# high voltage power distribution question

Discussion in 'Electrical Forum discussion & Blog' started by kevincw01, Jun 2, 2012.

1. ### kevincw01New Member

Joined:
Jun 2, 2012
Location:
san diego, ca
My neighborhood has a power substation attached too it and there are some very large poles that carry the power to/from from the substation. Each pole has 3 physically separated wires (like this http://imgur.com/uIuUv.jpg )

The other day we had a storm that knocked down a bunch of these metal poles leading away from the substation. I noticed that as a temporary solution the power company installed jumper cables connecting the 3 wires (top to mid and mid to btm). When they did this our power was restored (15hrs later). This confused me because I had always thought that the 3 wires were similar to residential wiring amd represented hot, neutral and ground. But this solution appears to show that they are 3 seperate "hot" sources. Can anyone enlighten me, Im a curious guy...

Last edited: Jun 2, 2012
2. ### jimboPlumber

Joined:
Aug 31, 2004
Location:
San Diego
High voltage transmission is 3 phase... 3 hots, no neutral, no ground.

4. ### kevincw01New Member

Joined:
Jun 2, 2012
Location:
san diego, ca
I thought the purpose of 3 phase was to consilidate 3 power sources on one conductor(each out of phase). Why are the separate for transmission? Im also wondering why they joined them as a temp fix?

5. ### Speedy PeteyLicensed Electrical Contractor

Joined:
Jun 16, 2007
Occupation:
Location:
NY State, USA
This is an extremely deep subject.
Three phase is three hots. Single phase is two (or even one) hots.

Utilities use the earth as a reference, NOT as any kind of safety return or backup.

The VERY high primary voltages are used to transmit the power over very long distances. The three primary lines are then stepped down to usable levels with transformers.

Joined:
May 16, 2008
Yes each of the 3 conductors is out of phase by 120 degrees. Added together you get 360 degrees which is one rotation of the source generator. It is a single power source producing power on 3 conductors. These conductors cannot be bridged together as it would short circuit the generator so I'm not sure what you are seeing.

Your house is wired to only one of the three phases. That voltage has been stepped down to 240V so you can use it. The transformer outside your house also has a center tap on the 240v single phase power going to your home. This is what you think of as the neutral. Any device connected between the center tap and either one of the other two conductors gives you 120V. This is called single split phase power.

Your grounding conductor in your electrical outlets is just a second neutral. Its purpose in life is to provide a second low resistance path for electricity to follow. In the event of a device failure we hope that the power will default to follow the grounding conductor back to the panel and trip the breaker. The ground wiring never leaves your house.

-rick

7. ### kevincw01New Member

Joined:
Jun 2, 2012
Location:
san diego, ca
Ok so I did some research on 3 phase distribution and understand the 3 conductors but I still cant understand why they connected all phases together to temporarily restore power while they repaired the poles.

8. ### kevincw01New Member

Joined:
Jun 2, 2012
Location:
san diego, ca
Oops,didnt see your post rick. nevermind, and thanks everyone.

9. ### Speedy PeteyLicensed Electrical Contractor

Joined:
Jun 16, 2007
Occupation:
Location:
NY State, USA
They probably did that and also grounded them while they work on them dead. This way any uncalled for re-power would trip a breaker.

10. ### jimboPlumber

Joined:
Aug 31, 2004
Location:
San Diego
In about an hour, you went from this """ I thought the purpose of 3 phase was to consilidate 3 power sources on one conductor(each out of phase). Why are the separate for transmission? Im also wondering why they joined them as a temp fix? """"

to this:
With all due respect, may I suggest you stick to plumbing, volley ball, ANYTHING but electricity!

11. ### DonLJack of all trades Master of one

Joined:
Mar 30, 2011
Occupation:
Rocket Scientist
Location:
Houston, TX
That is the correct answer, It is for Safety.

You should win a Prize.

12. ### jwelectricElectrical Contractor/Instructor

Joined:
Jun 14, 2007
Occupation:
Instructor
Location:
North Carolina
One conductor is one phase. There can't be three phases on one conductor