Contactor Relay vs Contactor: What's the Difference & When to Use Each
A contactor is built to switch a motor or heavy load directly, with contacts rated for the high inrush current a motor draws at start-up. A contactor relay looks almost identical and works on the same electromagnetic principle, but its contacts are only rated for small control-circuit currents — pilot lights, interposing signals, small solenoids — not for switching a motor's actual load current. Using one in place of the other, in either direction, either wastes money or risks welding the contacts closed the first time it switches a real motor load.
Here's exactly what separates them, how to tell which one a datasheet is describing, and where each belongs in a control panel.
Same Mechanism, Different Contact Rating
Both devices are electromagnetic switches — a coil pulls an armature to close a set of contacts, exactly like the mechanism inside any contactor. The entire difference is in what those contacts are built and tested to switch. A motor contactor's contacts are sized with an AC3 utilisation category rating for motor loads, meaning they're tested to make and break the high inrush current a motor draws at start-up without welding or excessive arcing. A contactor relay's contacts carry a much lower AC15 or general-purpose rating, sized for small control-circuit currents like indicator lamps, small solenoids, or signalling to a PLC input — not for a motor's starting current.
Side-by-Side Comparison
| Feature | Contactor | Contactor Relay |
|---|---|---|
| Contact rating | AC3 (motor loads) or AC1 (resistive) | AC15 or general-purpose (control signals) |
| Typical current | 9A to several hundred A | Typically under 10A, control-circuit only |
| Typical use | Switching motors, heaters, heavy loads directly | Interlocking, signalling, indicator lamps, PLC I/O |
| Overload relay pairing | Almost always paired with one for motor protection | Not applicable — no motor load to protect |
| Physical size | Larger, scales with current rating | Smaller and more compact |
Common Places Each One Belongs in a Panel
| Application | Correct Choice | Why |
|---|---|---|
| Switching a motor on/off directly | Contactor | Only contactor contacts are rated for motor inrush current |
| Interlocking two starters so only one runs at a time | Contactor relay | Only switching low-current control signals, not the motors themselves |
| Extending a contactor's auxiliary contacts for more signalling points | Contactor relay | Adding indicator lamps or PLC feedback, not more load switching |
| Switching a resistive heater load directly | Contactor | Load current still exceeds a contactor relay's rating in most cases |
Frequently Asked Questions
What happens if I use a contactor relay to switch a motor directly?
Its contacts aren't rated for the motor's inrush current, so repeated switching will pit, arc, and eventually weld the contacts closed — leaving the motor unable to be switched off, which is a genuine safety hazard, not just a reliability problem.
Is a "control relay" the same thing as a contactor relay?
They're closely related terms often used interchangeably by manufacturers and suppliers — both describe a lighter-duty electromagnetic relay for control-circuit switching rather than motor loads. Some ranges specifically badge them "contactor relay" because they share the same physical footprint and coil options as the manufacturer's contactor line.
Why would I choose a contactor relay over a standard control relay?
Mainly for panel consistency — a contactor relay sharing the same physical range as the panel's contactors often shares accessories, mounting, and coil voltage options, simplifying spares holding and panel design compared with mixing in a completely different relay family.
Can a contactor be used where a contactor relay would normally go?
Technically yes — a contactor's higher-rated contacts will happily switch a small control-circuit load. It's not dangerous, just an oversized and more expensive choice than the job requires, and it typically takes up more panel space than needed.
How do I confirm which one a datasheet is describing?
Check the stated utilisation category — AC3 (or AC1 for resistive loads) indicates a load-switching contactor; AC15 or a "control relay"/"contactor relay" designation with no motor kW rating indicates control-circuit-only contacts. If a motor kW or AC3 current rating isn't listed at all, treat it as control-circuit rated only.
Related Reading
Shop the Parts
| Product | Use | Link |
|---|---|---|
| ABB GJL131 Contactor, 24V ac Coil, 3-Pole, 20A, 5.5kW | Direct motor switching, AC3-rated | View product → |
| ABB B6 Contactor Relay, 24V dc Coil, 3-Pole, 9A | Control-circuit switching, interlocking, signalling | View product → |
| Full contactor range | Browse by pole count, coil voltage and AC3 rating | Browse contactors → |
| Full contactor relay range | Browse by contact configuration and coil voltage | Browse contactor relays → |
| All genuine ABB products | Contactors, relays and motor starter components from the same manufacturer | View all ABB products → |
Disclaimer: ABB, and any other manufacturer or brand names referenced in this article, are used solely for identification and compatibility purposes. Z&F Corporation is not affiliated with, authorised by, or an official representative of these manufacturers; all trademarks are the property of their respective owners.
