How Should a Single-Phase Motor’s Overload Relay Be Chosen? And The Benefits of Choosing a Motor Circuit Breaker


The amperage ratings of thermal overload relays are determined by the size of the electrical load circuit that they are safeguarding. It is important to select a relay based on the amp draw of your system. Relays that are too small will trip when overheating happens, but relays that are too big won’t trip when that happens. If you happen to choose the best thermal overload relay supplier in the Philippines, you will be happy with the results.

Varieties of thermal overload relays suppliers in Philippines.

Depending on how quickly they react to a motor overload, overload relays, and associated heaters fall into one of three types. There will be markings on the overload relay itself to identify the class to which it belongs. 

Classes 10, 20, and 30 are among them. The response time (in seconds) is indicated by the class number. A Class 20 overload relay is invariably unlabeled. Most NEMA-rated overload relays are Class 20, although many of them include a 15% adjustment range for their typical trip current.

Choose a thermal overload relay supplier in the Philippines.

Choosing is simple, provided that the brand and size are the same. This isn’t always feasible, though. Use the selection tables provided by the manufacturer if you have to choose a different heater. The motor’s full load amperage (FLA) and the motor starter you employ will determine which option is best for you.

Thermal Overload Relay Installation.

It’s simple to install thermal overload relays once you’ve chosen the appropriately rated models. The crucial actions are as follows:

1. Cut the power supply off from the load circuit.

2. Locate the wire terminals by opening the power panel.

3. Attach the input/output terminals to the relay and mount it inside the panel.

4. Attach the relay’s input and output wires to the load circuit’s current wiring.

5. Shut off the power source.

6. Turn back the electricity and check the relay’s operation.

The Upkeep and Examination of Thermal Overload Relays.

To guarantee that your recently installed overload relays continue to function properly after purchasing from a reputable thermal overload relays provider in the Philippines, you must do routine testing and maintenance. 

The following are recommended practices:

1. Visually check units once a year for damage or cracks on the outside.

2. To avoid loose connections, make sure the wire terminals are snug.

3. Press the test button by hand to check the tripping feature.

4. Clear the relay of any accumulated dirt or debris.

5. Verify that the amperage ratings for your loads are still valid.

MPCB functions include: 

  • Specialized electromechanical devices known as motor circuit breakers, or MPCBs, apply to motor circuits operating at 60Hz or 50Hz. It can supply motors with a secure electrical supply thanks to several functions: 
  • a mechanism that guards against electrical problems such as line-to-ground, line-to-short, and line-to-line failures. The board can interrupt electrical faults below the MPCB’s breaking capacity. 
  • When a motor draws more current than its nameplate value for an extended length of time, motor overload protection is triggered. Overload protection on the motor circuit breaker is often adjustable.
  • Defense against phase loss and imbalances. A three-phase motor can sustain significant damage in any scenario, which is why the MPCB disconnects the motor as soon as the issue is identified. 
  • Thermal delay allows motors to cool down by preventing them from being turned on right away following overloads. If a motor overheats and is then turned back on, it may sustain irreversible damage.