Self Activating Bell Units S.A.B.

To help prevent the outside bell unit from being removed from the wall or the bell cable from being cut, a small power supply, called a self activating bell unit (S.A.B. Unit), is fitted inside the bell box. This unit will power the bell/siren for about one hour.

Operation

The principle components of a S.A.B. Unit are a small battery and a switching unit such as a relay, as seen below.

A constant 12VDC supply is taken from the control panel and is connected to a relay such that the relay switch is “open circuit” until the power is removed when the relay switch will become “closed circuit” and thus sound the bell.

The battery used is a rechargeable nickel-cadmium type and is recharged by the 12VDC hold-off voltage from the panel so it is not necessary to replace after use.

WIRING S.A.B. UNITS

There are quite a number of different makes and models of S.A.B units available, however they all operate on the same principle as described on the previous page.

Below is shown a diagram of a universal unit, that is one which can be used in any system.

The following connections to the control panel will be necessary for the unit to operate:

BHO. [BELL HOLD OFF]

The self actuating bell unit requires a constant 12VDC to keep the bell from sounding. This voltage is supplied by the control panel from the 12VDC aux supply, however most panels will have a separate supply marked BHO.

Obviously if the cable is cut the ni-cad battery will take over and ring the bell.

BELL TRIGGER CONNECTION FROM PANEL

This is taken from the external bell output on the panel, and will ring the bell directly when the alarm system activates.

TAMPER

As with all wiring in an alarm system a tamper loop is required, and in this case is terminated at the S.A.B. Unit. This will indicate to the panel if the wire is cut, the tamper switch on the bell box is open op. The 12VDC hold-off is removed.

The diagram on the previous page shows the wiring arrangement between the panel and the S.A.B. Unit. In this case six wires are needed but for most systems this can be reduced to only four. (see over)

TYPICAL S.A.B. WIRING ARRANGEMENT