EOCR-PMZ (panel embedded) and EOCR-PFZ (embedded) motor comprehensive protector

EOCR-PMZ/PFZ Motor Protector: Comprehensive Protection and Intelligent Diagnosis in Practical Use

In the field of industrial motor control, the selection and configuration of protective relays are directly related to equipment lifespan and production continuity. The EOCR-PMZ/PFZ series electronic overload relays launched by Schneider (formerly Sanhe, South Korea) have become the first choice for many engineers to upgrade motor protection solutions due to their integrated functions of overcurrent, undercurrent, ground fault, current transmission, as well as intuitive digital display and programmable features. This article will systematically review the entire application process of EOCR-PMZ/PFZ from core functions, parameter settings, wiring points to selection and ordering, helping you quickly deploy and avoid common pitfalls in renovation or new projects.

Overview of core functions: Integrated protection with multiple functions for one machine

The EOCR-PMZ (window type) and EOCR-PFZ (terminal type) products share the same set of protection logic and operation interface, with the only difference being the structural form of the current detection terminal. Its core advantage lies in integrating protection functions such as overload, underload, ground fault, phase sequence, phase loss, imbalance, locked rotor, and blocking, and supporting 4-20mA current transmission output, greatly simplifying the number of components and wiring complexity inside the control cabinet.

1.1 Automatic cycle display and manual locking

The front of the device is equipped with a 5-digit 7-segment LED digital tube, coupled with a phase indicator light, which automatically displays the L1, L2, L3 three-phase current and leakage current every 5 seconds by default. During on-site inspection, pressing the SET button can switch to manual cycle mode, locking a certain phase or leakage value in sequence with each press, making it easier to observe specific parameters. Long press or press the reset button again to return to automatic mode - this design is particularly useful for debugging or troubleshooting.

1.2 Wide Range and External CT Expansion

Direct connection: The body provides a wide range setting of 0.5~60A (selected through internal dialing or menu), suitable for various wiring methods such as 5-hole core through type (0.1~2.0A), 2-hole type (0.25~5.0A), etc.

External CT extension: With the standard 5A output current transformer (CT), the range can be extended to 3600A. Users only need to set the CT ratio in the parameter Ct (for example, 200:5 is set to 200) to achieve precise protection for high current motors.

1.3 Fault records and pre maintenance reminders

Relays can remember the reasons for the last three trips and the current values of each phase at the time of the trip. Even if the power is disconnected and reconnected, the records will not be lost. In addition, the built-in cumulative running time timer (up to 65500 hours) and adjustable operation time reminder (1~9990 hours), when the motor reaches the set time, the panel will alternately display the current and remaining time, prompting maintenance operations such as bearing replacement - this is an excellent auxiliary means for preventive maintenance strategies.

Detailed explanation of protection function: engineering significance behind each parameter

2.1 Overcurrent Protection (OC) - Three optional characteristic curves

Overcurrent is the most common fault of motors. EOCR-PMZ/PFZ provides three action characteristics:

Definite (dE): After the current exceeds the set value, it trips after a fixed delay of ot (0.2-30 seconds). Suitable for situations where short-term overload is allowed but high delay accuracy is required.

Inverse, In: According to the I ² t characteristic, the larger the current, the faster the action, with a delay range of 1-30 seconds. Consistent with the behavior of thermal relays, it is more in line with the motor's thermal tolerance curve.

Thermal Inverse (th): Adding thermal memory function on the basis of inverse time. The heat generated during the operation of the motor will be accumulated, and the accumulated heat value will be automatically reset within 20 minutes after shutdown. If restarted immediately in a hot state, the protection action time will be shorter, simulating a real hot state.

Engineering suggestion: For ordinary fans and water pumps, dE or In can be used; for equipment that frequently starts and stops or starts under heavy loads, th is recommended to avoid the protection value set in cold state being insufficient to protect the motor in hot state.

2.2 Undercurrent protection (UC) - prevents idling or belt breakage

When the current is lower than the set value (which can be set to 0.5A to 0.1A less than the overcurrent value) and the duration exceeds Ut (0.5-30 seconds), the relay will activate. Typical application scenarios: Water pump idling, belt slipping or breaking, compressor lacking refrigerant. Attention: The undercurrent value and overcurrent value cannot be equal or higher than the overcurrent value, otherwise they cannot be set.

