What replaces Obsolete 855T stacklights
Article to discuss migration of Rockwell Automation 855T stacklights to 856T stacklights
Every 855T stack light maps to an 856T build of three part types: a mounting base (preassembled, or an adaptor plus a power module), 24V AC/DC light modules, and an optional sound module. The 856T keeps the same 70 mm diameter and modular design, so most swaps are one-for-one at the mount.
Bulletin 855T was taken off sale after October 1, 2019, and Rockwell names Bulletin 856T as its functional replacement (Rockwell migration guide MIGRAT-PP036A). The biggest change is voltage: all 856T modules are 24V AC/DC, so 120V and 240V AC stacks now use one of two AC power modules in the base instead of AC-rated modules.
Key differences|
Attribute |
855T |
856T |
|
Diameter |
70 mm |
70 mm |
|
Max modules per stack |
5 |
7 |
|
Module voltage |
12V DC, 24V AC/DC, 120V AC, 240V AC versions |
24V AC/DC only; AC supplies go through a power module |
|
AC control |
AC-rated modules |
856T-BAC3C (3 circuits) or 856T-BAC7C (7 circuits) power module |
|
Illumination |
Incandescent, LED, xenon strobe |
LED only |
|
Flashing and strobe |
Separate module types |
One multi-function module (856T-BB), set by DIP switch |
|
Rotating light |
Yes |
Yes, LED, six colors |
|
Combined light + sound modules |
Yes |
No; order the light and sound module separately |
|
Housing colors |
Several |
Black only |
|
DeviceNet bases |
Yes |
No; keep a black 855T DeviceNet base and add an 856T-ATM transition module |
|
Ingress rating |
IP65 (combo and some sound modules IP54) |
IP66/67 on all light and sound modules |
Sources: Rockwell migration guide
Two gaps have no 856T equivalent: 12V DC operation and 80 cm pole bases. Those applications need a design change, such as a 24V supply or a shorter pole.
Base cross-referencePick the 856T base by the old 855T base style and your control voltage. Preassembled 856T bases include the power module and cap. The "with cap" and "without cap" 855T versions map to the same 856T part.
|
855T base |
856T, 24V AC/DC |
856T, 120/240V AC, 3 circuits |
856T, 120/240V AC, 7 circuits |
Adaptor only |
|
855T-BCB(C), -BSB(C), -BRB(C) surface |
856T-B24SNC |
856T-BA3SNC |
856T-BA7SNC |
856T-BMASN |
|
855T-BVM(C) vertical |
856T-B24VMC |
856T-BA3VMC |
856T-BA7VMC |
856T-BMAVM |
|
855T-BTM(C) tube |
856T-B24T10C or -B24T25C |
856T-BA3T10C or -BA3T25C |
856T-BA7T10C or -BA7T25C |
856T-BMAT10 or -BMAT25 |
|
855T-BPM10(C), -BSPM10(C) pole 10 cm |
856T-B24P10C |
856T-BA3P10C |
856T-BA7P10C |
856T-BMAP10 |
|
855T-BPM25(C), -BSPM25(C) pole 25 cm |
856T-B24P25C |
856T-BA3P25C |
856T-BA7P25C |
856T-BMAP25 |
|
855T-BPM40(C), -BSPM40(C) pole 40 cm |
856T-B24P40C |
856T-BA3P40C |
856T-BA7P40C |
856T-BMAP40 |
|
855T-BSPM60(C) pole 60 cm |
856T-B24P60C |
856T-BA3P60C |
856T-BA7P60C |
856T-BMAP60 |
|
855T-BSPM80(C) pole 80 cm |
No equivalent |
No equivalent |
No equivalent |
— |
|
855T-BMM10C quick release |
856T-B24Q10C |
— |
— |
— |
|
855T-BMM25C quick release |
856T-B24Q25C |
— |
— |
— |
|
855T-BMM40C quick release |
No equivalent |
— |
— |
— |
|
855T-DM1B*, -DL1B*, -DS2B* DeviceNet |
Keep black 855T DeviceNet base + 856T-ATM |
— |
— |
— |
Source: MIGRAT-PP036A, mounting base tables.
