I just realised I don't really understand earth ground!

[ptricks]

I see, I have worked for a lot of utility engineers and every one has been great to work with.

In Colorado the utilty company's concern stops at the meter, I'm surprised they are complaining about a problem that's technically not yours.

We provide insurance for home owners  against surges for appliances and such and we often have to deny claims when we send out an inspector and see the reason the tv no longer works is because the cable guy did the grounding wrong .  In such cases we tell them to get a lawyer and sue the cable guy.

[IanB]

It isn't unusual to find sites that have the ground from the cable system to the home connected to something metallic that isn't part of the homes grounding or to find ground rods , 1ft long, yes 1 ft, driven in the ground for the cable system because the tech didn't want the work of running a proper ground.

I imagine the cable ground has potential ground loop issues, though? For instance, is the coax shield on the cable a signal ground or a protective ground? And if it is a protective ground, whose ground is it bonded to--the origin or the destination? And if both, what is to prevent loop currents flowing along the coax due to potential differences at each end? I suppose if everything is earthed to the actual ground at multiple points along the line the problem is minimized?

[ptricks]

I imagine the cable ground has potential ground loop issues, though? For instance, is the coax shield on the cable a signal ground or a protective ground? And if it is a protective ground, whose ground is it bonded to--the origin or the destination? And if both, what is to prevent loop currents flowing along the coax due to potential differences at each end? I suppose if everything is earthed to the actual ground at multiple points along the line the problem is minimized?

It is to be grounded at both ends. The idea is to protect from induced voltages. Loops do occur quite a bit and you can find lots of pages on google on how some people have solved them. The easiest would be isolation transformers on the line but those can be problematic as well. Most homes will not have a problem with the grounding but there are always exceptions.

[Monkeh]

I've seen coax turn into white smoke because of ground loops. They should be isolated at the point of installation. But that would cost money...

[TerraHertz]

Speaking of non-electricians not doing things right:

Ha ha! Lawnmower bait.

Because there's not enough confusion in this thread already, everyone should google 'global earth electric currents'.
Current, current everywhere! It's in the air, it's in the ground and oceans... And the entire planet is one plate of a giant capacitor, with the ionized solar wind forming the other conductor. And sometimes, so some people theorize, the planets develop enough voltage differential to arc directly across space between them. There are even claims that has happened within distant human history.

I'd like to see that. While watching from about a light-day away.

[Monkeh]

Speaking of non-electricians not doing things right:
https://lh5.googleusercontent.com/-5iHi0-Q2azw/UWOdL9nhUwI/AAAAAAAACPk/Hwvhy9oDupw/s702/IMG_20130314_141733.jpg

Ha ha! Lawnmower bait.

Not so much, it was originally under 4" of concrete step. Still not where it should be. Now it's under about 3" of block paving.

[xrunner]

Current, current everywhere! It's in the air, it's in the ground and oceans... And the entire planet is one plate of a giant capacitor, with the ionized solar wind forming the other conductor. And sometimes, so some people theorize, the planets develop enough voltage differential to arc directly across space between them.

I am finding some of this information shocking!

[c4757p]

And the entire planet is one plate of a giant capacitor, with the ionized solar wind forming the other conductor.

A "capacitor" is an abstraction, there is capacitance between every two conductive points in the universe.

And sometimes, so some people theorize, the planets develop enough voltage differential to arc directly across space between them. There are even claims that has happened within distant human history.

That seems a bit hokey. Any information on that worth reading?

I'd like to see that. While watching from about a light-day away.

For an arc between planets? I want more distance than that.

[ivan747]

The scary thing is that there's a water heater with the earth lead directly connected to the water pipes inside it.  An electrician came to install a ground lead yesterday, and he bolted it to the service box chassis, but the service box chassis is floating. He says it is grounded because it is embedded into the concrete wall but I wouldn't trust in that (that's not an Ufer ground by any means). The box is floating because the neutral terminals are isolated with a plastic separator.

