1756-OB16IS — 1756 16-Point 24V DC Isolated Sourcing Transistor Output Module

The 1756-OB16IS is a 16-point sourcing (PNP) 24V DC transistor output module for the 1756 chassis with individually isolated output channels. Each of the 16 outputs has its own isolated supply — no shared common, no electrical path between output points. The isolation voltage is 250V AC continuous between channels, which means the 16 outputs can simultaneously switch 16 devices that have completely different ground references, supply voltages within the rated range, or are on entirely separate electrical circuits.

Individual channel isolation is the defining feature. In most 24V DC control systems where all outputs share the same supply, a standard non-isolated output module is the correct and more economical choice. The 1756-OB16IS is the right tool when field devices come from different supply systems, when cross-circuit ground faults must be contained to a single point, or when the application requires each output to operate at a different voltage level.

Specifications

Parameter	Value
Part Number	1756-OB16IS
Platform	1756 Logix chassis
Output Points	16
Output Type	Sourcing (PNP) transistor, individually isolated
Output Voltage Range	10–30V DC (per channel, independently supplied)
Output Current per Point	2 A continuous
Channel Isolation	250V AC continuous, channel-to-channel and channel-to-backplane
Short-Circuit Protection	Electronic, per point
Leakage Current (OFF)	1 mA max
Backplane Current (5V)	500 mA
RTB Connector	1756-TBCH or 1756-TBS6H (36-pin)
Operating Temperature	0°C to 60°C
Standards	UL 508, CE, IEC 61131-2

2A per Point — More Than Standard 0.5A Modules

The 2A continuous rating per point is four times the 0.5A rating of standard 1756 transistor output modules. This higher current capacity serves loads that exceed 0.5A:

Large direct-acting solenoid valves (0.8–1.5A at 24V)
24V coil contactors for larger motor starters
Heating elements or resistive loads up to 48W at 24V
Multiple parallel LED strings or indicator arrays
Servo drive enable outputs with high input impedance networks

The combination of isolation and 2A capacity makes this module applicable to a broader range of field devices than standard output modules, potentially reducing the number of interposing relays needed in a panel design.

FAQ

Q: Do all 16 channels have to use the same supply voltage, or can they be mixed?

Each channel is independently supplied — any combination of supply voltages within the 10–30V DC range is permitted. Eight channels on 24V and eight on 12V is a valid configuration. Each channel's supply is connected independently at the RTB.

Q: Can the module switch AC loads?

No. The output transistors are rated for DC only (10–30V DC). For AC load switching, relay output modules or solid-state relays are required.

Q: Is the per-point short-circuit protection resettable without cycling power?

The electronic protection is self-resetting — once the fault condition (short circuit or overload) clears, the output can resume operation when the controller commands it back on. Whether the output automatically re-energizes or requires an explicit command depends on the controller program's output logic.

Q: What RTB is required for this module?

The 1756-OB16IS uses the standard 36-pin RTB — either the 1756-TBCH (cage-clamp) or 1756-TBS6H (screw-clamp). The RTB is ordered separately and is not included with the module. Given the per-channel wiring density on this module, the cage-clamp version is often preferred for faster wiring on initial installation.

Q: How does the isolated channel architecture affect the module's backplane current draw compared to a non-isolated module?

Isolated output channels require more internal circuitry per point than shared-common designs, resulting in higher backplane current draw — 500 mA at 5V versus ~250 mA for a standard 16-point module. Verify the chassis power supply can support this when planning slot allocations in a densely-populated chassis.

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