These old-fashioned radiant heaters are regarded as dangerous these days. The modern convection heaters are much safer. Once I used to use these as a good example of the need for an earth connection. The case has to be made of metal so that it doesn't melt. However if the live connection comes lose and touches the outer case, you would complete the circuit to earth if you touched the case and would get a nasty shock. So the earth wire is soldered to the case. If the live wire comes lose and touches the case, the current follows the route down to earth. It is a low resistance route so the current is high enough to blow the fuse and make the device safe.
