Excuse me if this has already been discussed. When studying Scott's excellent diagram of PME I note that the neutral and ground are bonded at the service main just as in the USA. Thus the neutral can flow on the bond to the water pipe in parallel with the neutral going back to the transformer. The water pipe interconnects with other services so the current can use their neutrals as part of the parallel path.
This parallel current can be a significant percentage of the service neutral, particularly if there is some corrosion or looseness in the service neutral.
When I was wandering around London and other cities in the Southwest during two visits I turned on my gaussmeter and found strong fields from currents under the sidewalk and streets, just as I find in US cities. I was able to verify at times that the fields were from water pipes.
Since the magnetic fields on the service cables are identical to those on the water pipes, these fields can affect computer monitors and other sensitive electronic instruments, even if the health concerns are ignored. My question (at last!) is whether there is any attempt in the UK to insert insulating connectors or spacers in the water system to stop these random currents?
Here in the UK water and gas mains are being converted to plastic so at some point in time the problem will go away.
Point is though if you have a poor earth/neutral connection, this could cause problems else where.
This on older properties this can cause a problem, in the old days they relied on the gas and water pipes,, usualy lead or iron.. for the earth to the property, the gas or water people come along and change there service pipes to plastic and whoops there goes your earth to the house..
must say they have improved on this,, they now give the owner a disclaimer letter, and ask them to get a spark to check the installation.
Re: PME and water pipe currents#139196 10/21/0307:17 PM10/21/0307:17 PM
Karl, I don't think this is perceived as such a big problem this side of the pond. As Paul said, new underground water & gas mains pipes are plastic.
In this area water service pipes from the street have been plastic since the late 1960's, and the water authority has a major mains replacement program in older areas where service pipes are lead & iron. All gas service pipes have been plastic (yellow polyethylene) underground since over 20 years. Once again Transco (gas distributor) has a mains replacement program in older areas with iron pipes, there have been problems with iron mains fracturing. This is why our roads are constantly dug up.
Bad connections on the PoCo neutral are probably less common in the UK due to the fact that most of our PME services are run underground in concentric (neutral screened) cables. If I understand correctly, in the US most services are overhead - often using single core conductors - with a slightly higher risk of broken or poor connections, & exposed to the elements.
To finally answer your question, to the best of my knowledge, there has not been any deliberate attempt to insert insulating sections in service pipes to reduce parallel currents.
Re: PME and water pipe currents#139197 10/22/0306:04 AM10/22/0306:04 AM
The situation's similar in Ireland with the majority of water mains (since the 1960s) and all gas mains being plastic. Natural gas only came to Ireland in the early 1980s although towngas systems were present in all of the cities and some of the major towns. However, the towngas network wasn't capable of carrying natural gas safely as methane having different characteristics to towngas was capable of seeping through joints so the entire network was rapidly replaced with those yellow plastic gaspipes. In some cases the new pipes were simply pushed through inside the old ones!
However, in older areas 1920s/30s and earlier there would be pretty serious networks of underground pipes which, although no longer in use, are still burried underground and could still provide a path for current.
Depending on the age of an area the cabling system in use would vary.
1920- until early 60s - Generally 4 wire overhead (uninsulated) with a 5th wire often present to control lighting (no longer in use but the cable is often still present). Each house picks off a 1 phase & neutral to spread the load over all phases or for larger services all 3 phases & N. This service will either run along the street or along a lane behind the houses. Its actually not that ugly as it's generally on dark brown wooden poles or on ornate metal equivilants.
From the 1960s the 4 uninsulated cables were often replaced by a 4 wire insulted platted cable which still runs overhead from pole to pole but looks like a single thick black twisted cable and has less visual impact. It's not neutral sheilded and you can see the individual cables twisting around eachother.
Similar cable was also used in underground distribution systems. The phases are identified by colour coding. Neutral sheilded cable is also used in more modern installations underground.
Also, all cable underground is carried in ducts making it quite difficult to damage accidently. Since the 1960s heavy red (or blue/yellow with ESB logos) plastic ducting has been used and before that the cable was usually layed inside concrete ducts. If a 1920s/30s area has underground service it's almost always very well structured and run in concrete tubes. The service would typically have come up through the bottom of the house and to a meter in the hallway (often under the stairs, which is now illegal for fire safety reasons). Phones wern't the norm back then an the phone company was extremely slow to do anything so almost all of the phone infrastructure would have been, and often still is, distributed overhead. Although in most cases the lines disappear underground at each pole and it's only cable from the pole to the house that's overhead. Amazingly enough those networks work pretty well for DSL compared to some of the messy underground 1950s/60s infrastructure.
[This message has been edited by djk (edited 10-22-2003).]
Re: PME and water pipe currents#139198 10/22/0304:56 PM10/22/0304:56 PM
The distribution in the U.K. follows the description that DJK gave for Ireland fairly closely, except for the "platted" 4-wire overhead cable.
All the 3-ph LV distribution here is on four individual vertically stacked conductors.
There has been a gradual move to underground services, but there is still quite a bit of this overhead distribution in rural areas.
