The DOLD MK9040N.12 Series Asymmetry and Phase Sequence Relay (German: Asymmetrierelais) is an advanced intelligent electrical protection instrument belonging to the prestigious VARIMETER family, researched and manufactured by E. DOLD & SÖHNE GmbH & Co. KG in Germany. Within 3AC 400V industrial networks, voltage unbalance between phases (asymmetry in voltage amplitudes or phase angle displacement) ranks among the primary causes of severe equipment degradation. Such abnormalities routinely arise from asymmetrical single-phase load distribution, degraded transformer windings, or high-resistance terminal connections. Even a marginal phase asymmetry of 2% to 3% can induce reverse-sequence currents within electric motors by 6 to 10 times, generating extreme thermal dissipation that destroys stator winding insulation, diminishes mechanical torque, and causes catastrophic motor burnout.

The DOLD MK9040N.12 series is engineered to eliminate these hazards through continuous algorithmic evaluation of phase angles and voltage symmetry. It integrates three vital surveillance functions within a single housing: precise voltage unbalance monitoring, immediate detection of total phase failure (even under deceptive regenerated feedback voltages induced by running induction motors), and verification of correct phase sequence to prevent hazardous reverse mechanical rotation. Built with a slim 22.5 mm module width for 35mm DIN-rails, it features the ".12" contact arrangement with 2 independent changeover contacts (2 C/O) boasting high switching capacity, alongside multi-color diagnostic LEDs providing instantaneous on-site status feedback.

This comprehensive entry consolidates five specialized variants of the MK9040N.12 family:
1. DOLD MK9040N.12/821 3AC 400V 50/60Hz (Tv on = 1 - 10s): Features an adjustable operate delay (Ansprechverzögerung) from 1 to 10 seconds. This capability filters out nuisance tripping caused by transient voltage dips during high-inertia motor starting cycles.
2. DOLD MK9040N.12/010 3AC 400V 50/60Hz (Tv = 0.5 - 10s): Features an adjustable release time delay (Rückfallverzögerung) from 0.5 to 10 seconds, stabilizing contact positions during short-term grid fluctuations to prevent rapid contactor chatter.
3. DOLD MK9040N.12/011 3AC 400V 50/60Hz (Tv = 0.5 - 10s): Optimized time-delay release variant with enhanced fault management circuitry and rapid trip response during complete phase severance.
4. DOLD MK9040N.12PC/011 3AC 400V 50/60Hz (Tv = 0.5 - 10s): Premium variant equipped with pluggable cage clamp terminals (PC). This architecture provides vibration-proof contact integrity without screw-loosening risks, while enabling rapid hot-swap module replacement in seconds without disconnecting individual wires.
5. DOLD MK9040N.12PS/011 3AC 400V 50/60Hz (Tv = 0.5 - 10s): Premium variant featuring pluggable screw terminals (PS), combining the familiarity of traditional screw torque connections with the maintenance convenience of pluggable modularity.

Certified under stringent international safety standards including IEC/EN 60255 and DIN VDE 0435, the MK9040N.12 series represents the optimal protection choice for chemical processing facilities, cement works, metallurgy plants, wastewater pumping stations, HVAC chillers, and automated assembly lines worldwide.

• Manufacturer: DOLD (E. DOLD & SÖHNE GmbH & Co. KG)
• Country of Origin: Germany
• Product Series: VARIMETER MK 9040N
• Contact Configuration Code: .12 (2 independent changeover contacts - 2 C/O contacts)
• Technical Category: Voltage Asymmetry and Phase Sequence Relay (Asymmetrierelais)
• Integrated Models in this entry:
  - DOLD MK9040N.12/821 (Operate delay Tv on = 1 - 10s, fixed terminals)
  - DOLD MK9040N.12/010 (Release delay Tv = 0.5 - 10s, fixed terminals)
  - DOLD MK9040N.12/011 (Release delay Tv = 0.5 - 10s extended, fixed terminals)
  - DOLD MK9040N.12PC/011 (Release delay Tv = 0.5 - 10s, pluggable cage clamp terminals PC)
  - DOLD MK9040N.12PS/011 (Release delay Tv = 0.5 - 10s, pluggable screw terminals PS)
• Nominal Measuring Voltage (UN): 3AC 400 V
• Nominal Frequency: 50 / 60 Hz
• Monitoring Parameters:
  - 3-Phase voltage asymmetry / unbalance
  - Total phase failure (including regenerated voltage detection)
  - Phase sequence verification
• Asymmetry Setting Range: Infinitely adjustable from 5% to 15% via front potentiometer
• Time Delay Characteristics (Tv):
  - Model /821: Operate delay Tv on = 1 ... 10 seconds
  - Models /010, /011, PC/011, PS/011: Release delay Tv = 0.5 ... 10 seconds
• Output Contact Arrangement: 2 Changeover contacts (2 C/O)
• Switching Capacity: AC-15: 3A / AC 230V; DC-13: 2A / DC 24V (according to IEC/EN 60947-5-1)
• Terminal Architecture:
  - Standard (.12): Fixed box clamp screw terminals
  - PC Version (.12PC): Pluggable Cage Clamp terminals (vibration-proof and maintenance-free)
  - PS Version (.12PS): Pluggable Screw terminals
• Diagnostic LEDs: Multi-status LEDs for power healthy, asymmetry unbalance, phase failure, and phase sequence fault
• Enclosure Dimensions (W x H x D): 22.5 x 90 x 97 mm (Ultra-slim MK enclosure)
• Mounting Profile: Snap-on mounting for standard 35 mm DIN-rail (IEC/EN 60715)
• Protection Degree: Housing IP40, Terminals IP20 (according to IEC/EN 60529)
• Operating Ambient Temperature: -20°C to +60°C
• Compliant Safety Standards: IEC/EN 60255, IEC/EN 60947-5-1, DIN VDE 0435, CE
• Common Industrial Deployments: 3-phase AC motors, screw compressors, HVAC chillers, water pumps, cranes, and automated conveyor lines