Losing neutral in the utility system

[krater]

There is absolutely no basis for evaluating the common North American electrical grounding standard as DIY ("do it yourself"). To suggest such is to assert that utilities do not do their own grounding which could not be further from the truth and neglegts the existence of PLENTY of residential split-phase services which predate modern grounding standards, were not installed to standard to begin with, or were modified because of old wives tales about "stray voltage" and "parallel paths to ground" and do NOT have their own grounding electrode connection, much as it sounds is the case in UK wiring practices.

At one time, in overhead power distribution, it might not have been uncommon for a utility to ground** the neutral of their systems maybe only as often as at one pole every five miles. Then standards were revised and it was done more frequently, maybe every mile. Today's standard is to make this grounding connection at every pole. Why the change? To ensure that zero is still zero at both the top and bottom of every pole, not just at every fiftieth or tenth pole. In order for the system to work (safely) zero has to be zero everywhere. And since transformers are quite often located remotely from the structures they serve, and said structures are often at the same potential as the Earth that surrounds and supports them, most NA utilites like to make sure that the same zero exits at the served structure as does at their transformer coil. The easiest way to ensure this is to connect them with a conductor. After this point on the wiring system the grounded conductor, so called because there has been made an intentional connection to ground on it, becomes separate from the equipment grounding conductor, a nominally non-current-carrying part of the circuit that functions as the backup path for any irregular or objectionable currents. Exactly where a grounding connection can be or is required to be physically made is a matter of regulation but it all works the same in the end.

Grounding and lightning protection are closely related but are done in somewhat different ways and electrical service grounding is not inteded to provide lightning protection specifically as its primary purpose. No conductor exists that can safely dissapate the entirety of an average lighning strike; anyone whos life was "saved" by just enough grounding as to not become a significant current path for a lightning strike is indeed quite lucky. But for a million volts, traversing thousands of feet of air, a short length of wet wooden pole and a very short length (likely 6ft or less) of buried metal connected through a puny wire to said pole some hundred or hundreds of feet away are going to look about the same. Truth is the average ground rod is an awful ground and while one is often better than nothing, two is often "just good enough."

It is my understanding that the main function of a grounding electrode system that is connected to a purpose-built lightning protection system is more or less to make the structure it is placed upon "look shorter", to help eqaualize buildup of gradients that are suspected to give rise to a lightning strike; think of it more as preventative maintenance with a lesser capacity to act as a sacrificial path in the event that lightning still does strike.

** (read: mechanically and electrically connect the circuit conductor with nominal zero potential with respect to ground to a local Earth potential)

 

[sophiecentaur]

There is absolutely no basis for evaluating the common North American electrical grounding standard as DIY

Well, in a number of posts on this thread, US contributors have described what they have done with their own installations. That implies, to me, that people can make far more modifications in the US than would be allowed in UK.
There is a requirement in UK for a connection between all appliance Earths to the company Earth [ Edit: if there is one] and that all conductors and services must be bonded together and to Earth. This Link is one of many that describe the requirements. An overhead, two wire supply is very rare as the layout of housing favours underground feeds to a large number of houses from a three phase transformer on the ground and with a third of the homes supplied with one single phase at 230V. The split phase system does not exist in UK (afaiaa). Large establishments may be fed with three phases. but the Neutral is still not earthed on the premises.
But the points you make relate to the company supply and not to what the customer can do or must do. My only point, throughout is that customers are forbidden to connect Neutral to any Earthed conductor. The Neutral has the same status as the Live, it's just the PD that's different.

 

[jim hardy]

The split phase system does not exist in UK (afaiaa). Large establishments may be fed with three phases. but the Neutral is still not earthed on the premises.

Got it at last...

The pictures in your link make things clear.

US resembles your TN-C-S system in fig 3, which I've annotated here
just we centertap the transformer, bring in both ends and the middle. One more wire.

I note that in both your TN-C-S above and TN-S fig1 you have an all metal path for fault current back to the transformer winding from which it came, as do we. I like your term 'protective conductor", we've called it at various times both "bonding" and "grounding" and that was source of much confusion.

As i said somewhere a few pages back i expect us to move toward a 4 wire residential service feed, separate conductors for neutral and 'protective conductor" as in your TN-S fig 1 but split phase.

Thanks . I'm less worried about you guys now !

old jim

 

[Averagesupernova]

I fail to see why the USA would be seen as a DIY free for all. While it is true ordinary average everyday folks can do electrical work in some circumstances that does not equate to DIHYW (Do It How You Want).

 

[jim hardy]

Well, in fairness to Sophie i did describe a significant DIY foul-up .

