The thick insulation prevents arcing from the cable to an earthed engine component. In "solid" or "directly" earthed neutral, transformer's star point is directly connected to the ground. They are usually ruggedly packaged, often in metal cases that can be easily grounded/earthed. An example would be a transformer earthed on both the primary and secondary side. By about 1910 the first three-pin earthed (grounded) plugs appeared. The mat would need to be grounded (earthed). When handling these boards, the user must be grounded (earthed). The resistors are great enough to prevent large currents flowing through the earthed infrastructure. The earthed consumer plug has several claimants to its invention. A voltage-sensing ELCB does not sense fault currents from live to any other Earthed body.