Information on NFPA 79

Ready for NFPA 79

Ready for NFPA 79

Machine builders beware: Since the 2018 edition, surge protection is mandatory for machines in parts of the USA. Ensure that your machinery is ready for NFPA 79.

Machine builders and systems manufacturers who export their products to or market their products within North America are subject to the laws and regulations applicable there. One of the most important technical standards apart from the NEC is the NFPA 79 standard. The NFPA 79 standard is revised every three years, following the NEC standard and adopting its additions and revisions.

Learn here about which mandatory NFPA 79 requirements are applicable for the use of surge protective devices (SPDs). You will always be on the safe side with us.

The state where the machine will be operated determines which edition is valid. This means that various editions are valid throughout North America. It is therefore advisable to always take the latest edition into consideration.

NFPA 79 – 2021 edition

  • Surge protection is mandatory for industrial machines with safety-relevant circuits (Safety) that are not yet sufficiently protected against overvoltages.
  • The surge protective devices (SPDs) must be UL-listed.
  • A type 4 SPD in the control cabinet must match the type location of the machine and be marked accordingly.
  • A type 4 SPD may only be installed by the control cabinet manufacturer.
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NFPA 79 – 2018 edition

  • Surge protection is mandatory for industrial machines with safety-relevant circuits (Safety).
  • The surge protective devices (SPDs) must be UL-listed.
  • A type 4 SPD in the control cabinet must match the type location of the machine and be marked.
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Our solution – your advantages

  • VAL-US products are UL-listed and can be used universally in all type locations
  • Short-circuit currents not exceeded due to the high short-circuit current rating of 200 kA
  • Simplified system approval by inspectors because NFPA 79 requirements are complied with
  • Products are available, useable, and mountable Europe-wide thanks to the CE marking
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Our FAQs regarding NFPA 79 (2018) for you

The NFPA 79 (Electrical Standard for Industrial Machinery) is an American standard defining the standard of safety for industrial machinery in the USA. It regulates those electrical and electronic concepts that, if implemented incorrectly, can lead to dangerous conditions in the machinery. Among other concepts, this includes overcurrent protection, cabling, and safety circuits, and, in the latest edition, the use of surge protection.
The NFPA 79 is revised every three years. The latest edition was published in 2018.

Every machine that is to be commissioned must first be inspected and approved by an inspector. Along with the National Electrical Code (NEC – NFPA 70), this inspection is also based on the NFPA 79 standard. If the inspector is of the opinion that the machine does not fully comply with the standard, approval – and therefore NFPA 79 certification – can be refused. In this case, the machine may not be commissioned.

This directive applies to all industrial machines in the USA. Which edition of the NFPA 79 standard is applicable in the respective state/area depends on the valid edition of the National Electrical Code in that state/area. For machines that are installed in “hazardous locations”, the NEC Article 500 et seq. also applies.

Control cabinets that are installed in industrial machines must also comply with the UL 508A standard in addition to the NEC and the NFPA 79 standard. In the event that there are varying demands between these three rules and standards, the strictest demand applies. In the case of overcurrent protection equipment, for example, the lowest value must be adhered to.

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Personal protection plays an extremely important role. In order to prevent dangerous situations for personnel on the machine, any surge voltages may not cause damage to the safety circuit in the machine. Considerations regarding further operational readiness of the machine after a surge voltage have no relevance here.

According to the NEC (2017) and the NFPA 79 (2018), the power supply for industrial machines that are equipped with safety circuits must be fitted with surge protective devices (SPDs). These devices must have a “UL-listed” approval in accordance with the UL 1449 standard. Furthermore, they must also feature a short-circuit current rating (SCCR) that is greater than the short-circuit current at the installation site.

Surge protective devices for the power supply are to be installed as close to the feed-in point as possible. Depending on the location of the machine in the installation, the appropriate SPD types (see NFPA 79 (2018), Article 7.8) are to be selected. The VAL-US series makes this particularly easy: As UL-listed Type 1 devices, they can be used anywhere in the installation. It may be necessary here to consider protecting the cables against overcurrent.

Surge protective devices for signal and data technology are not required in the NFPA 79 standard. Nevertheless, they can be installed in the machines. A surge protective device for the machine communication interface, for example to the control engineering system, is recommended here.

