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.

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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 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.

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.

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

What does the NFPA 79 standard regulate?

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. This includes, for example, overcurrent protection, cabling, 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.

Why does my machine have to comply with NFPA 79?

Every machine that is to be commissioned must first be checked 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.

Where is the directive applicable and what is its scope?

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.

How are differences in the content of the various rules and standards to be dealt with?

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.

Why is surge protection mandatory with the new edition of the NFPA 79?

Personal protection plays an important role. In order to prevent dangerous situations for personnel at the machine, any overvoltage may not cause damage to the safety circuits in the machine. Considerations regarding further operational readiness of the machine after an overvoltage have no relevance here.

How do I satisfy the demands of NFPA 79 in terms of surge protection?

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.

How are surge protective devices to be installed in order to satisfy the NFPA 79 standard?

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.

Where can I find comprehensive information on the NFPA 79?

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 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” grid types. There are, however, other supply system configurations, the most common of which are listed in the following.

Split phase
3-phase Wye
Corner-grounded/ungrounded delta
High-leg Delta
Split phase

This supply system configuration 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, so 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 supply system configuration 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 Wye

This supply system configuration is very similar to the TN system used in Europe. The live line 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 supply system configuration is mainly used in industrial applications.

Corner-grounded/ungrounded delta

This supply system configuration 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 circuitry. 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 line conductor is grounded directly. This supply system configuration is often used where high powers are required, for example for large motors.

High-leg Delta

This supply system configuration is not used in Europe. It 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 supply system configuration 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, 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.

SPD types in accordance with UL 1449




Type 1 SPDs Installation downstream of a transformer, but upstream of the main fuse/disconnector
Type 2 SPDs Installation downstream of the main fuse/main disconnector
Type 3 SPDs Min. cable length 10 m to the upstream overcurrent protection/disconnector
Type 4 SPDs* Part of a unit/control cabinet, entire unit requires short-circuit test according to UL
 *For a type 4 SPD, the type location of the unit depends on the test result 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 they have a “UL-listed” approval. They also can be used universally due to their short-circuit current rating (SCCR) of 200 kA (in accordance with UL 1449 ed. 4).

3-phase Wye


Name (item number)
Name (item number)

System voltage (phases)
277 / 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)

Corner-grounded/ungrounded delta


Name (item number)
Name (item number)

System voltage
480 V VAL-US-480D/30/3+0-FM (2910386)
600 V VAL-US-600D/30/3+0-FM (2910391)
Circuit diagram: 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.