Top 12 Questions to Ask a VCB Manufacturer (RFQ Checklist)

A vacuum circuit breaker RFQ goes sideways for two common reasons: suppliers quote a “standard breaker” that doesn’t match your real duty, or they quote the right nameplate numbers but leave gaps in testing, documentation, and interfaces that later stall commissioning. This checklist is designed to reduce both risks.

You’ll get 12 copy-paste RFQ questions, plus a simple scoring rubric so you can compare vendors without turning your evaluation into a debate.

Who this RFQ checklist is for, and what “good” vendor answers look like

This checklist is for panel builders, EPCs, and industrial/utility buyers who already know they need a VCB, but want quote-ready answers instead of sales language. A “good” answer is measurable, configuration-specific, and document-backed.

Use this scoring rubric on every question:

PASS (quote-ready)

• Quantified with units and scope (example duty stated as kV class, A, kA, plus what’s included).
• Traceable: datasheet + drawing + test/document list references (revision-controlled).
• Configuration matches your installation and control power (for example 110 VDC, 220 VAC) without “equivalent substitutions.”

CLARIFY (can proceed, but must close before PO)

• Partly quantified but missing boundary conditions (environment, enclosure, accessory scope).
• Uses ranges without committing to your line item (for example “630–1250 A available” with no selection).
• Mentions documents/tests but can’t list deliverables.

RED FLAG (high risk)

• Vague claims like “IEC compliant” with no deliverable list or test basis.
• Ignores fault duty or offers “equivalent” swaps without a technical justification.
• No stable model code, drawings, or traceability.

Question set A — System context you must provide before any quotation

Manufacturers can’t lock a correct configuration if your RFQ lacks system context. When you don’t provide it, they’ll often quote a generic build, then re-quote after clarification. That’s where time and scope drift usually start.

Use this “System Data Card” as your RFQ input block.

Q1) What are the required electrical duties (kV class, A, kA, and frequency)?
Include nominal voltage class (for example 12 kV or 24 kV), continuous current (for example 630 A or 1250 A), short-circuit interrupting duty (for example 25 kA or 31.5 kA), and frequency (50 Hz or 60 Hz).

Q2) What is the application duty: feeder, transformer protection, motor duty, capacitor bank, or generator tie?
Different duties change what “electrical endurance” means and what accessories/interlocks matter.

Q3) What installation type are you quoting: indoor withdrawable, indoor fixed, or outdoor cabinet/pole style?
If your team is still deciding, treat this as a gating decision: indoor vs outdoor VCB selection guide

Q4) What control power and interfaces are required (coils, aux contacts, interlocks, SCADA)?
State control power (for example 110 VDC or 220 VAC), required aux contacts (NO/NC count), and any interface expectations (wiring diagram, terminal style, protocol expectations if applicable).

Deliverable: A fill-in RFQ “System Data Card” (copy/paste)

• Voltage class: ___ kV
• Continuous current: ___ A
• Interrupting duty (sym.): ___ kA
• Frequency: 50 Hz / 60 Hz
• Application duty: ___
• Installation type: indoor withdrawable / indoor fixed / outdoor ___
• Control power: ___ VDC or ___ VAC
• Aux contacts: ___ NO / ___ NC
• Interface notes: drawings, terminals, CT/VT boundary, interlocks: ___

Question set B — Interrupter + insulation credibility checks (technical gate)

This is your “prove it” section. You’re not asking for a lecture. You’re asking the vendor to show that the interrupter, insulation system, and mechanism are engineered for your stated duty—not simply relabeled.

Q5) What is the interrupter duty basis for this exact configuration (not just the breaker nameplate)?
A credible answer restates your duty with units (for example 12 kV class, 31.5 kA, 50 Hz) and confirms the interrupter selection is tied to that configuration.

Q6) How is dielectric withstand and insulation margin handled in the assembly (internal clearances, external creepage, interface points)?
Ask them to describe where the controlling insulation path is (inside the pole, across external insulation surfaces, or at the terminal interface) and what conditions it assumes.

Q7) What mechanism type and operating margin are being quoted for the stated control power?
The vendor should state mechanism type (spring-charged or other) and confirm operation is within the assumed control supply (for example 110 VDC).

Standards anchor (authority link): IEC 62271-100

For quick internal context before you challenge a vendor’s interrupter claims: what is a vacuum interrupter
For nameplate/rating vocabulary that helps you interrogate quotes: vacuum circuit breaker ratings

[Expert Insight]

• If a vendor can’t restate your duty in one sentence with kV, A, and kA, expect clarification cycles after PO.
• “IEC compliant” without a deliverables list usually means you’ll be chasing drawings and test records late.
• Ask what is serialized (breaker, poles/interrupters, mechanism). Traceability is a reliability signal, not paperwork theater.

Question set C — Service life, reliability, and what lifecycle numbers actually mean

Lifecycle claims can be real—but only if you force the duty basis into the quote. Two vendors might both claim “10,000 operations,” yet one means mechanical operations with no electrical duty context.

Q8) What mechanical endurance is claimed (operations count), and what maintenance interval assumptions sit behind it?
Ask for the operations number and what inspection cadence they assume (time-based and operation-based). Example: inspections every 12 months, with mechanism checks at a stated operation count.

Q9) What electrical endurance is claimed, explicitly tied to fault duty (kA) and voltage class (kV)?
A credible answer looks like: “electrical endurance: X operations at 31.5 kA, 12 kV class,” plus what duty pattern they assume (rare faults vs frequent switching duty).

