I was thinking about this last night as I fell asleep. I was thinking that if neither of the wires in a single phase system were connected to ground then it would be like using an isolation xmfr. Touching either line and ground wouldn't shock me. But that's not the way we do it so there must be a good reason why not. Thanks, Eric
Current will flow through you to ground whether the power company references ground or not. In the past, I don't know if it's still true, farms would receive just the hot wire. It was up to the user to supply ground.
Because some parts of the electrical grid are at higher voltages (I've got 7200 volts or so coming up my driveway) and if something happened (storm, trees, transformer failure, etc) that shorted part of *that* wire, you might find that your 120 volt outlet was a couple thousand volts hotter than you'd expect.
And probably other reasons.
If current will flow to ground then why does an isolation xmfr protect me? Wouldn't the power company need to have one wire going to ground for me to get shocked?
The iso will prevent hot chassis. If the voltage is sufficient current will find ground.
With that much wire, something's bound to get connected to ground sooner or later. At which point, the other side would become live. And you wouldn't find out about this until you touched it.
Consider the following sequence of events:
Connecting ground to neutral means that a short between live and ground is a short between live and neutral, which will trip a breaker or blow a fuse. A short between neutral and ground will trip a RCD (GFCI) if there is one (but as neutral is already connected to ground not far away, it doesn't make that much difference anyhow).
In some industrial wiring, the phases all float (and when a fault occurs, the plant can keep running). But, when scheduled maintenance day comes around, there MUST be a resolution of that fault: otherwise, a second insulation failure will blow up the transformers...
Home wiring has breakers, and a fault is expected to pop a circuit breaker, giving warning that something must be repaired. Almost all insulation faiures are connections to grounded cases, or structure or plumbing metal, and by code all those must be bonded to the building's grounding system.
Oi. It's complerkated.
This is all from memory -- a search on "history of North American wiring" might find some interesting info.
A long time ago, in a galaxy far, far away, 110V was actually 110V, and the transformer was isolated at the pole, so both legs were floating. Appliances were on 2-wire cords with metal cases and not much isolation, because if there was any one fault -- well, the lines were isolated.
(And the wire was cloth-wrapped or bare, and set on insulators about three to six inches apart -- oh, those musta been the days!)
This ended up causing all sorts of problems when you _did_ get more than one fault, and sometime in the 60's or the 70's they changed over to the current system (perhaps with non-polarized plugs but with ground pins).
The way it's supposed to be done is that neutral is connected to ground at one point, in a way that ground remains at true ground potential, and neutral can float a bit off of that point (it can be several volts off of ground, depending on your setup and what you have turned on).
The ground wire is a safety ground, so that if either power or neutral shorts to ground, you don't greet your ancestors earlier than scheduled. In places where it's considered _really_ important, you're required to use GFI circuit protectors, which sense ground faults (basically, shorts to neutral), and turn the whole thing off.
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com I'm looking for work -- see my website!
Thanks Tim and Nobody. Those two answers really make sense and show how the system evolved. Eric
The power lines could be balanced, 60-0-60 volts line-ground-line. 60 volts is much less dangerous than 120.
The power lines usually run to a lot of houses, so it would be hard to keep the entire subnet truly isolated. The 60-0-60 thing could be done.
The US 240 volt standard is usually 120-0-120, which is safer than the european 240-0 thing.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
Edison was right: we should have a DC distribution system. But mosfet based dc/dc converters and VFD's weren't yet invented in Edison's time.
-- John Larkin Highland Technology, Inc lunatic fringe electronics
On 19 Jul 2016, John Larkin wrote (in article):
Why? Inquiring minds...
235/400 V 3-phase you mean XD ? That's the common arrangement nowadays, 3-phase to each home, but there are places where you haven't, where you have 135/235V delta 3-phase (potentially floating). For the 235/400 systems, N is usually tied to PE, like on your side of the pond.
There are pro's and con's with either voltage system and system frequency. Like, reactive losses are ever so slightly worse at 60 Hz, and from that standpoint a DC system would be super, but switching complicates it.
Resistive losses in wiring are higher at 120V, like for a vanilla household circuit you can't get much higher than 1,800W your side of the pond (assuming 15A breaker), while here, we gets 500W more juice and thinner wiring (assuming 10A breaker).
But I'm not much for voltage/frequency wars, a lot of it has to do with how the grid developed etc and changing the systems would be an undertaking unprecedented in cost and work. If there's anything I'd have the gall to suggest to you 'merkins it's to consider 3-phase to households (120/210-ish) as opposed to split-phase as you have now, I think it would give benefits in terms of power consumption as well as load being even over the phases. And all for just one extra wire.