The village in which I live has all overhead distribution in this way, although the main feeders from the substation run underground to the main "central" pole.
It's also the norm for new services to houses to be concentric-neutral cable, run down a pole and then underground to the house.
Originally the PME system was used in the U.K. only in certain rural areas where it was difficult to get a good ground connection. Being rural areas, these PME distribution systems were almost always overhead, with ground rods at regular intervals along the route.
Other rural systems grounded the house to a local rod (or water pipes) and there was no neutral-ground bond at the house, while urban areas used completely separated neutral and ground lines right back to the transformer, as you can see in the other diagrams.
PME has become much more widely employed in the last 20 years or so, and in my area at least, is available for all services if the customer requests it.
As the others have said already, I've not been aware of any specific use of iknsulating joins to prevent parallel paths on pipework, but plastic service pipes are becoming so much the norm that the problem will gradually disappear.
Although PME is now available on the service throughout this area, I'd estimate that only about 5 to 10% of homes are wired for PME in my immediate area.
Those that are wired as PME have been refurbished and remodeled in recent years, which means that they most likely have new PVC water service pipes.
The older properties still using metal service pipes generally still have TT earthing (local rod only).
By the way, the increasing use of plastic pipes on services resulted in the IEE disallowing a connection to a water pipe as a grounding electrode a long time ago. I'm not sure when this rule was introduced, but it's there in the 1966 edition.
Re: PME and water pipe currents#139199 10/23/0312:11 PM10/23/0312:11 PM
Thank you all for these excellent descriptions. We may have been slower to switch to plastic here (US) but new service is now plastic. However there is still a lot of neutral-on-water-pipe circulation here.
So - either the Picadilly Circus area still uses metal water pipes, or else there are other metal pathways for neutral current. Any ideas? I forget the town where I also traced currents to water pipes. Was it Falmouth?
We are slow to underground the lines here, partly because of distances involved, but I think it is inertia and the fact that the linesmen are used to servicing overhead lines. But slowly it is happening, usually for esthetic reasons. They don't seem to think about storm damage. I live on an island (Marthas Vineyard) and we have power outages from normal windstorms, not to speak of hurricanes which visit us occasionally. A neighboring island (Cuttyhunk) never has power outages because all their lines are underground.
Re: PME and water pipe currents#139200 10/23/0312:45 PM10/23/0312:45 PM
Putting distribution systems underground hasn't been a major priority here in Ireland. New installations are put underground and often when a major resurfacing / paving project is underway the ESB might take the opportunity to run duct work and burry the distribution network.
There is absolutely no 10/20/38kV distribution in urban above ground however there's plenty of 4 wire 380 (400V) systems in widespread use in suburbs that predate the late 1960s. In some instances even city centre areas, other than specifically historic areas may still have overhead distribution with large 3-phase service drops to each block.
Generally putting the system underground is seen as an unnecessary cost and disruption and to be quite honest in most instances the over head system's not that ugly it's very neatly wired.
Re: PME and water pipe currents#139201 10/24/0302:19 PM10/24/0302:19 PM
So - either the Picadilly Circus area still uses metal water pipes, or else there are other metal pathways for neutral current.
Piccadilly Circus must have hundreds if not thousands of pipes, conduits, cables and ducts running beneath the streets, and a myriad of sources for currents and magnetic fields. (For those of you who have never been to London, it's our nearest equivalent to New York's Times Square.)
The Underground (subway) station has tunnels extending around the area, with all its associated cables and ducts, and I'm not sure exactly where it passes but the Post Office even has its own small-gauge underground rail system to transport mail across the capital.
I forget the town where I also traced currents to water pipes. Was it Falmouth?
Use of water piepes as grounding electrodes has been outlawed here 01/01/01 (great date, very easy to remember). The water company put up a letter in each house telling the inhabitants to have an electrician check their wiring. Hardly anyone did. New ater mains are plastic, old ones were usually lead (only the house feeders, the real large mains in the streets were and still are in most of the cases cast iron). Gas mains are still iron with welded joints only. For residential gas piping threaded joints are also acceptable. Here they found some way to use the old pipes with natural gas, I think they add water vapor to prevent the hemp drying out. Still it's a problem when it comes to extending old resi pipe work 'cause they usually just refuse to do that. Overhead services are virtually only 3ph here, they do exist in more sparsely populated areas of Vienna. As far as I've seen they're always the Quadruplex cable djk mentioned. Underground services are wired with a very thick version of NYM, you can see that stuff in andy's Germany thread. I think they put some bricks over their wires and pipes and then lay thick yellow plastic sheets saying "Caution! Water line/power line/cable TV/gas/ whatever".
Re: PME and water pipe currents#139203 10/24/0304:38 PM10/24/0304:38 PM
It's good for the outlook to know that some countries prohibit using water pipes as grounding electrodes, while in the US it is mandatory. Which is a bit irrational, since so many buildings now are fed by plastic pipes. Our Water Works Association has been trying to get the current off their pipes for many decades.
Thanks for all the info. Since I am revising my book on magnetic fields re. wiring and grounding, I will mention some of these facts.