Case Study - 13A plug

Choosing the right materials at the right price

Component designers do not become rich by choosing unnecessarily expensive materials! So as well as considering the electrical conductivity when choosing materials, we also need to consider the cost. What's the easiest way of considering cost at the same time as making sure we have suitable conductivity?

One way of selecting the best materials would be to look up values for the conductivity (or values for the resistivity - its opposite) in tables for various possible materials: good conductors would have low values of resistivity whereas good insulators would have high values. From a list of suitable materials we could then choose those which are fairly cheap.

However, this method is time consuming and the designer may miss materials which they simply forgot to consider. A much easier method is to plot materials on a chart of electrical resistivity against cost...

Interpreting material selection charts

Polymers are good insulators and not too expensive

Metals are the only good conductors!

Cheap conductors lie nearest to this corner

Cheap insulators lie nearest to this corner

This kind of graph is called a materials selection chart. Note how materials of each class (e.g. metals) form clusters marked here by the shaded regions. The chart makes it easy to identify cheap conductors and the cheap insulators. We can now see why: most of the non-conducting parts in the plug are made from polymers all the plug components requiring good conductivity are metallic and, by expanding the chart, which particular metals might be most suitable

But, this isn't the whole story...