Eaton Moeller ZM-16-PKZ2 Motor Protector Trip Block – PKZ2 Series

Eaton Moeller ZM-16-PKZ2 Motor Protector Trip Block – PKZ2 Series: Thermal-Magnetic Protection Architecture in Motor Branch Circuits

The ZM-16-PKZ2 is the current-setting trip block that defines the protective operating envelope of the PKZ2 motor-protective circuit-breaker system. In a motor branch circuit, the trip block is not a passive accessory — it is the primary decision element. It carries the calibrated bimetal strip assembly responsible for inverse-time thermal response to sustained overloads, and the electromagnetic release mechanism that reacts to instantaneous short-circuit currents within milliseconds. Without a correctly rated trip block, the PKZ2 chassis is inert. Selecting the ZM-16-PKZ2 means specifying a 16 A upper-range trip block, appropriate for three-phase motors up to approximately 7.5 kW at 400 V AC, depending on motor efficiency class and ambient derating conditions.

The PKZ2 platform has been deployed across European and global industrial installations for decades, and the ZM-series trip blocks remain the standard replacement and upgrade path for existing PKZ2 installations. For procurement teams managing MRO inventories across multi-site manufacturing operations, the ZM-16-PKZ2 represents a high-velocity consumable: it is replaced on a defined maintenance cycle or following a fault event, and its availability directly determines how quickly a motor circuit can be restored to service. Sourcing from siemensplc.com provides access to verified stock with same-day quotation and rapid international dispatch from Xiamen, China.

Real-time Stock & RFQ: [email protected] | WhatsApp: +86 18359268345

Technical Parameters

Hardware Logical Analysis

The ZM-16-PKZ2 integrates two physically independent release mechanisms within a single compact housing, each optimized for a distinct fault regime.

Thermal Bimetal Assembly: The overload release uses a three-phase bimetal strip set, one per pole, heated by the load current passing through calibrated shunt resistors. The bimetal deflects proportionally to I²t accumulation, providing an inverse-time characteristic: a 150% overload trips in tens of seconds, while a 600% overload trips in under two seconds. This characteristic closely mirrors the thermal damage curve of standard IEC motor windings, which is the engineering rationale for Class 10 coordination. The bimetal assembly is temperature-compensated — an ambient-temperature bimetal reference strip is mechanically coupled to the main strips, ensuring that the trip threshold remains consistent across the rated –25 °C to +55 °C ambient range without requiring external compensation circuits.

Electromagnetic Short-Circuit Release: Each pole contains a solenoid-type electromagnetic release with a fixed instantaneous trip threshold, typically set at 12× to 14× the maximum current setting (approximately 192–224 A at the 16 A setting). When a bolted fault or high-impedance short circuit drives current above this threshold, the electromagnetic plunger actuates the common trip bar within 10–20 ms, well within the let-through energy limits that protect downstream motor windings and cable insulation from thermal damage.

EMC and Isolation Architecture: The trip block’s current-carrying conductors are fully enclosed within the thermoplastic housing, with creepage and clearance distances designed to IEC 60947-1 Pollution Degree 3 requirements. This is relevant in industrial environments where conductive dust, condensation, or chemical vapors are present. The mechanical trip linkage is entirely galvanically isolated from the control circuit — there are no electronic components in the trip path, which eliminates the failure modes associated with semiconductor-based electronic overload relays (e.g., capacitor aging, firmware faults, EMI-induced false trips).

Mechanical Endurance and Reset Logic: The trip mechanism is rated for a defined number of mechanical operations per IEC 60947-4-1. Following a thermal trip, the bimetal requires a cooling period before manual reset is possible — this is an intentional design feature that prevents repeated re-energization of a motor in a sustained overload condition, protecting both the motor and the trip block from cumulative thermal damage. The reset button is recessed to prevent accidental actuation.

System Integration Benefits

• Direct PKZ2 Chassis Compatibility: The ZM-16-PKZ2 engages the PKZ2 base unit via a keyed plug-in interface, ensuring correct mechanical alignment of all three poles simultaneously. Replacement in the field requires no tools and takes under two minutes, minimizing MTTR in production environments.
• Adjustable Current Setting Without Recalibration: The front-face rotary dial allows continuous adjustment from 10 A to 16 A, enabling a single trip block SKU to cover multiple motor ratings within that range. This reduces the number of distinct spare part numbers that a maintenance team must stock.
• Deterministic Trip Characteristic: The inverse-time thermal curve is defined by IEC 60947-4-1 and is consistent across production batches. Control system designers can rely on the trip time-current characteristic when coordinating upstream fuses or MCCBs for selective protection.
• No External Power Requirement: The trip mechanism is entirely self-powered by the load current. There is no dependency on a 24 V DC control supply or external relay coil, which eliminates a common failure point in electronic overload relay installations.
• Phase-Loss Sensitivity: The three-pole bimetal assembly detects single-phasing conditions: when one phase is lost, the remaining two phases carry increased current, causing the corresponding bimetal strips to deflect and trip the circuit before the motor reaches its thermal damage threshold.
• Modular System Expansion: The PKZ2 system accepts auxiliary contact blocks (NHI11-PKZ2, NHI20-PKZ2) that can be added to the chassis without replacing the trip block. This allows the addition of remote trip indication or PLC feedback signals to an existing installation without disrupting the protection circuit.
• Diagnostic Transparency via Trip Indicator: The ZM-16-PKZ2 provides a visual trip indicator that distinguishes between a thermal overload trip and a manual OFF operation, allowing maintenance personnel to immediately identify the fault type without instrumentation.
• Coordination with Upstream Protection: The trip block’s short-circuit release threshold is factory-set to coordinate with standard IEC gG fuses and upstream MCCBs, supporting Type 2 coordination per IEC 60947-4-1 when the correct upstream device is selected from the Eaton coordination table.

Quality Assurance & Global Logistics

Every ZM-16-PKZ2 unit supplied by siemensplc.com is sourced through verified industrial distribution channels carrying genuine Eaton Moeller branded product. Each unit is inspected upon receipt for correct part number marking, housing integrity, dial calibration markings, and absence of counterfeit indicators including label adhesive inconsistencies, incorrect font weights, and non-standard connector geometry.

A 12-month warranty against manufacturing defects is provided from the date of shipment. This covers trip mechanism failure, contact resistance out of specification, and housing cracking under normal operating conditions. Warranty claims are processed with a replacement-first policy — we dispatch a replacement unit before requiring return of the defective item for qualified B2B accounts.

Logistics operations are managed from Xiamen, China — a designated national-level port city with direct air freight connections to major hubs including Hong Kong, Singapore, Frankfurt, Los Angeles, and Dubai. DHL Express and FedEx International Priority are the standard carriers for urgent orders, with typical transit times of 3–5 business days to Europe and North America. For bulk orders, sea freight via Xiamen Port provides cost-effective delivery with full container load (FCL) and less-than-container load (LCL) options. All shipments include a commercial invoice, packing list, and certificate of origin compliant with Xiamen Customs requirements, facilitating smooth import clearance in destination countries. Multi-currency payment is supported: USD, EUR, HKD, and CNY via T/T bank transfer, with PayPal available for smaller orders.

Contact Information

Email: [email protected]
WhatsApp: +86 18359268345
Web: siemensplc.com
Location: Xiamen, Fujian, China
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