Difference between disconnector, circuit breaker and load break switch?
The main types of switch are:


Isolator / disconnector. Only suitable for opening at no-load. If you open the switch on load, you'll draw an arc. Cheap.
Load-break switch. Can be opened and closed under load. Cannot make or interrupt fault current.
Circuit breaker. Can be opened and closed under load. Can make and break fault current. Expensive. Generally have heavy, spring-driven mechanisms that operate very forcefully and wear out quickly. Not meant to be operated frequently.
Contactor. A kind of load break switch that is meant to be frequently opened and closed under load, i.e. to control a direct-on-line motor. (Circuit breakers aren't rated for frequent operation - attempting to use a circuit breaker as a contactor will result in rapid wear and failure. See "Utilisation Category".)
Fuse-switch - a switch combined with a fuse. Comes in off-load or load-break types. Common in overhead distribution systems, in the form of the "expulsion drop-out fuse" which can be operated using a hook on the end of a long stick. Provides short-circuit and overload protection.
Fused contactor - A fuse in series with a contactor. The fuse protects the contactor against fault currents which might damage the contactor, by welding its contacts together. (See: "Type 2 co-ordination".) Common for control of HV motors.


The IEC / Australian Standard symbols for these things are as shown below.