Direct-on-line starter cabinets
- Configuration: circuit breaker (short-circuit protection) + contactor (AC-3) + thermal overload relay (overload and phase loss)
- Application: 0.75–15 kW three-phase induction motors, where the grid and transformer capacity support 6–8 times starting current
- Multi-circuit version: 2–12 motor circuits in a single cabinet, each with independent protection and indication
- Control: manual push-button / automatic signal / remote dry contact, combined as required
- Components: Schneider / ABB / Siemens / Chint; brand can be specified, or customer-supplied components shipped to our plant
Specifications
The table below covers 80% of factory distribution room cases. Anything outside it we can still build — those are engineered items, quoted separately, with an indicative price the same day.
| Type | Wall-mounted (up to 4 circuits) / floor-standing (multi-circuit), single or double door |
|---|---|
| Standard sizes (W×D×H) | 500×300×600 (wall-mounted) / 800×600×1600 (floor-standing) mm, custom builds available |
| Enclosure construction | 1.5–2.0 mm cold-rolled carbon steel, bent and welded, electrostatic powder coated |
| IP rating | IP54 standard / IP65 optional |
| Operator panel | Start/stop push-button per circuit + run/fault indicator lights |
| Cable entry | Bottom cable entry; outgoing busbar on top optional for multi-circuit versions |
| Rated operating voltage | AC 380V / 400V, 50 Hz; control circuit AC 220V or DC 24V |
|---|---|
| Power per circuit | 0.75–15 kW, full-voltage direct-on-line starting |
| Protection configuration | Circuit breaker (magnetic trip for short circuit) + thermal overload relay (1.05–1.2 In overload and phase loss) |
| Upgrade option | Electronic motor protector instead of thermal relay; adds underload / locked rotor / phase imbalance |
| Control method | Manual pushbutton / automatic level or pressure / remote dry contact — combinable |
| Indication & metering | Run / fault indication per circuit; ammeter per circuit or optional |
| Component brands | Schneider / ABB / Siemens / Chint; customer-supplied components accepted for factory installation |
| Single-circuit standard | One motor, one small cabinet — the simplest, most reliable arrangement |
|---|---|
| Multi-circuit centralized | 2–12 circuits under centralized control, each with independent protection — common for fan and small pump groups |
| Automatic level control | Starts and stops automatically from a level switch — simple automation for drainage and water supply |
| Remote-controlled | Start/stop from a PLC or DCS dry contact, with local manual control retained for maintenance |
| Upgrade path | To add speed control later, swap the whole cabinet for a VFD panel; for soft starting, swap in a soft starter cabinet — interfaces are reserved |
| Assembly standard | GB/T 7251.1 / IEC 61439-1 |
|---|---|
| Routine tests (every unit) | Insulation resistance, power-frequency withstand voltage, and circuit-by-circuit energization and operation test |
| Temperature rise | Contactor and terminal connections ≤70 K |
| Documents with shipment | Schematic, terminal list, BOM, test report |
Five steps to specify your run
A configuration summary is generated as you go. It travels with your inquiry, saving a round of confirmation.
Build details
Systems have been in service for decades, and the failure points are always the same few: poor busbar contact, water ingress at the door seal, high temperature rise in the correction cabinet, and mis-phased outgoing feeders. The six hard rules below are written for exactly these points — every cabinet can be traced to them.
One protection loop per circuit
Each circuit has its own breaker + contactor + thermal overload as a group, fed from the vertical busbar — servicing any one circuit does not shut down the others.
Settings recorded in the documentation per nameplate
Thermal overload settings are recorded in the factory documentation based on the motor nameplate current, so they cannot be casually adjusted on site.
Energized operation checked one by one
Every circuit gets dual confirmation through an energized start/stop test and a protection simulation (via the test button) — no sampling, even on multi-circuit panels.
Power and control kept apart
Main circuits and control wiring run in separate ducts to reduce interference; wire markers correspond one-to-one with circuit numbers on the schematic.
Terminals and mounting rails
Terminal blocks and DIN rails each have 20% spare capacity, so adding a circuit later does not require a new cabinet.
Indicator lights reflect actual status
Run / fault indications are taken from contactor auxiliary contacts and protection relays — no dummy indicators.