2.3 Grounding Fault Protection (EC) - Zero Sequence Current Detection

Detecting leakage current through an external zero sequence current transformer (ZCT). Provide two ranges and characteristics:

Time limit (dE): Range 0.03~10A, adjustable delay Et of 0.05~10 seconds.

Inverse Time Limit (Inv): Only applicable within the range of 0.03~1A, following the inverse time limit curve.

In addition, the grounding fault delay Ed (1-10 seconds) during startup can be set separately to avoid false tripping caused by brief leakage current during startup.

2.4 Phase sequence, missing phase, and imbalance

Reverse phase (RP): When enabled, any two phase wiring errors will trip within 0.1~0.3 seconds to protect the safety of mechanical equipment rotation direction.

Phase loss: Detected any phase current loss, action time ≤ 3 seconds.

Unbalance: The calculation formula is (maximum phase current - minimum phase current)/maximum phase current x 100%. When the imbalance rate exceeds the set value (default action of 8 seconds), it can effectively reflect the short circuit between turns of the motor winding or the three-phase voltage imbalance.

2.5 LRT and Stall

Locked rotor protection: During the start-up process, if the current reaches 1.5 to 5 times the overcurrent setting value and the duration exceeds Ot (start-up delay), the protection will be activated.

Stall protection: In the event of mechanical jamming during operation, when the current reaches 2-10 times the overcurrent setting value, it will activate according to the OT time limit.

Parameter Setting and Operation Practice: From Beginner to Proficient

EOCR-PMZ/PFZ adopts five key operation (up, down, SET, reset), and the menu logic is clear. Taking a typical setup process as an example:

3.1 Basic steps

Mode selection: Press the up/down keys to switch to the menu item that needs to be modified (such as current setting oc).

Enter editing: Press SET once, and the displayed value will start flashing.

Adjust value: Press the up/down keys to change the value.

Save: Press SET again and the flashing stops to save.

Exit: Press the reset button or wait for 30 seconds to automatically exit.

3.2 Detailed Explanation of Key Parameters (Based on Etc Extended Menu)

After entering Etc mode, the following advanced functions can be set (some of which repeat the parameters directly set on the front panel, but provide additional options):

Parameter Code Function Description Optional Values and Recommendations

RPR reverse phase protection switch on/off, it is recommended to set it to on

E1c overcurrent characteristics dE (definite time limit)/In (inverse time limit)/th (thermal memory)

E2c grounding fault characteristics dE/In

E2o grounding fault output contact type a (normally open)/b (normally closed)

The 4-20 transmission output full-scale current setting corresponds to a current value of 20mA (e.g. if set to 50, 50A outputs 20mA)

RH operation time reminder set to OFF or 1-9990 hours, alarm upon arrival

The accumulated running time of rt is displayed as read-only and cannot be reset

Ct external CT ratio is set to the primary value of the transformer (e.g. 200/5, set to 200)

Trip fault record query shows the reasons and current of the last three trips

After entering the test self-test function, simulate a trip and verify the external circuit

3.3 Common Setting Traps

Switching between inverse time limit and definite time limit for grounding fault 0.03~1A: If a definite time limit needs to be used within the range of 0.03~1A, it is necessary to first enter Etc and set E2c to In (at this time, the range automatically changes to 0.03~1A), and then return E2c to dE in order to obtain the small current range under the definite time limit.

Undercurrent and overcurrent interlock: Uc setting value must be lower than oc, otherwise it cannot be saved.

Reset mode selection: H-r (manual reset, press panel button), E-r (reset by power off and then power on), A-r (automatic reset, adjustable from 0.3 seconds to 20 minutes). For faults such as phase loss, reverse phase, grounding, and locked rotor, even if set to automatic reset, it will not reset automatically and needs to be manually cleared.

Installation and wiring points: avoid the risk of "burning machine"

4.1 Power supply and output contacts

Power terminal A1/A2: Supports AC/DC 85-250V (50/60Hz) wide voltage input, be sure to confirm the voltage specifications before wiring. The 24V version is ordered separately.

Output contacts: OL (overload) is 2-SPST, OR (ground fault or alarm) is 1-SPST, contact capacity is AC250V/3A resistive load. The default contact state is b (95-96 normally closed, 97-98 normally open), and the a/b mode of the ground fault contact can be changed through parameter E2o.

