Allen-Bradley 1785-BCM
Allen-Bradley 1785-BCM
Allen-Bradley 1785-BCM
Allen-Bradley 1785-BCM
Allen-Bradley 1785-BCM
Allen-Bradley 1785-BCM
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  • Lifecycle status

    Discontinued
    Discontinued date: 2011-07-31
    Replacement category: Engineering Replacement

1785-BCM

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Allen-Bradley 1785-BCM is a PLC-5 backup communication module that coordinates primary and secondary processors over a dedicated high-speed serial link.
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Technical specifications for 1785-BCM

  • Manufacturer:
    Allen-Bradley
  • Part Number:
    1785-BCM
  • Product Family:
    PLC-5
  • Product Type:
    PLC-5 Backup Communication Module
  • Stock:
    1
  • Compatible Processors:
    PLC-5/15 Series B, PLC-5/20, PLC-5/25, PLC-5/30, PLC-5/40, and PLC-5/60
  • Module Location:
    Local 1771 I/O chassis
  • Backplane Current:
    1.0 A at 5 V DC
  • Keying Locations:
    Between 8 and 10; between 34 and 36
  • Wiring Arm:
    1771-WG
  • Customer Relay:
    0.25 A at 24 V DC resistive
  • HSSL Communication Rate:
    1.2 Mbaud
  • Operating Temperature:
    0 to 60°C
  • Storage Temperature:
    -40 to 85°C
  • Relative Humidity:
    5% to 95%, non-condensing
  • Dimensions:
    31.5 × 21 × 7.5 cm
  • Weight:
    0.82 kg
  • Tariff Code:
    8517623990
  • Country of origin:
    USA
  • Place of shipment:
    Xiamen,Fujian,China
By purchasing this item, you agree to the Terms & Conditions, ApterPower is not an authorized distributor for listed manufacturers or tradenames and therefore the manufacturer's warranty does not apply. All our products come with ApterPower's 1-year warranty.

More Information

Overview Manuals Backup Pair HSSL Link Commissioning Application
  • Record both modules’ switch settings and cable positions before disconnecting the backup pair.
  • Restore matching PLC-5 application files before placing the primary and secondary processors back in service.
  • Test normal transfer and forced switchover behavior after reconnecting the HSSL and relay wiring.

1785-BCM links the control responsibilities of two supported PLC-5 processors rather than operating as a standalone controller.

Its chassis interface, HSSL path, and external relay form the hardware layer used by the documented primary and secondary arrangement.

A service replacement should be evaluated as part of the entire backup pair, including processor catalogs, project files, wiring, and transfer behavior.

Availability, condition, price, and shipping time for 1785-BCM are confirmed during quotation.

Allen-Bradley 1785-BCM PLC-5 Backup Communication Module Manuals, Datasheets, Links

Important Notice: Other accessories, manuals, cables, calibration data, software, etc. are not included with this equipment unless listed in the above stock item description. All prices are shown in USD.

  • The official compatibility list covers selected PLC-5/15 through PLC-5/60 processors.
  • The module belongs in the local 1771 I/O chassis of the backup arrangement.
  • Primary and secondary projects must represent the same documented machine strategy.
  • The high-speed serial link communicates at the documented 1.2 Mbaud rate.
  • Cable continuity and connector seating are essential to backup-partner communication.
  • The customer relay can provide an external indication for the backup system.
  • Confirm keying positions and the 1771-WG wiring arm before insertion.
  • Restore the saved backup configuration before controlled switchover testing.
  • Verify processor ownership, I/O response, and relay indication before production.
  • Primary and secondary PLC-5 systems that require automatic transfer of control after a primary-processor fault
  • PLC-5 backup architectures using the 1.2 Mbaud HSSL link between paired 1785-BCM modules
  • Backup installations that use the customer relay for external status or switchover indication
Description
Allen-Bradley 1785-BCM coordinates a documented PLC-5 backup pair and provides the high-speed serial link used between the primary and secondary systems.

The Series B module installs in a local 1771 I/O chassis, communicates at 1.2 Mbaud over the HSSL connection, and provides a customer relay for external status indication.

Replacement planning must preserve processor compatibility, chassis placement, keying, wiring-arm assignment, backup configuration, and the physical HSSL path before the standby system is returned to service.
Revisions

Revision Part #

Also known as

1785-BCM Ser B
1785-BCM/B, Series B, Rev B
Alternative Names
1785-BCM Allen-Bradley 1785-BCM Allen Bradley 1785-BCM PLC-5 1785-BCM Bulletin 1785-BCM
Technical notes
1785-BCM replacement requires a compatible PLC-5 processor pair, Series B hardware, local-chassis placement, 1771-WG arm, preserved backup configuration, and a verified HSSL path; mismatches can prevent switchover.
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FAQS

The following is a list of questions commonly asked by our customers. Please contact us if you have a question about our process that is not answered below.
Does Allen-Bradley 1785-BCM support transfer to a standby PLC-5 after a primary-system fault?
In a correctly engineered backup arrangement, the module coordinates communication between compatible primary and secondary processors; the actual transfer sequence must be configured and proven during controlled commissioning.
When is an Allen-Bradley 1785-BEM needed with Allen-Bradley 1785-BCM?
Use the 1785-BEM only when the documented backup design extends communication to additional chassis; verify the installed backup architecture rather than assuming every 1785-BCM system requires it.
What records should be saved before replacing Allen-Bradley 1785-BCM?
Retain the primary and secondary PLC-5 programs, backup-system configuration, chassis layout, module-switch settings, wiring identification, and commissioning results.
Why might an Allen-Bradley 1785-BCM pair fail to establish the high-speed link?
Check the HSSL cable path, connector seating, compatible processor pair, chassis power, module keying, and the configuration expected by both PLC-5 processors.
How should switchover be tested after installing Allen-Bradley 1785-BCM?
Follow the official backup-system procedure, prove primary-to-secondary transfer under controlled conditions, and verify I/O control and external relay indication before restoring production.
Can Allen-Bradley 1785-BCM reuse any 1771 field-wiring arm?
No. The official specification identifies the 1771-WG wiring arm, so the installed arm and terminal assignment must be checked before replacement.
Is Allen-Bradley 1785-BCM interchangeable with a generic PLC-5 communication module?
No. Its backup-transfer function, processor compatibility, HSSL connection, chassis location, and Series B hardware distinguish it from ordinary PLC-5 network interfaces.

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