A written motor-starter scenario says the overload has tripped and the motor has stopped. Did the overload relay open the motor's power contacts? In the conventional starter described by Schneider Electric, it did not. The relay senses an overload and opens a control contact; the contactor then drops out and opens the motor power circuit. This is a study example, not a field-testing instruction.
What does each device do?
Schneider Electric's overload-relay guide says its conventional overload relay has no motor power contacts of its own. The relay's normally closed control contact is wired in series with the contactor coil. The contactor's separate main contacts carry and interrupt the motor circuit. A breaker or fuse is another device in the branch circuit, intended to handle short-circuit faults; do not label it as the overload relay.
Read a schematic by tracing two paths: control path through the overload contact and coil, then power path through the contactor's main poles to the motor. The contactor glossary explains the coil and contact relationship.
What happens when the relay trips?
In this simple example, the motor draws excessive current long enough to operate the correctly selected overload relay. Its normally closed control contact opens. The contactor coil loses its complete control circuit, so the contactor releases and its main contacts open. The motor stops. A memorization line is relay senses → control contact opens → coil drops → main contacts open.
The relay's thermal behaviour matters: Schneider explains that greater overcurrent can shorten trip time. A relay trip does not by itself identify why the motor drew too much current. Mechanical load, supply conditions and the actual equipment design still need investigation by qualified personnel.
Why is an overload trip different from a short circuit?
An overload is excessive running current over time; a short circuit is a fault with a much larger current path. Schneider's guide distinguishes motor running overload protection from branch-circuit short-circuit protection and explains that proper coordination lets the appropriate protective device act for its fault range. In a paper problem, ask which device sensed the event and which contacts opened the motor supply. Do not infer that every stopped motor has a tripped overload.
For example, “overload contact open, contactor coil de-energized” supports an overload-control sequence. “Branch fuse open” points to a different protective event requiring a different investigation. The words describe the circuit state; they are not enough to diagnose a real installation from afar.
How should a 313A candidate practise the distinction?
Sketch a coil, a normally closed overload contact in series with it, and three contactor main poles feeding a motor. Mark the state before and after a trip. Then explain why resetting a relay without finding the cause may lead to another trip. For real equipment, use its wiring diagram and authorized procedures; CCOHS lockout guidance covers hazardous-energy isolation. Never use a study diagram as permission to work energized or bypass protection.
The Ontario exam page and current-standard note identify the applicable study outline. Red Seal still lists its previous occupational standard as the basis for current exams, checked 2026-10-01. For a short reasoning check, use the free sample as original, unofficial draft practice awaiting certified-mechanic review. It cannot predict an exam result.
Sources
- Schneider Electric: Overload Relays and Thermal Unit SelectionControl contact, contactor, overload and branch-circuit protection; checked 2026-10-01
- CCOHS: Lockout/Tag outHazardous-energy isolation; checked 2026-10-01
- Red Seal: Refrigeration and Air Conditioning MechanicCurrent versus newer exam-standard status; checked 2026-10-01
Examen Studio is independent and not affiliated with the Red Seal Program or Skilled Trades Ontario. This article is a study aid; on the job, follow current codes, regulations and manufacturer instructions.