Mechatronics – EAS5407 Spring 2003 Kyle I. Platt Class Discussion 2.11

Class Discussion 2.11 Electric Drill Bathtub Experience An electric drill runs on household power and has a metal housing. You use a three-prong-to-two-prong adapter to plug the drill into the wall socket. You are standing in a wet bathtub drilling a hole in the wall. You are unaware that the black wire’s insulation has worn thin and the bare copper black wire is contacting the metal housing of the drill. How have you created a lethal situation for yourself? How could it have been prevented or mitigated?

3 Prong Vs. 2 Prong Neutral Line Hot Line Ground Neutral Line Hot Line

3 Prong Vs. 2 Prong 3 prong plug is most commonly used in household appliances, and most anything that has a metallic surface which interfaces with the operator of the equipment in question. 2 prong plugs should not be used when designing equipment with heavy current loads.

3 Prong Vs. 2 Prong When looking at a wall outlet, or even a plug, One can tell which is the hot line and which is the neutral (return) line. The left hole of an electrical socket is the neutral line. This slot has been designed such that the hot line plug does not have the ability to be plugged into the return line socket.

3 Prong Vs. 2 Prong Danger!!! Do not ever use an adapter which will allow you to plug a 3 prong plug into a 2 prong outlet. The device which you are attempting to use has been designed such that the chassis is grounded. In the class discussion, since the bare wire touched the drill chassis, and the adapter you used prevented the drill’s chassis from being grounded, you just became the ground!

Preventative Action Ground Fault Circuit Interrupter’s (GFCI) When a GFCI either at the local or even the master level, has been installed. A fatal injury has most likely been negated. A GFCI senses the amount of current returning on the neutral line, and if it is not responding properly, the GFCI will ground out, and prevent power transmission through the outlet. This action only takes a matter of milliseconds.