A mechanical-life rating does not establish how many times a DC contactor can interrupt your load. To evaluate electrical endurance, match the offered evidence to the voltage, current, load behavior, switching sequence, operating frequency and acceptance criteria of the application. Keep normal operation, maintenance switching and emergency interruption as separate requirements.
The purchasing deliverable should be a mission profile linked to an evidence matrix. That is more useful than a single target such as one hundred thousand cycles, because the same number can describe very different events. Closing onto a precharged circuit, opening under load and operating without load are not interchangeable evidence categories.
This guide supports supplier comparison and specification review. It does not select a contactor for an unidentified system, prescribe high-energy tests or establish a safety function. Engineering should approve the electrical duty and a competent evaluation team should control any testing. Published manufacturer examples below do not establish SINAWATTS stock, certifications or test capability.
Define mechanical and electrical endurance before comparing numbers
In its relay terminology guide, Omron distinguishes mechanical durability at a specified switching frequency without contact load from electrical durability at a specified frequency with the rated load applied. The coil still needs the specified actuation conditions; unloaded contacts do not mean that an electrically operated device is unpowered in every respect.
A mechanical-life figure therefore helps describe the mechanism's evaluated cycling capability under its stated conditions. It is not a loaded interruption rating. Electrical endurance adds the burden of the specified electrical duty, but that evidence is still conditional rather than a universal life promise.
Ask the bidder to identify which category each figure belongs to. If an offer states only life cycles, request the source document and test conditions before using the number in a comparison. Keep unresolved entries blank or marked as not supplied; do not silently assume that the largest advertised number is electrical life.
This distinction also prevents an invalid upgrade argument. A device with a larger unloaded cycle count is not automatically a better choice for the required loaded switching duty.
Separate current carrying, repeated switching and a fault event
Carrying current while closed is one requirement. Making a circuit and breaking it are two others. A short-duration withstand or a single interruption event adds another category. Each needs its own conditions and evidence.
Albright's SW200 product page presents separate interrupted and uninterrupted thermal-current columns and a separate mechanical-durability entry. Its data sheet explains the distinction between frequent on-load switching and little or no load switching. The example shows why a current headline should not be detached from its duty description.
For an RFQ, ask which current is carried during a dwell, which current is present at closing and which must be interrupted at opening. Retain the time associated with each. A continuous-carry claim does not answer how many loaded openings are supported, while a one-event fault claim does not establish repetitive endurance.
Keep the existing main-contact polarity guide alongside this review where current direction changes. Direction-specific suitability and lifetime evidence are separate questions that must both be resolved.
Read one real endurance table without combining unrelated rows
Sensata's SGX150 Aux data sheet, page 2, distinguishes 350,000 mechanical cycles at a 0.5-second on/0.5-second off ratio from resistive electrical endurance of 1,000 cycles at 1,000 VDC/150 A and 6,000 cycles at 1,000 VDC/30 A. It also lists a capacitive switch-on condition separately. Unless otherwise stated, its electrical-endurance note specifies 23 degrees Celsius and a 0.6-second on/5.4-second off ratio. The same page notes that the coil was not connected to a surge suppressor during the tests; confirm the exact tested configuration with the manufacturer.
These entries illustrate document reading, not a recommended part. Keep the entire relevant row and its notes together. The mechanical number cannot replace either resistive number. The capacitive switch-on entry cannot be relabeled as the same number of loaded openings. None of these rows establishes performance at an unlisted system voltage or circuit condition.
Record any ambiguity and ask for a written application response. A purchasing spreadsheet should preserve qualifications rather than selecting the largest number from several differently defined tests.
Describe the operating sequence before counting its repetitions
Write the intended sequence in ordinary language first. Identify the state before closing, the closing command, the current-carrying interval, the condition immediately before opening and the final state. Include any precharge, controller action or external switching that changes the main contact's duty.
Then connect those states to the actual circuit information. A command described as stop may remove current before the contactor opens in one design and require the contactor to interrupt current in another. Procurement cannot infer that distinction from a software label.
Record what establishes the condition: a design requirement, an engineering calculation, an approved measurement or a supplier application statement. If the current at opening is unknown, keep it unknown. Calling an event unloaded because that was the design intention can conceal a missing verification step.
