Relay logic control cabinets
- Logic core: interposing relays (interlock / memory) + time relays (sequencing) + counting relays
- No programming: all logic is fixed in the wiring — the schematic is the whole truth
- Noise immunity: no CPU, no software — outstanding stability in high-EMI environments (foundries, welding shops)
- Delivery: complete schematic + wiring with matching wire numbers, so maintenance follows the drawing
- 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 / floor-standing, single or double door |
|---|---|
| Standard sizes (W×D×H) | 600×300×800 (wall-mounted) / 800×600×1600 (floor-standing) mm, custom sizes 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 buttons, selector switches and indicator lights laid out to match the operating sequence |
| Serviceability | All relays are DIN-rail mounted — plug-in replacement without disturbing wiring |
| Control voltage | AC 220V standard; DC 24V for long cable runs and safety-related applications |
|---|---|
| Logic components | Intermediate relays (2/4/8 contacts), time relays (on-delay/off-delay), counting relays |
| Pilot devices | Pushbuttons, selector switches, rotary switches, indicator lights, buzzers |
| Protection configuration | Breaker + fuse branch circuits; contactors paired with thermal overload relays |
| Interlock method | Normally closed contacts wired in series (safety first); self-holding and mutual interlocking per standard wiring practice |
| Contact redundancy | Critical interlocks use dual contacts in parallel / series so a single contact failure does not drop the interlock |
| Component brands | Schneider / ABB / Siemens / Chint / Omron; customer-supplied components can be shipped to our plant |
| Sequence interlock type | Multiple machines start and stop in timed or positional sequence; the downstream unit will not run until the upstream unit is running |
|---|---|
| Interlock-priority type | Two-location operation / bidirectional equipment interlocking; safety interlocks wired through normally closed contacts in series |
| Timed rotation type | A group of time relays provides automatic duty/standby rotation (the classic pump room setup) |
| Legacy line replication type | 1:1 replication of the old cabinet's schematic for replacement, with wire numbers unchanged |
| Upgrade-ready type | Relay logic first, with PLC space and terminals reserved inside the cabinet for a smooth upgrade later |
| Assembly standard | GB/T 7251.1 / IEC 61439-1 |
|---|---|
| Drawing-to-wiring match | Wiring checked cabinet by cabinet against schematic circuit numbers (spot checks plus full inspection of wire number ranges) |
| Routine tests (every unit) | Insulation resistance, power-frequency withstand voltage, and circuit-by-circuit energization and operation verification per the interlock sequence |
| Contact life | Selected to match the duty cycle: high mechanical life type (≥10⁷ operations) for frequently switched circuits |
| Documents with shipment | Schematic, terminal list, wire number cross-reference, 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.
Wire Number = Circuit Number
Every wire carries a ferrule number matching the schematic; all number segments are 100% inspected; a senior technician can locate a fault point in ten minutes from the drawing.
Interlocks in series with NC contacts
Safety interlocks are always wired in series with normally closed contacts — a broken wire stops the machine (fail-safe), never substituted with normally open contacts.
Redundant critical circuits
Critical interlocks and self-holding circuits use dual contacts in parallel / series redundancy, so a single poor contact cannot defeat the safety function.
Full plug-in, DIN-rail mounted
All relays are DIN-rail socket type — pull the failed one, plug in a spare; stocking three universal models covers a major overhaul.
Interlock sequence energized step by step
At the factory, each circuit is energized in sequence per the interlock table to verify the action order, with every step checked off on the test record.
Wire numbers unchanged
Legacy wiring upgrades are replicated 1:1 from the old schematic, with terminal numbers matching the old cabinet, so field cables land in place without re-tracing.
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.
Pump house — duty/standby
Automatic alternation via level switch + timer relay. No PLC, no maintenance headaches.
Gate and valve interlocking
Switch interlocking and limit-switch shutdown. Simple, reliable logic.
Heating and temperature control circuits
Temperature controller + contactor + interlocking. For drying rooms and furnaces.
Foundry and welding shops
In high-EMI environments, the no-CPU design has a clear stability advantage.
Replicating and replacing an old line
1:1 replication from the old drawings. Changeover done in a single night shift.
Where the owner prohibits PLCs
Some water utility, defense and classified projects specify relay logic. This is exactly the fit.
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
When should you use relay logic instead of a PLC?
Prioritize relay logic if any of these apply: fewer than 20 interlocks, low actuation frequency (minute-level), site maintenance staff trained only in power electrics, owner specifies no PLC, high-EMI environment. If the logic is complex, you need data and reports, or processes change often, go with a PLC.
Is a relay cabinet easy to modify later?
Small changes (adding one interlock, adjusting one delay) are just wiring changes. Major logic changes amount to redesigning the wiring — at that point a PLC is the better move. When we build relay cabinets, we reserve a PLC mounting position and 20% spare terminals by default, leaving room for the future.
How long do the contacts last, and how is maintenance done?
DIN-rail intermediate relays have a mechanical life on the order of 10⁷ operations; electrical life is derated by load. For frequently actuated circuits, specify a high-life model and include it in annual inspections (check for contact erosion). Stocking three common models covers a major overhaul. Compared with replacing PLC cards, relay spare parts cost is negligible.
How does the cost compare with a PLC?
For small logic (≤10 relays), a relay cabinet costs 30–50% less than a PLC cabinet. Beyond about 30 relays, wiring labor overtakes it and the PLC becomes more economical. We build both, quote honestly against your logic table, and won't push the expensive option.
Can we send you the drawings of an old cabinet for replication?
That's routine work for us: send photos of the old drawings (even hand-drawn blueprints), we turn them into standard schematics and replicate 1:1, with terminal numbers matching the old cabinet so field cables reconnect in place. If drawings are missing, we can photograph and inventory the old cabinet wiring to reverse-engineer them.
What if the timer relay settings are lost?
All setpoints are recorded in the setup sheet shipped with the cabinet, with a copy affixed inside the cabinet door; restore them on the new relay per the sheet. Time parameter changes are also logged on the setup sheet — no reliance on a veteran technician's memory.
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.
Replicate from old drawings, or build from scratch
Send us your interlock requirements or the old cabinet schematics, and we'll provide a free relay logic proposal · quote 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.