My advice is to find a copy of your areas electrical code and read through the requirements.

Sure, I'm in the look for a copy of the Dominican electrical code... oh wait, it doesn't exist 

But since we are using the American voltage, frequency, outlets and wiring techniques, I assume we follow NEC.

[TerraHertz]

And the entire planet is one plate of a giant capacitor, with the ionized solar wind forming the other conductor.

A "capacitor" is an abstraction, there is capacitance between every two conductive points in the universe.

This abstraction works remarkably well in a practical sense though, if one 'point' is a sphere weighing 5.972 E24 kg, and the other 'point' is a conductive layer around it (the ionosphere) of surface area:   4 pi [Earth's radius: 6,371 km + atmosphere thickness: 480Km]^2 = 589E6 square Kilometers.

Hmm.... What's the Earth to Ionosphere capacitance in Farads?
  http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capsph.html
  http://hyperphysics.phy-astr.gsu.edu/hbase/electric/diverg.html#c1
  http://en.wikipedia.org/wiki/Relative_permittivity
  http://hyperphysics.phy-astr.gsu.edu/hbase/tables/diel.html

Taking the permittivity of the atmosphere as 1 (dielectric constant of air is very nearly equal vacuum), and working in mks (not 100% confident there) that's  1.143 x 10^9 Farads.

Oh yeah, I definitely would like to whack a screwdriver across that abstraction's terminals. Or a 'space elevator' cable, ha ha.

The net stored charge is a result of integration of long term changes in the flux density of the solar wind, the resulting charge input to the upper atmosphere of solar ions, cosmic rays, and small solid bodies (hundreds of tons of tiny icy and stony meteors each year, all of which carry some charge they accumulated from the solar wind and cosmic rays), and also the overall atmospheric dielectric leakage rate. The pissy little local discharges we know as lightning are just small side effects of this system.
It's worth bearing in mind that electrostatic forces are about 10^36 times stronger than gravity, for equivalent amounts of involved nuclear mass/charge.

And sometimes, so some people theorize, the planets develop enough voltage differential to arc directly across space between them. There are even claims that has happened within distant human history.

That seems a bit hokey. Any information on that worth reading?

Not if you want the effortless 1 minute reading version.
Book: Thunderbolts of the Gods, by David Talbott and Wallace Thornhill.
I guess as a last resort you could try googling something like 'electrical discharges between planets' or 'electric universe'.

One link collection here: http://everist.org/archives/links/!_Electric_Universe_links.txt

[SeanB]

NASA did release an article about the biggest lightning discharge they have seen in a galaxy recently.......

[G7PSK]

I am still thinking about the phase relationship in a center tapped transformer, if you think of the ac power as a rotating battery or rather in this case a pair of rotating batteries going around so first you have positive on top and then negative, if you have a connection between each cell as well as one at the positive and one at the negative you get V1 and V2 you can either run a load at V1 or V2 or a load at V1+V2 now if one of the batteries was 180 degrees out in polarity compared to the other you could still load them at V1 or V2 but if you connected so that you had V1+V2 you would now have positive connected to positive with the result that no power would flow.
The only way that I can square this in my mind with what is being shown on a scope is the scope is not right or rather not being used right, on one or the other trace you need to use the invert button.
Also if you think about the current flow as generated by the magnetic field in the transformer and apply the hand rule to that you realise that unless one half of the center tapped transformer is wound in the opposite direction from the other the power has to all flow in one direction. so the bottom leg at any one moment is at one potential the middle is at a higher potential than the bottom leg but lower than the top leg.

[johnwa]

It only doesn't cancel in a four wire system with 90 degree phase angle.

