Electrical Connections - Honeywell Searchline Excel Open-Path Technical Handbook

MAN0530 Issue 09 October 03
2104M0506
3. INSTALLATION AND OPERATION

3.3 ELECTRICAL CONNECTIONS

3.3.1 General
All ranges of Searchline Excel comply with the EMC requirements EN50081 and EN50082. In
order to maintain compliance with these standards it is essential that the electrical installation
of Excel is engineered correctly.
Electrical installation standards vary for different countries, companies and applications and it
is the responsibility of the installation design authority to determine the applicable standards
and ensure compliance with them. When designing electrical installations for Excel, Zellweger
Analytics recommend that the installation design authority considers the following:
a. The unit cases should not, if possible, be connected to electrically noisy (dirty) metalwork or
conductors. Preferably, the case (internally connected to the green/yellow GND wire) should be
connected to a low noise instrument (clean) earth. See also para e. below. In order to facilitate
electrical isolation of the Searchline Excel from a noisy earth an isolation kit is supplied. This kit
should be fitted as standard unless local regulations forbid this.
b. The entire length of the field cabling connected to each unit should be fully shielded. This should be
connected to a low noise (clean) earth.
c. The low noise instrument (clean) earth system should only be connected to safety earth (usually
dirty) at a single point on the entire site/installation. This connection should be made in such a
manner that it does not introduce noise onto the low noise instrument earth. Star earthing
arrangements minimise earth current crosstalk.
d. The shields of the field cabling should not be connected such that earth loops are produced, or in
a manner that will result in the shields carrying large currents from heavy plant or equipment.
e. Ideally, the field cable shield should be connected to the unit s green/yellow GND wire, providing a
single, continuous earth shield. This connection must not be allowed to complete an earth loop.
f. The earth bonding arrangement must ensure that the maximum peak voltage between the unit
case earth and any field cable conductor is less than 350V. Voltages in excess of this can cause
permanent damage to the unit s RFI protection filters.
g. The use of a single, screened cable for each gas detector ensures maximum screening and
minimum crosstalk. Cabling arrangements which use a single cable for connecting a number of
field devices compromise screening, increase the potential for crosstalk and prevent implementation
of true star earthing.
h. 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 EN50054. In practice,
this means that peak noise currents induced on the current loop should be no greater than ±
0.25mA
j. The 0V rail of the control card/control system is directly connected to one side of the 4 - 20mA
current sensing resistor. Electrical noise on this rail is therefore directly connected to the 4 - 20mA
input. In order to avoid additional noise being induced on the 0V rail, it should not be commoned
with the safety earth/ground, which frequently carries a high level of electrical noise.
k. All electrical equipment connected to the gas detector should comply with EN50081 and EN50082.
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Searchline Excel