1746-IA16 — SLC 500 16-Point 120V AC Input Module

The 1746-IA16 is a 16-point 120V AC digital input module for the SLC 500 modular chassis, accepting field signals in the 85–132V AC range from pushbuttons, limit switches, selector switches, and relay contacts wired on standard 120V AC control circuits. All 16 inputs share a single common, landing on a 20-terminal removable block that allows module replacement without disturbing the field wiring underneath.

Specifications

Parameter	Value
Part Number	1746-IA16
Platform	SLC 500 (1746 series)
Input Points	16
Input Voltage	85–132V AC, 47–63 Hz
Input Groups	16 points, single common
ON Delay / OFF Delay	35 ms / 45 ms (nominal)
Max Off-State Current	2 mA
Max Inrush Current	0.8 A
Backplane Current (5V)	85 mA
Terminal Type	Removable terminal block, 20 terminals
Operating Temperature	0°C to 60°C

Direct AC Sensing on a Legacy SLC 500 Panel

Many SLC 500 systems were originally built around 120V AC field wiring, common in plants where pushbuttons, limit switches, and pilot devices ran directly off the same 120V AC distribution feeding the rest of the panel — well before 24V DC became the default sensor standard. The 1746-IA16 lets a modern SLC 500 controller continue reading those AC signals directly, without retrofitting the field wiring to DC or adding interposing relays to convert each signal down to a lower voltage.

The 35 ms ON delay and 45 ms OFF delay are both meaningfully longer than a typical DC input's filter time, which is appropriate given the AC waveform itself — the module needs to recognize the AC signal across enough of the waveform cycle to register a clean state change, rather than just detecting an instantaneous voltage threshold the way a DC input circuit can.

FAQ

Q: Can the 1746-IA16 accept 240V AC inputs?

No. The rated range is 85–132V AC — applying 240V AC exceeds this module's voltage rating and risks damage. For 240V AC, a module specifically rated for that voltage class is required.

Q: Why is the input response time slower than a typical 24V DC input module?

AC signal detection requires recognizing the waveform across part of its cycle rather than a single instantaneous threshold, which inherently takes longer than DC level detection — the 35/45 ms delays reflect this AC-specific signal processing requirement.

Q: Can this module be replaced without disconnecting all 16 field wires?

Yes. The removable terminal block stays connected to the field wiring when the module body is unplugged, so a module swap doesn't require re-landing any of the 16 input wires.

Q: Is a current model available with the same function for newer Compact I/O-based systems?

A functionally similar 120V AC input module exists in the Compact I/O platform for systems built on that newer architecture — verify compatibility with the specific controller platform in use before substituting between the two families.

1746-IA16 New Sealed 1746IA16 Ser D SLC 500 PLC Input Module