Generic vacuum contactor RFQs generate quotes that don’t match requirements. “12 kV, 400 A vacuum contactor” describes perhaps 500 different product variants across manufacturers—some rated for motor starting duty at 50 operations/day, others for capacitor switching at 10,000 operations/year, still others for transformer switching or general load breaking.
The manufacturer receiving an incomplete RFQ faces two choices: quote conservatively (overspecified, expensive solution), or quote optimistically (underspecified, fails in service). Neither serves the buyer. The overspecified quote loses on price to competitors who guessed lower duty requirements. The underspecified contactor fails after 6 months when the buyer discovers their “general purpose” contactor can’t handle daily capacitor bank switching.
Vacuum contactors differ from circuit breakers in critical ways that RFQs must address. Circuit breakers primarily interrupt fault currents—specification focuses on short-circuit rating. Contactors primarily switch loads repeatedly—specification must define operational duty, switching frequency, load type (resistive/inductive/capacitive), and mechanical endurance requirements. Missing these parameters guarantees wrong selection.
This guide provides the complete RFQ template procurement engineers need when specifying vacuum contactors for motor control, capacitor switching, transformer switching, and load break applications in 3.6–40.5 kV systems.
Essential Parameters (Never Omit These)
1. Electrical Ratings
Rated voltage (Ur):
- Specify system voltage AND rated insulation level
- Example: “12 kV system, 17.5 kV rated insulation (Ur = 17.5 kV)”
- Common voltages: 3.6, 7.2, 12, 17.5, 24, 36, 40.5 kV
- Why it matters: Undersizing insulation causes breakdown; oversizing adds unnecessary cost
Rated current (Ir):
- Continuous current carrying capacity
- Example: “400 A continuous at 40°C ambient”
- Specify ambient temperature if >40°C
- Why it matters: Contactor must carry load current continuously without overheating
Short-time withstand current (Icw):
- Current contactor must withstand for specified duration without damage
- Example: “16 kA for 1 second” or “20 kA for 3 seconds”
- Typically lower than circuit breaker short-circuit rating (contactors don’t interrupt faults)
- Why it matters: Protects contactor during faults until upstream breaker clears
Making and breaking capacity:
- Making capacity (Icm): Peak current contactor can close onto
- Breaking capacity (Ib): Current contactor can interrupt
- Different for resistive, inductive, capacitive loads
- Example: “Making: 40 kA peak, Breaking: 630 A resistive, 400 A inductive, 400 A capacitive”
- Why it matters: Defines maximum load current contactor can safely switch
2. Duty Type and Operating Frequency
Duty category (per IEC 62271-106):
- AC-1: Non-inductive or slightly inductive loads (resistive heating, general distribution)
- AC-2: Starting of slip-ring motors
- AC-3: Starting of squirrel-cage motors (most common motor duty)
- AC-4: Starting/plugging/inching of squirrel-cage motors (severe duty)
- AC-5a: Switching discharge lighting
- AC-5b: Switching incandescent lighting
- AC-6a: Switching transformers
- AC-6b: Switching capacitor banks
Example specification: “AC-3 motor starting duty, 400 A motor FLA, 2,400 A inrush (6× FLA)”
Operations per day/year:
- How many close-open cycles?
- Example: “10 operations/day, 3,650 operations/year” (daily start-stop)
- OR: “2 operations/day, 730 operations/year” (standby duty)
- Why it matters: Determines mechanical and electrical endurance requirements
Load power factor:
- Inductive loads: specify power factor (e.g., “0.85 lagging for motor load”)
- Capacitive loads: specify capacitance (e.g., “3 × 50 kVAR capacitor bank”)
3. Application-Specific Requirements
Motor starting (AC-3/AC-4):
- Motor rated power (kW or HP)
- Motor full-load current (FLA)
- Starting current (typically 5–8× FLA for squirrel-cage)
- Starting method: DOL (direct-on-line), star-delta, soft starter, VFD
- Number of starts per hour
Capacitor switching (AC-6b):
- Total capacitor bank size (kVAR)
- Individual capacitor unit size
- Back-to-back switching? (existing energized capacitors on bus)
- Detuning reactor present? (specify inductance)
- Required mechanical endurance (capacitor duty demands high endurance—50,000+ ops)
Transformer switching (AC-6a):
- Transformer rated power (kVA or MVA)
- No-load magnetizing current
- Inrush current magnitude and duration
- Switching frequency (daily, weekly, emergency only?)