It does cancel just like three phase if you have two symmetrical phases 180 degrees apart (this is exactly what happens with 120/240 split phase systems) as illustrated below: (however this arrangement does not give continuous power as three phases do)

I agree, the 180 degree case ("split phase" or whatever you want to call it) will reduce/cancel the neutral current. It is possible to run a three wire 90 degree two phase system - this will reduce the current in the neutral, but cannot cancel it entirely (down from 2 * Ip to 1.4142 * Ip IIRC)

I am still thinking about the phase relationship in a center tapped transformer, if you think of the ac power as a rotating battery or rather in this case a pair of rotating batteries going around so first you have positive on top and then negative, if you have a connection between each cell as well as one at the positive and one at the negative you get V1 and V2 you can either run a load at V1 or V2 or a load at V1+V2 now if one of the batteries was 180 degrees out in polarity compared to the other you could still load them at V1 or V2 but if you connected so that you had V1+V2 you would now have positive connected to positive with the result that no power would flow.

The situation as you describe is correct for the first half-cycle G7PSK.(middle circuit diagram). In this state, there is already effectively 180 degrees phase shift, because one supply has its 'negative'/neutral connected to the common neutral, while the other one has its 'positive'/phase connected. On the second half cycle, V2 reverses polarity, as you have drawn in your bottom circuit. But V1 also reverses, so the voltages still sum.

Also if you think about the current flow as generated by the magnetic field in the transformer and apply the hand rule to that you realise that unless one half of the center tapped transformer is wound in the opposite direction from the other the power has to all flow in one direction. so the bottom leg at any one moment is at one potential the middle is at a higher potential than the bottom leg but lower than the top leg

It's not so much a matter of the direction they are wound in, as the way they are connected. One method of manufacture is to wind half of the secondary and bring the wire out to a tap. Then, without cutting the wire, take it back and keep winding the other half of the secondary in the same direction.

Alternatively, you can just have two separate and identical secondaries (possibly both wound at the same time), giving you four ends of the windings. Two of these are connected together, and depending on which two, the voltage at the ends of the combined winding will either add or cancel.

Anyway, it appears that the discussion has been sidetracked into the benefits of various earthing systems. All we need now is for someone to come out in favour of using a floating distribution system, and the sparks will really start to fly!

[Monkeh]

Don't tempt me.

[G7PSK]

In my thought experiment both batteries would turn what I was showing in the third drawing is how the voltage would add up if they were 180 deg. apart.
I have now connected up my scope with small capacitors in the circuit to isolate the earth clips so that I can show all the phase correctly with both halves and the two combined I get a photo showing all three traces at once with all the phase in sync.

[IanB]

I am still thinking about the phase relationship in a center tapped transformer, if you think of the ac power as a rotating battery or rather in this case a pair of rotating batteries going around so first you have positive on top and then negative, if you have a connection between each cell as well as one at the positive and one at the negative you get V1 and V2 you can either run a load at V1 or V2 or a load at V1+V2 now if one of the batteries was 180 degrees out in polarity compared to the other you could still load them at V1 or V2 but if you connected so that you had V1+V2 you would now have positive connected to positive with the result that no power would flow.
The only way that I can square this in my mind with what is being shown on a scope is the scope is not right or rather not being used right, on one or the other trace you need to use the invert button.

You can test this for real with your multimeter using actual batteries. You don't need to imagine the batteries turning; DC will work fine to illustrate polarity.

Place two batteries in series as in your second drawing. Take the middle terminal as the common (neutral or ground) reference point. Measure up to the top battery. Then measure down to the bottom battery. Remember that voltages have a direction (that is what polarity is), so it matters which way round you connect the meter leads. You always want to connect the black lead to the ground point if you are comparing voltages against a common reference.

What you will see is you have a positive voltage and a negative voltage. The difference between the positive and negative voltages is the total voltage. This makes sense because the voltage measured between two points is always a voltage difference, and difference means to subtract.

(If you put the ground point instead at the negative terminal of the bottom battery then the voltage difference would be 3 V - 0 V = 3 V giving the same total difference as you would expect.)

[4to20Milliamps]

not only do we have split phases we also have a split forum topic going.

with AC flowing through a coil the magnetic field expands and contracts according to the amplitude, splitting the coil in half is no different than taking a rotating string and making another node in the middle, the two halves will rotate opposite one another.

