CLAIMS 1. A low-voltage power circuit breaker comprising: -a first casing accommodating: -at least an electric pole comprising at least a fixed contact and a moving contact, said moving contact coupling/uncoupling with said fixed contact during the closure/opening operations of said low voltage power circuit breaker; and -actuation means operatively connected to said moving contact, said actuation means providing said moving contact with the energy required for coupling/uncoupling with said fixed contact, during the closure/opening operations of said low voltage power circuit breaker; and -a second casing, accomodating protection means for protecting said low- voltage power circuit breaker from abnormal events; characterized in that said first casing and/or said second casing comprise direct coupling means, said direct coupling means being suitable to connect said first casing and said second casing in a modular manner.

2. The low-voltage power circuit breaker, according to claim 1, characterized in that said first casing furthermore accommodates release actuation means, said release actuation means being suitable to cause the separation of said moving contact from said fixed contact in response to an electric fault signal.

3. The low-voltage power circuit breaker, according to claims 1 and 2, characterized in that said protection means are electrically connected to said release actuation means and are suitable to send a fault signal to said release actuation means.

4. The low-voltage power circuit breaker, according to one or more of previous claims, characterized in that said direct coupling means comprise at least an interlocking and sliding arrangement.

5. The low-voltage power circuit breaker, according to claim 4, characterized in that said interlocking and sliding arrangement comprises a plurality of insertion guides, which can be mutually coupled.

6. The low-voltage power circuit breaker, according to claim 5, characterized in that said interlocking and sliding arrangement is of the dovetail type.

7. The low-voltage power circuit breaker, according to one or more of claims from 1 to 3, characterized in that said direct coupling means comprise at least a snap-acting interlocking arrangement.

8. The low-voltage power circuit breaker, according to one or more of the previous claims, characterized in that said first casing and said second casing are made of insulating material.

9. The low-voltage power circuit breaker, according to one or more of the previous claims, characterized in that said protection means comprise one or more protection relays of the electromagnetic type.

10. The low-voltage power circuit breaker, according to one or more of the claims from 1 to 8, characterized in that said protection means comprise one or more protection relays of the electronic type.

11. The low-voltage power circuit breaker according to one or more of claims from 1 to 8, characterized in that said protection means comprise one or more protection relays of the magnetothermal type.

12. The low-voltage power circuit breaker, according to one or more of the previous claims, characterized in that the nominal current value is 160 amperes or less.

13. The low-voltage power circuit breaker, according to one or more of previous claims 1 to 11, characterized in that the width of said first and second casings is 90 mm or less.