How to pickout 856T stacklight

 How to Select a Rockwell Automation 856T Stack Light Overview

To spec an 856T stack light, you pick five things in order: mounting style, supply voltage (which sets the power module), light modules, an optional sound module, and whether to buy it preassembled or as parts. Everything else follows from those choices.

The Allen-Bradley Bulletin 856T Control Tower is a modular, 70 mm diameter LED stack light that holds up to seven modules in one stack (Rockwell migration guide). All light and sound modules run on 24V AC/DC, so the same module part numbers work whether the panel supplies 24V or 120/240V AC. It replaces the older 855T line, which went out of sale in October 2019. Housings are black only, and there is no 12V DC option.

How the system fits together

A complete 856T stack is built bottom to top from these parts:

1. Base mounting adaptor — attaches the stack to the machine (surface, vertical, tube, pole or quick-release).
2. Power module — sits on the adaptor, takes the field wiring and powers the stack. It includes the top cap.
3. Light modules — one per signal, stacked in the order you want them read.
4. Sound module (optional) — a top-mount or in-line audible alarm.
5. Cap — closes the top of the stack; supplied with the power module or preassembled base.

There are three power modules, and they decide how many signals you can drive directly:

The base adaptor and power module can be bought separately, or as one preassembled base with the cap included (for example, 856T-B24P10C). Beacon-style light modules share the same bases but cannot have anything stacked on them.

Step-by-step selection

Step 1: Choose the mounting style

Pick the base by where the light goes and how visible it must be. Taller poles lift the stack above guarding and other equipment.

Source: Rockwell 855T-to-856T migration guide. If you buy the adaptor only, add the matching power module (856T-B24C, 856T-BAC3C or 856T-BAC7C). Quick-release bases are 24V only, and there is no 80 cm pole.

Step 2: Match the supply voltage

Use a 24V base when the signals come from 24V PLC outputs or relays. Use a 120/240V AC base only when you must switch the lights directly from line voltage. Then choose 3-circuit or 7-circuit by counting how many independent signals you need. The power module's input switching frequency is limited to 5 Hz, so do not flash the lights from the PLC faster than that; use the modules' built-in flash instead.

Step 3: Choose each light module

Light module part numbers follow one pattern: 856T-B + module type + color digit. For example, 856T-BT4 is a steady red module.

Color digits: 3 green, 4 red, 5 amber, 6 blue, 7 white/clear, 8 yellow, 9 magenta. 

If you are unsure whether a signal will need to flash later, pick the multi-function (B) module. It can be set to steady today and changed by DIP switch in the field.

Step 4: Add sound if needed

Choose the transducer for loud areas or when different alarms need different tones. A recordable sound module is also offered; confirm its part number in Rockwell's selection tool.

Step 5: Decide preassembled or loose parts

Buy components when you need a custom order or want spares on the shelf. Rockwell also sells factory-assembled stacks, which reduce build time and part count on the order.

Worked example

A machine needs a red/amber/green status light and an alarm horn, driven by 24V DC PLC outputs, mounted on top of the control cabinet so it clears nearby guarding. Red must flash on a fault.

Stack order from the base up: green, amber, red, horn. The build uses four PLC outputs, one per module. Nominal draw is roughly 58 mA per steady module, 100 mA for the multi-function module and 120 mA for the horn, about 336 mA total at 24V (specifications). Check that each output card and your 24V supply can handle that, plus inrush.

Colors, brightness and environment

Follow your site standard first; if there is none, the common IEC 60204-1 meanings are a safe default.

Selection checklist

• ☐ Mounting style and pole or tube length chosen
• ☐ Control voltage confirmed (24V AC/DC vs 120/240V AC)
• ☐ Signal count fits the power module (3 or 7 circuits on AC)
• ☐ One light module per signal, color and function picked
• ☐ Sound module picked, if required, and placed correctly
• ☐ Total stack height is 7 modules or fewer
• ☐ Output current and 24V supply budget checked
  
  

• Ordering an adaptor-only base (856T-BMA…) without a power module. The stack will not work without one.
• Choosing a 3-circuit AC base, then needing a fourth signal. Pick the 7-circuit base if growth is possible.
• Trying to stack modules on a beacon (GB, SB, RB, MB). Beacons are always the only light on the base.
• Specifying a 12V DC or non-black housing. The 856T line offers neither.
• Blinking outputs from the PLC faster than 5 Hz on an AC base. Use a multi-function module's built-in flash instead.
• Migration Solutions: 855T to 856T 70 mm Control Tower Signaling System (MIGRAT-PP036A) — Rockwell Automation, July 2018
  
  
• 856T Control Tower Stack Lights product page — Rockwell Automation

Verify final part numbers and availability in Rockwell's product selection tool or with your distributor ES&E before ordering.