A contactor that can carry current in two directions is not automatically qualified to interrupt the required current in both directions. Specify the complete part number, marked main-terminal orientation, operating modes and separately documented make, carry and break duties. A supplier's description of “bidirectional” must identify which function it covers and the conditions attached to it.
This distinction matters when a battery charges and discharges through the same path, an inverter returns energy, or more than one source can feed a distribution assembly. A quotation that only repeats a headline voltage and continuous-current rating leaves the most important opening event unresolved. Buyers need a traceable answer for each required event, including the reverse-current cases identified by the system designer.
This guide provides an evidence and quotation method. It does not prescribe a high-energy switching circuit, terminal connection, protection setting or emergency operating procedure. The responsible designer must approve those details. Keep control-circuit questions in the separate contactor coil suppression and economizer guide; a coil's polarity and a main contact's load direction are different interfaces.
Separate five claims that sound similar in a quotation
Start by translating supplier language into functions. “Non-polarized,” “reverse current permitted” and “bidirectional switching” may describe different features. Do not reject an unfamiliar term automatically, but ask the bidder to connect it to a controlled document and the proposed ordering code. A catalog heading is a useful starting point, not a completed application review.
On small screens, swipe or scroll sideways to read every column. Keyboard users can focus the table and use the arrow keys.
| Claim in an offer | Question the buyer must resolve | Evidence that makes the answer reviewable |
|---|---|---|
| Bidirectional current | Is this continuous carrying, switching, or both? | Separate carrying and switching conditions |
| Non-polarized contactor | Does this refer to main contacts or the coil? | Main-terminal drawing and control pinout |
| High breaking current | At what voltage, direction and circuit conditions? | Applicable breaking-duty table or report |
| High short-circuit withstand | What remains permissible after that exposure? | Duration, protection assumptions and post-event criteria |
| Suitable for battery systems | Which operating modes were assessed? | Application-specific duty and acceptance record |
Keep contact position separate as well. A normally open contact form identifies a mechanical state under defined control conditions; it does not state the permitted direction of interruption. An auxiliary contact can support feedback, but its presence alone does not establish the actual condition of the power contacts after an abnormal event.
Give every unresolved claim an owner. The supplier provides product evidence, the designer checks it against the circuit, and purchasing records whether the offered configuration is approved or conditional. This prevents a sales phrase from silently becoming a system requirement simply because it appears in a purchase order.
Why terminal direction can affect breaking capability
TE Connectivity's high-voltage contactor FAQ explains a design in which magnets influence the arcs generated as the contact bridge opens. Its explanation distinguishes forward and reverse current: the arc behavior described for reverse current can reduce breaking capability. This is evidence that load direction can matter in a particular contactor design, not a universal statement that all DC contactors behave identically.
The purchasing consequence is straightforward: a mechanically symmetrical enclosure or pair of identical studs does not establish electrical interchangeability of the main connections. Obtain the manufacturer's terminal identification and directional duty information for the exact device. Do not infer the internal arc-control arrangement from a photograph or from another product's drawing.
Conversely, TE's dated CAP120 product announcement, published on 16 August 2016 and checked on 14 October 2026, explicitly describes bidirectional load switching and main contacts that are not polarity sensitive. That is a useful example of a claim specifically attached to the power contacts. The announcement does not replace current controlled drawings or application approval for an offered CAP120 ordering code.
Sensata's GTM500 series page, also checked on 14 October 2026, describes the series as fully bidirectional and lists different coil, connection and auxiliary-contact options. Use that wording to identify a candidate family, then request the detailed duty evidence for the selected part. No rating or approval transfers from either manufacturer's example to an unverified alternative.
Build a current-direction map before selecting a part
Ask the designer for a single-line diagram that assigns names to the relevant electrical nodes. Use stable names such as battery-side node and converter-side node, together with the manufacturer's actual terminal markings once a candidate is selected. Avoid using only “input” and “output” where power flow changes during operation.
For each normal mode, record the expected current direction and whether the contactor closes, stays closed, or opens while that current is present. Then add the abnormal modes that the project's engineering assessment requires. Purchasing should not invent fault magnitudes or assume that a normal-mode arrow covers every credible supply condition.
