10 MI Cables MI cables shall be t

10 MI Cables

MI cables shall be the heavy duty grade manufactured to BS 5468 comprising high
conductivity copper conductors, embedded in pure and pressure packed magnesium
oxide insulation, contained in a ductile seamless, solid drawn copper sheath.

MI cables shall be supplied and installed strictly in accordance with the maker’s
recommendations and instructions.

Jointing and termination of MI cables shall be carried out using cold seals and all
necessary short brass ring type universal glands, screw on pottype seals, compounds,
coloured neoprene sleeving for phase identification, cone shaped beads, fibre discs,
locknut and purpose made single or multi way, as required, two screw fixing, copper
spacer base saddles and other necessary accessories.

The following purpose made tools shall be provided for the purpose of installing MI

cables and these shall be produced for inspection prior to commencement of work:-

- Set of crimping tools (life limited to approx. 100 operations)

- Set of rotary stripping tools with spare blades

- Pot wrench in various conduit sizes

- Sheath cutter (universal size)

Insulation and continuity test shall be carried out before and after MI cable is installed.
The insulation resistance of a terminated cable should be greater than 100 Megohm
when measure with a 500V or 1000V insulation repeated immediately after sealing.
This test should be repeated not less than 24 hours later. A blow lamp may be used for
drying out cut cable ends if it is impracticable to cut to waste, in which event the cable
should be brought to cherry red heat at about 600 mm from the end of moisture
carefully driven towards the cut end.

Minimum bending radius shall not be less than six times the overall diameter of cable
saddle spacings not less than 60 times the cable diameter and not greater than 750 mm
whichever is the less.

An unsupported loop shall be left in the cable at terminations subject to vibration.

It is absolutely essential that greatest care shall be taken to ensure that hands and all
materials, particularly the compound, are perfectly dry and clean when terminating MI
cables. The length of tails shall be kept to the minimum.

Dirt and metallic particles in the compound and any loose traces of dielectric left at the
fact of the sheath after stripping shall be carefully removed prior to sealing.

Cold sealing compounds shall be forced down one side of the pot and up the other at
the same time ‘overfilling' in order to avoid trapping air at the base of the pot and to
ensure that when the sealing disc is entered before crimping a completely solid
insulation barrier is effected.


Electricians employed for termination of MI cables shall be fully instructed and
experienced in all stages of the operation and work will be stopped, if, in the opinion of
the Architect sufficient care and/or skill is not being exercised particularly in this phase
of the works.

All MI terminations shall be carried out using an earth-tall pot type seal to ensure
effective bonding of non-current carrying metalwork, including switch-boxes, to the
copper sheath of the cable. Reliance shall not be placed on metalwork for earth
continuity and separate copper connections shall be provided for this purpose.

For terminating large single MI cables to equipment, insulated end plates of Tufnol or
equivalent material shall be used.

Due to the low surge strength of MI cable, surge diverters of the gas discharge tube of
Metrosil type shall be installed on all discharge lamps and motor circuits and other
similar circuits where MI cables are used and the Contractor is to ensure that the cables
and other equipment are not damaged due to surges in the system whether caused by
the equipment used or by lightning.
11 Busbar Trunkings & Tap-Off Units (Not in use)