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Utility poles

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Re: Utility poles

#81

Post by dustinmoorenet »

I was looking at the transmission lines one day and was curious about why there are always 4 wires. Basically, 3 lines carry equal voltage phased 120 degrees apart from one another. This kind of power is easily generated from 3 phase power generators at the power plant. The 4th wire is a common return for all three wires. It is normally smaller than any single load wire because, if the power is distributed evenly, no load is carried on it.

The second part of the system, is that, normally, no one customer will use more than one of the three load lines. That is why most houses only have one transformer on the pole out side their house. The power company makes sure they balance connections evenly within a given area. If they do this properly, the common 4th wire has no load on it.

Some buildings do use all three phases, but they would be running large industrial machines that benefit from having that type of power.

I tried to find the Wikipedia article that covered all this, but can't seem to locate it specifically.

Re: Utility poles

#82

Post by [deleted] »

ars wrote: post #68
s_tec wrote: post #41

Regarding three-phase power: The electrical outlets in your home have two power-carrying prongs. The third prong is just for safety (it connects to the ground), and should never carry power unless something is going horribly wrong. In that case, the power should hopefully prefer to reach the ground through that third wire than through your human body. Anyhow, the voltage in those two power-carrying wires is constantl…

> The electrical outlets in your home have two power-carrying prongs. Only one of the prongs carries power. The other is attached to the earth, and is always at zero volts. > and then they will slowly switch places over the next 1/120 of a second so the right wire is at +170 volt No. The power prong (the smaller one) will switch from -170 to +170. The other one (the neutral) is always at zero (measured relative to yo…

[deleted]

Re: Utility poles

#83

Post by aidenn0 »

ars wrote: post #68
s_tec wrote: post #41

Regarding three-phase power: The electrical outlets in your home have two power-carrying prongs. The third prong is just for safety (it connects to the ground), and should never carry power unless something is going horribly wrong. In that case, the power should hopefully prefer to reach the ground through that third wire than through your human body. Anyhow, the voltage in those two power-carrying wires is constantl…

> The electrical outlets in your home have two power-carrying prongs. Only one of the prongs carries power. The other is attached to the earth, and is always at zero volts. > and then they will slowly switch places over the next 1/120 of a second so the right wire is at +170 volt No. The power prong (the smaller one) will switch from -170 to +170. The other one (the neutral) is always at zero (measured relative to yo…

While the second half of your comment is correct:

>> The electrical outlets in your home have two power-carrying prongs.

>Only one of the prongs carries power. The other is attached to the earth, and is always at zero volts.

Voltages are about potential differentials, so "zero volts" is relatively meaningless without context.

The neutral line is required by the electric code to be connected to earth at the electric panel, but even if it were not, any ungrounded appliances would work correctly.

Both prongs absolutely carry power. Slap an ammeter on the neutral line; it should be identical to that on the hot line. Don't actually do this, but if you were to cut the neutral line with a live circuit, you would see sparks. This is particularly important when working on circuits with a shared neutral (two hot lines on alternate halves of the split phase with a single neutral line); despite the breaker being off for your hot line, you can get shocked when working on junction boxes for the neutral line. Yes this is up-to-code in all states (though a few places either recommend or require ganging the circuit breaker when doing so).

>> and then they will slowly switch places over the next 1/120 of a second so the right wire is at +170 volt

> No. The power prong (the smaller one) will switch from -170 to +170. The other one (the neutral) is always at zero (measured relative to you).

Here you use voltages as a relative measure, which is correct. As a nitpick you do assume that the person is grounded. Walking on carpet in the winter, I can be at a potential of thousands of volts away from that though.

[everything from here after in ars's comment is correct and I have no more nitpicks]

Re: Utility poles

#84

Post by Dangeranger »

lovemenot wrote: post #53
Dangeranger wrote: post #25

Earlier quoted context omitted.

Yes, I am intimately familiar with this as this was also part of the services that I was involved in delivering. One of the deliverables for utility clients we provided was every "fall in" or "drop in" line violation for high power transmission lines, including their "between" location in relation to adjacent poles on the corridor. I could talk about this subject for hours so let me know if you have any other questio…

What's a typical range of amperage for a distribution line?

Most distribution transformers have a maximum rating of 200kVA. So depending on their voltage you can calculate the max amps by (200kVA / voltage). Minimum amps is a bit harder to calculate but I would make a best guess of 20% of the max 200kVA.

You can read a bit more about the calculations here[0]

[0] https://yorkcentraltechtalk.wordpress.com/2012/06/27/transfo...

Edit: noted that 200kVA is the maximum rating, not default rating.