 

[Svein]

For a concise description of the various standard power distribution systems, see http://www.electrical-installation.org/enwiki/Characteristics_of_TT,_TN_and_IT_systems.

It contains a description of the traditional power distribution system in Norway (the IT system) and shows why there is no "neutral" (in fact both wires are "live"). "Earth" is solely for protection and is not connected to any of the phases.

 

[jim hardy]

Thanks Svein

We're not so different. Your IT is what we call "Impedance Grounded" and it's widely used in industry. In my power plant even the 120VAC single phase Instrument Power System was that way.

Our residential standard is nearer your TN-S system fig E14 , just we have a split single phase not three. We use RCD's at individual branch or individual receptacles not at service entrance .

I again recommend to interested parties reading IEEE 142 "The Green Book" . It explains the basics so thoroughly that one can see from the drawings what "first principles" the designers had in mind. Doubtless there are other references, i always hark back to that one because it was such an eye-opener for me. I loaned it out to several co-workers who related similar epiphanies . It's always good to start with the basics.

p.s. That Mike Holt link put up by Averagesupernova a page or two back (post 55 if the post numbers still hold)
is really worth reading, it demonstrates just how puzzling neutral problems appear.

Another interesting read: http://forums.mikeholt.com/showthread.php?t=180591

 

[Averagesupernova]

Well, in fairness to Sophie i did describe a significant DIY foul-up .

Yes you did. But that is exactly, and ALL that it was. A foul up. The homeowner INTENDED to do it the correct way. My perception of sophies opinion, and my perception may be off, is that it is somehow acceptable to not adhere to much of a standard at all in the USA. It is quite the opposite.

 

[Averagesupernova]

The rising voltage caused by a poor neutral brought back a memory of something. A little off the subject but I will share it anyway. 20 years ago or more I had a clock radio with the incandescent pilot bulb that illuminated the scale for tuning. On the same outlet the radio was plugged into I had a small florescent desk lamp plugged in. This radio would increase in volume and the pilot lamp would get brighter when the florescent desk lamp was turned on. So one day I clear the room out for painting. Cover plates all removed on switches and outlets, etc. Plug the vacuum cleaner into the same outlet that the radio was plugged into to clean something up and sparks flew like crazy out of that outlet box when I turned the cleaner on. The receptacle was replaced and the poor connection was now gone and now the radio and florescent desk lamp lived in harmony.
-
Edit: Forgot to mention this was NOT in any way a shared neutral situation.

 

[sophiecentaur]

I realize that the US is not Dodge City where EE is concerned but I have to say that my experience of PF posts is that many more US contributors seem to talk about DIY experiences of domestic electricity situations than UK members. That may reflect a difference in the background of members on the two sides of the ocean. Or there may be more US EE members. It may even be something to do with style of presentation.
I wasn't actually using DIY in a purgoritive sense so please don't take offence, anyone.
I do find that many people in the U.K. are reluctant even to remove a plug too. I get my attitude from my Dad who was in the business and I treat the stuff with both care and confidence at the same time. Any time I do a circuit mod, I like to think I do the work to the same standard as a paid sparks.
The variations around the World are fascinating.

 

[jim hardy]

My perception of sophies opinion, and my perception may be off, is that it is somehow acceptable to not adhere to much of a standard at all in the USA. It is quite the opposite.

Quite so, well said.

I took it as a British ethnic joke poking fun at "the colonies'. Even Mary Poppins did that ,

Mr. Dawes Jr: In 1773, an official on this bank unwisely loaned a large sum of money to finance a shipment of tea to the American colonies. Do you know what happened?
George: Yes, sir, I think I do. As the ship lay in Boston Harbor, a party of the colonists dressed as red Indians boarded the vessel, behaved very rudely, and threw all the tea overboard, making the tea unsuitable for drinking. ... Even for Americans.

Where i live is quite rural. In most of the country the homeowner would have had to get a permit and inspections.
We're an anachronism, it's still like the 1950's around here. It's assumed you'll do the right thing.
I called my electric company,. They were fine with me pulling my own meter to do some repairs on the wall behind it, and said if i need it disconnected at the pole while i work just call and they'd send out a crew to do that for me. Try THAT in a big city !

old jim

 

[sophiecentaur]

I think we should all do an 'exchange' with someone 'on the other side' and have a play with our respective systems and do a bit of installation, with a certificated sparks to supervise. That would be interesting. The two systems really are poles apart, in many senses.

