With most applications, 3VA molded case circuit breakers are installed in a fixed position in switchboards or distribution boards. The breaker is normally secured by fastening bolts directly to the mounting plate or other suitable supporting stays of the cubicle. The cables or busbars of the main circuits are connected directly to the 3VA molded case circuit breaker by various terminals or connectors. A rigid, permanent connection is thus created between the 3VA molded case circuit breaker and the cubicle.
With certain applications such as those where regular maintenance and overhaul of circuit breakers is required, for example, it must be possible to replace the 3VA molded case circuit breakers quickly. To meet this requirement, 3VA molded case circuit breakers can be converted to plug-in and draw-out units.
The main differences between plug-in units and draw-out units are convenience of operation and the potential for functional expansion.
Plug-in technology is the less expensive and more space-saving of the two solutions. The 3VA molded case circuit breaker is inserted in the appropriate plug-in socket and fitted with plug-in contacts which make a keyed, friction-locked connection with the corresponding mating contacts (tulip-type contacts) in the plug-in socket. In this case, the device is plugged in and withdrawn manually.
Like the plug-in versions, draw-out versions of 3VA molded case circuit breakers are equipped with plug-in contacts at the main current paths. In addition, side walls including guide and support bolts are bolted to the sides of the 3VA molded case circuit breakers.
In this case, the mating contacts are in the draw-out socket. This is also equipped with a guide mechanism via which the molded case circuit breaker is moved into the draw-out socket by means of a crank handle in order to connect the breaker to the main circuits. The operator can clearly read from a position indicator whether the breaker is properly connected to the main circuits or is 100% safely isolated from them (so that it can be withdrawn).
With plug-in and draw-out circuit breakers, the cables or busbars are connected to the plug-in socket or the draw-out socket. The termination areas for these versions are designed in the same way as those of the molded case circuit breaker, i.e. all the connection technology which is available for 3VA molded case circuit breakers can be used in the same way for the plug-in and draw-out sockets.
3VA plug-in and draw-out units
Plug-in and draw-out technology as it is implemented in 3VA molded case circuit breakers is described below. But 3VA switch disconnectors in MCCB design can also be converted to plug-in or draw-out technology. The information given below therefore applies analogously to 3VA switch disconnectors.
When the 3VA molded case circuit breaker is moved into or out of the socket when the main contacts are closed (breaker position ON), arcs can form between contacts and result in irreparable damage to the circuit breaker or the electrical installation, and possibly cause physical injury to personnel.
Do not move the 3VA molded case circuit breaker into or out of the plug-in socket or the socket of the draw-out unit unless the main contacts are open, i.e. unless the breaker is in the OFF position.
Before moving the molded case circuit breaker into or out of the socket, use the handle to switch it to the OFF position. In order to prevent operating errors, 3VA molded case circuit breakers are equipped with an autotrip plunger when they are converted to plug-in or draw-out units. This plunger automatically trips the circuit breaker (breaker position TRIP) and thus opens the main contacts whenever an attempt is made to move a unit into or out of the socket when the breaker contacts are closed.