07/2023
NFPA 70 or NATIONAL ELECTRICAL CODE is the reference standard for electrical installations in premises and buildings in USA.
Being an Installation Code, it is addressed to the installer, more than to the Electrical Engineer who designs the electrical installation/distribution.
The first National Electrical Code was developed in 1897. In 1911, the National Fire Protection Association (NFPA) became the sponsor, and the Code has been revised on numerous occasions since that date. Now it is revised every three years. The latest edition is 2020. The NEC is available for adoption as the electrical law in a governmental jurisdiction. That governmental jurisdiction may add one or more amendments to allow for local needs, preferences, or conditions (see for example the Chicago Electrical Code).
The code was born soon after Thomas A. Edison's Pearl Street Station was installed in New York City in 1882. Electrical fires were becoming commonplace and, by 1897, the problem was reaching epidemic proportions. A diverse group of knowledgeable, concerned individuals assembled to address this critical issue. The need for standardization was apparent. The consensus of more than 1200 individuals produced the first set of nationally adopted rules to govern electrical installations and operations: the National Electrical Code was born. The NEC states its purpose as "the practical safeguarding of persons and property from hazards arising from the use of electricity". This objective has remained constant throughout the NEC’s existence, and the principles it contains continue to grow and change with the dynamic electrical industry.
The NFPA 70 or NEC is the reference standard for several electrical standards among which:
- UL 508A: the product standard for Industrial Control Panels
- NFPA 79: the reference for the electrical installations in Machineries
There are 2 main articles in the NEC dealing with Machinery:
- Article 409: Industrial Control Panels
- Article 670: Industrial Machinery
The latest Edition of the standard is the 2023, published in October 2022. Hereafter the key changes having a possible impact to the Electrical Equipment of Machinery.
THE USE OF SPDs INSIDE INDUSTRIAL CONTROL PANELS.
This is one of the recurring prescriptions. This is the latest language used in the standard.
[NEC 2023] 409.70 Surge Protection.
Safety circuits for personnel protection that are subject to damage from surge events shall have surge protection installed within or immediately adjacent to the control panel.
The same is valid for industrial Control Panels for Industrial Machineries
[NEC 2023] 670.6 Overvoltage Protection.
Industrial machinery with safety circuits shall have overvoltage protection.
The Rule has no exception anymore, however, industrial control panels are built in conformity with NFPA 79 and/or UL 508A. None of the two standards requires Surge Protection Devices inside the panel. In the first round of discussions, held in February 2022, for the 2024 edition of NFPA 79 the issue was raised that the NEC would have that new language, however, after intense discussions, the agreement was not to include the requirement in the NFPA 79. That may still change during the second round of discussions foreseen for I Quarter of 2023. UL 508A has never introduced any requirement and so far nothing is foreseen coming. Bottom line is that, if you build panels in conformity with one of the two above mentionned standards, no SPDs are required. Sadly to say, this new language in the NEC may generate confusion among consultants, manufacturers, NRTLs and AHJs.
EACH INDUSTRIAL CONTROL PANELS MUST HAVE AN ELECTRICAL LABEL VISIBLE ON THE OUTSIDE.
We recall discussions held in both the UL 508A and the NFPA 79 table round whereby people were pushing for having the least technical data shown outside the panel, citing situation of agressive ambient conditions that "delete" the information on the label within few years. GT Engineering never shared that reasoning and supports the fact key informations have to be shown plainly visible on the outside of the panel. Information like:
- Manufacturer's name;
- Complete electrical rating of each source of supply;
- Short circuit current rating of industrial control panel;
- Field wiring diagram number;
- Enclosure Type rating;
Should be indicated without the need to open the panel. People not in favor have always indicated that the NEC was simply stating "Plainly Visible" and that did not meant "on the outside". That is now clarified, detailing what can be indicated on the inside of the panel. There are two types of Industrial Control Panels: those for indistrial machineries and all the others (for Variable Speed Drives for example). Indications for the former are in article 670 and for the latter in article 409.
[NEC 2023] 409.110 Marking.
An industrial control panel shall have permanent markings that are visible after installation. The markings in 409.110(2) and (3) shall be attached to the outside of the enclosure. The markings in 409.110(1), (4), (5), (6), and (7) shall be attached to either the inside or outside of the enclosure. The following markings shall be included:
(1) Manufacturer's name, trademark, or other descriptive marking by which the organization responsible for the product can be identified.(2) Supply voltage, number of phases, frequency, and full-load current for each incoming supply circuit.
(3) Where the industrial control panel is supplied by more than one electrical source and where more than one disconnecting means is required to disconnect all circuits 50-volts or more within the control panel, marked to indicate that more than one disconnecting means is required to de-energize the equipment. The location of the means necessary to disconnect all circuits 50-volts or more shall be documented and available.
[…]
Unfortunately the SCCR is not in the list. However, it is compulsory for ICP for Industrial Machineries. I have to say, this time, the NEC has aligned with UL 508A!
[NEC 2023] 670.3 Machine Nameplate Data.(A) Permanent Nameplate.
A permanent nameplate shall be attached to the outside of the control equipment enclosure or on the machine immediately adjacent to the main control equipment enclosure that is visible after installation. The nameplate shall include the following information:
(1) Supply voltage, number of phases, frequency, and full-load current
(2) […]
(3) […]
(4) Short-circuit current rating of the machine industrial control panel based on one of the following:
a. Short-circuit current rating of a listed and labeled machine control enclosure or assembly
b. Short-circuit current rating established using an approved method(5) Electrical diagram number(s) or the number of the index to the electrical drawings
HOW TO BOND INDUSTRIAL CONTROL PANELS.
That is another recurrent subject of questions. Article 409.60 was rewritten to distinguish between single and multisection ICPs.
[NEC 2023] 409.60 Bonding.
Industrial control panels shall be grounded and bonded in accordance with 409.60(A) and (B).(A) Grounding. An equipment grounding conductor sized in accordance with 250.122 shall be connected to an equipment grounding bus or to an equipment grounding termination point provided in a single-section industrial control panel.
(B) Bonding. Multisection industrial control panels shall be bonded together using an equipment bonding jumper sized in accordance with 250.102(D).
AVAILABLE SHORT CIRCUIT CURRENT.
There is a difference between:
- The Short Circuit Current Rating (SCCR) of a Control Panel (that is the maximum current the the protections inside the panel can interrupt and extinguish without damages for people of the environmental
- The Available Short Circuit Current (also called Available Fault Current): That is the maximum short circuit current that is available at a certain point of the premise or building electrical distribution network.
An ICP for Machinery has to be labelled on the outside with its SCCR. The user has to add the available SS Current. That is to make it visible to an inspector or an AHJ that the SCCR > ASSC, otherwise there is a Safety issue. The NEC is now clear on that:
[NEC 2023] 670.5 Short-Circuit Current Rating.
(A) Installation. Industrial machinery shall not be installed where the available fault current exceeds its short-circuit current rating as marked in accordance with 670.3(A)(4).(B) Available Short-Circuit Current Field Marking. Industrial machinery shall be legibly marked in the field with the available fault current. The field marking(s) shall include the date the available fault current calculation was performed and be of sufficient durability to withstand the environment involved.