MSA Senscient ELDS 1000 series, Operating Manual

Page: 44 / 184

Installation Design & Engineering
44
Senscient ELDS™
Rev 15
GB
3.3. Electrical Connections
3.3.1 Electrical Installation Design & Engineering Recommendations
All ranges of the Senscient ELDS™ 1000 / 2000 Series comply with the electrical and EMC
requirements of EN50270 and FM6325. In order to maintain compliance with the applicable
standards it is essential that the electrical installation of ELDS™ 1000 / 2000 Series systems is
engineered accordingly.
Electrical installation standards and practices vary between countries, companies and
applications. It is the responsibility of the installation design authority to determine the applicable
standards and practices, and to ensure compliance with them.
CAUTION
In common with other infrared open path gas detectors, ELDS 1000 & 2000 Series OPGDs
require a reliable, stable supply of +24V power in order to operate as intended. Correctly
engineered PSU and cabling arrangements will contribute greatly to the reliability, safety and
availability of ELDS OPGD based gas detection. Save time, money and effort by investing in
quality cabling and quality power supplies.
When designing electrical installations for ELDS™ 1000 / 2000 Series systems, it is recommended
that the installation design authority takes into account the following:
a. In order to comply with the applicable electrical installation standards and practices, the metal
cases of units must be connected to earth / ground. Care should be taken in the design and
engineering of this earth / ground connection to ensure that any electrical noise or voltage
introduced onto a unit’s case is no greater than the levels specified in EN50270.
b. The case earth / ground bonding arrangement must ensure that the maximum transient
voltage between a unit’s case and any field cable conductor is less than 1000V. Voltages in
excess of this may cause permanent damage to the unit.
c. The entire length of the field cabling connected to each unit should be fully shielded /
screened. This shield / screen should be connected to a low noise (clean) earth / ground,
preferably at a single point.
d. The shields / screens of the field cabling should not be connected such that earth / ground
loops are produced, or in a manner that will result in the shields / screens carrying large
currents from heavy plant or equipment.
e. Where the shield / screen of field cabling enters the terminal compartment of an ELDS 1000 /
2000 Series unit, this shield / screen should not be connected to the unit’s earth / ground
terminal and should be prevented from making any contact with the unit’s case. (The unit’s
case will be connected to a local earth / ground which will typically be noisy, and this noise
should not be allowed to get onto the field cable’s shield / screen.)
f. Any electrical interference induced onto the 4-20mA loop conductors by the installation must
be kept below the levels necessary to comply with the general requirements of EN50270. In
practice, this means that peak noise currents induced on the current loop should be no greater
than ±0.25mA.
g. The use of ‘two wire 4-20mA' isolated configurations effectively eliminates the problems
associated with field devices being at different potentials to those in the control room, and
reduces susceptibility to noise and interference pick-up on a 4-20mA loop. Isolated ‘two wire
4-20mA’ configurations are therefore recommended for applications where there is a long
distance between the field device and the control room (e.g. > 750m), or where there are
particularly strong sources of electrical noise and interference (e.g. heavy electrical plant) in
the vicinity.