In a cable why is the earth wire not coated?

There are assumptions here:

(1) The "earth" wire is an outstanding conductor with low resistivity, and

(2) All the earth conductors are ultimately tied to earth at some point. If it's building wiring, that's usually done in the electrical box providing service into the building. If it's coax cables in a piece of electronics, then it's the power supply neutral point.

(3) It costs less to build a cable without an insulating jacket than one with insulation.

Under these conditions, all earth conductors are at the same potential, so that if they touch, no current will flow between them. Leaving them bare produces no adverse effects at the lowest cost.

Now, obviously, if another bare wire that is not at earth potential contacts an earth conductor, that can result in current flow (a short). One can argue that the earth conductor is as much at fault as the other conductor, but insulting just one of them will serve to protect them from touching.

In actual fact, there is always some resistivity to the earth conductors, and if current flows, a voltage drop will be manifest. There are times when this matters a great deal, such as the control or suppression of noise in electronic systems or medical medical instrumentation when shock hazard can be fatal. However, this is a big topic and a small space like this won't do it justice.

First answer by Purplepentode. Last edit by Purplepentode. Contributor trust: 25 [recommend contributor]. Question popularity: 14 [recommend question]