46
Reference Manual
00809-0100-4026, Rev HA
Section 4: Electrical Installation
November 2014
Electrical Installation
4.4 Grounding
When wiring the transmitters, the grounding should be completed such that:
The loop is grounded at the power supply.
When transmitters are installed on metal tanks, ensure there is a metal-to-metal
connection between the device and the tank.
If the tank is non-metallic, the housing must be grounded to an earth ground that is
separate from the power supply. The external ground terminal may be used for this
purpose.
If the tank is cathodically protected, the housing must be grounded to an earth ground
that is outside of the cathodic protection system ground. Use the external terminal for
this purpose.
When transient protection terminal block is used, the ground wire should be separate from the
signal wire. Use the external ground terminal.
Make sure grounding is done (including IS ground inside Terminal compartment) according to
Hazardous Locations Certifications, national and local electrical codes.
The most effective transmitter housing grounding method is a direct connection to earth
ground with minimal (< 1 :) impedance.
Note
Grounding the transmitter housing using the threaded conduit connection may not provide a
sufficient ground. The transient protection terminal block will not provide transient protection
unless the transmitter housing is properly grounded. Use the above guidelines to ground the
transmitter housing. Do not run transient protection ground wire with signal wiring; the ground
wire may carry excessive current if a lightning strike occurs.
Note
After installation and commissioning, make sure that no ground currents exist from high
ground potential differences in the installation.
4.5 Cable selection
Use shielded twisted pair wiring for the Rosemount 5400 Series. The cables must be suitable for
the supply voltage and approved for use in hazardous areas, where applicable. For instance, in
the U.S., explosion-proof conduits must be used in the vicinity of the vessel. For the ATEX
flameproof approval version of the Rosemount 5400 Series, suitable conduits with sealing
device or flameproof cable glands must be used depending on local requirements.
Use 18 AWG to 12 AWG wiring to minimize the voltage drop to the transmitter.
For Modbus
®
units (RS-485 bus), the following rules apply:
2 cables are used for communication: 24 AWG shielded twisted pair wiring is
recommended to get an impedance of 120 :
2 cables are used for power: AWG 16-18 cables must be used
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