Last Updated: October 7, 2026
Quick Answer: Effective input inrush current suppression starts with the exact supply and its documented energisation condition. Review cold start, short-interval restart and simultaneously switched supplies separately. Then qualify a supplier-supported arrangement for the actual upstream branch. A peak-current table entry does not establish the complete waveform, restart behaviour or protective-device coordination. Do not substitute a larger breaker for an engineering review.
Separate input energisation from DC load startup
An AC/DC supply has two different interfaces to review: the AC-side energisation event and the downstream equipment’s DC startup. Keep the evidence for those interfaces separate. A supply’s DC output rating is not its input inrush current, and a successful first start is not proof of acceptable behaviour through every interruption or switching sequence.
For an OEM project, begin with a controlled list of the supply model, revision, upstream protective arrangement and equipment conditions. Record which condition each observation actually addresses. Avoid a requirement labelled only “no startup problems”: define the energisation cases and the evidence that will close them.
This article is an engineering and procurement review framework, not instructions to modify mains wiring or install an improvised limiter. Qualified personnel and the responsible design owner should select and verify the actual arrangement. A component image or familiar product family cannot replace that decision.
Establish the exact model and documentary boundary
The WEHO NDR-75 English table identifies NDR-75-24 as the 24 V / 3.2 A version. Its complete NDR-75 specification lists a cold-start entry of 40 A at 230 VAC. The reviewed approved specification agrees. This is a documentary example, not a measurement of the illustrated specimen.
The real specimen’s main label reads 100–240 VAC / 1.6 A, 50/60 Hz, and 24 V DC / 3.2 A. The public sources describe a wider input range and different input-current conditions. Do not silently equate those descriptions with the photographed revision. This review uses the shared 230 VAC documentary point only; confirm the ordered revision with the supplier before wider qualification.
Keep source interpretation separate from the native label. Do not redraw a favourable nameplate, import a value from another family or transfer a startup approval between voltage suffixes. Record the source revision and the condition actually covered by each statement.
Ask what a peak entry leaves open
Prepare a source-evidence request that goes beyond “what is the inrush current?” Ask the supplier to identify the initial state, input condition, measurement method and applicable model revision. Request the waveform information needed by the upstream protective-device and switching-device owners. State whether the project needs a cold-start case, a restart case or both.
Treat a missing answer as an open evidence item. Do not turn an incomplete table entry into a favourable acceptance claim. Conversely, distinguish unavailable evidence from an observed failure: a controlled clarification or defined test may be the right next action before rejecting a model.
Purchasing should retain these questions with the quotation and approval record. A replacement voltage suffix, new revision or apparently equivalent supplier part should not inherit startup acceptance automatically. Give engineering a traceable source for every proposed equivalence.
Review short-interval restart separately
External technical notes on NTC inrush limiters describe an NTC limiter’s temperature-dependent resistance and identify continuous current, temperature and input energy as selection considerations. This is general component evidence, not proof of the NDR-75-24’s internal circuit or a prescribed waiting period for this supply.
For the equipment review, list the permitted interruption and restart cases. Ask whether the supplier’s documented cold-start condition represents each one. Avoid assuming that every return of power recreates the same initial condition.
Give each restart requirement an owner and an acceptance record. If the equipment permits frequent switching, discuss that duty explicitly rather than copying a cold-start statement into a restart requirement. The evidence request should identify the exact model, revision and control sequence that the design will actually use.
Coordinate simultaneous supplies at the branch level
When several supplies can start through one upstream switching device, prepare a controlled list of their models and revisions. Record the allowed energisation sequence and send the relevant startup evidence to the branch design owner. A list of separate headline peaks is not a completed coordination assessment.
Ask how the proposal will be checked against the exact fuse, breaker, relay or contactor data. Keep the requested observations and acceptance criteria together so that later changes in quantity or switching logic can be reviewed. Do not address a nuisance trip merely by increasing a protective-device rating.
Controlled energisation may be considered when the equipment design supports it, but it is not a universal substitute for evidence. Define who approves the sequence and which operating or abnormal cases must be evaluated. This article supplies no conductor, fuse, breaker or relay specification.
Compare suppression proposals by supported behaviour
Procurement may receive proposals for documented internal startup management, an external limiter or a controlled sequence. Request a model-specific description of the supported conditions and unresolved evidence for each option. “Soft start” or “inrush protection” on a quotation is not a complete acceptance record.
