Prof. D. Wilton ECE Dept. Notes 5 ECE 2317 Applied Electricity and Magnetism Notes prepared by the EM group, University of Houston.

Grounding Grounding: connecting a conductor to the physical earth Safety reasons Noise reasons equipment water pipe

Grounding (cont.) Ensures that there is no voltage drop between equipment and ground Ensures that there is no electric field outside of equipment Ensures that there is no charge build up on equipment equipment water pipe + - V AB = 0

Grounding (cont.) equipment ground Ground symbol: Note: grounding is NOT is the same thing as a reference point. (However, when a circuit is grounded, the ground is OFTEN chosen as a reference point of zero volts.)

Example reference point (choose 0 [V]) Find: voltage at the ground V G  12 [V] ground A B

Grounding (cont.) ground hot neutral (grounded back at junction box)

Grounding (cont.) ground hot neutral + - V I The neutral wire is grounded back at the junction box. junction box Note: The voltage of the neutral wire at the device is not the same as ground, because the neutral wire has a resistance. wall

Ground Protection ground hot neutral The metal casing of an electrical device is normally connected to ground.

GFCI (Ground Fault Circuit Interrupter) hot neutral IhIh InIn I g = I h - I n GFCI Circuit trips when I g > 5 [mA]

Double Insulated Tool hot neutral IhIh InIn The device is surrounded by an insulating plastic case. It does not require a ground. plastic case