[G7PSK]

Hard to do when your battery is spinning around the junction of the two poles. What I was trying to illustrate with the second battery was if you connected them thus (180deg reverse) no power would flow between the end contacts only between one or other end and the center. The same would happen if both halves of the transformer secondary were at opposite by 180 deg power could only flow with the neutral connected and that would have ti be 1.4 times bigger than the other legs, when operating 240 volt equipment the neutral center is not used and therefore you would have a wattless power situation.
Have the same situation in small generators when configuring for 110/220 volts where the windings are switched series/parallel get one winding the wrong way around in 220 configuration and there is no power out get it wrong in 110 and and only smoke comes out.

[4to20Milliamps]

A battery is designed to have an excess or depletion of electrons based on the materials it's made of, a coil of wire isn't, turn it any way you want the only thing that determines it's polarity is the ground connection.

[IanB]

Hard to do when your battery is spinning around the junction of the two poles. What I was trying to illustrate with the second battery was if you connected them thus (180deg reverse) no power would flow between the end contacts only between one or other end and the center. The same would happen if both halves of the transformer secondary were at opposite by 180 deg power could only flow with the neutral connected and that would have ti be 1.4 times bigger than the other legs, when operating 240 volt equipment the neutral center is not used and therefore you would have a wattless power situation.
Have the same situation in small generators when configuring for 110/220 volts where the windings are switched series/parallel get one winding the wrong way around in 220 configuration and there is no power out get it wrong in 110 and and only smoke comes out.

But did you see my picture? Is it showing up OK?

What I showed with the batteries is what happens with the centre tap on a transformer. The batteries don't have to be spinning at all. You can do that experiment with two 1.5 V batteries sitting on your bench. Try it and see, connecting your DMM as I showed. You will find the top battery measures 1.5 V and  the bottom battery measures -1.5 V (which is why the trace appears upside down on the oscilloscope in your other experiment). Yet, obviously if you measure the outer terminals of the batteries you will get 3 V.

[alm]

with AC flowing through a coil the magnetic field expands and contracts according to the amplitude, splitting the coil in half is no different than taking a rotating string and making another node in the middle, the two halves will rotate opposite one another.

A battery is designed to have an excess or depletion of electrons based on the materials it's made of, a coil of wire isn't, turn it any way you want the only thing that determines it's polarity is the ground connection.

OK. Explain this circuit to me:

Source

If polarity does not matter and they will always have 180° phase shift, how does the parallel circuit work? Would reversing the connections of one of the secondaries have any effect?

[G7PSK]

If the phase is 180 deg out compared to the other half of the winding (in other words reversed or opposite in polarity) that means that when the top half is on a positive excursion so is the bottom half with the negative excursions both being the center tap yet you have power at double voltage between the top connection and bottom connection with half voltage on the center. https://www.eevblog.com/forum/Smileys/default/bangheadonwall.gif

[alm]

So parallel operation is impossible? Or you can connect the windings in parallel regardless of their relative orientation?

[IanB]

If the phase is 180 deg out compared to the other half of the winding (in other words reversed or opposite in polarity) that means that when the top half is on a positive excursion so is the bottom half with the negative excursions both being the center tap yet you have power at double voltage between the top connection and bottom connection with half voltage on the center. https://www.eevblog.com/forum/Smileys/default/bangheadonwall.gif

The polarity depends which way round you measure it.

Get a battery, get your DMM. Measure the battery with the red lead on (+) and the black lead on (-). The meter says 1.5 V (ish), right? Now put the red lead on (-) and the black lead on (+). Now what does the meter say? What changed? Did the battery suddenly reverse its polarity, or did you just change how you measured it?

If you swap the connection between two terminals you reverse the polarity. This is the same with a battery as with a transformer winding.

I drew you a picture. I don't know how to make it any clearer.

[4to20Milliamps]

positive in......positive out, no matter which way you turn the current transformer.

http://en.wikipedia.org/wiki/Dot_convention


now add a ground connection and that changes things.