General load break:
- Load type (resistive, inductive, mixed)
- Maximum breaking current
- Power factor
Environmental and Installation Parameters
4. Environmental Conditions
Ambient temperature:
- Operating range: “−25°C to +45°C” (specify actual site conditions)
- Storage range: “−40°C to +70°C”
- Altitude: “Installed at 2,500 m elevation” (requires derating or altitude correction)
Enclosure protection:
- IP rating: IP54 (indoor clean), IP65 (outdoor/dusty), IP66 (washdown)
- NEMA rating if applicable: NEMA 3R (outdoor), NEMA 4X (corrosive)
Atmospheric conditions:
- Humidity: “95% RH non-condensing” or “tropical climate”
- Contamination: “Heavy dust” or “Corrosive atmosphere (sulfur, salt spray)”
- Vibration/seismic: “Seismic Zone 4 per IEC 60068-2-6” if applicable
5. Physical and Mechanical Requirements
Mounting:
- Fixed or withdrawable/drawable
- Panel mounting or floor standing
- Preferred: “Withdrawable design for easy maintenance without panel dismantling”
Dimensions and weight:
- Space constraints: “Maximum height 2,000 mm” if space-limited
- Weight limit if crane capacity restricted
Operating mechanism:
- Spring-operated, magnetic actuator, manual
- Preference for maintenance-free operation: “Magnetic actuator preferred (no lubrication)”
Control voltage:
- DC: 110 VDC, 125 VDC, 220 VDC
- AC: 110 VAC, 220 VAC, 380 VAC
- Specify: “125 VDC closing coil, 125 VDC trip coil, battery-backed supply”
Standards, Testing, and Documentation
6. Applicable Standards
Design and testing standards:
- IEC 62271-106 (AC contactors for voltages above 1 kV)
- IEEE C37.012 (Application Guide for Capacitance Current Switching)
- IEC 60470 (for capacitor switching applications)
- Others: UL, CSA, GB if required for specific markets
Specify: “Contactor shall comply with IEC 62271-106, with type test certificates provided.”
7. Type Testing and Quality Assurance
Type test reports required:
- Dielectric tests (power frequency withstand, lightning impulse)
- Temperature rise tests
- Mechanical endurance tests
- Making and breaking capacity tests
- Short-circuit withstand tests
Routine tests required (for each delivered unit):
- Dielectric tests across open contacts
- Auxiliary circuit tests
- Mechanical operation tests
- Contact resistance measurement
Quality certifications:
- ISO 9001 (quality management)
- ISO 14001 (environmental management) if environmentally sensitive site
- Factory inspection: “Buyer reserves right to witness factory acceptance test (FAT)”
Accessories and Options
8. Auxiliary Contacts
Number and type:
- Example: “4 NO + 4 NC auxiliary contacts, rated 10 A, 250 VAC/DC”
- For signaling, interlocking, remote indication
Position indication:
- Mechanical indicator on contactor (visible through panel window)
- Electrical position indication (auxiliary contacts for SCADA)
9. Interlocks
Mechanical interlocks:
- Prevent simultaneous closing of two contactors
- Example: “Mechanical interlock between Main and Bypass contactors”
Electrical interlocks:
- Undervoltage release (trips contactor if control voltage lost)
- Shunt trip (remote trip capability)
10. Protection and Monitoring
Built-in protection:
- Overload protection (thermal or electronic)
- Phase unbalance protection
- Ground fault protection
Monitoring capabilities (for smart contactors):
- Operation counter (tracks number of operations for maintenance scheduling)
- Temperature sensors
- Contact wear indication
- Communication protocol: Modbus RTU, Profibus, IEC 61850
Commercial and Delivery Requirements
11. Quantity and Delivery
Quantity:
- Example: “4 units for initial order, potential for 20 additional units over 3 years”
- Helps manufacturer assess volume pricing, spare parts strategy
Delivery schedule:
- “Delivery required by [date]”
- “Staged delivery acceptable: 2 units by [date 1], 2 units by [date 2]”
Packaging:
- “Suitable for international shipping, protected from moisture and shock”
- “Delivered with all mounting hardware, installation/operation manuals”
12. Spare Parts and After-Sales Support
Initial spare parts:
- “Quote shall include: 1 set of main contacts, 1 set of auxiliary contacts, 1 operating mechanism maintenance kit”
Long-term availability:
- “Manufacturer shall guarantee spare parts availability for minimum 15 years after purchase”
Technical support:
- “Commissioning support required: on-site presence for initial energization”
- “Training required: 1-day hands-on training for maintenance personnel”
- “Local service center within [region]: Yes/No, specify location and response time”
13. Warranty and Guarantees
Standard warranty:
- “Minimum 24 months from commissioning or 30 months from delivery, whichever is earlier”
Performance guarantees:
- “Mechanical endurance: Minimum 50,000 operations for capacitor switching duty”
- “Electrical endurance: Minimum 10,000 operations at rated breaking current (AC-3 duty)”
Complete RFQ Template
VACUUM CONTACTOR REQUEST FOR QUOTATION
Project: ________________________ Date: ____________
Buyer: __________________________ Contact: ___________
1. ELECTRICAL RATINGS
- Rated voltage (Ur): ______ kV
- Rated current (Ir): ______ A continuous at ____°C ambient
- Short-time withstand (Icw): ______ kA for ____ seconds
- Making capacity (Icm): ______ kA peak
- Breaking capacity (Ib): ______ A (specify resistive/inductive/capacitive)
- Rated frequency: ______ Hz
2. DUTY TYPE AND APPLICATION
- Duty category per IEC 62271-106: AC-___
- Load description: _______________________
- Rated operational current: ______ A
- Operations per day: ______ Operations per year: ______
- Load power factor: ______ (if applicable)
[If motor starting]
- Motor power: ______ kW/HP
- Motor FLA: ______ A
- Starting current: ______ A (____× FLA)
- Starting method: DOL / Star-Delta / Soft Start / VFD
[If capacitor switching]
- Capacitor bank size: ______ kVAR
- Number of units: ______
- Detuning reactor: Yes/No, if yes: ______ mH
- Back-to-back switching: Yes/No
- Required mechanical endurance: ______ operations minimum
[If transformer switching]
- Transformer rating: ______ kVA/MVA
- No-load current: ______ A
- Inrush current: ______ A for ______ ms
3. ENVIRONMENTAL CONDITIONS
- Operating temperature: ____°C to ____°C
- Storage temperature: ____°C to ____°C
- Altitude: ______ m above sea level
- Humidity: ______ % RH, condensing/non-condensing
- Contamination level: Clean / Moderate Dust / Heavy Dust / Corrosive
- IP rating required: IP____
- Vibration/seismic requirements: ________________
4. MECHANICAL & INSTALLATION
- Mounting: Fixed / Withdrawable / Drawable
- Installation location: Indoor / Outdoor / Semi-outdoor
- Operating mechanism: Spring / Magnetic Actuator / Manual / Other
- Space constraints (if any): W____mm × H____mm × D____mm
- Maximum weight (if limited): ______ kg
5. CONTROL & AUXILIARY
- Closing coil voltage: ______ VDC/VAC
- Trip coil voltage: ______ VDC/VAC
- Auxiliary contacts required: ____ NO + ____ NC
- Position indication: Mechanical / Electrical / Both
- Mechanical interlocks: Yes/No, describe: __________
- Electrical interlocks: Undervoltage / Shunt trip / Other
- Operation counter: Yes/No
- Communication protocol (if smart contactor): _______
6. STANDARDS & TESTING
- Design standard: IEC 62271-106 / IEEE C37.012 / Other: ______
- Type test certificates required: Yes/No
- Routine test required: Per IEC 62271-106 / Custom: ______
- Factory acceptance test (FAT): Required / Optional
- Quality certifications: ISO 9001 / ISO 14001 / Other: ______
7. COMMERCIAL REQUIREMENTS
- Quantity: ______ units (initial), ______ potential future
- Delivery required by: __________
- Packaging: International shipping / Domestic / Special: ______
- Initial spare parts required: Yes/No, specify: __________
- Spare parts availability guarantee: ______ years minimum
- Commissioning support: Required / Not required
- Training: Required / Not required (specify duration: ____)
- Local service center: Required / Preferred / Not critical
- Warranty: Minimum ______ months
8. DOCUMENTATION REQUIRED WITH QUOTE
[ ] Detailed technical datasheet
[ ] Dimensional drawings (PDF + CAD)
[ ] Type test certificates
[ ] Quality certifications (ISO 9001, etc.)