The same physical arrangement can have different evidence needs across operating modes. A system might normally reduce current before opening, yet still require a defined interruption function when that reduction does not occur. The RFQ must identify both cases if the designer requires them; a statement about normal sequencing does not answer the second question.
On small screens, swipe or scroll sideways to read every column. Keyboard users can focus the table and use the arrow keys.
| Mode to identify | What the designer supplies | What the bidder confirms |
|---|---|---|
| Discharge | Node-to-node current direction and opening duty | Applicable main-terminal orientation and evidence |
| Charge | Reversed or separate path and switching sequence | Whether the proposed part covers that duty |
| Regeneration or returned energy | Expected current path and relevant transitions | Conditions and limitations for that path |
| Normal shutdown | Expected current at the opening event | Supported switching conditions and sequence assumptions |
| Required abnormal opening | Defined electrical conditions and protection context | Model-specific interruption evidence or a declared gap |
A blank row means unresolved work. It is not a zero-current assumption. If the project does not include a listed mode, mark it not applicable with the design reference so a future reviewer can distinguish deliberate exclusion from an overlooked case.
Request make, carry and break evidence separately
Make concerns closing onto the specified circuit. Carry concerns the closed current path under stated thermal and installation conditions. Break concerns opening that path under the specified electrical conditions. Keep three separate evidence references even when a manufacturer collects them in one datasheet.
For carrying duty, request the applicable conductor or busbar configuration, ambient conditions, duty duration and any cooling assumptions. For making duty, ask which load characteristics and inrush conditions the manufacturer evaluated. For breaking duty, require voltage, current direction and the load or circuit conditions used to substantiate the claim. The design reviewer decides which additional parameters are relevant.
Do not calculate an acceptable breaking current by dividing a headline switching power by the project voltage unless the manufacturer explicitly supports that interpretation over the required range. A single operating point is not a continuous operating envelope. Likewise, do not scale an endurance result to a different current direction or an untested load by simple proportional reasoning.
Ask whether each value is typical, guaranteed, a qualification result, an absolute limit or a single-event capability. Those categories lead to different procurement decisions. A typical development measurement cannot silently become a guaranteed production acceptance value, and a maximum event capability does not establish repetitive service life.
Where available evidence is incomplete, retain the actual gap. A bidder can be commercially shortlisted while technical approval remains open. The quotation should identify the missing report, the organization responsible for producing it, and any effect on the offer. This is more useful than declaring a part compliant with an undefined “bidirectional requirement.”
Evaluate terminal markings without creating a wiring rule
Request an annotated manufacturer drawing that distinguishes power terminals, coil terminals and auxiliary connections. Ask for the permitted installation orientation and the meaning of every directional marking. If a product has several variants, obtain the drawing for the offered suffix rather than a generic family illustration.
Do not interpret a plus sign near a power terminal as an instruction to connect it directly to battery positive in every possible topology. The manufacturer's explanation and the system diagram must be reviewed together. Node potential, current direction and the location of the contactor in the complete circuit are related design questions, not interchangeable labels.
The quotation package should include a simple mapping record: project terminal identifier, manufacturer terminal identifier, drawing revision and reviewed mode references. Let engineering supply the approved mapping. Purchasing checks that the production and service documents preserve it and that the supplier has not substituted a differently marked device.
For assemblies that also include battery connections, align that mapping with the selected battery terminal interface. A terminal fitting the stud proves neither correct direction nor complete switching compatibility. Mechanical fit, connection hardware and electrical duty each need their own acceptance evidence.
Keep protection coordination and opening control in the review
A contactor should not be treated as a substitute for a fuse or circuit breaker simply because a high-current opening value appears in a datasheet. Ask the designer to identify which device clears each required abnormal condition, which devices are expected to remain intact, and which conditions require replacement or inspection before return to service.
Record the protective device's complete identity alongside the contactor. If a supplier changes the fuse, breaker or control revision, ask whether the existing contactor review remains applicable. A family-level statement about compatibility cannot answer a changed configuration without an appropriate engineering reference. The DC fuse holder selection guide helps keep the fuse, holder and complete assembly identities separate.
