Page 109 - Offshore Electrical Engineering Manual

96 CHAPTER 8 Electric Cables

Table 2.8.1 Recommended Stainless Steel Cleating/Banding Intervals
Maximum Spacing of Stainless Steel Banding
(mm)
Vertical Run (to
Overall Diameter and Type Horizontal Run (to 60 degrees 30 degrees from
of Cable From Horizontal) Vertical)
Single-core cables in trefoil 2000 1500
formation
Multicore cables (above 35 mm 1500 1000
outer diameter)

9. Where trefoil cleats are used for single-core cables, stainless steel banding
should also be fitted for fault current bracing at 1 m intervals, with a band
always located close to each cleat.
10. The positive and negative cables forming a direct current circuit should be run
side by side as far as possible to reduce magnetic effects.
11. Spare cores in multicore cables should be coiled back for future use, not cut
off at the gland.

TRANSITS, GLANDS AND CONNECTORS
Wherever cables have to penetrate a wall or enclosure which must remain gastight
or has a fire protecting function, it will need to be installed using a transit, gland or
connector.

TRANSITS
Transits consist of a steel frame which is welded or bolted on to the wall or floor
where a suitable slot has been cut. Some transit frames are split so that they can be
placed around existing cables without the need for the cables to be reinstalled. Where
the cables pass through the frame, they are individually enclosed in shaped flexible
packing blocks as shown in Fig. 2.8.2. Each layer of cables and surrounding blocks
is anchored into the frame by a stayplate. To fill up any unused space, blank blocks
are inserted and the whole assembly is compressed down by a compression plate
and threaded bolt. The space left at the top is then filled by an end packing which
is fitted with compression bolts to expand sandwiched flexible blocks and complete
the sealing process. The resulting arrangement provides an effective and reusable
method of penetrating a steel bulkhead or deck and can withstand gas pressures of
up to 4 bar. Good fire tightness properties can be obtained when the transits are used
in conjunction with mineral wool or compounds such as Mandolite 25 which cover
the entire fire wall.