Over the past two decades, power over Ethernet (PoE) delivered via category twisted-pair copper cabling along with data has become the primary remote powering technology for networked devices like wireless access point, surveillance cameras, digital displays, and LED lights. As defined by the National Electric Code (NEC), PoE is considered a Class 2 limited power circuit (Article 725), which cannot exceed 60 VDC and is limited to 100 Watts (W). At these levels, Class 2 limited power circuits are also considered safety extra low voltage (SELV) power per the International Electrotechnical Commission (IEC).
Not all Class 2 power is PoE—Class 2 power can also be delivered separately from data via 12 to 24 AWG copper conductors like those used in hybrid copper-fiber cables that are ideal for devices located beyond the 100-meter distance limitation of PoE. With all Class 2 power circuits limited to 100 W, there hasn’t been many safe options for devices that require more power. But that’s all changing with new Class 4 power making its way into the 2023 National Electric Code® (NEC) as Article 726.
In a Class of its own
Class 4 power, referred to as fault-managed power, is not power limited like Class 2 and can deliver hundreds or thousands of watts of power. The voltage can be up to 450V AC or DC, which sounds dangerous, but these systems intelligently limit the amount of energy that can go into a fault to mitigate risk of shock or fire. This allows Class 4 circuits to be installed in the same way as Class 2 power-limited circuits. One way Class 4 systems can limit the amount of energy that can go into a fault is to use DC (direct current) power partitioned into energy packets that each check for fault conditions before the next packet is sent. If a fault is detected, power immediately stops within milliseconds, which makes conductors safe to touch—even at its higher voltage rating of up to 450 VDC. This type of power is also sometimes called packet energy transfer (PET), pulsed power, smart transfer systems, or digital electricity (DE). In fact, the method was pioneered as Digital Electricity™ (DE) by VoltServer™, which has been instrumental in working with UL to define the specifications for the upcoming UL 1400 outline of investigation in support of NEC Class 4 Article 726.
“Class 2 power like PoE is ideal for devices that need less than 100 Watts, but there has been a huge gap between safe low-voltage Class 2 and unsafe higher power levels. That’s where Class 4 fault-managed power comes in,” says Luke Getto, director of product management and marketing for VoltServer. “While our DE power is deployed as Class 2 today, and will continue to be in the future, Class 4 allows us to safely deliver greater than 100 Watts. Our solution does that by delivering power at about 500 packets per second. If a fault is detected, the packets immediately stop sending. With each packet containing only a small amount of energy, the amount dissipated during a fault is so small that it feels like static electricity.”
In addition to being safe, Class 4 power systems are far more efficient and cost-effective than alternative methods of delivering greater than 100W, with the ability to deliver more power over greater distances using smaller 16 or 18 AWG conductors, which means less copper material with or without conduit or armored cable. VoltServer says its DE solution can deliver up to 2400 W of power, or up to a distance of 2km. Safety and efficiency of Class 4 power are also key messages from vendors like Belden and Panduit that have recently developed solutions.
Designed in conjunction with VoltServer, Belden’s DE Cables, which received the industry’s first Class 4 certification from UL, are available in copper-only and hybrid copper-fiber constructions. “We got involved with fault-managed power when I was introduced to VoltServer’s Digital Electricity at a hospitality convention. They liked the characteristics of our cable, so we collaborated with them to create a product line,” explains Ron Tellas of Belden. “We also got involved with the code-making panels because we wanted to make sure these systems could be installed by the same installers deploying category cabling and in the same pathways. That is key for this technology to take off.”
According to Tellas, the main differences between a Class 2 cable and a Class 4 cable is that the Class 4 cable is rated for 450 VDC, which means it has thicker insulation and can pass certain mechanical tests for higher voltage.
According to Panduit, their Fault Managed Power System can deliver 6 times more power and support 30 times the distance of PoE. For example, while a regular Class 2 DC power circuit can deliver 95 W of power to about 60 meters using 16 AWG conductors, Panduit says their Pulse Power solution can deliver the same amount of power with the same size conductors to about 1.8 kilometers. Like other fault-managed power systems, Panduit’s Pulse Power solution includes a source that takes AC power and converts it to Class 4 DC power and a converter (i.e. receiver) that converts power back into traditional analog DC power for powering devices.
While Panduit’s Pulse Power system will not be available in the market until the UL 1400 standard is finalized in the August-September timeframe to ensure compliance and safety, the company is excited about the potential opportunities that lie ahead. “We see Class 4 power as a huge enabler for PoE and smart buildings. We can now have a Class 4 backbone in a building to power all the PoE switches that then provide power and Ethernet connectivity for end devices like sensors, access control devices, surveillance cameras, and more,” says Mahmoud Ibrahim, business development manager for Panduit. “We also see it having the potential for large outdoor events that need to quickly and safely deploy power for lights, WiFi, access gates, digital displays, and sound systems and then pack up and go.”
Disruptive potential
To date, fault-managed power solutions primarily have been used for powering remote high-bandwidth small-cell, DAS, and WiFi radios in large venues and as a centrally managed DC power infrastructure for smart building devices and controls. It’s also being used for some specialty industry applications like horticulture LED lights in controlled indoor agriculture environments. The proprietary nature of available solutions that require matching power sources and receivers, and the lack of devices able to directly connect to a Class 4 circuit, have thus far limited adoption. But industry players are confident that will change with the release of the UL 1400 standard and inclusion of Class 4 in the NEC.
“We often have to convert DE to AC power because most devices plug into AC outlets, even if they run on DC power using adapters, wall warts, or dongles,” says Getto. “We’re happy about this technology making its way into the code and opening the door for other vendors because it will speed adoption and drive the development of more DC-powered devices.” He sees plenty of potential for devices like EV chargers, network switches, and large digital displays to integrate fault-managed power receivers and directly connect to a Class 4 power circuit.
Panduit’s Ibrahim agrees. “We will need to eventually figure out interoperability if we really want to drive adoption. The UL standard and the NEC adoption of Class 4 are the first big step. Eventually I foresee devices being standardized to directly take pulsed current,” he says. “As with any disruptive technology, it’s going to take time for installers, designers, consultants, end users, and AHJs [authorities having jurisdiction] to understand the value and embrace it.”
While it will take several years, some see Class 4 power as having the potential to become the primary power backbone infrastructure within facilities. With DC power from renewable sources like wind and solar distributed throughout a facility as fault-managed power, and with PoE to end devices, an all DC-powered facility that eliminates the inefficiency of conversion is no longer farfetched.
“The more I learn about the hazards of traditional AC power and look at all the outlets in a facility, the more I realize the need for a better and safer way to power devices. There is also a huge need to improve efficiency—every time we convert from AC to DC or vice versa, we’re losing efficiency,” says Getto. “Our hope is that 50 years from now, safe DC power like Class 4 is adopted everywhere.”
