AC Contactor Manufacturer for Motor Control and HVAC Panels

SMO Electric produces AC contactors in five current frames from 9A to 150A. Every unit is built to IEC 60947-4-1 with screw terminals and a choice of AC or DC coil voltage, supplied under your own brand or ours.

✓Nine to 150A in five frame sizes
✓AC-3 switching rated to 690V
✓Routine-tested to IEC 60947-4-1

SMO-K AC contactor range in five frame sizes, from 9A to 150A

SMO-K AC Contactor Series

Five frame sizes covering 9A to 150A. Select a model to open the full specification, drawing and ordering information, or compare the whole SMO-K range against the rest of the switchgear the factory builds.

SMO-K 80A-95A AC Contactor

SMO-K 25A-38A AC Contactor

SMO-K 115A-150A AC Contactor

SMO-K 40A-65A AC Contactor

SMO-K 09A-18A AC Contactor

Product range

AC Contactor Types We Manufacture

The SMO-K range is organised by frame size rather than by application, so the same five bodies cover motor starting, pump control, HVAC switching and lighting loads. Each frame differs in physical size, pole current and coil consumption, but all share the same terminal layout logic and mounting style, which means one spare part reference usually covers several ratings. If you are unsure which frame suits your motor, the SMO-K AC contactor selection guide walks through ratings, coil voltages and duty cycles frame by frame.

Motor ratings shown for 400V three-phase. Confirm the exact frame against your motor nameplate and the required making capacity.

Frame	Rated current	Typical motor rating	Coil options	Use
SMO-K 09A-18A	9A – 18A	2.2 – 5.5 kW at 400V	24V DC standard	Small motors, pumps, HVAC units
SMO-K 25A-38A	25A – 38A	7.5 – 11 kW at 400V	24V DC standard	Machine tools, compressors, fans
SMO-K 40A-65A	40A – 65A	15 – 22 kW at 400V	24V DC standard	Pumps, conveyors, mixers
SMO-K 80A-95A	80A – 95A	30 – 37 kW at 400V	24V DC standard	HVAC plant, large fans, hoists
SMO-K 115A-150A	115A – 150A	45 – 55 kW at 400V	24V DC standard	Heavy pumps, chillers, compressors

›Pole count can be specified beyond the standard three-pole version where the control circuit calls for it.
›Auxiliary NO and NC contacts mount on either side for holding, interlock and status feedback.
›Every frame is supplied with a complete set of main and auxiliary terminals, mounting screws and an instruction sheet.

Technical data

Common SMO-K Specifications

Values below apply across the SMO-K range. Confirm the exact rating for your frame size before ordering.

Parameter	SMO-K value	Note
Rated current (AC-3)	9A – 150A	Across five frame sizes
Rated operational voltage	Up to 690V AC	50/60Hz
Rated control voltage	24V DC standard	Other voltages on request
Number of poles	3P	Other pole counts on request
Terminal type	Screw terminals	Solder and PCB variants available
Mechanical endurance	1,000,000 cycles minimum	Tested per IEC
Short-circuit withstand (Icu)	6 – 8 × rated current at 380V	Varies by frame size
Utilisation category	AC-3	Also rated AC-1
Auxiliary contacts	NO / NC, customer specified	Mirroring and interlock options
Reference standard	IEC 60947-4-1	Routine-tested per batch

What Is an AC Contactor?

An AC contactor is an electrically operated switch that controls the main current path of a motor. It is designed for repeated switching of the motor load under normal operating conditions, and it is operated by a low-power control circuit rather than by hand.

Three parts do the work. The coil is a low-power electromagnet mounted on the contactor body. The armature is a moving iron core that the coil pulls towards the fixed pole when energised. The main contacts are the conducting parts that close onto each other when the armature moves.

In a motor control panel the contactor sits between the protective device and the motor. A circuit breaker or fuse handles short-circuit protection; the contactor handles the far more frequent switching of starting, running and stopping. Because those operations happen many times a day, mechanical endurance and contact wear matter more than raw breaking capacity in most everyday applications. The moulded case circuit breakers that sit upstream of it are covered separately, and a longer explanation of what an AC contactor is and where it is used works through the same points with more examples.

SMO-K 80A-95A AC contactor, side view with coil and main terminals

SMO-K 80A-95A AC contactor, front view showing three main poles

How Does an AC Contactor Work?

When the control circuit energises the coil, the armature closes and pulls the main contacts together, allowing current to reach the motor. When the coil is de-energised, a spring returns the contacts to the open position.