Deliverable: Comparison table template (drop into your evaluation sheet)

• Vendor / model code: ______
• Your duty: ___ kV class, ___ A, ___ kA
• Mechanical endurance: ______ operations
• Electrical endurance: ______ operations at ______ kA and ______ kV class
• Maintenance assumptions: ______
• Wear parts list (coils, charging motor, aux switch, springs, bearings): ______
• Warranty: ______ months; exclusions: ______
• Evidence (datasheet, endurance report, test record structure): ______

Question set D — Field conditions that change the design (altitude, heat, pollution, salt fog)

Field conditions are where “same rating” equipment separates into “stable in service” versus “trips, tracks, or corrodes.” Don’t let suppliers answer this with “no problem.” Make them either confirm suitability or quote the adaptations and any derating.

Q10) Given our site conditions, what must change in insulation, sealing, corrosion protection, or ratings?
Provide your site data, then ask them to respond with a specific confirmation or change list.

Deliverable: Site Conditions Addendum (buyer inputs + vendor confirmations)

Buyer inputs:

• Altitude: ___ m (for example 0 m, 2000 m, 3000 m)
• Ambient range: ___ °C min / ___ °C max (for example -25 °C to +40 °C, or -40 °C to +55 °C)
• Pollution/contamination: light dust / heavy dust / industrial fumes / conductive dust
• Coastal exposure: yes/no; distance to sea ___ km
• Installation: indoor room / outdoor kiosk / outdoor cabinet
• Maintenance reality: typical interval ___ months

Vendor confirmations:

• Altitude impact statement (confirm suitability or list design/derating changes).
• Thermal margin statement at max ambient (confirm current rating basis or specify derating).
• Sealing/enclosure strategy (what is protected, how ingress is managed, any heater/anti-condensation options).
• Corrosion strategy (materials/coatings for hardware and external insulation surfaces).
• Maintenance interval adjustment recommendations for heavy pollution or coastal exposure.

[Expert Insight]

• If your site is dirty or coastal, ask how they prevent tracking on external insulation surfaces and what they expect you to clean, and how often.
• “Outdoor” is not one configuration. Cabinet sealing, breathers, heaters, and corrosion strategy strongly influence nuisance issues.
• A vendor who offers a site-specific addendum early often reduces commissioning rework.

Question set E — Testing, documentation, traceability, and FAT/SAT expectations

If you want fewer commissioning surprises, define the document pack and acceptance flow in the RFQ—not after the equipment ships. This is also how you reduce the risk of “model code swaps” that still carry the same headline rating.

Q11) What is the exact deliverable pack tied to serial numbers (drawings, wiring, test records, as-built set)?
A strong answer lists the deliverables with revision control and ties routine test records to the breaker serial number.

Deliverable: FAT + documentation + traceability deliverables list

Quotation-stage:

• Model code breakdown + included accessories list
• GA drawing + interface dimensions
• Wiring diagram + terminal list (matched to control power like 110 VDC)
• Nameplate draft aligned to the quoted kV/A/kA duty

FAT package:

• Inspection and test plan with acceptance criteria
• Routine test records tied to serial numbers
• Functional check list (close/trip, interlocks, aux contacts, coils, charging motor)
• Photos of nameplate, wiring terminations, packing condition

Handover pack:

• Packing list with serial numbers
• Installation/operation manual + maintenance checklist
• Commissioning checklist (SAT-ready)
• Warranty statement with start-point definition

Commercial + logistics questions that prevent project delays {CTA}

This is the one block that keeps quotes comparable and reduces late re-quotes. Keep it short, but explicit.

Q12) What is the full commercial scope: lead time, warranty terms, spares strategy, packing, and after-sales response?
Make them commit in writing.

Deliverable: RFQ Commercial Block + CTA line

• Quantity: ___ sets (initial); forecast: ___ sets/year
• Lead time: ___ weeks from PO + drawing approval (request split: production + test + packing)
• Incoterms: EXW / FOB / CIF / DAP (port/city: ___)
• Export packing: seaworthy, moisture protection, shock indicators (yes/no)
• Warranty: ___ months (start point defined)
• Response commitment: reply within ___ hours; corrective action plan within ___ business days
• Spares: critical spares kit priced for 1 year and 3 years (list + quantity)
• Documentation language: English required (yes/no)
• Payment terms: ___
• Change control: what triggers re-quote and how revisions are logged

{CTA} If you’d like XBRELE to sanity-check your RFQ before it goes out, send the filled System Data Card plus your single-line and installation notes, and we’ll flag rating gaps and quote-compare traps early.

FAQ (RFQ Checklist Use)

1) What’s the quickest way to spot a weak VCB quotation?
Weak quotes usually avoid committing to configuration details or deliverable lists, which often shows up later as re-quoting or missing documents.

2) Should I share my protection philosophy in the RFQ?
A simplified protection concept can help suppliers align interfaces and accessories, while still keeping proprietary settings confidential.

3) How can I reduce back-and-forth with multiple suppliers?
Standardize your input block, require a named deliverables list, and ask vendors to restate duty and scope in their first response.

4) What vendor documents are most useful before placing a PO?
A stable model code breakdown, GA drawing, and wiring/terminal list typically prevent scope misunderstandings.

5) When is a factory acceptance test worth the effort?
FAT tends to pay off when schedule risk is high, integration is complex, or your handover process requires serial-tied records.

6) How do I compare two vendors with similar ratings but different prices?
Compare included accessories, documentation/traceability commitments, endurance assumptions, and support response terms; those often explain price gaps.