Thermal Magnetic Breakers

2)What is the main difference btw a contactor and a breaker and any clue on how to differentiate them practically?

I'll answer this one first so as get it out of the way. A "Breaker" is a protection device, a Contactor is a control device. There is almost no similarity, other than the fact that electricity passes through them both. It's like asking "What's the different between a fence and a gate?" A contactor alone does not protect and a breaker alone does not control (other than manually, but it's not a good idea).

1)How does a thermal magnetic breaker work? and how will it work when its just a magnetic or thermal breaker?

A Circuit Breaker is a mechanical device that isolates or allows current to flow in a circuit. A handle allows you to open or close the contacts manually. A simple ratchet mechanism holds the spring loaded contacts of the breaker in the Closed position, and if the trip elements are activated, they move the pawl of that ratchet and it lets go, so the springs force the contacts open and interrupt current flow.

A TM breaker has 2 sensing elements to provide protection for the wires from damage caused by excessive current; a Thermal trip element and a Magnetic trip element.

The Thermal element is typically a set of bi-metal strips that heat up slowly as current passes through them. But because they have two metals in them, the metals expand at dissimilar rates and cause the strips to bend (deflect). If there is a long period of excessive current flow, the deflection of any one of those strips will eventually cause a trip and stop the overload by killing power. The "rating" of the circuit breaker is based on the calibration of those trip points, which in turn is based on the damage curve from heating effects on the wires downstream, proven to be the square of the current times time, or I²t. This allows for short intervals of excessive current without false tripping, i.e. when a motor first starts or when a large change in mechanical loading occurs, but if it persists, it will eventually trip.

Magnetic trips are simple little plungers suspended in a magnetic core, around which the power conductor is wound. Under normal current flow, a very small amount of magnetic flux is expressed on the plunger and although it moves, it only moves slightly. But under a Short Circuit condition where there is a sudden steep increase in the current flow, the resulting spike in magnetic force causes the plunger to over-travel, hitting the release pawl of the spring ratchet and allowing the breaker to open. So under all but Short Circuit conditions, the Mag. trips do virtually nothing to protect the circuit.

Together, a TM breaker then has the Mag trips to sense and trip if there is a sudden and extreme current increase, i.e. short, and the Thermals, which although too slow to pick up a short circuit, protect against a long term over current condition.

A "Magnetic Only" circuit breaker, a.k.a. IT (Instantaneous Trip) or MCP (Motor Circuit Protector) is one in which the Thermal elements are non-existent; they were never put in. Their purpose is very narrow; they can ONLY be used in a factory assembled and listed "Combination Motor Starter" where there is a specific tested and listed Thermal Overload Relay already in the circuit. There is no other valid use for that device.

There are other types of "circuit breakers", but I don't know of any that are "Thermal Only" because they would not protect against short circuits, so they would need to have fuses in front of them, and who would want to bother with both?.