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Information on NFPA 79

Ready for NFPA 79

Ready for NFPA 79 (Edition 2018)

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

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 2018 revision of the NFPA 79 standard.
Learn here about which mandatory NFPA 79 requirements are applicable for the use of surge protective devices (SPDs).

Your advantages

  • Compliance with NFPA 79 (2018), thanks to UL-listed test mark on all VAL-US products
  • Short-circuit currents not exceeded, thanks to high short-circuit current rating of 200 kA
  • Simplified system approval by inspectors, because requirements of NFPA 79 (2018) are complied with
  • Universal use of all VAL-US products in accordance with the requirements of NFPA 79 (2018)
  • Products are available, useable, and mountable Europe-wide thanks to the CE marking
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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.

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 (SPD). 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.

American grid types

The American grid types, voltages, and their frequencies are in part significantly different to those known in Europe, and for historical reasons. Industrial machines are mainly operated on the "3-phase star" and "delta" grid types. There are, however, other grid types: the most common are listed in the following.

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Split-phase

Split-phase
This grid type is largely unknown in Europe today. It is created via a secondary-side center tap connection in a single-phase transformer. The center tap connection is grounded, such that the voltage between it and one phase is exactly half of the voltage between the phases. The voltage used is 120 / 240 V.
This grid type is used in almost all households and small office buildings in North America. Small and low-power devices such as computers, televisions and lighting are connected to the 120 V circuit. Devices with higher power requirements, such as air conditioning systems, are connected to the 240 V circuit.

3-phase star

3-phase star
This grid type is very similar to the TM system used in Europe. The live phase conductors are fed from a transformer with star topology, and have a phase shift of 120° each. The neutral point is grounded. Depending on requirements, the neutral conductor may or may not be connected. The voltages used are 277 / 480 V in the USA and Mexico, and 347 / 600 V in Canada.
This grid type is mainly used in industrial applications.

Corner-grounded / ungrounded delta

Corner-grounded / ungrounded delta
This grid type is unknown in distribution grids in Europe. The feeding transformer has a delta topology on the secondary side, the phase shift between phases is 120° each. A neutral conductor is not present due to the circuity. The voltages used are 480 V in the USA and Mexico, and 600 V in Canada. Depending on the grounding system, there are two different versions:

Ungrounded delta: The transformer is not grounded on the secondary side. This system behaves similarly to the IT system used in Europe.
Corner-grounded delta: One phase conductor is grounded directly.

This grid type is often used where high powers are required, for example for large motors.

High-leg delta

High-leg delta
This grid type is not used in Europe. This grid type is a delta and split phase hybrid. The delta system has a phase to phase voltage of 240 V. In addition, one of the three legs also has a grounded center tap connection. As a result, there are three voltages:

Phase A – N = Phase C – N = 120 V
Phase B – N = 120 V * √3 = 208 V
Between all phases = 240 V

This grid type is used in large office buildings and small industrial buildings. As in the split-phase system, low-power devices (computers, toasters, etc.) are connected to the 120 V circuit, and higher-powered devices (air conditioning systems, etc.) are connected to the 240 V circuit. The 208 V circuit is normally used for lighting.

SPD types in accordance with UL 1449

SPDs are categorized into various types. The types provide information on where in an installation an SPD may be installed. This categorization does not provide information on the performance of the devices or their areas of application in a lightning protection concept. This is not mentioned at all in the listed directives or standards.

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SPD types in accordance with UL 1449  
ClassificationDescription
Type 1 SPDsType 1 SPDs may be installed downstream of a transformer and 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.

Requirements on the products

Products of the VAL-US range are available for the various grid types 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, thanks to their short-circuit current rating (SCCR) of 200 kA (in accordance with UL 1449 ed. 4).

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3-phase star system voltage (phases)Name (Order No.)
3-phase star277 / 480 V (A, B, C, N, G)VAL-US-277/40/3+1-FM (2910374)
277 / 480 V (A, B, C, G)VAL-US-277/80/3+0-FM (1075896)
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 star system voltage (phases)Name (Order No.)
3-phase star277 / 480 V (A, B, C, N, G)VAL-US-277/40/3+1-FM (
)
277 / 480 V (A, B, C, G)VAL-US-277/80/3+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

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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