DC circuit breakers up to 600 V for branch-circuit protection in telecommunications equipment (USA).
The standard covers single- and multipole circuit breakers rated up to 600 V DC, intended for overcurrent and short-circuit protection of branch circuits in DC-powered communications equipment, for example base stations.
All poles of a multipole circuit breaker operate at the same potential. The standard supplements UL 489 and modifies the tests described in the base standard.
UL 489A certification confirms that a DC circuit breaker provides branch-circuit overcurrent and short-circuit protection in telecommunications equipment for the US market. The standard permits DC voltage ratings only and does not permit slash voltage ratings (Clause 15.1); an interrupting rating other than 5000 A must be marked on the circuit breaker (Clause 16.6).
The certification applies to use in communications equipment; full approval for branch-circuit protection in a general NEC installation requires UL 489 certification. In the EU, the certificate does not replace assessment to IEC/EN 60947-2.
Construction is evaluated to UL 489, with the exceptions in Sections 5–7: insulation spacings within the circuit breaker are evaluated to UL 489 (after installation, compliance with end-product spacings is sufficient); terminals may be connectors, screws, studs or spring terminals matched to the end-product part; manual opening and closing is required, and the use of an ordinary tool is permitted.
Tests (Sections 8–14) are performed to UL 489 with modifications: calibration to UL 489, and where the ambient temperature differs from 25 °C or 40 °C, additional calibration at the temperature marked on the product (for a temperature range, at the extreme values); overload at 150% of rated current in a circuit with a time constant of at least 0.003 s; temperature test without tripping until temperatures stabilize; endurance of 1000 make-break cycles under load or the lower number of operations specified in the UL 489 table; interruption testing to UL 489, where prospective current may be any value required by the application and the test current in sequence Y does not exceed the circuit breaker's rated short-circuit capacity; elevated-temperature conditioning at 100 ±2 °C for 7 h, followed by repeat calibration without exceeding allowable trip times.
Products are certified under the UL Listing system with production surveillance.
Check whether the datasheet distinguishes UL 489 from UL 489A; for UL 489A, identify the UL file number, certified DC voltage, marked interrupting rating (marking is required for a value other than 5000 A), and the ambient-temperature range marked on the breaker, because calibration at a temperature other than 25 °C or 40 °C is performed at the marked temperature.
