4.2.3 - Flexible low voltage cables and cords
By definition flexible cables have conductors
of cross-sectional area 4 mm² or greater, whilst flexible
cords are sized at 4 mm² or smaller. Quite clearly, the
electrician is nearly always concerned with flexible cords
rather than flexible cables.
{Figure 4.2} shows some
of the many types of flexible cords which are available.
a) Braided circular -
Fig 4.2a
| 1 - oversheath - PVC |
4 - insulation - pvc coloured |
| 2 - braid - plain copper wire |
5 - Conductors - plain Copper |
| 3 - inner sheath - pvc |
|
b) Unkinkable - Fig 4.2b
 |
1 - rubber
layer collectively textile braided semi-embedded |
| 2 -
insulation (Cores) 60°C rubber |
| 3 -conductors - tinned
copper |
c) Circular sheathed - Fig 4.2c
 |
1 - sheath
- rubber or pvc |
| 2 - insulation
60°C rubber or pvc |
| 3 - conductors
- tinned copper |
d) Flat twin sheathed - Fig 4.2d
 |
1 - sheath
- PVC |
| 2 - insulation
- pvc |
| 3 - conductors - plain
copper |
e)
Braided circular insulated with glass fibre - Fig
4.2e
 |
1 - glass
braided overall |
| 2 - insulation
- silicon rubber |
| 3 - conductors - stranded
Copper |
f)
Single core p.v.c. - insulated non-sheathed - Fig
4.2f
 |
1 - insulation
- pvc |
| 2 - conductors - plain
copper |
Flexible cables should not normally be used
for fixed wiring, but if they are, they must be visible
throughout their length. The maximum mass which can be supported
by each flexible cord is listed in (Table 4H3A), part of
which is shown here as (Table 4.2).
| Table 4.2 - Maximum
mass supported by twin flexible cord |
|
Cross-sectional area (mm²)
|
Maximum mass to be supported (kg)
|
|
0.5
|
2
|
|
0.75
|
3
|
|
1.0
|
5
|
|
1.25
|
5
|
|
1.5
|
5
|
The temperature at the cord entry to luminaires
is often very high, especially where filament lamps are
used. It is important that the cable or flexible cord used
for final entry is of a suitable heat resisting type, such
as 150°C rubber- insulated and braided. (Fig 4.3) shows
a short length of such cord used to make the final connection
to a luminaire.
Fig 4.3 - 150°C rubber-insulated
and braided flexible cord used
for the final connection to
a luminaire
|
