A contactor auxiliary contact rating must match the voltage, current, load type, switching frequency, fault protection, and required reliability of the control circuit. Do not choose it from the main contactor’s ampere rating. A small auxiliary contact that reliably reports a PLC input may be unsuitable for interrupting a DC contactor coil, while a contact rated for an inductive control duty may still have a minimum current below which signal reliability is not guaranteed. Select the exact NO or NC contact by its utilization category and manufacturer table, then validate the complete circuit and fault response.
Separate signal duty from switching duty
Auxiliary contacts commonly provide status, seal-in logic, electrical interlocking, alarms or controller feedback. Each function creates a different electrical duty. A PLC input may draw only milliamperes; a relay or contactor coil is an inductive load whose interruption produces a transient. A lamp can have a cold-filament surge. Do not use a single generic “10 A” number across those cases. Read the contact’s rated operational current at the actual control voltage and utilization category.
For IEC-style ratings, DC-13 is associated with switching DC electromagnets. Schneider Electric’s technical catalogue describes DC-13 for electromagnetic loads. This explains the category, but it is not a rating for a Sayoon auxiliary contact. Use the exact Sayoon drawing and data for the ordered option. For low-level signals, also request minimum permissible voltage/current or contact reliability data; a maximum rating does not guarantee dependable dry-circuit performance.
Collect the load information before selecting
Record whether the auxiliary contact makes, breaks or only carries the load; normal and fault voltage; steady and transient current; inductance or time constant; suppression; expected operations per hour and lifetime; ambient conditions; conductor size; and protective device. For controller feedback, include input leakage, diagnostic pulses and wetting-current requirements. For an interlock, document whether a normally closed contact must positively prevent the opposing coil from energizing and what happens if the contact welds, opens or is miswired.
| Application | Key rating evidence | Main risk | Verification |
|---|---|---|---|
| PLC status input | Minimum and maximum signal current/voltage, contact reliability | Oxide or leakage causes false state | Measure input thresholds over life and environment |
| Contactor coil switching | DC inductive category at actual voltage/current | Arc, erosion or welding on opening | Check category, suppression and endurance |
| Electrical interlock | NC contact duty and required fault behavior | Both coils commanded after contact failure | Fault test plus mechanical interlock where required |
| Indicator lamp | Inrush and steady lamp current | Cold-filament surge | Use lamp-specific manufacturer rating |
| Safety-related feedback | Defined contact architecture and safety data | Assuming ordinary auxiliary equals mirror contact | Validate complete safety function |
Check NO/NC state and mechanical relationship
“Normally” refers to the device’s defined de-energized condition. Confirm whether the selected block supplies NO, NC or changeover poles and map every terminal from the current drawing. Do not infer state from physical position or another model. For feedback, determine whether the auxiliary is mechanically linked in a way appropriate to the diagnostic claim. An ordinary auxiliary transition does not necessarily prove all main contacts opened or that hazardous DC voltage is absent.
Siemens documents auxiliary-circuit uses including signaling and interlocking and publishes model-specific low-level reliability boundaries. This reinforces two selection lessons: verify the intended function and use the exact device data. It does not transfer Siemens ratings to Sayoon products.
Account for suppression, protection, and endurance
When an auxiliary contact interrupts a coil, suppression changes arc stress and release time. A diode can reduce transient voltage but prolong DC coil current decay. A higher-voltage clamp may release faster while imposing more voltage on the switching device. Confirm compatibility with coil polarity, the contact rating and required timing. Do not add suppression when the coil already includes electronics without manufacturer approval.
Short-circuit protection does not turn an undersized auxiliary contact into an acceptable switch. Select a fuse or protective device within the manufacturer’s coordination guidance and conductor rating. Estimate electrical operations from real switching frequency and expected service life, not mechanical endurance alone. Environmental contamination, vibration and infrequent low-level operation can matter. Preserve replacement part numbers so maintenance does not substitute a block with a different contact material or category.
Commission the complete control function
- Verify the exact contactor, auxiliary block, terminal map and normal state.
- Identify load type, voltage, make/break current, suppression and switching frequency.
- Compare the manufacturer’s rating at the exact voltage and utilization category.
- Check minimum signal duty when feeding electronics.
- Confirm conductor, terminal and short-circuit protection requirements.
- Measure voltage and current during operation and capture the inductive transient if relevant.
- Exercise open-wire, welded-contact, stuck-coil and power-restoration scenarios defined by the design.
- Record state timing, contact resistance trend, drawings and replacement identity.
For an interlocking application, follow our DC contactor interlock guide. For controller status, the Guida per il controllo della bobina del PLC explains why command and feedback are separate. Use the selection guide to keep main-contact, coil and auxiliary requirements distinct.