Apart from the (perceived) higher voltage involved in the UK, I can't fault it. The (expensive) plugs and sockets are a bit on the clunky side for smaller appliances but they are very confidence inspiring - nice thick brass pins and nearly all plugs are moulded these days. Individual and appropriate fuses mean that the ring will often stay on whilst a faulty appliance will be isolated by its own fuse.
US members are worried about the 230V but the history of shock injury in UK is very sparse. This will be because the perceived risk is greater. People are just more careful, I guess. 'The Ringmain' is viewed with deep suspicion in the US but it has (afaiaa) very few problems and is a cheap way to provide an unlimited number of outlets around the walls of your home, with only two or three (maximum) circuits needed in most homes.
The US split phase system worries me and I don't think it would be good for the present distribution in the UK. https://www.physicsforums.com/threads/losing-neutral-in-the-utility-system.886787/members/averagesupernova.7949/ 's problem with a poor neutral connection could be shared with every third house in the street, with the two anti phase volts drifting up and down to accommodate the imbalance. I haven't managed to see any advantage with the split phase arrangement - except backwards compatibility with old installations and appliances.

I took it as a British ethnic joke poking fun at "the colonies'.

lol. As someone with what you guys still refer to as a "Tyrannical Government", I can appreciate your sensitivities to that sort of thing but the only US citizens I know personally are really quite nicely behaved and above reproach.

 

[jim hardy]

I can appreciate your sensitivities to that sort of thing

Sensitivities ?
I'm not offended. My roots are in the US's Southern Ozarks, "Li'l Abner" country , where self deprecating humor is respected.

this belongs in Youtube classics :


i was hillbilly before it was cool, and have remained so long after...

I think we should all do an 'exchange' with someone 'on the other side' and have a play with our respective systems and do a bit of installation, with a certificated sparks to supervise. That would be interesting.

That would be fascinating. You really get to know somebody by working with them, and i suppose that's part of the lure of PF. We work together vicariously through the third party of the forum..
I'm still chewing on concept of "Magnetic Vector Potential", many thanks to @dlgoff and @vanhees71 ... One develops a feeling of kinship here.

old jim

 

[krater]

The main issue with the DIY perception is the implication that a utility, should one request, will happily leave three wires hanging from a pole with taped-up ends, and a homeowner, electrician, or otherwise can happily do what they want just as long as they send a check every month. To the contrary one is required to file a legal affidavit with some utilities saying that a service which is to be connected complies with all applicable rules of said utility as well as any other locally enforced codes. Anyone desiring to do things their own way can DIY all the way to the prime mover (or alternate). Even then it is quite possible to be violation of the local law.

A google search reports estimates of roughly a hundred million homes and five million commercial buildings in the United States. There are maybe a quarter as many homes in Great Britain and probably many fewer commercial and industrial premises. The United Kingdom clocks in at something under a hundred thousand square miles, the greater USA places some distance over 3.5 million. Imagine the disparity the average inspector might have between two given jurisdictions and you can begin to understand the disparity between inside wiremen on both sides of the Atlantic.

Jim's tale of you-pull-it as applied to a meter was once more or less the rule, albeit a somewhat dangerous one, even if you didn't call and ask. Now that meters have become far smarter, pulling a live meter can be a good way to get a line truck to show up at your house within an hour as the utility sees your service go offline.

Jim, does your utility do "live metering", where the arrangement is xfmr-meter-disconnect-mainbus? If so, then I'm more than a little surprised the utility gave you blessing to remove it. As you said though, out in the styx...

...repeat after me...NO...LOADS...CONNECTED...*click*!

EDIT: "Live" metering confused with "Dead" metering. Subtle but crucial...

 

[krater]

Now then, time for a few of my own tales of the elusive neutral conductor:

One day, several years ago, I was called to the top of an emerging parking structure to check out an electrical problem. The rodbusters were building their PT deck and were being "nailed" by their cable stressing machine, which entailed maybe a half-horse hydraulic pump, attached to a tank and ram, contained within a wheelbarrow. When someone touched the metal case of the stressing machine while simultaneously touching another piece of ambient metal, one would possibly receive a hell of a jolt while the machine was running.

The cause? It was easily traced to the temporary construction service to the project, whose main purpose was to provide electric baseboard heat to the GC superintendant trailer during the winter months, with a backboard-mounted 240/120v single-phase service fed from a pole-mounted transformer that was located some three or four hundred feet away from the main disconnect. The two meager eight-foot copper-clad-alloy ground rods driven into several feet of pollution abatement sand fill was a poor substitute for the very, very good Earth reference that was located some couple thousand feet of (minimally sized) conductor away, in the form of about sixteen size ten or eleven reinforcing bars which were connected to structural pylons sunk one hundred eighty feet into the bedrock of "the big river".

