Untitled Document

Physics Demo Number: 103

Approximate Run Time: 10 min

Ground Fault Circuit Interrupter Safety Demonstration

Demo Description

Hook a 120VAC circuit up with some exposed bare wires and cause a carefully controlled ground fault in two different ways.

Scientific Principles

Technology can trip circuit breakers safely for ground-fault currents well below human electrocution levels.

Note however that technology cannot protect well against carelessness or stupid behavior when dealing with house or lab voltage supplies!!

Equipment

Portable Ground Fault Circuit Interrupter Unit
Heat Gun as Load for 120VAC outlet
120VAC Cheater Block and wires
Two Three Conductor Extension Cords

Equipment Location

[B-1-5] houses GFI Unit Kit (103)(including the Cheater Block and wires and 27K resistor).
Heat Gun Resides on Workbench [I] behind desk.
A spare Cheater block is in Kit (012) in [B-2-4].
Extension Cords Hang on Ladder Hooks on Wall Behind Desk

Instructions

SAFETY NOTE: ONE MUST BE EXTREMELY CAREFULL OF ALL THE COMPONENTS AND PROCEDURES IN THIS DEMONSTRATION. BARE 120 VAC IS NOT TO BE TAKEN LIGHTLY, IF ONE VALUES HIS BODY PARTS AND LIFE!!!!

A module ,shown in first photo, resides on [B-2-2] in Kit(103).

The second photo shows the basic electrical setup with the heat gun from [I] “plugged” into the red terminals of cheater block via two clip leads.

The terminal block is plugged into the GFI module in the more “sane” manner of dedicated molded wall outlet cord.

The GFI module is plugged into a molded three conductor extension cable in the normal manner.

Finally there is another three conductor extension cable used to provide a ground leg for producing a controlled ground fault.

The third photo provides a closer look at the crucial alligator clip wires and the extension cord grounding leg, complete with an expendable 27K resistor plugged into a neutral pocket of the cords' multiple-outlet end.

Note that there is also a black spade-lug- terminated hookup wire extending out from the hot side of the terminal block.

With the circuit breaker of the GFI module on , and the heat gun running, one may CAREFULLY touch the top resistor pig-tail lead to the bare spade lug to observe the GFI circuit breaker thrown with no sparking at the resistor-spade-lug point of contact.

This illustrates the safe throwing of the 20 amp circuit breaker with only a few milliamps draw through the resistor.

Repeating the process for contact between the bare spade lug and bottom resistor lead , thusly effectively removing the resistance of the resistor from the circuit, is an entirely different matter.

One gets a big ball of fire and flash of light accompanying the contact and subsequent throwing of the GFI 20 amp breaker in the conventional manner.