# one last question?

Discussion in 'General Electronics Chat' started by Mathematics!, Feb 27, 2010.

1. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
4
From another post that was locked I have this question

Can anybody give me the reason.
This question is not dangerous and shouldn't be locked.
It's vaild question
why the white neutral has the same potiential as the physical earth.
Must be physically touching ground some where

2. ### rjenkins AAC Fanatic!

Nov 6, 2005
1,015
69
I'm not sure of the formal standards in the USA, but according to the Wikipedia article the Neutral is electrically bonded to earth at each premises' distribution panel or fuseboard.

'Neutral is a circuit conductor (that carries current in normal operation), which is connected to earth (or ground) generally at the service panel with the main disconnecting switch or breaker.'

from http://en.wikipedia.org/wiki/Neutral_wire

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3. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
4
Ok , thanks I figured it out so the white wire coming of the pole is in common with the physical ground somewhere weather at the pole or grounded to the main panel box ,...etc

But does anybody know why they choose to ground them at the pole with a big metal spike and a wire running down the pole ...etc instead of just grounding it at your meter or main panel box.

I know some are and some aren't but is this just optional or is their a purpose or code reason why they do it at some transformer buckets on the pole?

4. ### Ron H AAC Fanatic!

Apr 14, 2005
7,012
681
Every article I found says that every power pole on the planet has a ground wire. The articles explain the reasons for the ground wires.

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5. ### ifixit AAC Fanatic!

Nov 20, 2008
650
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Here in Canada, the neutral is usually grounded at the pole via a ground rod and bonded to the ground rod at main service entrance of the residence.

From the service on into the house the safety ground and neutral are kept seperate and not connected to each other again even though they are equilivent to ground potential.

If overhead lines coming into your house are hit by lightning, it will usually take the shortest path to earth. Since both ends of the neutral are grounded there is a better chance the energy of the lightning bolt will find its way to earth without burning your house down. Yea! for bonding neutral to earth ground.

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6. ### Duane P Wetick AAC Fanatic!

Apr 23, 2009
420
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The ground wire out there on the pole transformer is a must. When a big ice storm knocked down power lines all around here, my father-in-law had some power, but the major appliances would not run. When he looked up at his incoming service, he could see the ground wire was torn off. The power company guys re-connected the ground and all service power was restored.

Cheers, DPW [ Everything has limitations...and I hate limitations.]

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7. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
4
Well, I physical have looked around this transformer pole for the wire that runs down thru the earth. But this pole by me and a few other poles I have seen here and their don't look to have been grounded at the pole?

So much for every transformer at the pole being grounded...
Unless they are grounding it at another pole by using a wire from the transformer pole to another pole and down into the ground that way.
If so then I am all set because their is a pole 5 poles away with a wire that runs down to earth... but not at my transformer pole...

8. ### SgtWookie Expert

Jul 17, 2007
22,201
1,809
If you have a transformer on your pole that does not have a grounded neutral, then ask your power company to fix it.

Otherwise, you are depending on only your individual home ground to protect against problems from other nearby homes that are on the same transformer.

They need to fix the problem. This should be at no direct cost to you.

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9. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
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yes but I see them in alot of different places.
Are you sure they have to be grounded at the specific pole that the transformer is on or could they run a wire from that pole to another pole and down to ground instead?

Also for a typical bucket looking transformer on the power lines to the houses , I have read convert from around 1 to 100kvolts probably 7200volts in usually distribution points on the distribution gride down to 240 volts with a center tap for 120 volts to be obtained.

But I am just curious how many houses could be hosted off of one of these transformers. Basically I know some houses have main panels rated for 150 , 200 amps even seen 300 amp main house breakers.
From this and if some one knows how much the transformer max current ratings are I could approximate how many houses one transformer can support before becoming overloaded...

10. ### SgtWookie Expert

Jul 17, 2007
22,201
1,809
I am NOT a licensed electrician. Therefore, what I write on the subject is mere speculation. If you want a qualified answer, ask a licensed electrician.

It would be my personal preference to have each and every transformer's neutral grounded at every pole. However, I am not a licensed electrician, and therefore not qualified to write anything about the subject with requisite authority.

The power company will install a transformer suitable to power the homes it provides. However, if the neutral is not grounded, it may overload your distribution panel - if your neighbor's house has a more capable panel than yours, and they have a fault.

This is why I suggest that you need the advice of a licensed electrician. I am not a licensed electrician. I have long experience with E&E, but I hold no current licenses, and try to give the best "scoop" I can on here.