The solution? Disconnect and insulate the equipment ground. The "neutral" was much too heavily leaking to "ground" far after the main disconnect.

The several hundred or so permanently connected amps we had running around this complex were fed through locally grounded systems which were interconnected via thousands of feet of buried, bare, AWG 3/0 copper which probably provided a better ground plane reference than any of the "grounding electrode systems" that we installed onsite.

Fun fact of NA wiring: the term "neutral" has been systematically removed from NFPA70 : National Electrical Code as of the last couple code cycles, and ubiquitously termed "grounded conductor." Terminoligly can be very important in this discussion.

 

[krater]

...I haven't managed to see any advantage with the split phase arrangement - except backwards compatibility with old installations and appliances.

That's like saying that nobody is making 120VAC motors anymore except for backwards compatibility, when 120V systems are widely available. If everybody said tomorrow, there will be no more except 200V motors, your argument would have creedence. However, should you ask ANSI, OSHA, ect, one hundred twenty volts to ground is still a commonly acceptable maximum potential to ground than any given operator should be regularly exposed to. Your RCDs on the east side of the Atlantic seem to correspond to what electricians on the NA side call "ground fault protection for equipmnent." This is a fuzzy term that can range up to thousands of amps. However, a GFCI Class A on this side of the pond corresponds to a device interrupting at FIVE MILLIAMPS... take a look again at your crazy ring arrangement!

 

[sophiecentaur]

That's like saying that nobody is making 120VAC motors anymore except for backwards compatibility, when 120V systems are widely available.

I know my comment was the sort of comment Historians make, to explain some past event - or the present situation. It was speculative. of course but our whole lives revolve around the status quo. There is very little pressure for the US to change to the higher voltage system so why should they change? But, given the choice of starting with 230V, it would make a lot of sense. 110V uses more copper and it clearly is not suitable for high power appliances (you only use it for small appliances) but you have millions of homes with 110V wiring and appliances are sold for use at that voltage. That is what I meant by backwards compatibility.
The 'safety' aspect for the 110V system was probably a lot more relevant when the original choice was made and wiring used rubber and cotton insulation etc.. PVC and other plastics are so much better for strength and durability and, as I have already commented, shock accidents are extremely rare in the UK.
I think you would have rioting in the streets in the US if there was a move to change.

 

[sophiecentaur]

When someone touched the metal case of the stressing machine while simultaneously touching another piece of ambient metal, one would possibly receive a hell of a jolt while the machine was running.

That sort of accident can only happen when the temporary or permanent installation are not right. A system with a Live and Neutral conductor can be covered with an RCD and that will detect whenever there is an imbalanced current. Whatever is done about bonding other metal structures together and to the local Earth, an RCD will protect users. The only possible objection to active protection like an RCD is reliability. That argument would stop us using ABS in motor cars and fly by wire aircraft and it is a non-starter these days.

 

[krater]

That sort of accident can only happen when the temporary or permanent installation are not right. A system with a Live and Neutral conductor can be covered with an RCD and that will detect whenever there is an imbalanced current.

In this case an RCD, as well as the GFCI that actually did exist somewhere along the circuit was useless. The stray current was coming from the connection between the utility neutral and the equipment ground. The neutral currents at the main were not finding a good enough path back due to inadequate grounding and said current was taking all available paths to ground, as always, and one of those existed between the equipment ground and the steel of remotely located foundation columns.

GFCI/RCD watches for L-N imbalance but is indifferent to what happens on the equipment ground. Also the only device which would have had any chance to catch the imbalance would be the main which as I understand would not be an RCD even in Europe. It is important to remember as well that should you be unfortunate enough to wind up between the line and neutral of a circuit while you are relatively well insulated from ground (think dry wood floor), a GFCI/RCD will happily cook you as from its point of view you are totally indistinguishable from a load. Injury from electric shock is a function of current and duration. Higher voltage = more current = a close call at low voltage is a death sentance at a higher voltage. This is all before we address the issue of reliability; ABS braking systems and aircraft are systems are normally well monitored and maintained. When is the last time YOU tested your RCD/GFCI? If it wasn't manufactured in the last decade or so it probably lacks any self-diagnostic or failure indication capacity. I personally don't put that sort of faith in (especially electro-)mechanical devices.

The resources angle is a good one to point out since a lower voltage is obviously a tradeoff that requires larger conductors. No doubt mineral scarcity carries more weight for nations that don't have millions of acres of mine sites within their own borders. I wonder, at what point would any savings in material from only requiring half the amps to power equipment be outstripped by the replacement cost in resources to junk all the old low volt stuff and manufacture everybody a new fridge, TV, all new wall plugs, ect. My guess, that point is long, long gone.