Photos & enclosure construction
Below are photos taken in our own shop — from the complete unit down to the internal busbars and secondary wiring. Every build detail can be checked item by item.
Image key: 01–05 are shop photos (the numbers match the shot list). The line drawing shows the front elevation of the enclosure; dimensions match the specification table above.
Where these cabinets go
These are the routine applications — we can talk scheme and configuration directly. For the industry view, see the industry pages.
Small workshop fans and exhaust fans
Full-voltage starting has low inrush impact — direct-on-line is the most economical choice.
Small pumps and chemical dosing pumps
Add a level or pressure switch for simple automation.
Small conveyor motors
No-load starting; single or multiple circuits under centralized control.
Mixers and feeding equipment
No-load starting duty; switch to soft start for heavy, viscous media.
Small air compressors
Unloaded starting is acceptable; for larger models, follow the manufacturer's requirement for star-delta or soft start.
HVAC fan coils and pump groups
A dozen or more circuits on one cabinet — a compact fit for building plant rooms.
Commercial terms
Specification dated September 2026; quotations follow this.
| Drawings & design | Free |
| MOQ | 1 unit (5 or more recommended for production) |
| Production lead time | 15-25 days after drawing approval |
| on-time delivery | 98% |
| Warranty | 12 months |
| Loading port | Ningbo / Shanghai, China |
| Component brands | Schneider / ABB / Siemens / Chint |
| Factory visit & dispatch confirmation | Factory visits welcome; finished-cabinet photos and video before dispatch |
| Capacity | 5,800+ units / year |
Documents for your engineering team
Selection manual, outline dimensions and RFQ checklist — for the customer's electrical engineer. All three documents are being organized by product line; download links go live once complete.
Six questions procurement and electrical engineers ask most
How large a motor can be started direct-on-line?
Rule of thumb: motor capacity should not exceed 1/10 of the supply transformer capacity (1/15 for frequent starting), or the busbar voltage drop during starting should not exceed 15%. In a typical 380V workshop, motors up to 15 kW can generally be started direct-on-line. Send us your transformer capacity and existing load, and we will check it for you.
Direct-on-line starting draws 6–8 times rated current — can the grid take it?
Small motors have short starting times (1–3 seconds), so voltage drop and transformer temperature rise are limited. The real concern is sensitive equipment on the same busbar (contactors dropping out on undervoltage, lights flickering). For these conditions, star-delta or soft start is recommended.
How do I choose between a thermal overload relay and a motor protection relay?
Thermal overload relays are inexpensive and reliable, covering overload and phase loss. Electronic motor protection relays add underload (anti-dry-run), locked rotor, phase imbalance and temperature inputs — very useful for pumps to prevent dry running. When the price difference is small, go straight to a protection relay.
How many motors can one cabinet handle?
Based on circuit current and heat dissipation, typically 2–12 circuits. Above 12 circuits or with high total current, split into multiple cabinets or switch to an MCC configuration. In multi-circuit cabinets, each circuit is independently protected and does not affect the others.
What is the difference between manual and automatic?
Manual = local start/stop via pushbuttons; automatic = runs on level / pressure / temperature signals; remote = controlled by dry contacts from a higher-level system. The three modes can be combined; during maintenance, switch to manual to block automatic operation for safety.
What if we want to switch to variable frequency later?
Terminals and DIN rail inside the cabinet are sized with 20% spare capacity. For a retrofit, you can add a VFD or replace the whole cabinet — the motor and cables stay as they are. Tell us your upgrade intent at the time of order and we build the interface provisions into the drawing.
Other cabinet types in the same main circuit
Related products use color-block placeholders for now (product photos not yet complete; they will be replaced together). Internal links will be filled in once live URLs are confirmed.
Group control for small motors — one cabinet takes them all
Send us your motor list (power / quantity / control requirements) and we will provide a multi-circuit solution and quotation free of charge, with a reply within 24 hours. Direct from the source factory, MOQ 1 unit, 15–25 day delivery, 1-year warranty.
ISO 9001:2015 · CE(LVD+EMC) · CQC · IP65
When you write, include: single-line diagram or primary scheme, switch room layout, load list, and component brand requirements. You do not need complete drawings — capacity and cabinet type are enough to start.