As to safety, I would say anything above 60-70V or so is inherently dangerous, but the lower you are in voltage the more forgiving it tends to be in terms of small mistakes. I mean, dead shorts at 235 are LOUD, and 400 dead shorts are more or less as loud as gunshots. If anything, living in 235 territory has taught me to respect the authoritae of mains and to design and wire accordingly.
Oh, and don't get me started on my pet peeve of the connectors on this side of the pond...
/Teo.
-- teostupiditydor@algonet.se | for you are good and crunchy with Remove stupidity to reply | ketchup.
Yeah, I can see several advantages to having a DC system, especially with today's electronics. I was reading a while back about some extremely high voltage DC systems used for transferring power from one AC system to another. Pretty complicated rectifying and inverting stations, large and expensive, along with some pretty fancy breakers with systems to extinguish the arc when the breaker blows. But apparently worth it. Eric
It would be quite feasible today. In fact somewhere I know they did use DC, there was this story about s guy using a potato to find out the radio was plugged in backwards and that was why it did not work.
I wonder how the hell to Google that...
If you want to find out about high voltage DC transmission lines then google for 'HVDC transmission lines'.
I have stood under the Pacific Intertie which first came online in 1970
The fact that it is a DC transmission line is very obvious by the use of two conductor bundles instead of the usual three for AC transmission.
If you want to google about the potato, good luck with your search.
Dan
A guy got busted many years ago for stealing power. What he did was to lay a wire parallel to the power lines and pick it up inductively. If you know electronics you know that if anything he was increasing the efficiency of t he transmission line by doing that but the court ruled that anytime you get something for nothing you are stealing.
Funny how that doesn't apply to them or the businesses that bribe them.
My Uncle and cousin tried to magnetize the electric meter to slow it down. With the electric furnace and diodes from shithouse (ESI, and we should not call it that but so what) they told me weird stuff happened. All kinds of funny noises and a few other things.
Actually DC has the advantage of not having inductive losses, and what that guy "stole" was the inductive losses. If he got any current out of it it h elped them, but it did not matter.
My Uncle ? Well he was a RADAR technician in the air force and the a tech s pecialist for Big Blue. He saw them coming, he saw them sticking it up his ass and decided to do something about it. Grampa taught us well.
I am starting to think that with all this G3 and bluetooth ad whatever else , all the radio and TV stations and whatever, you could almost pick up enou gh energy from the air to run a device, or charge it. We are probably getti ng close to the point where an antenna could pick up enough power to slow c harge something.
When I put my hand on the scope probe I almost always get more that 50 volt s P-P. Not much current behind it but all this new shit runs on what, four volts ?
But then, am I stealing power and have to worry about a SWAT team breaking down the front door ?
Incorrect.
It's stealing because it increases the amount of power the utility has to generate.
An inefficient transformer is still a transformer. Drawing current from the secondary increases the current in the primary.
You seem to lack basic electricity. The transmission line was the primary o f a transformer in series with the load. He created secondary. When that s econdary is loaded the impedance of the primary is lower.
All he did was to pick up some of the loss. It would not show up on anyone' s meter, nor would the power company have to generate more, in fact they wo uld have to generate less.
If the story is in fact not a suburban legend I would have liked to argue t he court case. I could make a setup to demonstrate the effect. The jury wou ld have come out with a little bit of education.
Let me ask you this, in a basic audio power amp, how come when the outputs short in blows the main AC fuse on the PRIMARY side of the transformer ? Be cause when you overload the secondary the impedance of the primary drops.
Now the idea of a wire is to pass current. The better it dies that the bett er the wire is. Whatever losses are just lost. Resistive losses are just go ne unless you can use the heat somehow, but this guy was tapping into the i nductive losses.
I have alot of questions about that case and information is very sparse. Fi rst of all, how the hell did he get caught ? Did a busybody neighbor call t he police because he had a wire laying on the ground ? Or did they accident ally come across it while running spectography on a 12 acre cornfield looki ng for a pot plant ? Or did someone know he had no electric service on the property and call the power company and say "He got lights, he got lights".
Not that I doubt it. There is a town in Ohio where someone called the polic e on their neighbor for having a jetski in their driveway. Ironically the n ame of the town is Independence. It is also known as one of the most corrup t place around, and buddy we got some corrupt towns here. Simple revenue ge nerators, and for two or three families.
Another thing, if they pollute my property with their EMI, I have a right t o tap it. If I have a crystal radio, do I owe the radio stations for the po wer to run it ?
Fuck them and the hearse they ride out in.
Right now there are many sensors that are powered by radio waves. Some charge a capacitor and transmit periodically. And there is a passive device that looks through walls to see people by using ambient wifi radiation. See the link:
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