An auxiliary contact is useful evidence only when its documented relationship to the main contacts matches the diagnostic function you need. A coil command, a generic status output and a specified mirror contact do not make the same claim. Require the exact ordering code, contact diagram, state relationship, operating conditions and system-level interpretation before accepting “weld detection” in a quotation.
The distinction matters in battery distribution, energy storage and electrically controlled disconnect assemblies. A controller may request opening without proving that the main current path reached the required state. Purchasing teams need to know what the offered device actually reports, what it cannot report, and which responsibilities remain with the system designer.
This guide is for RFQ preparation and evidence review. It does not provide a safety circuit, a live test procedure, a method for repairing welded contacts or permission to work on equipment. Feedback indication is not a substitute for the approved isolation and verification procedures applicable to the system.
Define the diagnostic requirement before choosing an auxiliary option
Begin with the decision the system must support. Does the designer need ordinary operating indication, confirmation that an expected transition occurred, detection of a specified failure condition, or feedback used within an assessed safety function? These are different requirements and may need different evidence.
Ask the design authority to write a short functional statement in plain language. It should name the monitored device, the expected physical state, the conditions under which the statement must hold, and the response when that state cannot be confirmed. Purchasing should not fill in missing safety assumptions from a catalog illustration.
Then identify which portion the contactor supplier is expected to support. The supplier may document a relationship between contact positions, while the integrator remains responsible for wiring, input interpretation, software behavior and the complete safety assessment. Record that division in the RFQ.
Keep main-contact current-direction capability separate. The DC contactor polarity and interruption guide addresses whether a device can perform its required switching duty. Evidence that a contactor can interrupt a load does not automatically establish how it reports a subsequent fault.
Separate commands, position indications and measured circuit conditions
Use distinct names for each information source in the project documents. “Open command issued” describes a controller output. “Auxiliary input changed” describes a received signal. “Main-contact open state supported by the specified feedback arrangement” is a more specific claim that requires the applicable product evidence and system interpretation.
Similarly, a measured circuit quantity belongs to its measurement arrangement and conditions. It should not be casually renamed as a direct mechanical observation. Ask engineering to identify what each signal can establish and what alternative explanations remain possible.
On small screens, swipe or scroll sideways to read every column. Keyboard users can focus the table and use the arrow keys.
| Information in a specification | What it directly describes | Clarification needed before approval |
|---|---|---|
| Coil-off command | Requested control state | How actual movement is checked |
| Generic auxiliary output | State of the offered auxiliary circuit | Documented relationship to main contacts |
| Specified mirror contact | Defined main/auxiliary state relationship | Exact contact, configuration and applicability |
| Voltage or current observation | Electrical measurement at defined points | Interpretation, limitations and fault coverage |
| “Weld detected” software flag | Result of diagnostic logic | Inputs, conditions and validated meaning |
The table is a document checklist. It is not an instruction to combine these inputs into a particular circuit or an assertion that one method is sufficient for every system.
Understand what a mirror-contact claim actually covers
Schneider Electric's explanation of mirror and mechanically linked contacts describes a mirror contact as a normally closed auxiliary contact whose defined relationship prevents it from closing while the relevant normally open power contact remains closed, including the welded-contact example discussed there. The page distinguishes this from a relationship between auxiliary contacts themselves.
The purchasing implication is to ask which physical contacts the claim covers. A document that discusses an auxiliary block does not necessarily answer the relationship to the main power path. Request the contact identifiers and the manufacturer's explicit statement for the exact assembled configuration.
Do not infer mirror behavior merely because an auxiliary is normally closed. Schneider's product-specific mirror-contact FAQ identifies applicable contacts and configurations rather than treating every auxiliary option as equivalent. That is a useful example of the level of specificity an RFQ should request.
These manufacturer explanations are not a certification assessment of the offered product. Ask for the manufacturer's current applicable declaration and supporting documentation; do not claim compliance from terminology alone.
Avoid treating a mirror input as a complete closed-state indication
Schaltbau's mirror-contact function and limitations article explains an important asymmetry: the mirror arrangement can support identification of the main contacts' open state, while the opposite indication does not by itself prove that the main contacts reached their fully closed end position. An intermediate condition can require additional interpretation.
For an RFQ, describe each required state explicitly rather than using a single “on/off feedback” checkbox. If the project needs evidence of completed closure as well as opening, ask the manufacturer which documented outputs support those two requirements and under what conditions.
