MEDC Ex ResistTel - Manual (Page 11)

11
Explosion protection – device construction
The unvarnished housing of the ExResistTel telephone consists of an
electrostatically conductive cast-moulding equipped with a stainless
steel keypad. The keypad front plate contains a display sealed by a
viewing window.
The ZB version comprises no keypad and no display area, but a solid
front plate.
The housing consists of a rectangular lower part, in which there has
been placed a tray for mounting the electronic parts, as well as a
vaulted cover with a keypad.
The cover and the lower part of the housing, divided by a surrounding
seal only, are pressed together by four screws. The cover makes up
both the non-intrinsically safe and the intrinsically safe electrical
enclosure. The electronics circuit board is situated in the tray of the
lower part of the housing, completely embedded in a protective
compound.
Non-intrinsically safe terminals in increased safety:
Protruding from the compound (see connecting diagram on page 17), a
4-pole increased-safety terminal row is intended for connecting the non-
intrinsically safe telephone network (A, B), terminals 13 and 14, as well
for connecting an optional, external, explosion-protected secondary
ringer (Bell shunt1, Bell shunt), terminals 15 and 16.