And once you get it, don't try to do the same things they do, as you don't have their training.

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11. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
4
The only reason why I ask this transformer question SgtWookie
Is I asked my master electrician and we agreed that they should have one at every pole that a transformer bucket was at. But when I showed him one that had no wire runing down it . Me and him both didn't have a answer why some did and some didn't... we both came to the conclusion that every pole with a transformer that didn't have a grounding wire to earth must have the grounding wire running to another pole which does run down to earth... Just wanted to know if anybody new for sure what is going on with that stuff.

As for the max rating of a the powerline transformer bucket does anybody know what their max rating is.

Since I see streets that have a transformer every house or 2 and then I have seen a street that has maybe one transformer for the whole long street....

Wondering how they calculate how many houses can be supported by a given transformer ...etc
I am thinking it is by amperage ratings for that given transformer...
Like if it was rated for max current of 300amps you could support a few houses off of that... but if it had a rating of 3000amps then you could probably support multiple streets off of it....

Thanks for any clarity

Last edited: Feb 27, 2010
12. ### retched AAC Fanatic!

Dec 5, 2009
5,197
315
When we tap of the 4kv lines around my place of employment, we typically use 200amp. Each building will have 200a service. If that particular building (or house) needs more, a transformer upgrade is in order.

13. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
4
I guess then my current questions are

Question one
The coil ratio determines the amount of voltage step up or down...
But what determines the max current ratings the transformer can supply...

In general for these transformers we can assume power in = power out for a rough approximation which we then can derive the vin/vout = coil ratio

Iin/Iout = 1/coil ratio

But to know the max current a transformer can put out would be to know the input voltage and the power , or to know the input voltage and the internal resistance

My main thing is no matter what transformer you use they will always have the same coil ratio to give the same voltage step up or down....
But what affects the amount of max power or current supported by these devices... (in general what makes these transformers upgrades better and able to support more current output)

Also what happens if you where to short the main line coming into your house before the main panel or meter is their some circuit breaker on the transformer or basically would you fry the transformer and make it so nobody has electric on your street???? ( I would think they would have some protection for the transformer on the pole maybe not though?)

Question 2
I have seen on power lines and big plyon lines these funny tesla coils holding the wires at each pole....what are these for what purpose because I would have just used a metal hook or something to secure it...
so their must be some reason for them... I have seen longer ones and short ones .....etc
They look like this last picture http://images.google.com/imgres?imgurl=http://www.themodernapprentice.com/power_lines9.jpg&imgrefurl=http://www.themodernapprentice.com/electrocution.htm&usg=__rOJP-GyurKBf7pQQ3xz6MZhdPzE=&h=386&w=450&sz=43&hl=en&start=5&um=1&itbs=1&tbnid=F7Mvp1aIuHfX6M:&tbnh=109&tbnw=127&prev=/images%3Fq%3Dpower%2Blines%26um%3D1%26hl%3Den%26sa%3DX%26tbs%3Disch:1

Althougth they say it is for insulation so the pole doesn't become electrically charged or a short is provided....etc
But I thought wood itself wood be a great insulator so why the need but maybe these cermic insulators can insulate better then wood........ wondering what the resistace of those are to the resistance of wood to put it into perspective.

Last edited: Mar 2, 2010
14. ### SgtWookie Expert

Jul 17, 2007
22,201
1,809
You know, you're about 20 or 50 questions over that one question you wanted to ask.

15. ### kubeek Expert

Sep 20, 2005
5,585
1,094
The wire thickness. If the wire is too thin for the current -> has too big resistance -> high power dissipation -> the wire melts

Serisously, try to think for about an hour about the question you want to ask before you dare to post it. That will save us a LOT of other stupid quiestions.

Wood, when completely dry, can be more or less good insulator, up to some breakdown voltage. Now try to imagine the pole sokaing wet. What happens now?
The insulators (the ones you call for some weird reason tesla coils) are made of some stable and "unsoakable" kind of ceramics, so that they are safely insulating at any condition like heavy rain or (melting) ice and snow buildup.

16. ### Ron H AAC Fanatic!

Apr 14, 2005
7,012
681
While I tend to agree with you, it could be that out OP has never picked up a dry 2X4 and then a wet one, or driven a nail into a wet board with a hammer, getting splashed in the face on the final stroke. Anyone who has done this should realize how much water wood can absorb. Anyone even slightly familiar with electricity should know that water (unless distilled) is a good electrical conductor.