Connect the choice to an actual product order
Il Sayoon QZJB200A product page is the featured product reference. A normally closed main-contact description does not automatically specify an auxiliary block. Send the required NO/NC count, signal or load details, control voltage, utilization duty, switching rate, life expectation, protection, environment and drawing requirements with the RFQ. Ask for explicit confirmation of terminal mapping and auxiliary ratings for the exact order code.
Avoid recurring selection mistakes
Do not use thermal carry current as make-and-break duty, apply an AC rating to a DC inductive circuit, assume a power contact will reliably switch microamps, count an ordinary auxiliary as a safety mirror contact, or treat a compatible mounting shape as electrical approval. Each shortcut removes a condition that manufacturers specify separately.
Contact bounce and controller filtering matter. A PLC may see several transitions during one operation, while another filter hides a slow change. Define timing from measured behavior. For seal-in logic, verify loss and restoration of power. For alarms, decide whether an open wire appears normal, alarm or fault. The electrical rating alone cannot answer those system questions.
Control replacements and maintenance
Record block model, position, terminal numbers, conductor range and permitted number of blocks. Mark installed NO and NC poles. During maintenance, verify de-energized continuity only after isolation, then perform an approved functional test. Low resistance at test current does not prove future inductive breaking capability.
If contacts fail, investigate load duty, suppression, frequency, contamination, loose terminals and fault current before installing a larger device. A relay interface separates low-level feedback from coil switching but adds its own coil, contacts, suppression and failure modes. Select the whole chain. For safety-related systems, use components and architecture supported by the applicable validation plan.
Revisione finale del progetto e pacchetto di prove
Prima della messa in commercio, fissa un altro collaboratore oltre al progettista originale per effettuare una comparazione tra la cablazione esistente e la progettazione approvata e i documenti relativi al prodotto. Verifica l’identificazione dei terminali, la disposizione dei conduttori, la documentazione relativa al torsione, la protezione, l’alimentazione della bobina, la soppressione, lo stato dei contatti e le impostazioni del controller. Assicurati che ogni limite di accettazione dichiarato sia verificabile e che gli esempi illustrativi non siano diventati valutazioni non ufficiali del prodotto. Le fotografie aiutano a identificare l’installazione, ma non sostituiscono i disegni, le misure o la conferma del produttore.
Ripetere le operazioni di ripristino alle condizioni di controllo basse e alte previste e negli stati freddi e caldi pertinenti. Include carichi di controllo simultanei, configurazione del cavo e dell’alloggiamento realistici e la sequenza di commutazione prevista. Registrare le operazioni inattese invece di reimpostarle e eliminarle. Se il valore desiderato non è ancora disponibile, segnalare l’articolo per la revisione ingegneristica e non approvare la funzione interessata in base a un altro contattore.
Trasmettere il pacchetto finale all'area acquisti e manutenzione nonché all'ingegneria dei controlli. Questo dovrebbe includere il codice completo dell'ordine, le alternative approvate, la revisione dei disegni, la configurazione dei test, le misure effettuate in loco, i criteri di accettazione, le deviazioni, la versione del software, l'identità dei dispositivi di protezione e le istruzioni di sostituzione. Ciò evita che una bobina o un modulo ausiliario visualmente simili venga installata in seguito con un comportamento diverso. La convalida è necessaria quando le modifiche sostanziali apportate alla bobina, al driver, alla soppressione, al cavo, al contatto ausiliario, alla tensione di controllo, alla programmazione del firmware, all'installazione o all'ambiente operativo comportano cambiamenti significativi.
La revisione finale deve inoltre confermare che ogni fotografia del prodotto e l’etichetta visibile corrispondono alla famiglia e all’opzione effettivamente ordinate.
Video: contactor interlocking context
This independent schematic lesson shows why auxiliary state is used in interlock logic. It is educational and does not provide Sayoon ratings.
Watch the interlocking circuit lesson on YouTube.
Domande frequenti
Can the main contactor current rating be used for the auxiliary contact?
No. The auxiliary circuit has its own voltage, current, load type, utilization category and endurance ratings.
Is a high maximum current rating enough for a PLC input?
No. Low-level inputs may require minimum switching current or contact-reliability data in addition to maximum ratings.
Can an ordinary auxiliary contact prove the main circuit is isolated?
Not by itself. Confirm the mechanical relationship and safety architecture, and use the required independent voltage or isolation verification.
Why does DC inductive duty matter?
Interrupting an electromagnet produces stored-energy stress and arcing. Use the exact DC utilization rating and approved suppression.
