Page 201 - Offshore Electrical Engineering Manual

188 CHAPTER 1 Notes on Design Project Organization and Documentation

solved in conjunction with the routing of pipework and ventilation ducting in
areas already congested by the process or power equipment itself, the struc-
tural steelwork of the installation and all the other ancillary equipment such as
lighting, communications and instrumentation.
It is no surprise that computer-aided design (CAD) systems are used
extensively for the draughting representation of such areas, so that clashes
between pipework and cable rack routes can hopefully be avoided.
Typical illustrations of cable rack diagrams are shown in Fig. 3.1.3. These
drawings must also identify the width and number of tiers of rack and tray
required between any two adjacent nodes in the cable network. Calculations
must be performed to size this racking based on the following:
a. The degree of segregation required (see PART 2 Chapter 8 on cable

installation).
b. The number and size of cables passing through this section.

c. The allowance to be made for growth in numbers of cables during the
operational life of the tray/rack. This will depend on the location of the
particular section of rack/tray, the age of the installation and the stage
reached in the project, but allowances in the region of 300% have been
known.

d. The dimensions of the space available for the racking. If multitier
racking is necessary, it is important to ensure that there is sufficient
space between each tier for reasonable access. Unless it can be guaran-
teed that all the cables are of small diameter, a minimum of 300 mm is
recommended.
e. The maximum rack loading in kilogram per metre length of rack as quoted

in the manufacturer’s catalogue. The calculation for each section is best
done on a prepared calculation sheet similar to that shown in Fig. 3.1.4.
4. Cable routing diagram
For the smaller less complex systems, racking and cable diagrams may be
combined. However, in the more complex arrangements, it is more informa-
tive to present the information on two or more separate drawings so that the
service, route, identification number, etc., of each cable can be easily identi-
fied. Separate diagrams may be produced for each service, such as power,
instrumentation, communications and fire and gas. The disadvantage with such
separation is that there will be less likelihood of spotting a clash if one exists,
unless an integrated CAD system is being utilised which can identify such
clashes. A typical example of this drawing is shown in Fig. 3.1.5.
5. Equipment schematic and block diagrams
These diagrams would normally be produced by the equipment manufacturer,
but in some cases the manufacturer’s drawings only describe the skid mounted,
factory produced unit. These would need to be supplemented by a block
diagram showing an overview of the whole platform-wide system and also, if
necessary, a comprehensive schematic. Fig. 3.1.6 shows a typical example of
an equipment schematic.