A supplier's low resistance number is useful only when you know which connection was measured, where the measurement began and ended, and what happened to the specimen beforehand. A thermal image needs its own operating conditions and sample identity. Neither record should be accepted as a substitute for the other.
Review the resistance record and heating evidence as two linked checks on an identified mated pair. This guide develops a purchasing evidence package. It does not provide a universal resistance limit, temperature-rise allowance or procedure for testing an energized PV installation.
Identify the pair before reviewing the number
Record the manufacturer and complete part number of both halves, contact variants, cable construction, assembly revision and sample identifiers. Link those details to the offered bill of materials. “Solar connector, same appearance” does not provide sufficient identity for a report.
Use the PV connector compatibility and termination guide for the separate mating and assembly review. Passing a resistance measurement does not establish permission to mate two products or approve an undocumented substitution.
Distinguish new production samples, conditioned qualification specimens and returned field parts. They answer different questions. Request the relevant receipt condition, mating history, conditioning and previous electrical exposure. Preserve the report's sample-level history; a photograph of an unmarked connector cannot establish that the image and measurement belong together.
Define what the resistance measurement includes
A result may describe a mating interface, a defined path between termination locations, or a complete lead containing cable and multiple joints. Give the measured path a name and require an annotated diagram. Different boundaries prevent a fair numerical comparison even when both reports use milliohms.
Phoenix Contact's page for PV-C1M-C-HSG, item 1050770, includes a resistance entry explicitly identified as crimp-to-crimp. That wording illustrates why the measurement boundary belongs alongside the value. It does not supply a limit for another connector or explain every detail of a supplier's test fixture. Phoenix Contact item 1050770, electrical properties.
Keithley's measurement handbook explains four-terminal contact measurements, including the importance of voltage-sensing locations and avoiding mechanical disturbance of the contact. Using four wires does not, by itself, identify which internal portions lie between those sensing locations. Keithley handbook, section 4.7.1.
For quotation review, request the named method, measurement diagram, instrument identity, calibration record and reported uncertainty. Ask how fixture contributions and offsets were handled. If a cable contribution is subtracted, require the documented basis and resulting quantity rather than accepting an unexplained corrected figure.
Keep test level and sequence visible
A baseline measurement and a reading made after higher-current exposure are not automatically equivalent. Keithley's discussion of contact testing explains that excessive measurement voltage or current can change surface films or contact conditions and reduce the measured resistance. Its dry-circuit discussion addresses limiting that disturbance; the handbook is not a PV connector acceptance specification. Keithley handbook, contact testing and dry-circuit discussion.
Ask the supplier to identify the prescribed test level, measurement timing, temperature, conditioning and sequence. The responsible manufacturer or laboratory should select the applicable method. Do not insert a generic low-current setting into every RFQ or replace a specified baseline measurement with whichever reading looks most favorable.
NREL's 2024 connector study presents resistance-current sweeps in which some field specimens differed between initial and stabilized readings. Its forensic method also preserved the received plug-and-socket connection during nondestructive examination. These observations support recording timing and specimen history; they do not establish a purchasing threshold or recommend a buyer-run current sweep. NREL study, slides 9 and 12.
Request the initial and subsequent results separately when the agreed evaluation includes both. Preserve deviations, invalid readings and retest reasons. A retest may close an investigation, but it should not silently overwrite the result that triggered it.
Read heating evidence on its own terms
Ask for the actual current and its duration, ambient conditions, cable dimensions, mounting arrangement and measurement locations. Identify whether the record reports an absolute temperature or a rise above a defined reference, and how stabilization was determined.
Phoenix Contact notes that its named connector warms during normal operation and that ambient conditions affect surface warming. A warm housing alone therefore needs context before it becomes a pass/fail statement. Phoenix Contact item 1050770, safety notes.
A surface thermal image records a different observation from a contact-resistance measurement. Request the measurement method and any interpretation that connects the observed location to the acceptance criterion. Do not label a housing-surface reading as the internal contact temperature without supporting evidence.
Basic resistive-loss reasoning relates current and resistance to dissipated power; it does not independently establish the temperature of an assembled connector. Require the applicable thermal evidence instead of converting a resistance number into an assumed temperature rise. The current-rating and temperature-derating guide addresses the separate rating-selection decision.
Use one evidence matrix for every bidder
The following worksheet is an original procurement framework. Have the responsible reviewer establish the applicable methods, limits and decision rules before comparing results.
On small screens, swipe or scroll sideways to read every column. Keyboard users can focus the table and use the arrow keys.
| Evidence item | What the bidder should provide | Hold condition |
|---|---|---|
| Mated-pair identity | Both part numbers, contact and cable variants, sample-to-order link | Report cannot be traced to the offered pair |
| Measured path | Diagram with sensing points and included joints or cable | Boundary is absent or differs from the requirement |
| Measurement conditions | Method, test level, temperature, timing and uncertainty | Results lack conditions needed for comparison |
| Specimen history | Received condition, mating, conditioning and prior tests | A later reading is presented as an untouched baseline |
| Heating evidence | Current/time record, ambient, arrangement, locations and criterion | Image or peak value lacks the required context |
| Acceptance record | Applicable limit source, reviewer decision and exceptions | “Passed” appears without a defined decision basis |
Keep individual results where required by the agreed sampling plan. An average alone can hide a specimen that needs separate disposition. Request the sample-selection basis and the treatment of missing, excluded or repeated measurements; this guide does not prescribe a sample size.
A hypothetical supplier comparison
The following offers are invented to illustrate document review, not real supplier performance.
Offer A advertises the lower resistance. Its spreadsheet does not identify sensing locations, and the value was recorded after an undocumented load run. A thermal image contains no sample identifier or current record. Hold: neither the resistance comparison nor the heating conclusion is adequately supported.
Offer B supplies identified pairs, a boundary drawing, baseline and subsequent results, measurement conditions and a linked thermal report. Its reported resistance is higher than A's headline value. Review against the agreed criteria: fuller evidence makes B assessable, but does not guarantee acceptance.
If B's results fail the defined requirement, request a revised proposal or reject the scoped claim. If evidence is merely missing, request the specific document. Record these as different dispositions. Neither a low number nor a complete-looking report should bypass the responsible technical review.
Close the RFQ with traceable deliverables
For an enquiry about the solar power connector category, attach the pair identities, cable details, intended duty and evidence matrix. Ask the bidder to identify available reports, unresolved conditions and any proposed additional evaluation.
Link the accepted report revisions and exceptions to the purchase record. Require review of substitutions that change either mating half, contact or cable configuration. Request separate pricing and schedule confirmation for samples and additional evaluation; no availability or testing capability is implied by this guide.
Buyer FAQ
What contact-resistance limit should I put in the RFQ?
Use the requirement applicable to the exact pair, measurement boundary, specimen condition and evaluation method. Have the responsible reviewer approve the limit source and uncertainty decision rule. A value copied from another product is not sufficient.
Does a low resistance result approve a mixed-brand pair?
No. Measurement evidence does not grant mating permission or establish the required product approval. Resolve pair compatibility and documentation independently before treating the offered assembly as acceptable.
Can a thermal image replace the resistance report?
Not as evidence of contact resistance. The two records describe different quantities. Where both are required, retain their separate measurement conditions, specimen links and acceptance decisions; an image cannot close a missing resistance result.
What is missing when the supplier only sends a pass certificate?
Request the covered pair and samples, measurement boundary, method and conditions, result record, acceptance criterion and report revision. Clarify which evidence is included in the quotation and which requires additional work.