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2.3 Control unit installation
The control units should be installed in an area suitable to their specifications. They are designed to
be used indoors, but could be installed outside using a suitable weatherproof enclosure. The front
panel should be accessible to the operator.
The standard control unit MEP*L is installed by undoing the two screws on the top and bottom of the
unit, and removing the base. This can now be mounted as required, making sure that the connection
terminals are on the left-hand side of the base.
The 19” rack unit should be mounted in a suitable cabinet in the usual fashion. It accepts up to
fourteen rack modules to type MEP*R. It should be noted that I.S. control units MEP3R will only fit
into an I.S. rack MEP3B and that the rack is included in the approval. Mounting details are shown on
the previous page.
Allow at least a 50mm gap between each rack on multiple rack installations to allow air circulation.
On installations of multi-rack systems, the fitting of a cabinet air circulating fan is recommended.
Wires to the MEP*B rack units are connected to the terminal blocks mounted on the rear panel of the
rack. In the factory the modules are fitted starting from the left hand side when viewed from the front
of the rack. If desirable, the connectors and modules can be repositioned in the rack. To assist with
cable wiring, the connector block wire access faces the rear of the rack and the screw terminals are
therefore angled. To fit cable to the 5 modules closest to the right hand end of the rack (numbers 10-
14) it is necessary to release the connector and rotate it slightly to allow screwdriver access.
2.4 Wiring
i) Cable
The connection from amplifier to the control unit should be made with two-core twisted pair instrument
cable with overall screen. The cores should be at least 0.5mm
2
and the cable length not more than 1
km, the screen may be omitted on cable runs of 10m or less, provided that the installation will not be
subject to excessive electrical noise.
A summary of wiring arrangements is shown in figure 2.4.
Please consult the factory if this specification does not cover your needs, and for recommended
cables.
Refer to section 2.5 for I.S. requirements
Figure 2.4 - Wiring summary for illustration only
Sensor
Head amplifier
Control unit
35m *Max
(cable supplied with sensor)
MEP*A* and MEP*X*
only
* 15 max on i.s. systems
N.B. Relays are
shown in their
‘normal’
operating states
Do not connect
screen
1km max.
Alarm relay
Fault relay
(MEP*R only)
N.B. Control unit contacts
may not be in the order
illustrated
Cores
Min. area 0.5mm
2
Max loop Impedance 35Ω
Screen
Outer Sheath
Inner Sheaths
SECTION THROUGH CABLE
Supply
Protective
earth
Connect screen at
this end only