NEC CLASS 2 FAQs
What is NEC Class 2?
For fire and safety purposes, the National Electrical Code (NEC) has developed specifications for using low voltage DC circuits (<60Vdc) for powering indoor devices. Class 2 circuits are limited to 100 Watts of power per circuit, do not require the cables to be housed in conduit and can be installed by DAS technicians rather than licensed electricians. To ensure compliance with the 100W limitation, the power distribution equipment employs active current limiting circuitry.
How Are Class 2 Circuits Used in IDAS Installations?
Traditionally, battery backup has been provided at each remote iDAS node. Though effective, the deployment of batteries, power conversion equipment and enclosures at each site significantly impacts the capital budget. Maintaining the batteries and paying for the recurring cost of multiple AC outlets also increases operating expenses.
Class 2 circuits utilize the highly reliable power and battery equipment at the DAS Host to deliver current over copper cables to power the remote IDAS nodes. The cost of power distribution equipment and copper cables is much less than the cost of multiple remote power systems, plus the battery maintenance is focused on the centralized node so Opex costs are reduced.
How Far Can It Reach?
In addition to the active current limiting circuitry, the power distribution equipment also includes built-in DCDC converters that increase the output of the 48Vdc hot power system to 57Vdc. The 57Vdc output delivered over 12AWG cable can power a typical node located up to 1500 feet away from the host.
Can a Traditional Fuse Panel be the Power Distribution Device?
The NEC and CSA/UL mandate that the power distribution equipment meet the 60Vdc and 100W requirements with the primary protection disabled. For traditional fuse panels, the fuse is the primary protection device, so the 100W limitation can be exceeded when the fuse is disabled. Consequently, if a fuse panel is the power distribution device, compliance with NEC requirements can only be achieved by placing the cable in conduit, a technique that adds tremendous cost to the business case.
Can Devices That Consume More Than 100W be Powered with Class 2 Circuits?
Yes, by using multiple cable pairs and an approved Class 2 Circuit Aggregation Device at the remote node, devices that consume up to several hundred Watts can be powered. To comply with NEC Class 2, the aggregation device must provide current limiting circuitry on both the “hot” and “return” legs of the circuit in order to ensure that the failure of a single Class 2 circuit will not cause more than 100W of power to be delivered onto the other connected cable pairs.
- Class 2 circuits eliminate the need for AC sources and battery backup units at each remote node
- Class 2 circuits improve reliability and resiliency by utilizing the DAS Host power system
- Class 2 circuits can be installed by DAS technicians rather than licensed electricians
- Class 2 circuits lower cost by using surface-mounted cable (no armored cable or conduit required), reaching distances of up to 1500 feet
- Traditional fuse panels are not compliant with the NEC unless expensive conduit is used
- High power IDAS nodes require a circuit aggregation device at the node to be compliant with Class 2