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Why Ground Split Phase Residential?

by Averagesupernova
Tags: ground, phase, residential, split
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Averagesupernova
#1
Aug22-14, 01:44 PM
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http://forums.mikeholt.com/showthread.php?t=162981

I thought this would be a link worth sharing here on pf. We seem to have heated arguments going on this forum from time to time about which country has the best electrical system. There are some interesting things to read in the above link. I do not post nor am I a member on mikeholt.
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jim hardy
#2
Aug22-14, 06:05 PM
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Interesting discussion there. I'm not a member at Mike Holt either , but i do like his explanations of code and have occasionally quoted him .

I didn't see in it though what i believe is the reason we earth the house side neutral at the pole:

Should a fault connect the transformer's primary(several KV) to its secondary(240V) you want something to disconnect primary power, else you'll have kilovolts floating around inside a residence that's only insulated for hundreds not thousands of volts.
That fault might be a broken primary distribution wire falling onto a secondary
or it might be a transformer internal fault
or it might be a neighborhood cat who got across the terminals while investigating a bird's nest up there.

Solidly earthing the transformer's secondary assures that should it get a dose of several KV from primary side a lot of primary current will flow into earth opening a primary side fuse, which removes those kilovolts from inside your home.
The reason primary current will flow to earth is:
the substation transformer feeding the primary line is also earthed back at the substation. So primary fault current flows into earth and back toward the substation without having to enter your house.

That's why it is important to call the electric company when neighborhood urchins steal that copper wire coming down your pole. It goes from the top where it ties into transformer secondary centertap all the way to bottom of the pole where it's wound into a spiral for good earth contact. It does double duty - it's also a lightning rod.
If it's not there primary voltage and lightning can get to your house.

I looked for a photo of a pole bottom, to no avail. Take note of next pole you see on a truck - bottom end has that coil of earthing wire.
good pictures here, though
http://science.howstuffworks.com/env...rgy/power9.htm





That little bare wire coming down the pole is more important than you might think. Keep an eye on yours.



old jim
FOIWATER
#3
Aug22-14, 08:29 PM
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Was doing some work (residential) the other day, and some ones main ground from the panel wasn't going to the main water shutoff of their house (only determined because house was undergoing major renovations and it was accessible). It was connected to a random part of the water line which is against code, since if any part of the water pipes are removed you lose your main ground, for the reasons that Jim illustrated (you lose continuity to that bare ground wire coming down the pole)

jim hardy
#4
Aug23-14, 05:48 AM
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Why Ground Split Phase Residential?

With more and more water companies going to plastic pipe.....
I like a driven ground rod .
Averagesupernova
#5
Aug23-14, 10:05 AM
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The big deal now seems to be concrete encased electrodes for the main ground. I am coming up to speed on a new house construction these days and that is the only ground required at the building.
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Back to the main discussion about a grounded system vs. a completely isolated system, it was mentioned in the link that it is impossible to guarantee that all parts of a large system will always remain isolated. Jim Hardy, your example of primary to secondary shorts is a perfect example of this that would have horrible consequences.
sophiecentaur
#6
Aug25-14, 04:01 PM
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No one on this thread seems to have mentioned the danger, without a centre earth, that an earth fault on one side will suddenly double the volts on the other side (assuming they were floating fairly symmetrically about Earth potential to start with). It's clearly a good idea to avoid a floating system, in any case. You could imagine all sorts of nasty high volts situations when there are capacitors and switches involved.
Averagesupernova
#7
Aug25-14, 07:44 PM
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Quote Quote by sophiecentaur View Post
No one on this thread seems to have mentioned the danger, without a centre earth, that an earth fault on one side will suddenly double the volts on the other side (assuming they were floating fairly symmetrically about Earth potential to start with). It's clearly a good idea to avoid a floating system, in any case. You could imagine all sorts of nasty high volts situations when there are capacitors and switches involved.
Didn't think it was necessary to repeat what was already said in the link I provided.
foolios
#8
Aug25-14, 08:58 PM
P: 13
The reason primary current will flow to earth is:
the substation transformer feeding the primary line is also earthed back at the substation. So primary fault current flows into earth and back toward the substation without having to enter your house.


Are there dangers/accidents that can occur from this current as it flows along a path back to the substation?
Is it possible for the current to travel along other paths on the way? Doesn't something get toasted along the way? worms, etc?
Averagesupernova
#9
Aug25-14, 09:07 PM
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Quote Quote by foolios View Post
The reason primary current will flow to earth is:
the substation transformer feeding the primary line is also earthed back at the substation. So primary fault current flows into earth and back toward the substation without having to enter your house.


Are there dangers/accidents that can occur from this current as it flows along a path back to the substation?
Is it possible for the current to travel along other paths on the way? Doesn't something get toasted along the way? worms, etc?
Yes. This is why when a person is very near down power lines that are still live you can get shocked just by walking. There is a voltage between your feet. If it is imperative that you move you are supposed to hop with both feet close together or run in such a way so that only one foot is on the ground at a time. Realize this raises the risk of tripping or falling which could give you a shock hand to foot.
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As far as the worms go, I have pulled nightcrawlers (large earthworms used for fishing) out of the ground in this manner. They don't like it and come to the top.
foolios
#10
Aug25-14, 09:40 PM
P: 13
thank u for the explanations


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