Changeover boxes
- PC class: integral double-throw contacts, transfer time down to tens of milliseconds, suited to motor loads and critical loads
- CB class: two breakers + mechanical interlock, with short-circuit protection, suited to circuits that need downstream protection
- Transfer logic: auto-restore / no auto-restore / mutual standby — three options
- Generator interface: sends start signal on voltage loss, transfers after generator voltage stabilizes (with AMF logic)
- Monitoring: three-phase voltage, phase loss, undervoltage, overvoltage, frequency; transfer status visible via indicator lights
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.
| Enclosure type | Wall-mounted (≤160 A) / floor-standing (higher currents), dual-source incoming lines clearly labeled |
|---|---|
| Standard dimensions (W×H×D) | 600×800×250 (wall-mounted) to 1000×1400×400 (floor-standing) mm, custom sizes available |
| Enclosure construction | 1.5–2.0 mm cold-rolled steel, electrostatic powder coated |
| IP rating | IP54 standard / IP65 optional |
| Indicator panel | Three indicator groups — main, backup and load — with visible transfer switch position |
| Cable entry | Dual bottom cable entry; load exits top or bottom |
| Rated voltage | AC 380V / 400V, 50 Hz |
|---|---|
| Rated current | ≤630 A (PC-class integral type); CB-class sized to the breaker frame |
| PC-class features | Integral double-throw, mechanically held, no overcurrent protection (protection provided upstream) |
| CB-class features | Two breakers + mechanical interlock + motor operator, with short-circuit protection |
| Transfer Time | PC class: tens of milliseconds at best; CB class: 1–3 s (including the dead time) |
| Switching logic | Auto transfer / auto transfer with auto return / mutual standby, selectable on the panel |
| Generator interface | Volt-free start signal (dry contact); transfers to backup after the generator stabilizes and the delay elapses |
| Four-pole optional | For TN systems, 3P / 4P is selected by grounding arrangement to prevent back-feed and support maintenance safety |
| Component brands | ATS specialists such as Schneider / ABB / Chint / HANKWANG, customer-specified brands supported |
| Dual utility supply type | Two utility feeds, one normal and one backup — common for data rooms and production lines |
|---|---|
| Utility + generator type | Loss of voltage initiates the start signal; transfer occurs once the generator is ready, with auto return on restoration |
| Fire load end-of-line transfer type | End-of-line dual-source transfer for fire equipment (supply scope confirmed per project requirements) |
| Mutual standby type | Both sources have equal priority; whichever has power is used, decided by the transfer box itself |
| Multi-load grouped type | Branch outputs after transfer, with critical and general loads on separate circuits |
| Assembly standard | GB/T 7251.1 / IEC 61439-1; ATS devices comply with GB/T 14048.11 |
|---|---|
| Interlock verification | CB-class mechanical interlock and PC-class contact position verified unit by unit |
| Routine tests (every unit) | Insulation resistance, dielectric withstand and simulated loss-of-voltage transfer sequence tests |
| Temperature rise | ≤70 K at contact and terminal connections |
| Documents with shipment | System diagram, transfer logic description, 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.
The two sources never parallel
PC-class contacts are mechanically held in mutual exclusion; CB-class uses a mechanical interlock. Verified unit by unit: under no condition can the two sources parallel — if it fails this, it does not leave the plant.
Transfer logic hard-coded on the board
Loss-of-voltage detection delay, generator start wait, and return confirmation delay are set to the application and written into the delivery documentation, so nothing gets readjusted on site.
Start signal before transfer
With a generator, loss of voltage first sends a dry contact start signal; backup power is only switched in after generator voltage and frequency stabilize — we do not gamble the load on a generator that has not come up.
Incoming and outgoing lines color-coded separately
Main and backup incoming lines and load outgoing lines are color-coded and tagged, so no one switches the wrong source during manual emergency operation.
Transfer test on every unit
At the factory, a variac simulates loss of voltage / phase loss / undervoltage; the full logic is run through and transfer times are recorded.
Grounding system decides
For TN-C-S and systems with a generator neutral, 4P is specified per code to prevent back-feed on the backup neutral — pole count is set by the grounding system, not by habit.
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.
Server Rooms & Data Centers
Dual utility-source transfer at the point of use — PC-class high-speed transfer keeps equipment online.
Production Lines & Precision Equipment
For equipment sensitive to voltage sags — pair with a generator or a second utility feed.
Hospitals & Laboratories
Point-of-use transfer between two sources for critical loads (supply scope confirmed per project acceptance requirements).
Shopping Malls & Buildings
Point-of-use transfer box for fire and emergency loads (supply scope confirmed per project requirements).
Pump Stations & Water Treatment Plants
Dual-source supply for unattended pump rooms — automatic transfer and automatic return.
Telecom Base Stations
Transfer between utility power and battery / generator combinations.
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
PC-class or CB-class — how do I choose?
Need speed and reliability, with upstream protection already in place: PC-class (integrated dual-throw, tens of milliseconds). Need short-circuit protection inside the transfer box itself, with few circuits: CB-class (breaker plus interlock). Rule of thumb: PC-class for server rooms and critical loads, CB-class for general building distribution.
How fast is the transfer, really?
A PC-class integrated switch transfers in tens of milliseconds — ordinary equipment never notices. CB-class goes through open — interlock — close, taking 1–3 seconds, which IT equipment and precision loads cannot ride through; they need a UPS or a high-speed transfer transition. For exact millisecond figures, the datasheet of the selected switch ships with the unit.
Can it interlock with a generator?
Yes — this is standard practice: on loss of voltage, a passive dry contact in the box sends the generator start signal; once generator frequency and voltage stabilize (time-delay setting), the load transfers over; when utility power returns and stabilizes, the auto-transfer / auto-return logic switches back and the generator shuts down after cooldown. When we supply the AMF panel for the generator, the entire logic sequence is built in-house.
What is the difference between auto-transfer with auto-return and without?
Auto-return: after utility power is restored, the load switches back automatically — used in unattended locations. No auto-return: the load stays on the standby source until an operator confirms the utility supply is stable and switches back manually — used for critical loads where utility fluctuations could cause repeated transfer. Selectable on the panel or built to order.
Why do some installations require a four-pole (4P) switch?
Where the neutral of both sources may be live (for example utility plus generator, or two transformers with different grounding), the neutral is switched along with the phases to prevent back-feed and stray currents. The grounding system determines the pole count — we document the basis in the proposal.
Will transfer arc and damage equipment?
Any on-load transfer arcs, so contact material and arc-quenching design are the core cost of an ATS. For frequent transfer (multiple times a day), choose a motor-operated transfer switch and verify its switching-cycle life; for normal duty, a PC-class mechanically held design commonly lasts ten years.
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.
Send us the parameters of both sources — the transfer logic follows them
Send us your source combination (dual utility / utility plus generator) and load class, and we will provide a free transfer scheme · quotation within 24 hours. Direct from the source factory, MOQ 1 unit, 15–25 day lead time, 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.