Why does multiplying 120 by 1.73 give me 208 volts in a 3 phase system?

In summary, the conversation is about the confusion regarding the voltage in a 120/208 3 phase system. The system has 3 hot leads that are 120 degrees out of phase with each other, and the voltage between two points is equal to the difference in their voltages, not their sum. The calculator may show the answer as 120@60 degrees, but the correct calculation is 120 - 120@120 degrees.
  • #1
Evil Bunny
241
0
Ok... This is a simple question that I'm having a hard time with. I'm forgetting something that I learned and I want to clear it up...

I know that a 120/208 3 phase system has 3 hot leads that are 120 degrees out of phase with each other with respect to the neutral.

If you multiply 120 X 1.73 (square root of three), you get 208 volts. I'm not sure why...

If I add 120 + 120@120 degrees, my calculator tells me the answer is 120@60 degrees.

I expected it to say 208.

Why? What am I getting confused here?
 
Engineering news on Phys.org
  • #2
Hi Evil Bunny. The voltage between two points is equal to the difference in their voltages, not their sum.

Try calculating 120 - 120@120 degrees. :smile:
 
  • #3
Thank you!
 

1. What is 3 phase power?

3 phase power is a type of electrical power transmission that uses three alternating currents with a phase difference of 120 degrees. It is commonly used in industrial and commercial settings.

2. How is 3 phase power different from single phase power?

The main difference between 3 phase and single phase power is the number of alternating currents used. Single phase power only uses one alternating current, while 3 phase power uses three. This allows for a more efficient and balanced distribution of power in 3 phase systems.

3. How do I calculate 3 phase power?

To calculate 3 phase power, you need to know the voltage, current, and power factor of the system. The formula for calculating 3 phase power is P = √3 x V x I x PF, where P is power in watts, V is voltage in volts, I is current in amps, and PF is power factor (typically between 0 and 1).

4. Can I use a regular calculator for 3 phase power calculations?

Yes, you can use a regular calculator for 3 phase power calculations as long as it has the necessary mathematical functions (e.g. square root, multiplication, division). However, there are also specific calculators designed for 3 phase power calculations that may be more convenient and accurate.

5. What are the practical applications of 3 phase power?

3 phase power is commonly used in industrial and commercial settings, such as factories, power plants, and large buildings. It is also used in certain household appliances, such as air conditioners and washing machines.

Similar threads

Using complex numbers to model 3 phase AC
    • Electrical Engineering
Replies
7
Views
1K
Line voltage in 3 phase as single sine wave
    • Electrical Engineering
Replies
15
Views
4K
120 volt to 440 volt 3 phase
    • Electrical Engineering
Replies
14
Views
12K
Find Protective Relays for 3 Phase 120/208 Volt Generator System
    • Electrical Engineering
Replies
1
Views
2K
Single phase AC 3 wire neutral conductor shock potential?
    • Electrical Engineering
Replies
6
Views
2K
Can a generator safely handle full load amps at different power factors?
    • Electrical Engineering
Replies
4
Views
3K
What Does a Three-Phase Stator Without a Neutral or Ground Connection Mean?
    • Electrical Engineering
Replies
12
Views
3K
LV Harmonic Filters for Utility Customer's Power Outages?
    • Electrical Engineering
Replies
16
Views
3K
Sizing 3 Phase motor run capacitors
    • Electrical Engineering
Replies
8
Views
16K
Calculating 208V load, purpose of sqrt(3) and power factor?
    • Electrical Engineering
Replies
11
Views
3K

Hot Threads

Recent Insights

Back
Top