4.2 Current Transformer and ZCT Wiring

Main circuit core penetration: For EOCR-PMZ (window type), the three-phase wires need to pass through the built-in CT holes. Pay attention to the consistency of current direction. Although EOCR uses average value detection internally, it is recommended to maintain consistent direction to avoid phase to phase interference.

Zero sequence current transformer (ZCT): The matching ZCT (35mm, 80mm, 120mm aperture optional) must be used, and the ZCT secondary line must be connected to the Z1 and Z2 terminals. ZCT secondary side must not be grounded, otherwise it may cause measurement errors and even damage the internal circuit.

Star delta starting wiring: ZCT must be installed above the main contactor (Main MC) and below the main circuit breaker (Main CB), that is, it must be bridged outside the delta switching area to avoid distortion of the current waveform during the starting process, which may cause misoperation.

4.3 4-20mA transmission output

The transmission output terminals+and - are used to connect PLCs or instruments. The output is active 4-20mA, isolated from the power supply. Set the current value in parameter 4-20 to correspond to a 20mA output (for example, if set to 150A, output 20mA at 150A, and output 4mA at 0A or below 0.5A). Shielded twisted pair cables (such as CVV-SB 2 × 1.25mm ²) must be used, with the shielding layer grounded at one end to prevent interference from sources such as frequency converters.

4.4 Fault Safety Mode (FS)

When the FS parameter is set to on, the relay's output contacts will switch to an alarm state (i.e. "fail safe") when the power is cut off or the self-test is abnormal. At this time, special attention should be paid: if the control power is taken from the main circuit of the motor, the change in contact state after power failure may cause misjudgment by the upper computer. It is recommended to set FS to on in important interlocking circuits and cooperate with UPS or independent control power supply.

Selection guide: Quickly locate the suitable model

5.1 Interpretation of EOCR-PMZ Order Code (Window Type)

Taking EOCR-PMZ-WRDZ7W as an example:

WR: Wide range of 0.5~60A (no need for external CT)

D: Output contact form (95-96 normally closed, 97-98 normally open)

Z7: Power supply AC/DC 85~250V, 50/60Hz

W: Hole Type

If an external CT is required, change the WR to H1 (100:5), HH (150:5), H2 (200:5), H3 (300:5), H4 (400:5), etc., and order the matching CT accessories separately.

5.2 EOCR-PFZ Ordering Code (Terminal Type)

Similar to the rule, the last T represents Terminal Type. For example, EOCR-PFZ-WRDZ7T is a wide range, 85-250V power supply, terminal type.

5.3 Attachment Selection

ZCT: Choose aperture sizes of 35mm, 80mm, or 120mm based on the outer diameter of the cable, such as ZCT-035.

Connecting cable: 15 pin flat cable, used for split installation (up to 10m in length), model such as CABLE-15-002 indicates 2 meters. When installing separately, the host can be installed on the cabinet door, and the CT unit can be placed inside the cabinet for easy inspection.

Fault diagnosis and reset: Quickly restore production

When EOCR trips, the panel will display fault codes (such as OC, UC, EC, RP, PL, etc.). Enter trip mode by pressing the up/down keys, and press SET to view in sequence:

Recent tripping reasons (such as OC)

L1, L2, L3 current values during tripping

Second and third trip records

Reset method:

Manual: Press the panel reset button.

Electrical: Disconnect the control power supply and then reconnect it.

Automatic: A-r needs to be set to the desired delay (0.3 seconds to 20 minutes) in advance. Attention: Automatic reset is invalid for faults such as reverse phase, phase loss, grounding, and locked rotor.

Common troubleshooting for false tripping:

Frequent OC tripping and actual current not exceeding: Check if the OC setting value is too low or if the OT delay is too short; For motors powered by frequency converters, high-order harmonics may cause false detections. You can try changing the action characteristics to In and increasing the delay appropriately.

EC (ground fault) misoperation: Check if ZCT is installed in the correct position (away from the output line of the frequency converter), and if the secondary line is damp or insulated; Temporarily set EC to OFF to confirm if it is external interference.

When powered on, RP (reverse phase) will be displayed: simply swap any two incoming lines to solve the problem.