Keep the meanings in the controller specification aligned with the product documents. An input label should not claim more than the underlying arrangement establishes. The responsible designer should approve any translation from physical contact state to a software status or operator message.
This distinction also belongs in acceptance review. A demonstration that a lamp changes during normal operation does not, by itself, establish the behavior of the proposed diagnostic under the failure conditions that the project requires.
Read partial-weld evidence as a product-specific warning about assumptions
Sensata's application note on partially welded power contacts describes a GIGAVAC arrangement where one side of the main bridge can remain welded while the other opens. For the normally open auxiliary arrangement discussed in that note, the auxiliary can remain closed until the main contacts fully open on both sides.
The example shows why two apparently conflicting observations should not be resolved by guessing that the auxiliary is faulty. It also demonstrates why a generic continuity description may fail to describe the complete mechanical condition. The behavior is specific to the design discussed; it is not evidence that every normally open auxiliary provides equivalent information.
Request the proposed manufacturer's explanation of partial or asymmetric main-contact states where relevant to the project's assessment. Ask how the selected feedback option behaves and which states remain ambiguous.
The application note also discusses a recovery action. This purchasing guide does not adopt that action as a repair instruction or authorize return to service. Suspected damage requires the manufacturer's disposition and the system owner's approved process.
Build a contact-state requirements sheet with explicit unknowns
Use one row per required condition, with separate columns for the command, expected main-contact state, expected auxiliary indication, evidence reference and approved interpretation. Leave unresolved fields marked as unresolved; do not fill them with an assumed inverse of another row.
Include normal idle, normal commanded operation and the abnormal conditions identified by engineering. Where the project requires a response to missing or contradictory feedback, record that requirement without specifying an improvised wiring solution.
On small screens, swipe or scroll sideways to read every column. Keyboard users can focus the table and use the arrow keys.
| Review condition | Evidence requested from supplier or integrator | Decision to record |
|---|---|---|
| Normal opening completed | Applicable main/auxiliary relationship | Meaning of accepted open indication |
| Normal closure requested | Position and timing information for offered outputs | Whether completed closure is established |
| Main path does not reach required state | Documented fault-state behavior | Diagnostic response approved by designer |
| Feedback signal unavailable | Interface fault assessment | Treatment of unknown state |
| Feedback contradicts another observation | System diagnostic rationale | Escalation and investigation ownership |
A blank entry is a work item, not an automatic product rejection. The useful outcome is to identify who must resolve it and which evidence will close it. That approach prevents an unsupported assumption from becoming embedded in a purchase order.
Specify the exact auxiliary hardware and contact identifiers
A family brochure may list several auxiliary options. Require the offered ordering code to identify the actual configuration, including built-in or attached accessories, contact form, terminal designations and any relevant installation constraints.
For example, the Schaltbau C320 product page describes configurable auxiliary switches and distinguishes the availability of mirror-contact functions within the arrangement. It illustrates why a buyer should identify the selected option rather than transferring a family-level feature to every possible configuration.
Ask the supplier for a drawing that matches the offered product, not a generic diagram copied from another model. The drawing should identify the power contacts, control connection and feedback contacts in a way that can be referenced by the harness and controller documentation.
If an auxiliary block is separately supplied or replaceable, include its part number and the approved combination. Ask who controls assembly and inspection of the final configuration. A correct contactor and an incorrect accessory are still an incorrect purchased assembly.
Review the signal interface separately from the main power rating
Request the electrical specifications for the auxiliary circuit itself. The main contactor's headline rating does not define the auxiliary contact's permitted load or the controller input conditions. Ask engineering to compare the actual input interface with the manufacturer's auxiliary-contact requirements.
The RFQ should identify whether the offered indication is a passive contact arrangement or an electronic output, and should include the relevant pinout and interface documentation. Avoid treating two physically similar connectors as electrically interchangeable.
Record any manufacturer-specified minimum operating conditions, maximum duty, polarity, isolation relationship and environmental limitations that apply to the selected feedback interface. Purchasing should request these values rather than inventing defaults. The designer must decide whether they suit the system.
Include the harness connector and terminal configuration in the evidence package. A product-level feedback function can only be evaluated in the context of its actual interface. The OEM and ODM inquiry page can support a discussion of the required assembly documents without implying that an unspecified design has already been validated.
Ask for timing evidence without inventing a diagnostic delay
Feedback timing matters because the controller observes a transition over time rather than reading a static drawing. Ask the supplier for the applicable timing definitions and conditions, and ask the integrator to explain how those definitions are used in the proposed diagnostic.
