Page 298 - Offshore Electrical Engineering Manual

Cable Support Systems 285

Where practicable a minimum segregation distance of 1 m should be maintained.
Crossovers should be kept to a minimum and as near perpendicular as possible. Some
vital circuits associated with fire and gas, emergency shutdown or other safety related
systems may have supply and/or signal cables duplicated. Such cables should be run
on separate routes so that a single fire cannot destroy both cables.

SUPPORT STEELWORK

Drawings showing details of standard steel supports and brackets should be supplied
as part of the design drawing package. If not, perhaps because a particular situation
was not envisaged, then the installer will need to sketch a suitable arrangement and
obtain approval for its use. The work will be made easier if one of the proprietary
steel framing systems such as ‘Unistrut’ or ‘Leprack’ is used.
The steelwork is usually stainless or hot dip galvanised mild steel and should be
free of sharp edges and burrs likely to damage cables. Nuts, bolts, etc. may be stain-
less or cadmium plated mild steel and ISO metric threads should be used throughout.
Once installed, the whole arrangement may be given the standard paint finish before
the cables are installed.
Supports for horizontal tray or rack should be spaced according to the type, width
and estimated maximum loading, but should never exceed 3 m.
Supports for vertical tray or rack should be spaced at approximately 1 m inter-
vals and should provide a clear space between the rack and the structure of at least
400 mm to allow for pipe lagging.
Steel or concrete members forming part of the module or installation structure
must not be drilled or welded to provide a fixing point for supports, unless written
permission has been obtained because such drilling or welding could weaken the
structural integrity or reduce the seaworthiness of the installation.

CABLE TRAY
A variety of different types of cable trays are in use offshore and are made from
a number of different materials. The following are two common types found
offshore.

1. Heavy duty admiralty pattern: This may be stainless steel or high-quality
‘Corten A’ which has been hot dip galvanised several times.
2. Heavy duty reverse flange: This is much stronger mechanically than the
equivalent admiralty pattern because of the doubling over at the edges (reverse
flange). Again the material may be stainless steel or hot dip galvanised Corten
A. Epoxy-coated mild steel types should be avoided, as they will deteriorate
quickly, once any damage to the coating occurs.

TRAY INSTALLATION
The following points should be considered when specifying and installing trays.