Physics 220 Class 39

1
Physics 220 Class 39

• Today you will learn about
• wiring houses
• wire, switches, outlets
• grounding and GFCIs

2
Reminders

• Chapter Test 12 due today
• HW 13 due Dec 14
• Chapter Test 13 due Dec 14

3
Wiring Your Home

• Most of what well discuss today is very applied

4
Wires

• Wires are bundled into cables of three or four
  wires.

ground
hot
neutral
ground
hot
hot
neutral
5
Wires

• Conductors are either copper or aluminum.
• Copper is a better conductor, more flexible, and
  corrodes less.
• Aluminum is cheaper.
• Special components are made for aluminum wires.

6
Wires and Heat EM

• The source of heat is resistance in the wire. A
  length of wire generates heat at the rate

7
Wires and Heat Physics 123

• Heat is lost through conduction

8
Wires and Heat

• The net heat remaining in the wire is

9
Heat and Temperature

• Heat causes a change in temperature

10
Differential Equation

• The equation is
• The solution is

11
Differential Equation

• After a long time, the temperature becomes

12
Two Wires of Different Diameters
13
Copper Wires
14
Wires

• Rough rule of thumb
• Cu can take 4 A/mm2
• Al can take 2.3 A/mm2

15
Switches
16
Switches
17
Switches
18
Switches
19
3-Way Switches
20
3-Way Switches
down
down
21
3-Way Switches
down
up
22
3-Way Switches
up
up
23
3-Way Switches
up
down
24
3-Way Switches
25
Outlets
ground
hot
neutral
26
Series Outlets
27
Series Outlets
28
Parallel Outlets
29
Parallel Outlets
30
Outlets

• Series outlets are easier to wire.
• GFCI outlets are better wired in series, as the
  GFCI works for all downstream outlets.
• However, if the connection to one series outlet
  is bad, the connection affects all downstream
  outlets.

31
No Ground
32
Ground
33
Ground
34
Ground
two resistors in parallel
small resistance
big resistance
35
GFCI

• Ground Fault Circuit Interrupter
• Shuts of power when current in the hot wire is
  different than current in the neutral wire.
• Makes use of a differential transformer.
• Used in kitchens and bathrooms.
• Built into outlets.
• Wired in series.

36
Differential Transformer
neutral wire
hot wire
solenoid switch
37
AFCI

• Arc Fault Circuit Interrupter
• Shuts of power when there is arcing between hot
  wire and ground or neutral wires.
• Used in bedrooms.
• Built into circuit breaker.
• When arcing occurs, spikes, squared waves, etc.,
  are typical. Various methods of detection are
  used.