This sequence becomes the reference for every life claim. It also helps the supplier identify which part of the duty is covered by existing evidence and which needs clarification, additional analysis or application evaluation.
Build a mission profile with separate event classes
A mission profile is a structured account of the events expected during service. It should include frequency and duration, but it should also distinguish events that place different demands on the device. Normal switching, installation checks, maintenance tests and abnormal interruptions should not be merged merely because all involve a command to the coil.
On small screens, swipe or scroll sideways to read every column. Keyboard users can focus the table and use the arrow keys.
| Event class | Information to supply | Evidence question |
|---|---|---|
| Normal start | Circuit state and closing duty | What make evidence applies? |
| Normal stop | Current and voltage at opening | What break evidence applies? |
| Closed operation | Current, dwell and environment | What carrying conditions apply? |
| Maintenance cycling | Load state and expected frequency | Is it counted in the same life basis? |
| Abnormal interruption | Defined event and post-event policy | Is continued service permitted? |
| Retry sequence | Maximum attempts and interval | Is repetitive operation covered? |
Give each event class an identifier and retain its source. Production acceptance tests may add operations before the equipment reaches the customer. Service procedures may add further operations that a duty estimate based only on daily use would miss.
Where usage varies across installations, present the relevant range or separate application profiles approved by engineering. An average can be useful for planning, but it should not silently replace the required boundary condition.
Reconcile cycles, operations and counters
Ask what the supplier means by one cycle or one operation. A report may count a close-open pair, individual transitions or a stated sequence. Your controller may record commands, confirmed state changes or completed operating sessions. Those are not automatically the same denominator.
Create a short counter definition: which event increments it, whether failed commands count, whether a power reset preserves it and whether service replacements reset or transfer the record. This is a proposed evidence requirement for the equipment team, not a universal control-system design.
For comparison, express the mission requirement in the same defined unit as the evidence. If the report's convention is unclear, request clarification rather than applying an assumed factor of two. Retain the original reported value next to any explained conversion.
Also separate total mechanical activity from the number of events belonging to a particular electrical duty. A shared lifetime counter can support traceability, but it cannot reveal which operations were loaded unless the event classification is also recorded or otherwise justified.
Use a hypothetical count without turning it into a life prediction
Consider a fictional machine expected to complete 24 normal close-open sequences per operating day, for 300 days each year over ten years. That produces 72,000 normal sequences. Suppose an additional maintenance routine adds two sequences per week for 50 weeks each year: another 1,000 sequences over the same period.
Under the explicit assumption that one complete close-open sequence is the counting unit, the planning total is 73,000 sequences. This is arithmetic for a fictional requirement, not a predicted service life or a manufacturer's rating.
Now classify the duty. The design team intends the 72,000 normal openings to occur after another device removes load current, while the maintenance procedure contains 1,000 loaded openings. Both statements require confirmation against the actual sequence. Closing duty must also be defined; reduced current before opening does not describe what happens at closing.
The evidence request must therefore address the 73,000-sequence mechanical activity and the separately defined electrical events. A 100,000-cycle mechanical claim alone does not answer the 1,000 loaded openings, and a 1,000-cycle electrical claim at different conditions does not automatically answer them either.
Keep abnormal interruption outside routine-life arithmetic
Emergency or fault interruption can have a different acceptance basis from routine service. Ask the system designer which event the contactor is required to perform, how often it is assumed to occur and what inspection or replacement policy follows it.
Do not add one emergency interruption to thousands of normal cycles as though it were merely another identical event. Equally, do not divide a published single-event capability into an annual maintenance allowance. The required application assessment should determine whether evidence covers the event and the post-event state.
Record whether the supporting document requires continued function, specified insulation performance, containment or another endpoint. These criteria are not interchangeable. A device surviving an event without an external hazard is not necessarily approved to return to normal service.
For diagnostic requirements, use the weld-detection and auxiliary-contact guide. Feedback can support an approved diagnostic strategy, but it does not create missing electrical-endurance evidence or independently establish safe isolation.