Re: Utility poles

#85

Post by throwaway7645 »

joeframbach wrote: post #3

Old utility poles can be reused in many ways too, but they must be outdoors, and not where it can have direct contact with people. Back in 2003 I called a local electric company if they could donate a few used poles to be used as beams for a bridge I was constructing for a local park. They we're happy to oblige. You can sometimes see these poles used in retaining walls and buried alongside hiking trails, used as wate…

They're treated with something called creosote which if it touches your clothes you must burn them. They'll last a good long time though.

Re: Utility poles

#86

Post by agwa »

andyjohnson0 wrote: post #42

A good book on this and related subjects is Infrastructure: The Book of Everything for the Industrial Landscape by Brian Hayes. Published in 2006 so almost certainly out of print, but probably easy enough to get on Amazon or similar.

Thanks for the recommendation; that book looks amazing!

And there's a revised 2014 edition in print: http://industrial-landscape.com/#/buy

Re: Utility poles

#87

Post by limaoscarjuliet »

dnm wrote: post #63
s_tec wrote: post #41

Regarding three-phase power: The electrical outlets in your home have two power-carrying prongs. The third prong is just for safety (it connects to the ground), and should never carry power unless something is going horribly wrong. In that case, the power should hopefully prefer to reach the ground through that third wire than through your human body. Anyhow, the voltage in those two power-carrying wires is constantl…

> the voltage in those two power-carrying wires is constantly switching directions I'm not buying this (in the USA). I've been in my breaker box. For a typical 110 volt outlet, the black (hot) wire is connected to the breaker, which is connected to one of the wires coming into the house from the street. The white (neutral) wire is connected to the same ground bracket that the bare (ground) wire is connected to. 240 v…

There are two phase wires and one neutral. Diff between phases is 240V, the diff between any phase and neutral is 120V.

In Europe, you have three phases (R,S,T) and neutral. Here the diff between any phase and neutral is 250V, and the diff between any two phases is 380V.

Re: Utility poles

#88

Post by throwaway7645 »

Faaak wrote: post #24
sevensor wrote: post #9

Earlier quoted context omitted.

> and not where it can have direct contact with people. Could you expand on that? My elementary school had a playground structure made of old utility poles. Other than getting pitch on our clothes, they didn't seem particularly hazardous.

It may be the same thing as railway sleepers: they are treated with Creosote, which is not a very good chemical

Can confirm they use creosote....nasty nasty stuff.

Re: Utility poles

#89

Post by ars »

aidenn0 wrote: post #83
ars wrote: post #68

Earlier quoted context omitted.

> The electrical outlets in your home have two power-carrying prongs. Only one of the prongs carries power. The other is attached to the earth, and is always at zero volts. > and then they will slowly switch places over the next 1/120 of a second so the right wire is at +170 volt No. The power prong (the smaller one) will switch from -170 to +170. The other one (the neutral) is always at zero (measured relative to yo…

While the second half of your comment is correct: >> The electrical outlets in your home have two power-carrying prongs. >Only one of the prongs carries power. The other is attached to the earth, and is always at zero volts. Voltages are about potential differentials, so "zero volts" is relatively meaningless without context. The neutral line is required by the electric code to be connected to earth at the electric p…

> Both prongs absolutely carry power.

Both carry current. But not power. Power is volts * amps, and the neutral is defined as zero volts (if you ignore the voltage drop).

> you can get shocked when working on junction boxes for the neutral line

Only from the voltage drop on that wire. It's not the full 120v. (Unless it's cut of course, but that's a whole different story.)

> Here you use voltages as a relative measure, which is correct.

First you introduce the concept, then later, explain other less important details. And that's how I wrote it.

> Walking on carpet in the winter, I can be at a potential of thousands of volts away from that though.

It's a good nitpick :)

Re: Utility poles

#90

Post by mindslight »

aidenn0 wrote: post #83
ars wrote: post #68

Earlier quoted context omitted.

> The electrical outlets in your home have two power-carrying prongs. Only one of the prongs carries power. The other is attached to the earth, and is always at zero volts. > and then they will slowly switch places over the next 1/120 of a second so the right wire is at +170 volt No. The power prong (the smaller one) will switch from -170 to +170. The other one (the neutral) is always at zero (measured relative to yo…

While the second half of your comment is correct: >> The electrical outlets in your home have two power-carrying prongs. >Only one of the prongs carries power. The other is attached to the earth, and is always at zero volts. Voltages are about potential differentials, so "zero volts" is relatively meaningless without context. The neutral line is required by the electric code to be connected to earth at the electric p…

> Don't actually do this, but if you were to cut the neutral line with a live circuit, you would see sparks

Only if something were actually drawing moderate current to cause the arc. But yes, one side of that cut is likely to end up "hot" and could give you a decent shock.

(How many levels deep can we nitpick here...)

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