1. Electrical Engineering for Physicists How to get from the 208 VAC 3-phase power in the building to 110- and 220-VAC
Code issues
All work must be done in conformance with the National Electrical Code and the Uniform Plumbing Code.
NFPA 70: National Electrical Code

2. National Electric Code
If you don’t know what Code requires
Learn What the Code requires
Hire a licensed electrician.
This applies to all utility issues
Plumbing (gas and water)
Electrical
Phone.
Violating the code is a very bad idea
Unsafe for fire (flood or contamination for plumbing violations)
Unsafe for proper equipment operation
Gets you in trouble with Plant Operations

3. That having been said, simple things you can fix, build or modify yourself. Here’s how!

4. Good reference http://science.howstuffworks.com/power9.htm
Good description of how the electrical power distribution grid works
Source of photos on following slide

5. House Wiring in the US House wiring 220 V, 110 V and ground.
AC or DC? Why? How do you know?

6. Center Tapped Transformer
110 V
Input voltage
Typically 7200 V
220 V
110 V

7. Single Phase Breaker Box

8. Single Phase Feed

9. AC Voltage as a Function of Time

10. For a sinusoidal AC voltage:
In the US, rad/sec
The power delivered to a simple resistive load is given by

11. Average power delivered over some number of cycles (like 1):
T = period =
Knowing the rms voltage allows you to calculate the power delivered to a load without having to do the integral every time!

12. “110 V” House wiring “Hot” conductor “Neutral” conductor
Always black
Potential is sinusoidal
177 V zero-to-peak with respect to neutral
If you touch it with one foot in the bathtub, you will die!
“Neutral” conductor
Always white
Potential within a few volts of ground
Wire carries current “back from device”
“Ground” conductor
Green or bare
Common potential of interconnected water in earth
Ground conductor carries current only in emergency

13. House Wiring “220 V” From center-tapped transformer 110 V
Input voltage
Typically 7200 V
110 V
220 V

14. House Wiring “220 V” From center-tapped transformer
Two hot leads, each 110 V from neutral.
110 V leads are 180 degrees out of phase from each other
No neutral is required for a load that is only 220 V
Common uses
Stove elements
Water heaters
Air conditioners
Hot tubs

15. Center Tapped Transformer
Input voltage
Typically 7200 V
110 V
220 V

16. Expanded Version of “House Wiring”
House wiring.pdf on website

17. Fuses, Breakers and GFIs
Purpose of all: health and safety
Fuse
Contains a metal strip designed to quickly melt if the rated current is exceeded
Melted fuse breaks circuit
Single use
Fuse is ALWAYS inserted into the “hot wire” Why?
Breaker
Same function as fuse but can be reset
GFI (Ground fault interrupter)
Breaks circuit when net current in hot and neutral wires is non-zero
Activate when current flows to ground
Required in bathroom and outdoor applications
Two varieties: in breaker box and in outlet

18. GFI Outlet and Breaker

19. 3-phase Power

20. 3-phase Breaker Box

21. Advantages of 3-phase Power
3-phase motors have higher starting torque, higher efficiency and lower current draw compared to the same size single phase motor.
Usually don’t need capacitors, switches or relays for start-up
Better for heavy duty applications
Stolen from McMaster-Carr catalog, p. 993!

22. All power towers like this have three wires for the three phases
All power towers like this have three wires for the three phases. Many towers, like the ones shown above, have extra wires running along the tops of the towers. These are ground wires and are there primarily in an attempt to attract lightning.

23. Current Capacities of Wires (from some website that looked authentic)
Wire gage
“Chassis” Free Air 12
0.0808
1.588 41
9.3
4150 Hz 13
0.072
1.8288
2.003 35
7.4
5300 Hz 14
0.0641
2.525
8.282 32
5.9
6700 Hz
These are just plain wrong and not by a small factor!

24. This really is Code!
“Young people must
be careful!

25. Field Trip! Investigate a 3-phase breaker box
Measure voltages among phases
Measure voltage from each phase to neutral and ground
Measure voltage of neutral with respect to ground
What is phase difference between two phases?
Investigate properties of volt-, current- and resistance-meters
Digital
Analog
How many ways can you find to get the wrong answer?
Young people must be careful!