Fault-managed power systems (also known as Class 4 or Digital Electricity® systems) are showing up often in discussions about energy infrastructure and smart building design. They’re changing how building owners, operators and designers think about power delivery across long distances.
But, as interest grows, we’ve noticed something: The cables that carry power to these systems aren’t getting the attention they deserve.
This disconnect was apparent at a recent TIA (Telecommunications Industry Association) TR-42 meeting, where members of the Fault-Managed Power Alliance (FMPA)—including me on behalf of Belden—demonstrated a Class 4 system in operation. People left with a solid understanding of how fault-managed power behaves and what makes it different from traditional power distribution, but a big question lingered: What about the cable?
In the early days of Class 4 adoption (just a couple of years ago), Belden was one of only a few manufacturers offering cables to support it. Today, however, the landscape looks different.
These cables are governed through UL 1400-2, which is now an ANSI-approved standard. When you search “DLPY” in Product iQ, UL’s database of certified products, you find pages of manufacturers producing cables that work with the active components in Class 4 systems. And that list will continue to grow.
As you evaluate the options for cables that carry power to fault-managed power systems, these are the characteristics that matter.
What makes Class 4 cable different?
As a technology that sits between structured cabling work and electrical work, fault-managed power relies on the same wiring methods as Class 2 and Class 3. This means either trade—limited-energy integrators or electrical contractors—can install it as long as they’re qualified.
The cable types defined in UL 1400‑2 for Class 4 are familiar to anyone who’s worked with traditional power‑limited and control cables. They share the same ratings and temperature/flame requirements. In other words, Class 4 cables are just a new application for the cables that industry professionals already know how to install.
But there are certain characteristics these cables need so they can deliver on the reach and reliability requirements of fault-managed power systems.
1. Low capacitance for maximum reach
For fault-managed power systems to operate reliably over long distances, cable capacitance must be low. High-capacitance construction can’t support the reach and behavior required by Class 4, especially when multi-conductor designs are used. They can slow down or distort signals, cutting into the maximum distance that fault-managed power systems support.
To achieve this, Class 4 cables should be designed to keep capacitance as low as possible without compromising installation. Instead of large, generic multi-conductor bundles, cables should feature paired conductors with a controlled, slight twist (different from the “twisted pair” in traditional Category cabling). This keeps pairs tightly coupled and ensures consistent spacing to minimize capacitance between conductors and improve system reach.
2. Low resistance for efficient power delivery
For efficient power delivery, fault-managed power systems also require low resistance. This means keeping voltage and current within expected ranges along the run. When resistance is high, losses increase and the system can’t deliver power the way it was designed. To resolve this, you have to shorten cable lengths, decrease power levels or compensate at the source.
To reduce resistance while avoiding tradeoffs, cable conductors should be made of pure copper, not copper-clad alternatives. This aligns with resistance limits referenced in UL 1400‑2, reduces voltage drops and helps ensure that the cable performs the way the system needs it to.
3. Conductor sizes that balance distance and power
Conductor size determines how well a cable handles distance and resistance tradeoffs. If conductors are undersized, you quickly run up against practical limits that dictate cable length and what can be powered at the end of a run.
While UL 1400‑2 allows copper conductors between 24 AWG and 6 AWG, system requirements naturally steer designers toward the larger end of that range. Cables for fault-managed power systems usually rely on 16‑ or 18‑AWG conductors. Those sizes align with run lengths and power levels that fault‑managed power supports in real applications.
4. Corrosion resistance for reliable terminations
At larger gauges, conductor construction also affects how easy the cable is to install and terminate. Solid conductors at 16 or 18 AWG are stiff enough to make routing and termination difficult. To address this, Class 4 cables should use stranded construction to stay flexible during pulling and land cleanly in screw terminals, terminal blocks and patch panels.
The strands should also be tinned to prevent corrosion (bare copper corrodes over time, increasing contact resistance at termination points). This tinned layer keeps contact resistance low and stable over the life of the installation so fault-managed power systems can constantly monitor circuits and maintain accurate readings at connection points.
Getting fault-managed power system cables into the standards
With cable characteristics for fault-managed power systems defined and UL certification requirements in place, the next logical step is to reflect this reality in structured cabling standards.
Incorporating Class 4 cabling into the standards would give designers and integrators guidance on design and installation: they would know where these cables can be installed, which cable characteristics to look for and how they should be supported and protected.
That’s what Belden is working toward alongside other manufacturers: to encourage TIA and BICSI to recognize not only structured cabling for data but also for power. It would be a strong step toward bringing fault-managed power into standard practice.