When an interruption claim depends on more than one switching device, request the manufacturer's supported arrangement and the project's review of timing and failure assumptions. Do not create an arrangement by combining individual headline ratings. A result for a tested assembly belongs to that assembly and its stated conditions.
Control changes deserve attention even though this article focuses on main contacts. Refer the exact coil driver, suppression and economizer combination to the designer where it affects the approved opening behavior. Avoid duplicating a control-circuit design in the purchasing specification; instead, link the power-duty approval to the controlled interface document that already governs it.
A practical supplier evidence matrix
Use the following matrix during quotation comparison. Each row should have a supplier document reference and a project disposition. “Confirmed by email” is more useful when the message identifies the offered part, the requirement revision and the person or organization accepting responsibility for the statement.
On small screens, swipe or scroll sideways to read every column. Keyboard users can focus the table and use the arrow keys.
| Evidence row | Minimum identifiable content | Buyer disposition if absent |
|---|---|---|
| Product identity | Manufacturer, full code and drawing revision | Keep technical approval open |
| Main-contact direction | Terminal mapping and direction-specific statements | Do not infer from appearance |
| Carrying duty | Relevant installation and thermal conditions | Request the applicable envelope |
| Making duty | Required load and closing conditions | Record the unsupported mode |
| Breaking duty | Direction, voltage, current and circuit conditions | Request the missing evidence |
| Operating life | Duty sequence and acceptance criteria | Do not substitute mechanical life |
| Protection relationship | Identified protective devices and assumptions | Refer to the system designer |
| Change control | Revisions and substitutions requiring notification | Include them in the purchase terms |
For a configuration review, Send a contextual RFQ with the current-direction map, approved circuit revision and candidate documents. State which points remain undecided. Product availability, qualification support, pricing, MOQ and delivery require a written response; this guide does not establish those terms or claim a particular SINAWATTS contactor capability.
Worked example: two quotations with different evidence gaps
Consider a hypothetical battery-to-converter project that requires normal charging and discharging through the same contactor. The designer has defined two normal opening duties and one abnormal opening condition. No numerical values are supplied here because they would depend on the actual system. This example illustrates document review, not an approved design or a reported customer installation.
Offer A identifies the part and provides a continuous-current value. Its description says reverse current is allowed, but the attached switching report covers only one stated direction. Offer B identifies another part and supplies separate supported breaking conditions for both required directions. Its evidence does not yet cover the project's abnormal opening condition.
Both offers therefore have open technical questions. A is missing evidence for the second normal opening duty as well as the abnormal condition. B has resolved more of the normal-duty comparison, but that does not make it approved for the whole project. The correct comparison records the gaps instead of awarding a general compliance checkmark to either bidder.
On small screens, swipe or scroll sideways to read every column. Keyboard users can focus the table and use the arrow keys.
| Review decision | Offer A | Offer B |
|---|---|---|
| Identity complete | Yes, in this hypothetical example | Yes, in this hypothetical example |
| Both normal opening directions substantiated | No | Yes, for the stated conditions |
| Abnormal opening requirement substantiated | No | No |
| Commercial comparison possible | Conditional, with missing work listed | Conditional, with missing work listed |
| Release for the complete application | Pending engineering disposition | Pending engineering disposition |
Next, purchasing asks both bidders to price the same supply scope and disclose the effort needed to close their gaps. Engineering may determine that a candidate is unsuitable, request further evidence or approve a supported operating restriction. Those outcomes must be explicit. A promised future report is not equivalent to a completed qualification result.
Compare cost on a common scope
Separate the unit price from one-time engineering, qualification samples, testing, fixtures and documentation charges where those items are proposed. Do not assume that a more expensive part has better evidence or that a low quotation necessarily omits work. Ask each supplier to list included and excluded items so the comparison rests on actual commitments.
Include the coil connector, mounting hardware, terminal covers, auxiliary interface and identification labels if they belong in the required assembly. A contactor body and a complete serviceable assembly are different deliverables. If accessories are supplied by another party, identify who checks their compatibility and who owns the resulting assembly record.
Request separate lead-time statements for samples, qualification work and repeat orders. Do not merge those into an unsupported delivery promise. The project may choose to reserve a commercial option while technical review proceeds, but any commitment should state its conditions and avoid describing the candidate as production approved prematurely.
