Question

How does resistivity relate to the fact that most sets of Christmas lights say not to connect more than 3 strands together?

Answer 1

First of all let us understand...What is Resistivity ??

It is the resistance to the flow of an electric current and while some materials resisting the current flow more than others. It depends on material to material.

Now, when we connect more than 3 strands of light in series, the current which comes out of the battery goes through the first strand before going to second, third and so on. It means the wires in the first couple of strands will likely overheat and melt the insulation. Now Here comes the resistivity part. If we have a material with high resistivity, it can resist the overheating. However, the material used in christmas lights is not of high resistivity and people usually connect strands of wires in series which makes the first strand to bear all the current flowing through.

Now , for example if one bulb in a strand goes out then all other bulbs and strands will stop working as they all are in series. That is why it is recommended not to connect more than 3 strands together.