Question/Problem
 
The controls system is reporting a motor overload and the conveyor will not run.
Motor overload alarm but overload is not tripped.
Motor circuit protector not tripped but overload detected.

 
Environment

• ICW
• BOSS
• MC4
• PLC 

Answer/Solution

Motor overload logic is used to logically stop motors and VFDs when an overload condition is detected.  However, due to the requirements of the software logic and the hardware involved, motor overloads can be falsely reported by the controls.  This article will go over what is used for the hardware and how the logic determines an overload condition.

For the three-phase power, there are typically four components involved: the motor circuit protector (#1), the motor contactor (#2), the motor disconnect (#4), and the motor (#5).  Using the schematic below, the wiring leaves the control panel at point #3 indicated by the solid and dashed lines. 

Additionally, the motor contactor (and sometimes the disconnect switch) have auxiliary contactors, typically using 120VAC, which serve as inputs to the control system. The only output from the controls in this setup is the motor contactor coil to turn on the motor contactor.

An overload alarm is triggered in the controls if the output is activated for the contactor but the corresponding auxiliary input is not detected within a certain amount of time (typically 1-2 seconds).  With the schematic below, this would mean that the output MTR10190 has been activated and the controls expects to see the input M10190 activated.  If the input is not detected, an overload alarm is shown and the output is deactivated.

Troubleshooting a Motor Overload

1. Check the motor circuit protector.  If it is tripped, reset it and attempt to run the motor again.
2. If the motor runs and trips the motor circuit protector, begin troubleshooting for an electrical or mechanical issue (short circuit, burned out motor winding, rollers binding/not running smoothly, etc.)
3. If the motor runs without tripping the motor circuit protector, begin troubleshooting the from the auxiliary contactor to the input point using the following as a starting point.

The following components are potentially at fault, but reference the schematics for any other components that could be present.  This assumes that only one motor is showing an overload.  Otherwise check the 120V power going to the motor contactors for all of the affected motors.

• The motor contactor
• The input card
• The wires between the contactor and the input card (may pass through a terminal block)
• The terminal block which the wire passes through (if present)

Troubleshooting is straightforward and involves replacing the components one at a time and checking for the overload to clear in the controls software.  Wiring can be temporarily ran directly from the contactor to the input card (bypassing the terminal block), but should be permanently replaced and properly routed  in the panel as soon as possible.

Very rarely the electrical and mechanical components are not at fault, in which case, software solutions should be researched.

Please see below forreference.

Overload Detection

DISCLAIMER:

Information in this document is subject to change without notice and does not represent a commitment on the part of Intelligrated. This information is typical of the questions and general advice given; however, your particular case and circumstances may produce different results or require different recommendations. Therefore, use of this information is not a suitable replacement for contacting Intelligrated Technical Service engineering for specific recommendations and solutions to your application.

No part of this article may be reproduced or transmitted in any form or by any means including recording, or information storage and retrieval systems, for any purpose without the express written permission of Intelligrated. All information contained within the article is private and confidential and the sole property of Intelligrated.

In no event, shall Intelligrated be liable for any damages whatsoever including, without limitation, damages for loss of business profits, business interruption, loss of business information, or other pecuniary loss, even if Intelligrated has been advised of the possibility of such damages. Because some states do not allow the exclusion or limitation of liability for consequential or incidental damages, the above limitation may not apply to you.