For broader sourcing discussions, the OEM/ODM inquiry page can help organize the assembly requirements. Its presence is an inquiry route, not evidence that a particular switching design, certification or test capability has already been confirmed.
Define acceptance without improvising a high-energy test
A procurement acceptance plan can identify documents and responsibilities without telling receiving staff to reproduce an interruption event. Ask qualified engineering and the relevant test provider to define the required method, equipment, safety arrangements, sample identity and decision criteria. Purchasing verifies that the delivered evidence corresponds to that agreed plan.
Receiving inspection should confirm ordered identity, revision, markings, supplied accessories and traceability against the approved records. It cannot demonstrate the full switching capability merely by checking continuity or operating the coil. Similarly, a successful bench action at an unrelated low-energy condition is not proof of a required high-energy interruption duty.
Require a report to identify the tested specimens, tested configuration, applicable directions and actual conditions. Where a result is summarized, preserve access to enough detail for the design reviewer to judge relevance. Distinguish successful completion, deviations and untested requirements rather than presenting all attached reports as equivalent compliance evidence.
If an unexpected event occurs in service, use the manufacturer's and system owner's authorized procedure to determine the disposition of the contactor. Do not assume it is reusable because it still closes or because an auxiliary signal changes state. Record the event and the decision so the next replacement order does not repeat an unresolved selection problem.
Preserve the approved configuration through substitutions
Define changes that require review before substitution: manufacturer, complete ordering code, main-contact construction or direction statement, coil option, terminal geometry, auxiliary interface and controlled documentation. The supplier may propose an equivalent, but the proposal must identify what changed and which evidence supports equivalence in this project.
A dimensional cross-reference is useful for packaging review, yet it cannot settle interruption equivalence. Ask for a requirement-by-requirement comparison and retain the original approval record. Where confidential design information is unavailable, request an application-specific statement from the responsible manufacturer rather than speculating about the replacement's internal construction.
Keep service stock under the same identity controls as production material. If a repair kit permits several versions, the service instructions must explain their approved scope. A warehouse label saying “DC contactor replacement” loses the direction and duty evidence that justified the original selection.
Buyer FAQ
Does “non-polarized” mean that both the coil and the main contacts can be reversed?
No. Ask which interface the statement describes. Main-contact direction and coil supply polarity need separate evidence. The full ordering code can also select different control electronics. Use the offered part's drawing and manufacturer instructions instead of extending one label to every connection.
Is continuous bidirectional current enough for a charging and discharging system?
Only if the approved application requirements are fully covered by the supplied evidence. If the contactor must open under current in either direction, request the applicable interruption conditions for both directions. A carrying claim alone does not resolve that opening duty or the project's abnormal conditions.
Can a higher current rating compensate for missing reverse-direction data?
Do not treat it as compensation. A larger headline carrying value does not document the missing switching event. Ask for the relevant direction-specific evidence or select a candidate whose documented conditions cover the requirement after engineering review.
Is a published manufacturer's example an approval for an equivalent-looking device?
No. Manufacturer examples help identify questions and documentation practices. They do not transfer ratings, materials, internal arc behavior or certifications to another device. An alternative needs its own identity, evidence and project disposition.
What should I ask when a supplier cannot provide a complete test report?
Identify the exact claim and missing conditions. Ask whether a controlled datasheet, manufacturer application statement or reviewable report summary can substantiate them. Let the responsible engineer decide whether that evidence is adequate; record any gap and related commercial condition explicitly.
What determines quotation cost and delivery time?
The selected part, quantity, accessory scope, traceability, documentation and any agreed qualification work affect the quotation. Obtain written commercial terms for the actual requirement. This article does not establish prices, minimum quantities, stock or a fixed delivery schedule.
RFQ: submit a direction-specific contactor requirement
Prepare the circuit revision, node names, required current directions, separate making/carrying/breaking duties, selected protective devices, control-interface revision and candidate part numbers. Add the required evidence, sample scope, quantities and a clear list of open questions.
Request a SINAWATTS quotation with those documents attached or summarized. Ask for a written response that separates supported conditions, deviations and items requiring engineering review. That gives the buyer a comparable proposal while leaving final application approval with the responsible design authority.