Stainless steel 855T poles map to standard aluminum 856T poles. If you buy an adaptor only, add a power module: 856T-B24C (24V AC/DC), 856T-BAC3C (120/240V AC, 3 circuits) or 856T-BAC7C (120/240V AC, 7 circuits). Each power module includes the cap.
Module cross-referenceThe same 856T module replaces the 24V, 120V and 240V versions of each 855T module. Only the 855T voltage code changes: B24 (24V AC/DC), B10 (120V AC) or B20 (240V AC). The asterisk (*) is the color digit, which carries over unchanged.
|
855T module (use B24, B10 or B20) |
856T replacement |
Notes |
|
855T-B__DN* steady incandescent |
856T-BT* |
LED |
|
855T-B__TL* steady LED |
856T-BT* |
— |
|
855T-B__FN* flashing incandescent |
856T-BB* |
Multi-function LED, set to flash by DIP switch |
|
855T-B__GL* flashing LED |
856T-BB* |
Set to flash by DIP switch |
|
855T-B__BR* xenon strobe |
856T-BB* |
Set to single or double strobe by DIP switch |
|
855T-B__RL* rotating |
856T-BR* |
LED; six colors |
|
855T-B__DC*, -B__DD*, -B__TC* steady + sound |
856T-BT* + 856T-BP1 |
Order as two parts |
|
855T-B__FC*, -B__GC*, -B__BC* flashing/strobe + sound |
856T-BB* + 856T-BP1 |
Order as two parts |
|
855T-B__SA1, -B__TA1 transducer |
856T-BTR3 |
1, 3 or 7 tones depending on circuits available |
|
855T-B__SA2, -B__SA3 piezo, one tone |
856T-BP1 |
One-circuit, 8-tone piezo |
|
855T-B__TA2, -B__TA3 piezo, two tones |
856T-BTR3 |
Multi-tone transducer |
Color digits: 3 green, 4 red, 5 amber, 6 blue, 7 clear/white, 8 yellow. The 856T also adds 9 magenta.
For 120V or 240V stacks, the modules are the same 24V parts, but they only work on an 856T-BAC3C or 856T-BAC7C power module. Source: MIGRAT-PP036A, module tables.
Worked exampleAn existing 120V AC stack on a 25 cm pole has steady green, flashing amber, steady red and a one-tone piezo horn. That is four signals, which is more than a 3-circuit AC power module can drive, so it needs the 7-circuit base.
|
855T part (existing) |
856T part (new) |
|
855T-BPM25C |
856T-BA7P25C |
|
855T-B10TL3 (green, steady LED) |
856T-BT3 |
|
855T-B10GL5 (amber, flashing LED) |
856T-BB5, DIP switch set to flash |
|
855T-B10TL4 (red, steady LED) |
856T-BT4 |
|
855T-B10SA3 (piezo, one tone) |
856T-BP1 |
Keep the same order from the base up: green, amber, red, horn. The existing 120V AC field wiring lands on the 856T base terminals, so no control voltage change is needed.
Migration steps- Record the existing stack. Write down the base catalog number and every module from the base up, including voltage code and color.
- Pick the 856T base from the base cross-reference. On AC stacks, count the signals: use the 3-circuit base for up to three and the 7-circuit base for more.
- Convert each module using the module cross-reference. Split any combined light + sound module into two parts.
- Handle the exceptions: 12V DC stacks need a 24V supply; 80 cm poles and 40 cm quick-release bases need a shorter length; DeviceNet stacks need an 856T-ATM.
- Order and install. Lock out, label the signal wires, then swap the base and stack the new modules in the same order.
- Set the DIP switches on any 856T-BB modules to match the old flashing or strobe behavior.
- Test every signal from the PLC or HMI, then update the drawings and spare-parts lists.
Sources
- Migration Solutions: 855T to 856T 70 mm Control Tower Signaling System (MIGRAT-PP036A) — Rockwell Automation, July 2018
- Signaling Specifications, Bulletin 856T (855-TD001I) — Rockwell Automation, December 2019
- 855 Control Tower Stack Lights overview and comparison — Rockwell Automation
Confirm final part numbers and availability with your Rockwell distributor ES&E before ordering.