Supply load information that makes an endurance claim comparable
Include the system voltage range, current at make and break, current direction, load type and relevant transient information. For an inductive duty, ask engineering to provide the applicable load description or time-constant basis. For a capacitive duty, provide the approved circuit and precharge information rather than only the steady current.
The RFQ should distinguish values at the main contacts from a battery's nominal label or a controller's nameplate. Identify whether a figure is a measured condition, a specified maximum, a calculated case or an unresolved estimate. That distinction helps the supplier avoid treating a preliminary value as a final design input.
Avoid compressing a waveform into one peak without its duration and context when those are material to the review. Supply the available engineering record and ask which additional information is needed for a conclusion.
Send the switching sequence and mission-profile table for a contactor RFQ. Request a response that maps the offered device to each event class and clearly identifies any unsupported condition.
Keep timing, temperature and coil configuration in scope
The evaluated on-time, off-time and switching frequency belong to the evidence. A cycle count achieved with one dwell pattern should not be assumed to apply to another merely because the total number is the same. Record the ambient and installation conditions used in the evaluation alongside the electrical duty.
Identify the exact coil option, control supply, suppression arrangement and economizer configuration where applicable. The coil-suppression and release-time guide addresses those interface details. For endurance purchasing, the action is to establish whether the tested and offered configurations match.
Ask the manufacturer to explain any permitted difference and retain the response. Do not add a suppressor, alter a drive sequence or change a coil option simply to match a convenient test description without the appropriate design approval.
The installation record should also identify conductor connections and cooling assumptions relevant to the supplied evidence. A general operating-temperature range does not by itself establish an electrical-life result at every temperature within that range.
Request the evidence behind a curve or a headline
A useful submission identifies the exact device configuration, document revision, load conditions, test sequence and endpoint. Where a life curve is supplied, ask whether it represents measured points, a typical characteristic, an estimate or an application guideline. Preserve the manufacturer's stated basis.
Request enough sample and result information to understand the conclusion. How many specimens were evaluated? What happened to each? Were failures or deviations recorded? Does the reported count represent a completed test, a failure point or a lower bound after testing stopped? These questions are more informative than a graph copied without its notes.
Do not extrapolate beyond the stated evidence or create a reliability probability from a cycle count alone. A statistical life claim needs its own basis and scope. If the supplier cannot share a complete proprietary report, ask for a controlled summary that answers the necessary application questions.
Record withheld or unavailable information explicitly. A documented limitation can support a bounded decision; silently filling it with an assumption cannot.
Define end-of-test acceptance before samples are ordered
A test can reach its scheduled count while leaving important performance questions unanswered. Ask what characteristics are checked during and after the sequence, and which limits determine acceptance. Relevant categories may include switching function, contact condition, insulation and timing, as specified by the responsible technical authority.
Keep actual limits in the approved plan or applicable product document. This article supplies no universal end-of-life resistance, dielectric threshold or allowable delay. Borrowing a value from an unrelated relay can make an otherwise orderly sample plan misleading.
The report should identify the result for each required characteristic, the measurement conditions and any deviation from the plan. If a specimen was replaced during the exercise, the final summary must preserve that event rather than presenting the replacement's count as uninterrupted endurance of the original unit.
Agree who reviews the result and what the approval permits. A laboratory exercise can support a defined application decision without establishing unrestricted suitability across other voltages, loads, service environments or maintenance policies.
Compare two hypothetical offers on evidence coverage
Return to the fictional 73,000-sequence requirement. Assume the 1,000 maintenance openings remain the critical unresolved electrical duty. Supplier A offers a device with a large mechanical-life headline. Supplier B supplies a lower mechanical figure plus a loaded-switching report, but the report describes a different voltage from the machine.
On small screens, swipe or scroll sideways to read every column. Keyboard users can focus the table and use the arrow keys.
| Hypothetical offer | What is documented | What remains unresolved |
|---|---|---|
| A: high mechanical count | Unloaded cycling at stated conditions | Required make and loaded-break evidence |
| B: loaded test report | Specific voltage, current and sequence | Applicability to the machine's conditions |
| Revised A response | Application-specific evidence index | Review of all remaining conditions |
| Revised B response | Written assessment of the difference | Whether additional evaluation is required |
Neither initial offer should be declared the winner from the headline alone. A may eventually provide suitable evidence; B's report may or may not support the required duty after assessment. The comparison should remain conditional until the technical authority closes the gaps.
