Circuir Breaker and Motor Circuit Protector (MCP)

Yes, it does depend on what country you are in, because in different parts of the world the terms have different meanings.

But from the way the OP was worded, I would guess he is in the US, in which case the first response was correct. What we traditionally call a plain "Circuit Breaker" is an MCCB and it is a Thermal-Magnetic Device. Both the thermal trip and the magnetic, or "instantaneous" trip elements are set by the manufacturer and not adjustable. That magnetic setting can be anywhere from 250% to 1000% of the rating of the breaker. In the case of a motor starter, the starting current can be as high as 600% of the motor FLA. This may or may not fit within the tripping range of a standard Thermal-Magnetic circuit breaker. For example letssay you have a 25HP 460V motor, 32A FLA. If you chose a 40A circuit breaker to go in the motor starter, the magnetic trips may be fixed at 400%, or 160A. But the motor may draw 600% of 32A at startup, so that is 192A and the breaker will trip every time you try to turn it on.

So motor starter manufacturers can use what is called an IT (Instantaneous Trip) circuit breaker. An IT breaker has no thermal trip element, because it is only intended to be used as part of a factory assembled motor starter combination which will include a thermal overload relay. Most people are unaware of this, but it is ILLEGAL to use IT breakers in any other fashion that as part of a FACTORY ASSEMBLED motor starter! You can buy them all day long, but that is for replacement only; you cannot use them to build your own motor starter unless you want to go to the expense of having UL test the specific combination of components together, at a cost of about US$20,000. So if you are building your own combination motor starter from scratch, you must use a Thermal Mag. Circuit Breaker, in which case you have to be morecareul about knowing what the trip settings are.

The term "Motor Circuit Protector" (MCP) by the way is actually a registered trade name of Westinghouse, now owned by Eaton. But everyone uses the term indescriminately now to describe IT breakers.

Outside of the US, the term MCP is sometimes used to describe what we call "Motor Starter Protectors" or MSPs. These are thermal-magnetic devices with both the thermal and the magnetic trips being adjustable to be used on motor starter circuits either as a Manual Motor Starter or in combination with a contactor. But these are not typically UL listed for use in the US without having a true UL489 Listed Circuit Breaker somewhere up stream. A few are, and if you are wise enough to know the differences you can do that, but because some are not, you have to be very careful.