For a thermal-limiter proposal, ask the responsible supplier to address continuous-current, thermal and energy limits. For an active pre-charge or bypass proposal, request its startup and fault-behaviour evidence. These are questions for a qualified design review, not directions to connect an improvised device to exposed mains terminals.
Do not infer the suppression method from the enclosure or the DC OK marking. Likewise, do not use an attractive product photo as evidence that a limiter or protective arrangement has passed the project’s conditions.
Compare candidates on like-for-like evidence. A lower unexplained peak is not automatically more useful than a larger, clearly bounded documentary entry. Ask which sources, conditions and exact revisions are being compared, and keep the remaining gaps visible in the purchasing decision.
Preserve mechanical identity in the equipment record
The complete mechanical drawing gives 32 mm front width, 125.2 mm vertical height and 102 mm front-to-rear depth. The product’s actual rear DIN clip and the public TS-35 mounting statement support rail-form mechanical illustrations. These sources do not establish ventilation clearance, terminal-access space or a verified powered load.
Use the full drawing and actual sample views for an equipment-fit review. Do not confuse the slim front width with depth or place the unit on cable duct as if that were its mounting structure. Where a photographed feature and a drawing revision differ, retain the source distinction and obtain supplier clarification rather than inventing a hidden face.
The two application illustrations are disconnected dry-build concepts in different equipment settings: an indoor dosing-skid service column and an air-handling damper control bay. They do not establish an electrical pairing, environmental rating or installation approval. Their real mounting rail is a dimensional reference; it is behind the front face, so perspective and depth must be considered rather than claiming a raw same-plane measurement. Final source identity and visual scale require independent image inspection.
Make release and change control traceable
Before release, agree which evidence closes cold start, restart and shared-branch requirements. Retain the supplier’s applicable sources with the design record. Separate an observed result from a documentary statement, and identify the owner of any unresolved item.
Review the affected acceptance evidence when the model, revision, simultaneously switched quantity or energisation sequence changes. Do not silently transfer approval from one voltage suffix or equipment configuration to another. If the photograph, label and specification differ, resolve the source-control question rather than altering the label or selecting a favourable number.
Ask WEHO's technical team for exact-model clarification and supported startup documentation. A precise request gives procurement and engineering a common evidence baseline. The goal is an agreed equipment release decision, not simply a completed checklist or an attractive illustration.
Key Takeaways
- Input inrush current and DC load startup need separate evidence records.
- Attach model, revision and test conditions to every quoted startup value.
- Review cold start, restart and simultaneous energisation as distinct cases.
- The NDR-75-24 example is a documentary cold-start point, not a pictured-sample measurement or completed coordination assessment.
- Suppression proposals require qualified branch-level review, not an improvised mains modification.
- Preserve exact labels, three-axis dimensions and source-supported mounting in equipment records and images.
Conclusion
Effective input inrush current suppression begins with a controlled source baseline and an honest account of what remains unknown. Obtain exact-model startup and restart evidence, define the permitted energisation cases, and qualify the supported arrangement for the actual branch. This keeps a peak-current entry within its evidence boundary and gives OEM engineering and purchasing teams a shared release decision.
Frequently Asked Questions
Is input inrush current the same as rated DC output current?
No. Keep the AC energisation event and the downstream DC rating in separate evidence records. A DC output rating is not a startup waveform or an upstream protective-device assessment.
What does the NDR-75 documentary cold-start entry establish?
It supplies a bounded source point for an exact-model evidence review. It is not a measurement of the illustrated specimen and does not establish pulse width, restart behaviour or complete branch coordination.
Why review short-interval restart separately?
Ask whether the supplier’s cold-start condition represents each permitted interruption and restart case. Do not transfer one documented initial condition to every return of power without applicable evidence.
Can a nuisance trip be solved by fitting a larger breaker?
Do not substitute a larger protective device for a qualified assessment of the exact upstream arrangement. This review supplies no breaker, fuse or conductor prescription.
Do the application images prove an accepted powered pairing?
No. They illustrate disconnected dry-build fit review in two equipment contexts. The actual load, input, environment, wiring and acceptance conditions require their own qualified review.
What should purchasing retain when a supply revision changes?
Retain exact-model source documents and the cold-start, restart and shared-branch acceptance records. Ask engineering to review affected evidence when model, revision, simultaneously switched quantity or energisation sequence changes.
