The ELRX-300 are power saving End-of-Line resistors which eliminates the need for an additional battery cabinet or larger batteries in order to meet the 60 hour standby requirement. (Please refer to Battery Calculation Chart in manual for more details.) The ELRX-300 can also be used when larger batteries than can fit in the cabinet are required. The ELRX-300 are available with or without a mounting plate.