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Safety - The Cable Clamp

First published: 05th December 2009


Mains electricity is dangerous. Electrical work should be performed by a QUALIFIED ELECTRICIAN.

So, if all mains wiring is done by qualified professionals, why are there so many badly-wired plugs and adapters? This article illustrates one common problem (mis-use of the cable clamp), and how it can be fixed. If you notice a plug or adapter with this problem, but are not a qualified electrician, please ask one to fix it for you.

The Problem

The coloured wires can be seen between the fixed end and the cable sheath. In this example (Figure 1), we have a multiway adapter and the three wires (brown, blue and green/yellow) can be seen between the end of the black outer sheath of the cable and the entry into the adapter. This can also happen where cables enter plugs or equipment.

WARNING: Make sure the equipment or device is unplugged before proceeding.

We remove the cover, and can see the cable clamp (Figure 2) over the coloured wires. Why is this a problem? The purpose of the cable clamp is strain relief, when the cable is moved around or pulled, we don't want the conducting wires to be pulled out of their connections or broken. In the worst case, the live wire might be pulled out of the cover, with the risk of electric shock; in any case, if the connection is broken, things stop working.

The Fix

We want the cable clamp to hold onto the outer sheath of the cable - the purpose of the outer sheath is to protect the wires inside. Here, the wires are too long to allow the cable sheath to fit under the cable clamp, so we remove them and shorten them (Figure 3. Note that the end of each wire has been neatly stripped, twisted, and folded. The folding gives a larger, firmer area for the screw to press down on, making a firmer connection (other styles of terminal will need different wire ends).

Fit the wires into the terminals and screw down the cable clamp on the cable sheath (Figure 4).

Finally, replace the cover, all neat and done (Figure 5).

There are many different styles of cable clamp, please understand what you are working on.

A Joke, and Final Warning

What is black and hangs from two wires?

A stupid electrician.

Be careful. Electricity can be dangerous.


Figure 1: A badly-wired adapterFigure 1: A badly-wired adapter hi-res
Figure 2: Inside the adapter, the cable clamp does not hold the cable sheathFigure 2: Inside the adapter, the cable clamp does not hold the cable sheath hi-res
Figure 3: Wire-ends shortened to the correct lengthFigure 3: Wire-ends shortened to the correct length hi-res
Figure 4: cable clamp holding the cable sheathFigure 4: cable clamp holding the cable sheath hi-res
Figure 5: fixed adapter.Figure 5: fixed adapter. hi-res