Both the NEC and NFPA 79 standards can be purchased from the National Fire Protection Association or can be viewed free of charge. Both electronic and print formats are available for purchase.

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American supply system configurations

The American supply system configurations, voltages, and their frequencies are in part significantly different to those familiar in Europe, and there are historical reasons for this. Industrial machines are mainly operated on the “3-phase Wye” and “delta” supply system configurations. There are, however, other supply system configurations, the most common of which are listed in the following.

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SPD types in accordance with UL 1449

SPDs are categorized into various types, depending on the short-circuit current rating achieved. In addition, installations are categorized into type locations depending on the short-circuit currents arising.

The type location of the machine connection site defines the minimum SPD type that has to be used. Type 1 SPDs may therefore be used in all type locations. Type 2 SPDs may be used in type 2 locations and in type 3 locations.

This categorization of the SPDs does not provide information on the discharge capacity of the devices or their areas of application in a lightning protection concept, as is specified in the IEC standard. The types in accordance with UL are only based on the short-circuit current rating test specified in UL 1449.

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ClassificationDescription
Type 1 SPDsType 1 SPDs may be installed downstream of a transformer, but upstream of the main fuse or the main disconnector of the installation.
Type 2 SPDs

Type 2 SPDs must be installed downstream of the main fuse or main disconnector of the installation.

Type 3 SPDs

Type 3 SPDs must have a clearance (= cable length) of at least 10 m to the upstream overcurrent protection or disconnector.

Type 4 SPDsType 4 SPDs are components that may not be used as stand-alone devices. They always have to be a part of a unit, for example a part of a control cabinet. In this case, the short-circuit current rating of the entire unit must be evaluated in accordance with UL.
The unit’s type location depends on the test results of the type 4 SPD in terms of the short-circuit current rating.

Requirements on the products

Products of the VAL-US range are available for the various supply system configurations and voltages. They satisfy the requirements of NFPA 79 because on the one hand, they have a “UL-listed” approval, and on the other hand they can be used universally due to their short-circuit current rating (SCCR) of 200 kA (in accordance with UL 1449 ed. 4).

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3-phase Wye system voltage (phases)Name (Order No.)
3-phase Wye277/480 V (A, B, C, N, G)VAL-US-277/40/3+1-FM (2910374)
277/480 V (A, B, C, G)VAL-US-277/40/3+0-FM (1199369)
347/600 V (A, B, C, N, G)VAL-US-347/30/3+1V-FM (1079099)
347/600 V (A, B, C, G)VAL-US-347/30/3+0-FM (2910383)
3-phase Wye system voltage (phases)Name (Order No.)
3-phase Wye277/480 V (A, B, C, N, G)VAL-US-277/40/3+1-FM (
)
277/480 V (A, B, C, G)VAL-US-277/40/3+0-FM (
)
347/600 V (A, B, C, N, G)VAL-US-347/30/3+1V-FM (
)
347/600 V (A, B, C, G)VAL-US-347/30/3+0-FM (
)
Corner-grounded/ungrounded delta system voltageName (Order No.)
Corner-grounded/ungrounded delta480 VVAL-US-480D/30/3+0-FM (2910386)
600 VVAL-US-600D/30/3+0-FM (2910391)
Corner-grounded/ungrounded delta system voltageName (Order No.)
Corner-grounded/ungrounded delta480 VVAL-US-480D/30/3+0-FM (
)
600 VVAL-US-600D/30/3+0-FM (
)

Fuses

Surge protection devices that have type 1 listed approval in accordance with UL 1449 do not need overcurrent protection (1). However, the NEC prescribes that the conductors are to be protected against overcurrent. It can therefore be necessary to equip the conductors to the SPD with overcurrent protection devices (OCPD) (2).

According to NFPA 79, the OCPD is not to be rated or defined by the manufacturer of the installed device, rather by the system planner – in this case, by the machine builder. This also applies to SPDs. The procedure for designing the OCPD for surge protective devices is the same as for all other devices. However, since an SPD has no load current, the information specified by the SPD manufacturer can be used for the connecting cable. This information includes both maximum and minimum cross sections, as well as the permitted cable material. Based on this information, the surge protective device can then be designed as usual with the aid of the respective NEC tables.

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