Electrical Install; Detector Electronics Subassembly; Earthing & Screening Requirements - Dräger Flame 5000 Technical Manual

Installation of the Dräger Flame Detector 5000

Electrical Install

Detector Electronics Subassembly

The fi eld wiring is accessed by removing the rear enclosure cover and all terminations are accessible without the need
to access the electronics module mounted in the front portion of the enclosure.
Earthing & Screening Requirements
It is important to ensure that the system is correctly connected to earth. Incorrect or poor earthing can adversely aff ect
system operation and may result in intermittent RS485 communications and poor video image quality.
The system 0V should be connected to a clean earth at only one point; generally this should be at the panel power
supply (or 0V bus bar). Where PC equipment is connected to the RS485 and Video signals, care should be taken
to ensure that the PC's and Panel's power supply are at the same ground potential. Even small diff erences in earth
potentials can cause an earth fault current to fl ow resulting in video corruption. Where this is not possible either the
PC's local supply should be isolated and the PC's connected to the 'system clean earth', or alternatively, the Video and
RS485 signals should be isolated. The Dräger Safety UK Ltd twisted pair to BNC video converter (VTP4) and RS232
to RS485 converter (RS2485IF) can be used so long as the maximum potential diff erence between each earth does
not exceed ±5V, as identifi ed below.
In distributed systems with multiple DC-DC power supply units all 0V supplies must be connected together to a
common clean earth. Where this is not possible each system can either be connected to a local clean earth so long as
the maximum potential diff erence between each earth does not exceed +4 to -1Vdc, alternatively the Video and RS485
signals can be galvanically isolated from the central system. Where earth fault monitoring is used care should be taken
to ensure that the system 0V to earth potential is not exceeded.
The detector enclosure is to be connected to a local earth and the detector cable screens (shields) should be cut back
to the crotch and not terminated within the detector. If the detector enclosure cannot be connected to a local earth
12
WARNING
!
For European (ATEX) installations, IEC/EN60079-14 'Electrical
Installations in Hazardous Areas' and ICE/EN60079-17
'Inspection and Maintenance in Hazardous Areas' should be
strictly observed.
WARNING
!
For installations all Local and International regulations should
be strictly observed.
WARNING
!
The equipment must be properly earthed to protect against
electrical shock and to minimise electrical interference.