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BP-4A Power Failure Transfer Unit


BP-4A PFT Unit

The BP-4A Power Failure Transfer Unit is designed to connect two-wire Central Office (CO) ground start or loop start trunk lines to selected station telephones in the event of a power failure or telecommunications system malfunction. When used with ground start trunks, the BP-4A includes automatic loop start to ground start conversion circuitry to provide the signaling required to draw CO dial tone when a station telephone is brought off-hook. This eliminates the need to add ground start push buttons to the station telephones. In the normal, non-transfer mode of operation, the BP-4A connects the CO trunk lines to trunk ports on the associated PBX system; PBX extension ports are connected to the station telephones.

BP-4A features include four circuits of power failure transfer (PFT), delay transfer on each of the PFT circuits, LED status indicators, manual transfer switch, ground start or loop start trunk selection, two auxiliary relay contacts, return to normal mode delay timer, and universal powering. Also included are provisions for a normally open, normally closed, or logic level signal to control the operating mode.

BP-4A Specifications

Transfer Voltage:
Minimum voltage to go from normal mode to transfer mode: 7 Vac, –10 Vdc, approximate
Minimum voltage to go from transfer mode to normal mode: 9 Vac, –18 Vdc, approximate

Number of PFT Circuits: 4

Trunk Compatibility: loop start or ground start, switch selectable on a per-circuit basis

Return to Normal Mode Delay Timer:
Time Interval: 0 to 15 minutes, selectable in 60-second increments
Accuracy: ±10% of selected time interval

PFT Circuitry Delay Transfer:
Off-Hook Recognition: 10 ±5 mA trunk loop current recognized as valid off-hook
Off-Hook to On-Hook Duration: 1 second (nominal) break in loop current recognized as valid on-hook

Auxiliary Relay Contacts: 2
Type: one normally open (not shorted), one normally closed (shorted), both break before make
Rating: 0.5 A maximum at 60 Vdc or 60 Vac (resistive)

Transfer Control Inputs:
Contact Input: the contact connected to the contact input must be capable of handling 1 mA at –20 Vdc; contact inputs on multiple BP-4A units can be bridged (connected in parallel)
Logic Input: transfer is enabled by applying a logic low to the logic input. Minimum logic current for logic high: 1 mA. Input current is limited via a 1800 ohm resistor in series with the logic input’s optical coupler. If sufficient logic current is available, logic inputs on multiple BP-4A units can be bridged (connected in parallel).
Operating Mode: switch selectable for normally open contact input, normally closed contact input, or normally high logic input

Environment: 0 to 50 degrees C, humidity to 95% (no condensation)

Safety Compliance: Underwriters Laboratories Inc. LISTED Telephone Equipment

FCC Registration:
Registration Number: BVV8VH-60403-PX-N
Ringer Equivalence: 0.1B

Radiated Noise Compliance: contains no circuitry subject to EMI regulations

Reliability: MTBF 20.1 years, per Method 1 of Bellcore TS-TSY-000332, Issue 3, September 1990

Interconnections: contains one 25-pair plug and one 3-position screw terminal strip; installer must supply one 25-pair connector (female)

Power Requirement:
18 to 30 Vac, 80 mA maximum
Class 2 power transformer only, minimum 5 VA rating –22 to –56 Vdc, 70 mA maximum

8.75 inches high (22.2 cm)
8.75 inches wide (22.2 cm)
3.25 inches deep (8.3 cm)

Mounting: wall mounts with four #8 pan-head screws

Weight: approximately 2 pounds (0.9 kg)


Specifications subject to change without notice.


Additional Information:



Data Sheet

Technical Practice


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