Distributing DC Power options

There are multiple options for distributing DC power to building loads:

Class 1 Circuits: Limited to 600VDC, Class 1 circuits are ideal for larger power loads, including 380VDC used to power networking equipment in data centers, HVAC systems, electric vehicle (EV) chargers, elevators, and other large loads.

Class 3 Circuits: Limited to 150VDC and considered safe from a fire initiation standpoint, Class 3 circuits are primarily used in specialty systems, including nurse call, public address, and some security and life-safety systems.

Class 2 Circuits: Class 2 circuits are considered safe from a fire initiation AND electric shock perspective as they are limited to less than 60VDC and 100W. Familiar Class 2 circuits in commercial buildings include 24VDC or 12VDC power distribution over multi-circuit (MC) cables for LED lighting, alarm panels, legacy CATV surveillance, relays, and more. Class 2 Circuits also include the following:

• Power over Ethernet (PoE)—This type of Class 2 power is transmitted from power sourcing equipment (PSE), such as a network switch, over twisted-pair Ethernet cabling (e.g., Category 6A, 6, 5e). PoE is delivered simultaneously with data and control information to networked IP-based powered devices (PDs). PoE is increasingly used for powering and controlling LED lighting via direct connections to fixtures or intelligent nodes that manage power and control for multiple fixtures. The various levels of PoE power are defined by IEEE 802.3 Ethernet standards, with Type 1 delivering up to 15W, Type 2 up to 30W, Type 3 up to 60W, and Type 4 up to 90W. PoE lighting systems typically require the higher power levels offered by Type 3 or Type 4 PoE.
• Single-pair Power over Ethernet (SPoE)—This type of Class 2 power is a PoE-based technology used with emerging Single-pair Ethernet (SPE) for connecting and powering low-speed OT devices, such as controllers, sensors, actuators, and meters used in building automation systems. Like PoE, SPoE is transmitted in parallel with data and can deliver up to 52W of DC power.
• Universal Serial Bus (USB) – Traditionally used for computer peripherals, the latest USB technology can deliver data and up to 240W of DC power to shorter distances of about 1 m (3.3 ft) via much smaller connectors. USB can be delivered via computers or other power and data rendering devices (e.g., network switches) or via receptacles with built-in USB ports per Article 406 of the NEC.

Class 4 Circuits: Class 4 power was recently adopted in Article 726 of the 2023 NEC with a voltage limit of 450VDC. Class 4 power is considered fault-managed power (FMP), a technology pioneered as Digital Electricity (DE) by VoltServer. FMP systems safely transmit bulk DC power to building loads using centrally managed transmitters and remote receivers to intelligently detect faults and immediately stop transmission, providing the same level of protection from electric shock and fire initiation as Class 2 circuits. The power and distance capabilities of an FMP system vary based on specific vendors’ technology and the number and size of conductors. For example, VoltServer’s DE system operates at 336VDC, delivering 300W and 600W to about 365 m (≈1200 ft) over one and two 18 AWG conductor pairs, respectively. It can reach levels up to 2000W using multiple pairs of larger conductors.

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