Protecting Softstarters Against A Phase-To-Phase Fault

Training

Question:
What are recommendations to protect PCS, PF and PCEC soft starters if a motor has a phase-to-phase fault?

Answer:
Circuit breakers and fast acting SCR fuses, which are normally located on the line side of the P Series soft starter, will not be effective to protect against a phase-to-phase fault on the motor side of the circuit. Using protective fuses on the load side of the P Series soft starters will not be practical as the fuses will become fatigued with the reduced voltage starting that is provided by the soft starters to start the motor load.

The following recommendations may help to reduce damage to the soft starters if there is a phase-to-phase fault in the motor:

PF Series:

Install the a ground fault sensor and enable Ground Fault Protection in the PF soft starter. Configure parameter 73, Ground Fault Level, for 1 amp (the lowest setting). The highest setting is 5 amps.
Install a motor with built in PTCs and enable PTC over temperature protection via Parameter 79, PTC Enable, in the PF soft starter.
Install the appropriate PFP Protective MOV module on the load side of the PF product, if you are not using PFB Pump Stop or PFD Smart Motor Braking control (and not Delta Connected). However, if there is a phase-to-phase fault in the motor the Protective Module may not provide enough protection and will be damaged. Depending upon the magnitude of the fault, the MOV module may not be able to prevent damage to the PF soft starter.

PCS Series:

The PCS soft starters do not provide parameter configuration or inputs for the Ground Fault Sensor and PTC over temperature protection. However, there are PCP/PFP MOV Protective modules available for the PCS soft starters. For Line Connected motors the MOV Protective module may be installed on the line and/or load side. For Delta Connected motors the MOV Protective module must be installed on the line side only (this will not protect against phase-to-phase motor faults). Depending upon the magnitude of the fault, the MOV module may not be able to prevent damage to the PCS soft starter.

Sprecher & Schuh Series PFP 108...480 v replacement protective module

PCEC Hydraulic Elevator Softstarters:

The PCEC soft starters do not provide parameter configuration or inputs for the Ground Fault Sensor and PTC over temperature protection. However, there are PCP/PFP MOV Protective modules available for the PCE soft starters.
In most cases, the PCE is Delta Connected which means an MOV must be installed on line side only which will not protect against phase-to-phase motor faults. This will however protect against faults upstream of the MOV line side device (BCPD, feeders, utility source…).
For Line Connected motors the MOV Protective module may be installed on the line & load side of the PCE. Depending upon the magnitude of the fault, the MOV module may not be able to prevent damage to the PCE soft starter.

A simple, solid-state solution for the operation of motors that drive hydraulic elevators and escalators

For additional information please contact your nearest authorized distributor, sales representative, or call our customer service or technical support lines.