[ ] Operation and maintenance manuals (draft or sample)
[ ] Spare parts list with pricing
[ ] Local service center locations and contact details
[ ] Reference installations (similar application, provide contact)
[ ] Delivery schedule and lead time
[ ] Itemized pricing (base unit, options, spare parts, services)
9. SPECIAL REQUIREMENTS OR NOTES
________________________________________________
________________________________________________
10. EVALUATION CRITERIA
Technical compliance: ____%
Price: ____%
Delivery time: ____%
After-sales support: ____%
Other: ________________: ____%
SUBMISSION DEADLINE: ____________
Submit to: ________________________
Contact for clarifications: ____________ (email/phone)
Common RFQ Mistakes and How to Avoid Them
| Mistake | Consequence | Solution |
|---|---|---|
| Omitting duty type | Manufacturer guesses—either overpriced or underspec | Always specify AC-1 through AC-6b category |
| Specifying only voltage/current | 500+ variants match; quote doesn’t fit actual need | Include application, operations/year, load type |
| No altitude specified | Contactor derated at site elevation, overheats or fails dielectrically | State actual installation altitude (>1,000 m critical) |
| “Capacitor switching” without capacitor size | Manufacturer can’t determine inrush/making capacity | Specify total kVAR, number of units, detuning reactor |
| “Similar to [competitor model]” | Lazy specification leads to non-comparable quotes | Define requirements independently, not by competitor product |
| No mechanical endurance requirement | Standard 10,000-op contactor fails in high-frequency application | State operations/year; capacitor duty needs 50,000+ |
| Forgetting control voltage | Quoted contactor has 220 VDC coil, your system is 125 VDC | Specify both closing and trip coil voltages |
| No spare parts/support discussion | Contactor works great but manufacturer has no local support | Require local service center, spare parts availability guarantee |
Key Takeaways
- Complete RFQ must specify 4 critical categories: electrical ratings (voltage, current, making/breaking capacity), duty type (AC-1 through AC-6b per IEC 62271-106 with operations/year), environmental conditions (temperature, altitude, IP rating), and application details (motor FLA/inrush, capacitor kVAR, or transformer MVA)
- Duty category selection drives cost and reliability—AC-3 motor starting contactor costs 30–50% less than AC-6b capacitor switching equivalent due to different mechanical endurance requirements (10,000 vs 50,000+ operations)
- Altitude >1,000 m requires explicit specification—每1,000 m derating factor ~10%, so 3,000 m installation needs contactor rated 1.3× nominal voltage or accept 23% current derating
- Capacitor switching RFQs must include total kVAR, individual unit size, detuning reactor presence, and back-to-back switching requirement—missing any parameter prevents accurate inrush current calculation
- Mechanical endurance requirement separates appropriate quotes from failures—capacitor/motor frequent switching needs 30,000–100,000 op rating; transformer/feeder occasional switching accepts 10,000 ops
- After-sales support specification (local service, spare parts 15-year availability, commissioning support) belongs in RFQ not post-purchase discussion—avoids surprises when manufacturer has no local presence
- Documentation requirements (type test certificates, FAT witness, CAD drawings) must be explicit—“standard documentation” means different things to different manufacturers
External Reference: IEC 62271-106 — IEC 62271-106 standard for AC contactors
Frequently Asked Questions
Q1: What’s the difference between making capacity and breaking capacity?
A: Making capacity (Icm) is peak current contactor can close onto (typically 2.5× rated short-circuit withstand for motor inrush/capacitor energization). Breaking capacity (Ib) is RMS current contactor can safely interrupt. Example: 12 kV contactor might have 40 kA making, 16 kA short-time withstand, but only 400 A breaking capacity—designed to close onto high inrush but not interrupt faults.
Q2: How do I determine required mechanical endurance for my application?
A: Calculate total operations over desired life: (operations/day × 365 × years). Example: Motor started 3×/day for 20-year life = 3 × 365 × 20 = 21,900 operations—specify 30,000+ mechanical endurance for safety margin. Capacitor switching (daily): 365 × 20 = 7,300 minimum, specify 50,000+ due to severe electrical stress.
Q3: Can I specify “equivalent to [competitor model]” instead of detailed requirements?
A: Not recommended—creates legal ambiguity and prevents apple-to-apple comparison. Different manufacturers interpret “equivalent” differently. Better: obtain competitor datasheet, extract key specifications, include those as requirements. This allows multiple manufacturers to quote fairly.
Q4: What altitude correction factor should I apply?
A: Per IEC 60694, correction factor Ka = 1 + 0.012(H – 1000) where H is altitude in meters. At 2,500 m: Ka = 1 + 0.012(2,500 – 1,000) = 1.18. Either specify contactor rated 1.18× nominal voltage or accept 1/1.18 = 0.85 (15% current derating). Always state site altitude in RFQ.
Q5: How specific should I be about capacitor bank configuration?
A: Very specific—manufacturers need: total bank kVAR, number of individual capacitor units, connection (wye/delta), detuning reactor value (if present), existing energized capacitors on bus (back-to-back switching), and switching frequency. Missing any parameter forces manufacturer to guess inrush current, leading to over/under-specification.
Q6: Should I request FAT (factory acceptance test) for all contactor purchases?
A: For critical applications (capacitor switching, high-duty motor starting, expensive equipment protection): Yes—FAT confirms performance before shipment. For standard applications with proven manufacturer track record: Optional (adds cost and delivery time). Always require FAT for custom/first-time configurations.
Q7: What warranty period should I specify for vacuum contactors?
A: Standard: 24 months from commissioning or 30 months from delivery. Capacitor switching duty: Request extended warranty (36 months) due to higher electrical stress. Also specify mechanical/electrical endurance guarantees: “Minimum 50,000 mechanical operations, 10,000 electrical operations at rated current” for capacitor duty.
Related Reading and Selection Resources
- CKG Vacuum Contactor ? practical checks, limits, and commissioning notes
- Lcz Vacuum Contactor ? selection logic and failure-prevention details
- jcz vacuum contactor ? field troubleshooting patterns and acceptance criteria