I think any riots over a new system voltage would be marked by large crowds all carrying signs that simply read, "WHY?"

EDIT: Another point from the safety side. Power limited operator circuits have been moved to ever decreasing voltages as the cost of installing relatively tiny, isolated control circuits in appliances has been matched with the increase in safety afforded by only placing 24, 12, or even fewer volts in close contact with a potential operator. In other words, even though 120v is accepted as safe enough, it is widely recognized that, put plainly, lower is safer. Do you really think anyone would incurr the added cost of a low volt power limited control circuit that doesn't expose an operator to mains voltage if it had no safety benefit whatsoever?

 

[sophiecentaur]

signs that simply read, "WHY?"

One very good reason is in that described incident, which would not occur in the UK system. If the wiring involves no connection between Neutral and earth, downstream, then an inadequate (HR) Neutral (or an inadequate Live - same status) would give an output with Volts that would dip whenever a load was added and 'someone' would be aware of the problem. A user who ignores lights dipping has only himself to blame, if there is no good reason for it - and only the supply company can advise him that "it's ok in this premises". An RCD cannot be operated if the neutral current, downstream, is shared with an Earth because there will be a built-in current imbalance.
As far as I can see, the reason for the move to 12V and lower for appliances is due to the fact that an increasing number of appliances can be operated from batteries or car systems. The gauge of cable needed for 12V heating and other power devices would make it very unattractive. Who would want a 3kW electric kettle, working at 12V? The cord/flex would be incredibly fat / heavy and connector contacts would need to be maintained regularly to make sure they were adequate.
I can't understand the apparent obsession for wanting the Neutral to have a local connection to earth. I have already made the point that the Neutral conductor has the same status as the live conductor so why not treat it in the same way? The 220V circuits in US houses have two conductors that are treated with the same 'respect' so why should the Neutral be different. If the circuits that carry power are completely isolated from the local Ground (define it as zero potential) and all non-electrical metal is bonded to that, then what is done with the Neutral, somewhere up the line is not relevant to the safety situation on site. Systems that require power to be carried through the Earth may have their place but I cannot see where they should come in for house wiring. What is the advantage?

. take a look again at your crazy ring arrangement!

That is just being Xenophobic. It is a very safe (and cheap) way to provide many outlets around every room, without the need for multi-way adaptors, long leads to appliances and many star radials, run in parallel to every outlet around the wall. You don't appear to understand much about the rationale behind the design and have just taken against it because it is unfamiliar. One of the reasons that it is successful in the UK is that the regulations are tight and level of inspection is pretty stringent. The clunky connectors are something we all get used to and they are not an issue. Read around about it and you could even grow to love it!
Your comment on the available range of RCDs is hardly more relevant to the situation than saying that fuses exist from 10mA to 1kA so they are of no use; they have to be selected for the purpose.

 

[krater]

One very good reason is in that described incident, which would not occur in the UK system. If the wiring involves no connection between Neutral and earth...

You're most likely incorrect. If I understand what was pointed out elsewhere in the thread, the "protective earth" or equipment ground as it is properly called are simply connected on the utility's side, and not the customer's. The connection still exists. Unless one presumes some sort of magical infallibility to the design of the utility's system there is absolutely no reason the exact circumstances cannot occur. Think, in the noted example would the same phenomenon have existed if the utility's transformer was so well grounded that virtually no current found a return path along any other means? You note yourself that you can observe a slight potential difference between PE and neutral. Imagine if the nearest spot they were connected together was thousands of feet away electrically. Not good. The nonexistance of mains level RCD means nothing is done to mitigate the hazard.

Your comment on the available range of RCDs is hardly more relevant to the situation than saying that fuses exist from 10mA to 1kA so they are of no use; they have to be selected for the purpose.

5mA is a personnel protection standard widely recognized in NA and elsewhere, from what I'm seeing your equal is 30mA and we are talking at twice the voltage, meaning it can get through twice the path resistance. Ventricular fibulation occurs between 50-100mA and this is why in NA the 30mA standard is considered for equipment protection only and is insufficient to protect people from electric shock. You call me xenophobic, I call you reckless and where does it get us? But go ahead and argue how a smaller tolerance is somehow less safe.

 

[sophiecentaur]

You note yourself that you can observe a slight potential difference between PE and neutral.