This method does not assume that every difference requires a new test. It requires a documented basis for accepting the difference, with any restrictions carried into the purchase and service records.
Make commercial comparison follow the approved configuration
Request the complete ordering code and separate pricing for any agreed options, documentation and sample work. A base part with a different coil or auxiliary arrangement may not be the configuration covered by the technical response. Reconcile the quote line with the evidence index before issuing the order.
Ask which current price, quantity conditions and delivery estimate apply to the approved scope. Do not infer availability from a public data sheet or assume that a configuration discussed during technical review is a standard stocked item.
The OEM and ODM enquiry page provides a route to describe the assembly and sourcing requirement. Confirm the actual offered scope in writing; no particular switching design, test service or manufacturer relationship is established by the enquiry route.
Include the acceptance documents and change-notification requirements in the order. This reduces the chance that a purchasing substitution preserves the housing outline while changing the configuration on which the endurance decision depended.
Plan service observations without claiming guaranteed replacement dates
Omron's maintenance guidance relates contact-wear assessment to load voltage, current and type, and notes the importance of actual operating conditions when published conditions differ. This supports using an application-based maintenance basis rather than converting any catalog cycle count directly into years.
Ask the equipment owner how actual event counts, abnormal operations and replacements will be recorded. A counter is useful only if its definition matches the event being tracked. Retain the replacement date, device identity and reason so that later reviews can distinguish scheduled maintenance from an investigated failure.
If actual usage differs materially from the approved mission profile, route that information for review. The response may involve revised maintenance, further evidence or a configuration change; it should not be an automatic numerical adjustment made by purchasing.
Do not promise a fixed service interval from this guide. The appropriate policy depends on the application's evidence, operating history and safety requirements, with decisions made by the responsible engineering and maintenance teams.
Buyer FAQ
Does a million mechanical cycles mean a million loaded operations?
No. Mechanical endurance describes a specified unloaded-contact cycling condition. Loaded switching requires electrical-endurance evidence at relevant conditions. Keep the two entries separate and ask the supplier to identify the test basis for each figure instead of transferring the larger number to the loaded duty.
Is the continuous-current rating enough to select electrical life?
No. It addresses a carrying condition rather than a complete repeated make-and-break sequence. Identify the current and voltage at each transition, the load behavior, the dwell pattern and the required count. A device may have useful carrying evidence while the proposed interruption duty remains unresolved.
Can fewer loaded operations compensate for a higher switching voltage?
Do not assume a tradeoff. A lower required count does not establish performance at an unlisted voltage or load condition. Request an applicable manufacturer assessment or approved evaluation. Keep both the duty difference and the number of operations visible in the evidence matrix.
Can a capacitive make-life figure be used for loaded opening?
No. Closing onto a stated capacitive circuit and interrupting a load are different events. Read the manufacturer's wording and notes carefully. A make-only figure should remain labeled as such, with separate evidence requested for any required loaded opening and its post-event acceptance criteria.
Does an electrical-life figure guarantee years of service?
No. A year-based estimate needs an event profile and evidence applicable to its conditions, and it still does not become a universal guarantee. Usage, environment, abnormal events and maintenance policy matter. Label any arithmetic as a planning assumption and retain the technical basis separately.
Must every delivered contactor undergo a loaded endurance test?
Not automatically. Qualification, production control and receiving acceptance serve different purposes. Agree the applicable records and inspections with the supplier and design authority. High-energy evaluation belongs in an approved test program; it is not an improvised receiving check or a test performed through an RFQ form.
What should a supplier provide when no applicable life curve exists?
Ask for a written statement of what is covered, what differs and how the application can be assessed. A controlled report summary, engineering response or agreed evaluation plan may be useful. Absence of a curve should remain visible rather than being replaced by an unsupported mechanical-life comparison.
Send a switching-duty endurance RFQ
Request a contactor quotation with your event classes, cycle definitions and evidence requirements. Include make, carry and break conditions, expected counts, coil configuration, installation limits and the policy after abnormal interruption. Ask the response to name the offered part and close each application question explicitly.