The practical consequence is that the contactor never carries the start-up surge by itself. A motor drawing six times its rated current at start would destroy the contacts in a fraction of a second, so a contactor is always paired with a protective device and a thermal overload relay. The relay measures motor current and trips the contactor coil if the motor is overloaded or stalled, and the panel is normally completed by a motor protection breaker at its head.

In a direct-on-line starter the contactor is switched on by a single push button and the motor runs until it is switched off. Adding an auxiliary contact in parallel with the start button latches the circuit so the motor keeps running after the button is released, and adding a second auxiliary contact in series with the stop button allows the same control circuit to stop the motor from several places. DOL, star-delta and soft starter are the three common ways of arranging that circuit, and the choice starts to matter once motors pass roughly 7.5 kW.

Where we are

Based in Liushi, the Low-Voltage Switchgear Cluster

SMO Electric works out of Liushi Town in Yueqing, Wenzhou, the corner of Zhejiang where most of China’s low-voltage switchgear is produced. Being inside that cluster is practical rather than promotional: moulds, springs, coils, plating and test equipment are a short drive away, so a change to a contact or a spring does not wait on a shipment from another province.

Visits are welcome. Buyers, distributors and panel builders can compare the full SMO-K range on the bench before committing to an order, and the technical contact who quotes the job stays with it through production and shipment. If you are weighing up sources for a first order, why overseas distributors and OEMs work with Chinese manufacturers sets out what is worth verifying before you commit.

Address

Chandong Village, Liushi Town, Yueqing City, Wenzhou, Zhejiang, China

Phone

+86-18079491179

Sales email

helge@wzsmo.com

General enquiry

blackd@wzsmo.com

Suppliers within reach

Moulding, coil winding, plating and testing all sit in the same industrial area. A revised spring or contact reaches us in days, not weeks, which is what makes small custom runs possible.

Sample before volume

A frame you have not used before can be sent as a sample for bench testing and panel fit before the production order is placed, so the first bulk shipment is not the first time you see the part.

One contact, start to finish

The person who answers the technical questions at quotation follows the batch through inspection and packing. Specifications do not get re-negotiated between departments. More background on the company is under about SMO Electric.

A quotation in one working day

Send the frame size, coil voltage and quantity, and the quotation comes back with the model, the unit price and the lead time — usually the same working day, rather than after a week of internal forwarding.

Manufacturing and testing

How Every Contactor Is Built and Tested

A contactor fails in service for predictable reasons: a weak spring, a coil that drifts, a contact that was never properly seated, or flash left on a moulding that lets the arc escape. Each of those is caught at the step where it can still be corrected, not at the end of the line.

Incoming material check

Contacts, coils, springs and moulded cases are checked against the purchase specification before anything reaches assembly. A batch that does not match is rejected at the door rather than sorted out later on the bench.

Assembly and mechanism setting

Coil, armature, contacts and arc chambers are fitted, then the mechanism is set so the moving contact travels the designed distance under the spring force. Set too loose the contactor chatters; set too tight it will not pick up cleanly at low control voltage.

Pick-up and drop-out test

Every unit is energised and released to confirm it closes at the rated control voltage and opens when the coil is de-energised, without sticking and without contact bounce beyond tolerance.

Dielectric and contact resistance

A dielectric test is applied between the main poles and between the coil circuit and the main circuit. Contact resistance is measured at the same station, so a badly seated contact is caught here instead of in a panel on site.

Packing and shipment documents

Units that pass are packed with the routine test record and the packing list, marked with the frame size, coil voltage and batch. Units that fail are taken off the line for teardown, not adjusted and pushed back into the batch.

Visiting before shipment: Customers who want to see a routine test run on their own batch are welcome to attend before the shipment is released. The same checks are what catch the failures described in AC contactor troubleshooting.

Delivered projects

How Our Contactors Are Used On Site

The photographs below are taken from switchgear rooms and panels supplied by SMO Electric. They show the finished installation rather than the product on a bench, which is the part buyers usually want to check before they order: how the devices are mounted, how the cable entries are made and how the layout compares with the drawing they supplied.

MCCB installation inside a distribution cabinet on a delivered project

Distribution cabinet, Indonesia

Moulded case circuit breakers and terminal blocks assembled in a wall-mounted distribution board, with the incoming and outgoing cables dressed to the terminal blocks.

