External Bell Boxs

All audible warning devices to be fitted to the outside of a building should be housed inside a suitable enclosure (bell box). Bell boxes are generally made from materials such as mild steel, zinc or polycarbonate plastics

TYPE OF EXTERNAL BELL BOXS

Mild steel boxes are the least expensive but rust badly after a few years even with protective coatings such as paint or plastic. However, they are strong and give good protection from tampering.

Zinc boxes will not rust and have a greater strength than mild steel but tend to be rather more expensive.

Polycarbonate plastic of course will not rust and has reasonably good strength, it also has the advantage that it can be moulded into more complex shapes giving a greater variety of types and styles. The cover itself can be made semi-transparent so that the strobe can be fitted inside for greater tamper protection.

The previous diagram shows a view of a typical bell box with the cover removed, inside can be seen the bell and the S.A.B unit (self activating bell unit, see next section). The strobe light is mounted on the top of the box, in this case, but its location is a matter of personal choice. The cover is prevented from being removed by the use of a tamper switch and in some cases another may be fitted to prevent the box being removed from the wall, called a back tamper.

Where possible the wiring should be introduced into the back of the box by drilling through the wall. A drill bit of about 50 cm will be necessary for this. Where this is not possible and the wiring has to be run on the surface of the wall then it is wise to run it in metal tubing to protect it from being damaged.