NEC Class 4 fault managed power provides an economical solution for many industrial applications
By Tom Valentine, Vice President of Sales and Marketing, Remee Wire & Cable
May 2024, Journal of Power Systems Design
Review of the department’s chapters
Class 1, 2, and 3 circuits are classified as remote control, signaling, and power limited circuits in the National Electrical Code (NEC). NEC defines these circuits as that portion of the wiring system between the load side of the overcurrent protective device (OCPD) or limited power supply and all connected equipment.
These circuits are characterized by their limited use of electrical energy, which distinguishes them from light and energy circuits. These circuits are also classified according to their voltage and power limitations.
NEC divides Class 1 circuits into two types: power-limited circuits and remote control and signaling circuits. Class 1 circuits are power limited to 30 volts and 1000 volt amps. Class 1 remote control and signal circuits are limited to 600 volts, but there are limitations on the power output of the source.
In general, Class 1 remote control and signal circuits must meet most of the same wiring requirements as power and lighting circuits. We typically use Class 1 remote control circuits in motor controllers (which operate mechanical processes), elevators, conveyors, and in equipment that is controlled from one or more remote locations. Class 1 signal circuits are used in hospital nurse call systems, electric clocks, bank alarm systems, and factory call systems.
Power constraints differentiate between the three main classes of power (Class 1, Class 2 and Class 3). Class 2 is concerned with fire safety and provides some protection against electrical shock. Category 3 takes into account fire safety only.
Class 2 and 3 circuits are power limited circuits that limit the potential for fire or ventricular fibrillation. Devices in these categories must be listed as a limited power supply (LPS). Power over Ethernet (PoE) is an example of Category 2.
Class 2 and 3 systems do not require the same wiring methods as power, light, and Class 1 systems. There are instances when 2-in. Separation is required between these systems.
Limitations of Power over Ethernet (PoE)
The PoE standard is covered by IEEE 802.3, and wiring is defined in NFPA 70, Article 725 Category 2. The UL standard is 62368-1. The maximum power at the source is 90 watts. The maximum distance is 100 meters or 328 feet. Maximum power at maximum distance is 71W (with Cat 6A).
Although these constraints have worked well for many enterprise networks, they do not accommodate the longer distances now required to place many devices beyond 100 meters in length. The development and growth of Internet of Things or IoT devices, along with other industrial technology developments, has increased the need to place devices over longer distances.
What is Cl4 (Class 4) and how does it work?
NEC added the first new strength class in more than 45 years with the 2023 edition of NFPA 70. Class 4 is defined in new Article 726, part of Chapter 7, which deals with special conditions. Class 4 power systems are called “fault managed power systems” (FMPS). It is not power limited and can provide hundreds of thousands of watts of power. 1 Voltage can reach 450V AC or DC. This may seem dangerous, but an FMPS has intelligent controls that limit the amount of energy that can trigger a fault, mitigating the risk of fire or shock. It also allows Class 4 circuits to be installed using methods such as power-limited circuits.
The new article in NFPA 70 covers specifications for instrument tray cables used to connect alternative power systems to utility equipment, as well as Power Class 4 managed power systems and cables. Category 4 is the new standard for fault-managed power systems, which includes package energy transfer (PET). , digital electrification* (DE) and other intelligent transportation systems, as they are not covered in Categories 2 or 3.
Class 4 power systems use low voltage power for safety and ease of installation. However, these systems can transmit approximately 20 times the power of PoE systems, which are limited to 100 watts, and operate over a distance of hundreds of meters. PoE paths are limited to 100 meters (328 feet). Therefore, Category 4 systems can use a single cable to transmit data and power over much longer distances. This eliminates the need for separate cabling for electrical power and the assembly of parts required for the installation (junction boxes, conduits, and fittings), and an FMPS system can reduce the amount of copper used, not to mention the additional labor cost.
This innovative technology enhances pulse transmission to deliver significant power over long distances, in a similar way to packet data transmission over enterprise networks. As a line power supply system, it is a means of energizing remote equipment from a central location via twisted copper pairs or hybrid cables with Category 4 powered power. These types of power systems limit the power and energy available during a fault event. For example, if someone touches an exposed wire, the system will shut down immediately before any damage occurs.
Transceivers continuously monitor line conditions. If there is a fault such as incorrect wiring, a short circuit, or someone touching the transmission lines, the system recognizes the condition in milliseconds and stops power transmission. The result is “touch-safe” electric transmission with high power levels. This “clean power” also eliminates sags and lifts.
Benefits of Fault Managed Power Systems (FMPS)
Safety – With low-voltage and fault-free shutdown features certified by OSHA’s NRTL laboratory to use the same wiring practices as Ethernet and PoE; Allows hundreds of watts per pair of conductors Allows equipment to be placed and cable run over long distances – thousands of feet Low copper content Conductors are typically smaller – 18 to 14 AWG Allows remote monitoring and control of power distribution, allowing action to be taken for external events Efficient installation – can be run in the same path as Category 2 or 3 circuits, fiber cables, or hybrid cables; Eliminates the need to run separate power lines; Only one cable pull required No conduit required Intelligent power usage control – FMPS can tell the difference between a load and a person connected to the lines
Category 4 FMPS: Energy Industry 4.0
Fault-managed power solutions can significantly reduce the complexity, time, and costs associated with deploying edge-based networks. By enabling the freedom and flexibility to locate modular IDF resources anywhere in the industrial environment, a simplified, scalable network is created that solves the challenge of supporting connected industrial devices both today and in the future.2
Industrial facilities face challenges in meeting 4G LTE, 5G, and WiFi connectivity requirements. FMPS provides an economical, efficient and secure solution for powering remote devices, such as radios and access points. FMP systems also enable IoT technologies that drive automation, manufacturing and logistics.
There are many applications for CL4 power systems and cables in the industrial environment. Some examples include:
Distributed Antenna Systems (DAS) – Provides WiFi in factories, railway tunnels, etc. Power over Ethernet (PoE) – 328 feet limit, plus long distance LED lighting, security cameras, access control – card readers, door entry systems, etc. Wireless Access Points (WAPs) Building Automation Systems (BAS) – HVAC, lighting, security, etc. Data centers IoT sensors Indoor agriculture
Remee has experience manufacturing robust cables that can withstand harsh industrial conditions. They offer a full range of standard cables, and specialize in modifying standard cables, as well as custom-designed cables. Below are some case studies that demonstrate Remee’s exceptional capabilities, especially with Activate™ Powered Cable Solutions.
FMPS Case Studies
Hardy’s 50,000-square-foot vertical farm system produces five types of lettuce. Its vertical system allows for up to 9 levels of plants – the equivalent of 9 acres. It has a 1.1 MW solar facility and uses 22 miles of digital electricity* (DE) cable. DE technology powers the lighting and on/off and dimming controls. Only 2 connectors are needed per fixture versus 5 connectors required for AC power and control. The DE* FMP system was an ideal solution for the large metro rail transit system, with DE equipment running the DAS radio system from equipment stations through its tunnels. Thousands of watts of power were needed to operate radios at thousands of feet. Cables are designed and approved for use with VoltServer DE equipment.
Click here for more information about Remee’s Activate™ PowerPipe™ cables.
See article in the May 2024 issue of Power Systems Design magazine.
*VoltServer trademark