Yes. In the same way that your two split phase lines show a large voltage to local ground. It isn't particularly relevant.
Suppose, hypothetically, the company were to supply you with three wires. one with 120V, one with 10V, in phase with the first and one with 100V 180° in phase and they also give you an Earth conductor at 0V relative to the spike in your garden. What would be the problem? You can connect 220V and 110V equipment as normal. The earthed water and gas pipes etc would be bonded to the incoming Earth conductor and also to the spike. Your protection equipment in the house would be quite happy with it and, should there be a path to Earth, through an equipment case (with, of course, an Earth wire), there is no danger of shock. A fuse might blow if the path resistance is low enough but an RCD will also have operated. If the supply company do not happen to have a 'good' earth, your RCD will still operate whilst a fuse may not blow (no problem). The only possible problem would be if the company neutral was disconnected AND there happened to be a connection between your local neutral and your Earth conductor due to a fault within the house. The latter fault would have already tripped an RCD but, if there were no such connection in the house, the supply would have been interrupted. A nuisance situation but not a hazard.
By allowing the possibility of Earth return as an allowable condition, it would be possible for the neutral interruption to go unnoticed and for a dangerous potential to exist somewhere amongst the Earth network.
It strikes me that the Neutral path to the transformer is treated less 'reverently' than the other two paths and that seems to have meant that neutral is not designed to the same standard. No one would be surprised if one of the live cables came into contact with the ground and you had problems so what's the inherent difference? IS it just to do with cost?

 

[sophiecentaur]

5mA is a personnel protection standard widely recognized in NA and elsewhere, from what I'm seeing your equal is 30mA

Is this relevant to the neutral problem?
I agree that there is quite a difference and I have no idea why two different specs are applied, bearing in mind that both will have been arrived at after looking at a lot of statistics from accident data. (Pity we can't subject humans to a more rigorous study of the effects of shock. If we could, then a more reliable figure could be used. haha)
I remember a similar set of information was found to indicate the decompression times for diving at depth. But the naval divers who supplied the information were more like guinea pigs because they were actually ordered to explore the envelope. Likewise, I seem to remember being told that American (I think) soldiers were used to establish the relative risks of exposure to nuclear weapons by getting them to stand at various distances from test explosions and then studying their health over their subsequent time in the army. Drug testing has been done, using convicts, in various parts of the world. So much for Ethics.
The difference between the figures could represent something about the statistics about the difference between overall risk that each system poses. Or it could be just figures, snatched from the air - like the recommended alcohol and salt intakes. You can bet the guy who actually took the decision knew very little about health or engineering. He should have been a member of PF.

The connection still exists.

(Earth / neutral)
Of course there is a connection because, if there were not some defined potential to earth, there would be the possibility of the three phases and neutral from a transformer drifting out to any, unspecified potential - kVs even. The neutral of the transformer only needs to be loosely 'moored' somewhere in the region of 0V, rather than tied up hard to a cleat in the electrical sea.
I asked, higher up, for opinions about the pros and cons of local N/E connection, rather than just one connection back at the substation and no one offered one. I always assumed that a floating neutral ensured a better balance between the supply volts at each (single phase) consumer along the line and less I²R losses.

 

[sophiecentaur]

You call me xenophobic, I call you reckless and where does it get us?

OK let's not fall out about this. The ring system confuses pretty well everyone who hasn't used it. The diagrams in many UK school books are actually wrong. What is true is that it is very successful, with very few 'incidents'. You cannot have a star system at the same cost, to provide the useful number of outlets that you find in most UK homes and offices. Hence, it continues to get my vote.
AS for RCD's, you pays yer money and you takes yer pick. I guess I might feel a bit safer with a lower cut out current but I would probably get very cross about the increased number of spurious trips. Hardly "reckless" though. Perhaps, as I get older, I may be more susceptible to cardiac arrest with a fault current of 30mA - we shall see.

 

[krater]

Well the one point I would like to make would be your theorized 10V main lead. What happens when you get between it and the 0V protective earth? Of course current will flow. If you are part of this current path it can be, well, uncomfortable. Even if, say, a resistance of just the right value might fall between the two lines, it could involve enough current to create enough heat to start a fire.

I think where a lot of the difference in perception comes from is the way OCP is handled in the two situations and really has little to do with how many grounded or ungrounded lines are coming in, and at what potential. First off, let me point out that especially until recently there was not commonly an equal to the RCD found in NA branch circuit panelboards. Beginning in the 1990s standards came about to require ground fault protection for personnel in selected areas, most often where someone is likely to encounter electricity and moisture or moist, well-grounded surfaces at the same time. This was normally handled at point of use, or the receptacle (plug-in, outlet maybe...the thing the prongs go in. Terminology!).

