Surge Protection for
CNC Milling Machine

NFPA 70 Article 670.6 (NEC 2020)
NFPA 79 Electrical Standard for Industrial Machinery (2018)
CNC Milling Workshop
NFPA 79 Industrial Machinery - CNC Milling Workshop

NEC-2020 The latest release of NEC/NFPA 70 edition 2020 (NEC 2020) has placed a greater emphasis on increasing personnel safety by mandating the use of Surge Protective Devices (SPDs).

From 2014 to 2020, the number articles now requiring SPDs has increased significantly for applications ranging from Modular Data Centers, Fire Pumps, Elevators, Critical Power Systems, Dwellings (Dormatories, Homes, Hospitals, Hotels), etc.

Threat to industrial machines

Various codes and standards possess safety interlock criteria including the American National Standards Institute (ANSI) standards and NFPA 79 for Industrial Machinery. However, until now, these standards have only just begun to address the expanding role that surge protection plays preserving the integrity of equipment and, more importantly, protecting the lives of personnel.

A study commissioned by the Fire Protection Research Foundation, “Data Assessment for Electrical Surge Protective Devices”, provides results of a survey of facility managers concerning surge damage. (NFPA 2014) The study shows that 26 percent of facility managers had damage to safety interlocking systems on industrial machines due to surges . The main purpose of these safety interlocking systems is to protect workers and maintenance personnel from contact with exposed live parts and electric shock. Failure of these devices can put personnel at an increased risk of injury.

CNC Milling Machine
CNC Milling Machine

The solution for NFPA 70 and NFPA 79

To make the installation of a Surge Protective Device (SPD) at the industrial machines interlocking safety circuit mandatory which in turn increases the equipments reliability.

NFPA 70 Article 670.6 Surge Protection.
"Industrial machinery with safety inter-lock circuits shall have surge protection installed.”

In addition, the future NFPA 79 is considering the following changes:

7.8.1 Surge Protective Devices (SPDs).
"SPDs shall be provided for industrial machinery with safety interlock circuits to protect against the effects of overvoltages due to lightning or switching surges.”

as well as

4.5.2 Electromagnetic Compatibility (EMC).
"Transient suppression, isolation, or other appropriate means shall be provided where the equipment of an industrial machine generates electrical noise or transients, which can affect the operation of equipment that is on or part of the industrial machine."
CNC Milling Drill Bit
CNC Mill

Selecting an SPD for CNC Milling Machine

NEC/NFPA 70 require that Surge Protective Devices (SPDs) shall be UL1449 Listed . This means selecting a surge protector is easier than it has ever been. There are only a few choices available for SPDs that are UL Listed for any of the most commonly used surge standards including UL1449 5th Edition, UL497B, and UL497E.

Recommended SPD for CNC Milling Machines

LocationEquipmentSystemSurge Protector Model#Link
Service EntranceMain Service Panelboard480Vac MDS750E-480D MDS750E-480D
Branch PanelEquipment Panelboard480Vac${ITEM_LINK#2178948}<-No Item, #2178948 M50-480D-A${ITEM_LINK#2178948}<-No Item, #2178948 M50-A
Local EquipmentControl Panel480Vac
Power Input
DS74US-480D DS74US-480D

Power Supply120-240Vac
Power Input
DS72US-230S/G DS72US-120S/G

24Vdc Power Output DS220S-24DC DS220S-24DC

Control UnitEthernet Cat 6A MJ8-C6A MJ8-C6A

RS232 DLA-12D3 DLA-24D3

Wireless P8AX09-6G-N/FF P8AX09-6G-N-FF

Types of machines covered by NFPA 79

Machine ToolsMetal Cutting
Metal Forming
Plastics MachineryInjection molding machines
Extrusion machinery
Blow molding machines
Specialized processing machines
Thermostat molding machines
Size reduction equipment
Wood MachineryWoodworking machinery
Laminating machinery
Sawmill machinery
Material-Handling MachineryIndustrial robots
Transfer machines
Sortation machines
Inspection/Testing MachinesCoordinate measuring machines
In-process gauging machines
Packaging MachinesCarton-strapping machines
Drum-filling machines
Palletizing machines

Contact us to develop a surge mitigation solution for your application

Where to purchase Citel SPD's


1NFPA 70 edition 2020, Article 670 Industrial Machinery, 670.6 Surge Protection
2NFPA 70 edition 2017, Article 670 Industrial Machinery, 670.6 Surge Protection
3NFPA 70 edition 2014, “Data Assessment for Electrical Surge Protective Devices”
4NFPA 79 edition 2018, Electrical Standard for Industrial Machinery, Chapter 7,
7.8 Protection Against Overvoltages Due to Lightning and Switching Surges
7.8.1 Surge Protective Devices (SPDs)
5NFPA 79 edition 2018, Annex C, Examples of Industrial Machines Covered by NFPA79
6ANSI C62.41, Low-Voltage AC Power Circuits
7UL1449 4th Edition, Surge Protective Devices
8UL1449 5th Edition, Surge Protective Devices
9UL497B, Surge Protectors for Data Lines and Fire-Alarm Circuits
10UL497E, Antenna Lead-in Conductors
11IEC 61643-11, Low-Voltage Surge Protective Devices - Part 11: Surge Protective Devices Connected To Low-Voltage Power Systems - Requirements And Test Methods
12IEC 61643-21, Low Voltage Surge Protective Devices - Part 21: Surge Protective Devices Connected To Telecommunications And Signalling Networks - Performance Requirements And Testing Methods
13IEC 61000-45, Electromagnetic Compatibility (EMC) - Part 4-5: Testing And Measurement Techniques - Surge Immunity Test
14CSA 22.2
15NOM-001-SCFI, Standard for Electronic Equipment
16NOM-003-SCFI, Electrical Products - Safety Requirements
17SEMI S22, Safety Guideline for the Electrical Design of Semiconductor Manufacturing Equipment