10
Explosion protection – device description
Regarding the explosion protection the ExResistTel telephone and the
ExResistTel telephone in ZB version are identical.
The explosion protection enables the user to make and receive calls
within hazardous areas of zone 1 and zone 21, in presence of an
explosive gas or dust atmosphere.
The ExResistTel telephone is designed for connection with analogue
telephone networks.
The accessories headset, second earpiece and external secondary
ringer are not parts of the ExResistTel telephone, but optional extras.
The housing of the ExResistTel telephone consists of an electro-
statically 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 16), 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.
