How to apply a bending radius correctly?

Cables can be bent, that goes without saying. But if you bend a cable too far, this considerably shortens the lifespan of your cable and you even risk short circuiting and/or causing a fire. On the outside of the bend you have after all 'stretched out' the cable materials too much - they become thinner or perhaps even show cracks - as a result of which the original electrical properties of the conductor insulation are lost.  

So, how do you do it safely?

What is the bending radius of a cable?

The bending radius expresses the smallest possible bend with which one can safely bend a cable without kinking it, damaging it or shortening its life span.  The smaller the bending radius, the shorter bends you can make.

The bending radius is usually expressed as a multiple of the outer diameter of the cable, for example: 4xD or 12xD where "D" is the outer diameter of the cable. Sometimes this is already calculated specifically for your cable and is then expressed as a value in mm. Bending radii vary according to the type of cable and the section. The bending radius that applies to a cable is stated in its technical data sheet.

The bending radii stated always apply at an ambient temperature of (20 ± 10)°C and are always measured at the inner curvature of the cable.

How to correctly apply the bending radius?

The cable should be bent around an imaginary circle whose radius is at least the bending radius of your cable.

How to calculate the bending radius of a section?

Let us take as an example an YMvK Dca 4G95 mm² of which

• bending factor when laying = 10xD
• nominal outer diameter = 41,3 mm (this must always be measured on the cable)
• So: 10 x 41,3 mm = 413 mm.

This 413 mm is the minimum bending radius. The YMvK Dca 4G95 mm² can be bent according to a circle with the smallest permissible radius 413 mm.

Bending radii of standard installation cables for fixed installations

Singe-time bending

For unarmed cables, a reduction of the bending radius by 50% is allowed by the construction standards during installation under the following conditions:

• by a skilled worker
• single-time bending
• the cable is heated up to 30°C
• and cable is bent by means of a template

Can I have my cable follow the angle between the wall and ceiling?

Yes, but only if you respect the bending radius properly. Your cable will then bridge the angle between wall and ceiling. It is not permitted to push the cable as far as possible into the corner to get as little as possible away from the wall and ceiling. What you are doing then is applying a much smaller bending radius than permitted.