Distinguish the start of a command, removal or application of coil drive, movement of the main system and transition of the auxiliary indication. A quoted time is incomplete if the document does not identify its start point, end point and conditions.
Coil-control choices belong in this review when they affect the relevant timing assumptions. Use the contactor coil suppression and release-time guide for that separate interface. Do not copy a delay from a contactor with a different coil or suppression arrangement.
The result should be a reviewed timing requirement with a named owner. This article supplies no universal timeout, debounce setting or operating sequence. Those values require the exact product data and the system's engineering assessment.
Document diagnostic coverage without promising a safety level
“Weld detection included” is too broad unless the supplier explains the included function. Ask which failure conditions are addressed, which inputs are used and which assumptions the claim requires. Where the function belongs to a controller rather than the contactor, identify that boundary clearly.
A useful response distinguishes normal operating feedback from a diagnostic claim and from a claim about an assessed safety function. Request the applicable evidence for each claim actually made. Do not add a safety integrity level, performance level or certification to the RFQ response merely because a mirror contact is present.
Schneider's discussion of safety contactor terminology cautions that informal labels can blur the distinction between main-to-auxiliary mirror behavior and mechanically linked auxiliary contacts. Use precise product documentation instead of relying on the adjective “safety” in a commercial description.
If the required system assessment is outside the supplier's scope, record that as a responsibility for the integrator. A clear exclusion is more useful than an ambiguous promise that neither party can substantiate.
Compare three hypothetical bids for one feedback requirement
Consider a fictional buyer procuring a contactor assembly for a battery equipment project. Engineering has asked for documented feedback supporting its opening-state diagnostic. The comparison below contains no real prices, test results or product recommendation.
Bid A includes a named contactor, a controlled auxiliary diagram, explicit state relationships and the document references needed by the integrator. Bid B provides a generic normally closed auxiliary and calls it “mirror type” without identifying an applicable manufacturer statement. Bid C offers only a controller output that repeats the requested coil state.
Bid A can move to detailed engineering review because its claim is traceable. It still needs evaluation against the actual system requirements. Bid B needs clarification or a revised configuration; a label is not enough. Bid C may provide useful command information, but it has not answered the requested feedback requirement.
Compare the total approved scope after those differences are resolved. Include the required auxiliary option, connector, harness documentation, evidence package and agreed sample evaluation. Do not award the order solely on the price of the bare main contactor.
Send the contactor feedback requirement and offered diagrams for an RFQ. Identify which state must be supported and which portions of the diagnostic remain the integrator's responsibility.
Plan sample acceptance around evidence and responsibility
Before samples arrive, define what the sample review will establish. Identification and drawing conformity can be separate from an engineering evaluation of behavior. A sample demonstration should have an approved purpose and must not be described as comprehensive fault qualification unless the evidence supports that scope.
Require sample labels, ordering codes, accessory identities and document revisions. Ask the supplier to describe any differences between samples and the proposed production configuration. A hand-modified demonstration unit should not silently become the production approval reference.
Where testing is necessary, the responsible qualified team must define the facilities, procedures, safeguards, conditions and acceptance criteria. This guide does not recommend deliberately welding contacts or reproducing hazardous failures at a buyer's premises. Relevant existing manufacturer evidence may be part of the review, with any gaps explicitly identified.
Record the outcome as approved, conditional or rejected for a defined purpose. A conditional result should list the remaining evidence and the person responsible for closing it. Keep commercial release separate from an incomplete technical review.
Review disagreement as an investigation, not as a nuisance alarm
A report that the coil is off while the auxiliary state remains unexpected needs a documented investigation. Do not assume that repeated actuation, a software delay change or replacement of the auxiliary will resolve the underlying issue.
Collect the information already available through the system's approved procedures: device identity, application revision, recorded commands and indications, event timing and any relevant operating history. Preserve the distinction between recorded evidence and an operator's interpretation.
Ask the supplier to explain which observations are consistent with its documented design and which require further examination. If the product is returned, agree on handling and evidence preservation with the investigation owner. Purchasing should coordinate the process without improvising electrical checks.
The final report should identify the supported finding, the limits of the investigation and the disposition of affected devices. A statement that a symptom could not be reproduced is not equivalent to proof that the original event was harmless or that all devices remain suitable for service.