There were a few reasons why normally the preferred route. Sometimes due to what's called multiwire circuiting it was not possible to install a panelboard device that could watch current going out and coming back on the pair comprising a circuit, and rewiring would have been necessary. Also, at the time the already costly GFCI devices were especially costly in circuit breaker form, maybe three to five times the price. Either way it was usually most economical to install the few receptacles needed in the bathrooms and kitchens than to install even one GFCI breaker.

Here's where I'm going with this as it relates to the local grounding electrode. Aside from places where one stood at a decently high risk for a shock, the only sort of current monitoring on a general use branch circuit was the relatively dumb thermal-magnetic trip unit in the 15 or 20 amp breaker, connected in series with the ungrounded conductor or "hot". Nothing watched, let alone interrupted the neutral no matter how much current flowed on it, or where for that matter. This did pretty well in keeping wires from melting. It didn't do much for shock hazard though, but since the system was designed with one conductor referenced at 0V to ground anyway, it made sense to create a local connection to ground potential via a grounding electrode system and connect that 0V conductor to it.

Another reason this makes sense is that it gives transients on the line as well as potential fault currents between ungrounded conductors and either grounded or grounding conductors another path to facilitate the clearing of some device meant to interrupt the fault. If the only paths to and from the transformer are the wires comprising the transformer's secondary it has some implications for eletromagnetic choke effects that could hinder an OCP sufficiently that the circuit conductors could fail before the circuit was broken. You still talk of Earth return as if it is used as a normal current flow path which has been depreciated for quite some time. However under a fault condition, with respect to paths for current return, more is better.

You seem to get the impression that the neutral has a depreciated place in the circuit hierarchy; I would say we just use it to its fullest potential, pardon the pun. You won't convince me that letting a neutral float to arbitrary height from a local ground is OK so long as some electronic device is upstream from me that will *try* to break the circuit if it senses something is amiss. What happens if that device fails? Better hope you're only floating a couple volts above ground. Better also hope that your zero connection at the transformer is quite solid as your role as a parallel path is defined by all the other paths available. And you better hope that no situation ever comes along where amps, wire length and electromagnetism conspire in such a way that some large number of amps find a way out around your main and get "three stooges syndrome" on the way back to the transformer. I don't like designing things with the hopes that nothing breaks and everything will just keep working fine...

That argument...is a non-starter these days.

As far as the 5mA protective standard it actually has more to do with children whos smaller bodies are more succeptable to shock than an average adult. So we figure that if the adult safety value is 50mA, then one order of magnitude less should be more than safe for everybody. I would imagine there has been quite a lot of human research of some form relating to electric shock due to its very, very wide range of applications. Do you suppose research done to develop pacemakers for example would be somewhat relevant to designing a device made to actually protect the heart from shock? I certainly would.

I don't agree with your dismissive attitude towards the development of GFCI personnel standards. This stuff wasn't handed down by the king or written up by "the guy" you speak of, it was developed by multiple groups of people, entites, and industries, who form a consensus standard. And I can't understand why you would expect some increase in spurious trips. First of all if no fault exists that let's current out of the circuit why should anything trip, ever? And secondly, do you not realize that scores and scores of 5mA GFCI devices are in use every day, even on things like vending machines? What, do you think someone has to go around and reset GFCIs every week or two so that they can ensure their sodas are still selling?

 

[sophiecentaur]

You are being a bit over-protective about the system you are familiar with. 'Different' doesn't necessarily mean 'better' or 'worse'. I am not 'attacking' your neutral = Earth system. Rather I am casting doubt on it and I want to hear a good argument in favourite of it. I really haven't heard one yet - except that it is established practice so there's no point in changing.

What happens when you get between it and the 0V protective earth?

What happens if you get between any non-zero potential conductor and earth? The system should not be exposing you to the possibility of touching neutral or live sides.

This was normally handled at point of use, or the receptacle

As in the UK (you have introduced another thing here, which is just confusing the main issue). Electric Showers and outdoor (garden) outlets are protected by RCDs. ('power breakers' etc)

the only sort of current monitoring on a general use branch circuit was the relatively dumb thermal-magnetic trip unit in the 15 or 20 amp breaker,

That was used in UK where the Earth resistance was too high for many faults to blow a fuse. If you can't measure the imbalanced current (i.e. years ago) that's all you can do. It protects against fire, only.

