What can the 3VA MMB300 (Maintenance Mode Box) be used for?

MMB300 maintenance mode box

Operating principle of the MMB300 maintenance mode box
The 3VA6 molded case circuit breakers with the electronic trip system ETUs 3-series, 5-series and 8-series can be functionally expanded with an MMB300 maintenance mode box. With the MMB300 maintenance mode box, the Dynamic Arc Sentry mode (DAS mode, chapter Arc energy reduction (Page 81)) of the molded case circuit breaker is activated and the setting parameters for the instantaneous short circuit current Ii and the ground-fault current Ig are set to the lowest setting values of the circuit breaker. This reduces the let-through energy of the molded case circuit breaker under fault conditions. This results in improved protection when personnel is in the vicinity of the installation and the installation is in maintenance mode. This parameter changeover can occur, for example, through a door contact at the switchboard or an externally actuated switch. In addition, a signal lamp or horn, for example, signals when the circuit breaker is in maintenance mode.A series connection of up to eight 3VA6 molded case circuit breakers with the associated MMB300 maintenance mode box is possible.

Configuration of MMB300 with a 3VA6 molded case circuit breaker 

The possible configuration of the MMB300 maintenance mode box with the associated molded case circuit breaker is shown in the following diagram:

Alternatively, up to eight 3VA6 molded case circuit breakers with MMB300 boxes can be connected in series. This ensures that the external status display only signals that maintenance mode is activated when all series-connected molded case circuit breakers are in DAS mode. It is also possible to combine the power supplies. 

For more information on the MMB300 and other 3VA circuit breakers or accessories, refer to the 3VA System Manual: 

https://digitalcontentcenter.compas.siemens-info.com/SIE_IM_3VA6_Systems_Manual.pdf