Keep service replacement and change notification within the same boundary
A replacement contactor can fit mechanically while changing the feedback arrangement. Record the approved contactor number, auxiliary option, connector, relevant document revisions and compatible system configuration in the service parts list.
Require a review when a supplier changes the feedback hardware, ordering suffix, internal relationship or declared operating conditions. Changes to the controller interface can also require review even when the contactor itself is unchanged. Purchasing should route those changes to the responsible technical owner.
For equipment already in service, ask whether the proposed replacement supports all installed revisions or only a defined subset. The service instruction should provide a reliable identification method. Avoid a single stock description that merges variants with different diagnostic assumptions.
Maintain the evidence behind the approved combination. Future buyers should be able to see why the replacement was accepted and which limitations still apply. This protects the review from becoming dependent on a person remembering an old email or a supplier's verbal explanation.
Establish a useful RFQ evidence index
Organize the response around a small number of controlled records. The first record identifies the offered configuration. The second maps each required feedback claim to a manufacturer document. The third captures the integrator's interpretation and remaining system responsibilities. The fourth records deviations and approval decisions.
Keep product marketing pages as supporting context, not as substitutes for all controlled evidence. The official sources cited in this guide were checked on 15 October 2026 and illustrate specific concepts or product arrangements. Their claims do not transfer to another manufacturer's contactor or to an unspecified SINAWATTS assembly.
Request actual commercial terms for the approved scope, including any additional auxiliary option and documentation requested. Do not assume a standard price, stock position, lead time or sample availability from a technical feature description.
For ordinary remote switch indication rather than a welded-contactor diagnostic, the battery-switch auxiliary feedback guide covers the adjacent procurement question. Keeping the scopes separate makes the required evidence easier to review.
Buyer FAQ
Does every normally closed auxiliary contact detect welded main contacts?
No. Contact form alone does not establish the documented relationship to the main power contacts. Request the manufacturer's statement for the exact contactor and auxiliary configuration, together with the diagram and applicable conditions. The system designer must then evaluate how that feedback supports the intended diagnostic.
Does an open mirror-contact signal prove that the main contacts are fully closed?
Not by itself. The feedback meaning must follow the manufacturer's documented relationship and timing. Do not assign a completed-closure meaning to a signal merely by reversing the logic used for an accepted open-state indication. Ask which evidence supports the closure requirement separately.
Can an auxiliary indication prove that equipment is safe to touch?
No. Feedback is not a substitute for the system's approved isolation and verification procedures. It does not, by itself, establish absence of hazardous voltage, eliminate other sources or address stored energy. The responsible safety and engineering teams must define the required procedures for the actual equipment.
Are mirror contacts and mechanically linked auxiliary contacts interchangeable terms?
They should not be used interchangeably without clarification. Ask which contacts are related and what behavior the manufacturer declares. A requirement concerning the main power contacts needs evidence about those contacts; a statement about relationships within an auxiliary contact set may answer a different question.
Can the same contactor use different auxiliary feedback options?
Some product families offer configuration choices. Identify the exact ordering code, selected contacts and assembly arrangement rather than relying on the family name. Request confirmation that the documents supplied with the quote apply to that configuration and that production and service orders preserve it.
What should happen when feedback and a recorded electrical observation disagree?
Treat the disagreement as unresolved until the responsible team interprets it using the product and system evidence. Preserve available records and obtain the manufacturer's guidance. Do not assume that one channel is faulty, that the contactor is undamaged or that cycling the device authorizes continued operation.
Does adding a mirror contact automatically certify the entire assembly?
No. A component feature does not establish the assessment or certification status of the complete assembly. Request evidence for the actual claims being made and identify who is responsible for the system-level review. Avoid using certification language in purchasing or marketing without supporting documentation.
What information makes a weld-detection RFQ reviewable?
Provide the required diagnostic statement, system context, proposed contactor and auxiliary numbers, contact diagram, interface requirements and evidence expectations. Identify unresolved timing and fault-state questions. Ask the bidder to distinguish documented product behavior from additional functions supplied by the controller or integrator.
Send a DC contactor feedback RFQ
Prepare a requirement that names the physical state to be supported, the exact offered configuration and the evidence needed to justify the indication. Include the approved contact diagram, controller-interface information and any installed-base constraints. Mark unresolved diagnostic assumptions clearly.
Send your DC contactor auxiliary-contact and diagnostic evidence requirements. A precise evidence request helps compare offers on their documented behavior and gives the responsible designer a clear basis for acceptance.