Cables Flashcards
How should all cables, cores and terminals be marked?
They should be marked for identification purposes by permanent indelible methods. A means of cross referencing should be used. These details should be documented.
How should cable ends be made off?
Crimped terminations are generally preferable to non-crimped as there is less risk of stray strands causing circuit faults and crimped connections are more readily inserted and removed. Crimping tools of the hand ratchet type (hydraulic in large sizes) are to be used. The simple plier type hand tool often results in joint inconsistency.
What is the general rule for core per terminal?
A good general rule to follow is only one wire per terminal. Special conditions of types of terminal may sometimes apply and the manufacturers documentation may need to be referred to.
What provisions are there for re-terminating cables?
Sufficient length of conductor core, particularly where multi-core cables are used, should be left to allow for at least on re-termination.
Small terminal boxes may have inadequate room inside to leave spare cable. In these cases, particularly where instrumentation cables are affected, it is preferable to make an external loop in the cable adjacent to the box.
What should be done with unused cores?
They should not be left unterminated. Where the equipment has not been provided with sufficient terminals to individually terminate and insulate all unused cores, additional terminals are required. The possibility of adding additional terminals into a certified terminal box should be checked with the manufacturer, or it may be included in the box details.
How should intrinsically safe cables be run?
May be run on the same cable as power cables provided that either the intrinsically safe cables or power cables are armoured, metal sheathed or screened. Clear spacing of intrinsically safe cables from power cables is good practice.
What are the restrictions on copper and aluminium conductors?
Copper conductors may be used in any size required. Aluminium conductors are not permitted unless their cross sectional area is at least 16mm2.
What are the colours of power cables?
Phase colours - brown, black, grey
Neutral - blue
Protective conductor - yellow/green.
What conductor insulation should be used for instrument cables?
Normally thermoplastic or elastomeric material, but alternatively MICC can be used. Refer to IEC 60079-14 for more details.
Is armour required?
It is not essential provided that the cables are protected against mechanical damage.
What wire armouring is allowed?
Galvanised steel wire is acceptable for use with multi-core cable.
Can braiding be used?
Braiding may be used, but if aluminium braided cables are used, exposure of lengths of aluminium is to be avoided as if it is in contact with rusty steel, sparking could occur.
Where screening is used to minimise parasitic signal interference, what needs to be done?
It needs to be protected from mechanical damage.
Can single core cables to BS 6724 be used?
No. They are manufactured with aluminium only. Single core cables to BS6346 with non-magnetic steel wire are suitable.
Note: In installations using armoured cables, the armouring is earthed to maintain earthing integrity. Where non-armoured cables are used, earthing integrity may need special consideration and a dedicated earth core may be required. Earthing of steelwork may also require special consideration.