Distribution board interior with busbar and circuit breakers on a delivered project

Busbar panel, Chile

A multi-stage distribution board with copper busbar, phase and neutral labels, and circuit breakers fitted across the outgoing ways.

Switchgear assembly in progress on a delivered project

Switchgear assembly, Africa

Panel assembly during commissioning, with the protective devices, wiring and phase conductors visible before the enclosure is closed.

Standards and documentation

Built to International Standards

Every SMO-K contactor is manufactured and routine-tested against IEC 60947-4-1, the standard that governs low-voltage switchgear and controlgear for motor starters, covering utilisation category AC-3.

Paperwork for a specific destination is prepared before the goods leave the factory once the destination country and model are confirmed, which is worth arranging in advance if your customer runs an internal audit. For private-label work the ODM/OEM process sets out what has to be settled before production starts.

IEC 60947-4-1

Manufacturing and routine test follow this standard, including the AC-3 rating that applies to motor starting duty.

Routine test record

Results for the batch can be supplied with the shipment, covering mechanical operation, coil pick-up and drop-out, and the dielectric check.

Export documents

Commercial invoice, packing list and certificate of origin can be prepared for customs clearance at the destination.

Project experience

What Buyers Ask Us For Most

The following are the configurations that account for a large share of the contactors we build. They are not endorsements from named customers, but they are the real order patterns that come out of our panel builder and distributor accounts, and they are the best guide to what a typical project needs.

We needed the same 40A frame on both 24V DC and 220V AC, with our own nameplate and packaging, shipped as two separate pallet sizes to two markets.

Distributor order pattern

Our panel builder asked for a specific terminal arrangement so the incoming cables land on the same screw positions across all five frames, which cut assembly time on site.

Panel builder order pattern

The routine test report was the part that mattered, because their customer audit required the breaking capacity to be documented per unit rather than per batch.

OEM order pattern

Request a Quote or Technical Support

Send the coil voltage, pole count, current rating and quantity. We reply with a quotation and the matching catalogue pages.

AC Contactor FAQs

What information do you need for an AC contactor quotation?

Coil voltage, rated current, number of poles, mounting method, whether you need auxiliary contacts, and the annual quantity. If you have a motor rating in kW, send that instead of the current and we will select the frame for you. A motor nameplate photo is usually enough for us to quote from.

Can you supply contactors with our own brand name?

Yes. We manufacture under customer brands, covering the unit finish, nameplate, packaging, manual and the certification documents. Minimum order quantity depends on the frame size and the level of customisation, and it is confirmed with the quotation rather than quoted as a fixed figure.

Which coil voltage should I specify?

24V DC is our standard for panels because it allows the control circuit to share one supply with other 24V devices such as push buttons and indicator lamps. 220V and 380V AC coils are also available on request. If your panel already runs on 24V, specifying a DC coil avoids adding a separate control transformer.

What is the difference between AC-1 and AC-3 ratings?

AC-3 covers switching squirrel-cage motor loads and is the rating that matters for motor starters, because it covers both making and breaking the high inrush current a motor draws at start. AC-1 covers resistive or non-inductive loads with a much lower making capacity. Every SMO-K frame is rated AC-3, and the AC-3 figure is the one to check against your motor. Coil voltage and AC-3 rating goes through the numbers in more detail.

Do the contactors come with auxiliary contacts?

Auxiliary NO and NC contacts can be added on either side of the contactor to provide holding, interlock or status feedback. Specify the combination you need when ordering, for example 1NO + 1NC for a standard starter or 2NO for a reversing contactor pair. The full range sits under auxiliary contact blocks and accessories.

What certifications are supplied with the shipment?

The routine test record and packing list go with the shipment, and a certificate of origin can be arranged for the destination market. If your customer audit needs a specific document set, tell us the country and the model before the order is placed, so the paperwork can be prepared before the goods leave the factory.

How long does production take?

Lead time depends on the frame size, coil voltage and order quantity, and is confirmed with the quotation. Frames with standard coil voltages and no special branding are the shortest, while private-label units and non-standard coil voltages take longer because the nameplate and packaging are produced separately.

Are the contactors suitable for use with a thermal overload relay?

Yes. An SMO-K contactor is normally paired with a thermal overload relay in a motor starter, and the relay mounts directly on the contactor body. Give us the relay frame you plan to use with the quotation and we will confirm the mechanical fit for that frame size.

Send Your AC Contactor Requirement

Tell us the current rating, coil voltage, poles and quantity. A quotation normally comes back within one working day. If you would rather write directly, both addresses are on the contact page.