Relay

A relay normally have 4 connection (two connection for the switch and two for coil)however I can't see how some relay is connected with 10 wires?!

Relays can have numerous contact points. In the case of power contactors (basically a "big" relay), it is the norm to have a dozen or more connections.
  
     
  
It's actually fairly rare to have just a single set of  contacts. 
  
     
  
That dashed line on the Hyd Transfer Relay represents a mechanical connection. All contacts open or close at the same time.
  
 

Is it possible to install contactor in external power supply line without the breaker?Is there any circuit breaker assy that contains a contactor?

You're way out there on all this.

These power systems are designed with differential protection. Reference  rotate.aero/forum/troubleshooting-tips-g...rent-transformer#799

Smaller relays installed in working systems "can" be controlled by circuit breakers, but the CB usually removes power from a complete system. Relays, computer, switches, actuators, lights.....

Some relays actually have a breaker (or over-current sense) built into them. Fuel pump control relays often are this type.

When we're talking external, APU, or generator power..... this is high amperage current. Circuit breakers are used. They are three phase breakers. Any one of the three phases can make them pop open.

Read the link above and visit chapter 24 of your schematic manual. It should be clear how power protection is designed.

 

Just a moment ago, I sent an email attached with pages of the catalogue, equipment list and the wiring diagram regarding APU generator breaker item 607 in IPC that is equivalent to breaker C890&C889 in the equipment list and the wiring diagram as indicated. However item 606 contactor also may be used as per IPC (that is not in WDM equipment list), that is a bit odd, given the differences of the circuit breaker and the contactor you explained thoroughly.

Please refer to  rotate.aero/forum/boeing-737-classic/601...-pitot-heat?start=10