You seem to get the impression that the neutral has a depreciated place in the circuit hierarchy;

From the fact that you seem to regard the Earth conductor as a possible backup for the neutral circuit, I would say that is precisely the situation with your neutral circuit. How about using the Earth as a possible return path for the live? Obviously a nonsense idea because, by definition, the neutral potential is 'safer'. It is not unheard of for systems to use two floating power conductors. Which one would you choose for the Earth return then?

As far as the 5mA protective standard it actually has more to do with children whos smaller bodies are more succeptable to shock

You keep bringing in extra issues. The tripping current is decided upon by a committee, on the basis of statistics and total cost - same as many other 'recommended levels' throughout our lives. There will be many other factors taken into consideration and, despite what you think, the decision is made 'on balance'. As it happens, the US decided on a different value to the chosen UK value. I doubt that you have read all the committee papers and you really can't know the arguments used to justified the chosen levels. Yes; the US standard is tighter than the UK standard but what statistical effect does it have? Data is needed here and not a gut reaction. I would also 'feel' safer with a 5mA level, of course. Perceived danger is very important to us.

First of all if no fault exists that let's current out of the circuit why should anything trip, ever?

In an ideal world, you are right but elements in ageing water heaters are notorious for small but finite Earth currents. There is always the possibility of an unbalanced current at switch on. Google "Spurious RCD trips". It's a rich vein of information.

 

[sophiecentaur]

Even if, say, a resistance of just the right value might fall between the two lines, it could involve enough current to create enough heat to start a fire.

I just re-read this. Isn't the fuse supposed to deal with that?

 

[jim hardy]

When someone touched the metal case of the stressing machine while simultaneously touching another piece of ambient metal, one would possibly receive a hell of a jolt while the machine was running.

The cause? It was easily traced to the temporary construction service to the project, whose main purpose was to provide electric baseboard heat to the GC superintendant trailer during the winter months, with a backboard-mounted 240/120v single-phase service fed from a pole-mounted transformer that was located some three or four hundred feet away from the main disconnect. The two meager eight-foot copper-clad-alloy ground rods driven into several feet of pollution abatement sand fill was a poor substitute for the very, very good Earth reference that was located some couple thousand feet of (minimally sized) conductor away, in the form of about sixteen size ten or eleven reinforcing bars which were connected to structural pylons sunk one hundred eighty feet into the bedrock of "the big river".

The solution? Disconnect and insulate the equipment ground. The "neutral" was much too heavily leaking to "ground" far after the main disconnect.

A picture would help me understand that one.
Had there been an all metal path for fault current to flow between that machine and the"separately derived system" 's transformer winding at construction service , which code requires, (even if that path were just the neutral conductor, ) the guys could not have experienced more than the voltage drop along that all metal path..

Seems to me something was elevating local Earth potential atop that garage so by disconnecting those ground rods you isolated your rodbusters from whatever that was.

 

[sophiecentaur]

A picture would help me understand that one.

Definitely. It strikes me that, if the neutral was high resistance, there would / should have been visible effects like dipping lights when a motor / heater was turned on etc..
I know you guys could take offence again but the described scenario (affairs) seems so random that I can't imagine that setup occurring in the UK. (Could be my rosy tinted spectacles, of course). Construction site setups are the highest risk*, of course and that's why they have transformers all over the place, special connectors for everything and 110V appliances.
*Next to rock concert stages.

 

[jim hardy]

I know you guys could take offence again but the described scenario (affairs) seems so random that I can't imagine that setup occurring in the UK. (Could be my rosy tinted spectacles, of course). Construction site setups are the highest risk*, of course and that's why they have transformers all over the place, special connectors for everything and 110V appliances.

Well, going back to that link you posted in #62(if numbers still hold)
you and we should have an all metal path back to the transformer winding from which the current originates.

The two meager eight-foot copper-clad-alloy ground rods driven into several feet of pollution abatement sand fill was a poor substitute for the very, very good Earth reference that was located some couple thousand feet of (minimally sized) conductor away,

Hmmm.
IF that couple thousand feet of 'minimally sized conductor ' served as both neutral AND earthing conductor, as is allowed at a service entrance,
THEN the drop along it could explain the shock especially if things were wet. I guarantee a 12 boat battery will zap you good when your skin is soaked with seawater.
Nowadays that'd be disallowed under code for neutral and protective conductor can join only back at that man disconnect and that local panel would be called a sub-panel , so there'd be a separate conductor for fault and/or leakage current ...

I don't know how long ago Krater fixed that one. Might well have been under a previous revision of the US code.

Every little lesson like this improves our ability to work systems in our head. This thread, along with my guest house wiring, have clarified several points in my alleged brain... Codes evolve as we (collectively) learn from our mistakes.

old jim