to the 16th Edition IEE Regulations
   
   
   
 
 

chapter 5
Earthing

chapter 6
Circuits

Cables, conduits and trunking
  4.1 - Cable insulation materials 4.4 - Cable supports, joints and terminations
  4.2 - Cables 4.5 - Cable enclosures
  4.3 - Cable choice 4.6 - Conductor and cable identification


4.4.2 - Cable bends

If an insulated cable is bent too sharply, the insulation and sheath on the inside of the bend will be compressed, whilst that on the outside will be stretched, This can result in damage to the cable as shown in {Fig 4.16}.
The bending factor must be used to assess the minimum acceptable bending radius, values for common cables being given in {Table 4.11}.

Fig 4.16 Damage to cable insulation due to bending

Type of insulation
Overall diameter
Bending factor
p.v.c.
Up to 10mm
3 (2)
p.v.c.
10mm to 25mm
4 (3)
p.v.c.
Over 25mm
6
mineral
any
6 *
The figures in brackets apply to unsheathed single-core stranded p.v.c. cables when installed in conduit, trunking or ducting.
* Mineral insulated cables may be bent at a minimum radius of three cable diameter provided that they will only be bent once.  This is because the copper sheath will ‘work harden’ when bent and is likely to crack if straightened and bent again.

Table 4.11 Bending factors for common cables

The figures in brackets apply to unsheathed single-core stranded p.v.c. cables when installed in conduit, trunking or ducting.

* Mineral insulated cables may be bent at a minimum radius of three cable diameter provided that they will only be bent once.  This is because the copper sheath will ‘work harden’ when bent and is likely to crack if straightened and bent again.

The factor shown in the table is that by which the overall cable diameter {Fig 4.12}
must be multiplied to give the minimum inside radius of the bend. For example,
2.5 mm˛ twin with protective conductor sheathed cable has a cross-section 9.7 mm
x  5.4 mm. Since the Table shows a factor of 3 for this size, the minimum inside
radius of any bend must be 3 x 9.7 = 29.1 mm.

 

 

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Extracted from The Electricians Guide Fifth Edition
by John Whitfield
Published by EPA Press Click Here to order your Copy

Click here for list of abbreviations