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Dipole-2 different wire sizes?
"J. C. Mc Laughlin" wrote in message
.. . Some 110 responses have been made to the fellow who may, or may not, be in Poland. This does not count a similar number of messages from the fellow, as those are blocked. Why, oh why, do you continue to be the mechanics described so well by Mr. O'Nella? Stop feeding the fellow. 73, Mac N8TT Hello Mac. As I've said before, it is fun and we do have some interesting discussions amongst ourselves about aerials. I've a feeling that Szczepan is looking for the engine and we're telling him that he is looking at a trolley and not a car. Please don't push the analogy too far; some of us may say that we rolled the car downhill and Szczepan can't understand that gravity moved the car so an engine wasn't needed at all. 73 Ian. |
Dipole-2 different wire sizes?
On 7/14/2012 3:33 AM, Ian wrote:
"J. C. Mc Laughlin" wrote in message .. . Some 110 responses have been made to the fellow who may, or may not, be in Poland. This does not count a similar number of messages from the fellow, as those are blocked. Why, oh why, do you continue to be the mechanics described so well by Mr. O'Nella? Stop feeding the fellow. 73, Mac N8TT Hello Mac. As I've said before, it is fun and we do have some interesting discussions amongst ourselves about aerials. I've a feeling that Szczepan is looking for the engine and we're telling him that he is looking at a trolley and not a car. Please don't push the analogy too far; some of us may say that we rolled the car downhill and Szczepan can't understand that gravity moved the car so an engine wasn't needed at all. 73 Ian. Don't forget, this stunt was done later with a much more effective punch line. They installed an electric motor in the rear and had batteries in the trunk. She would hear that her engine could not be fixed because it was missing. She would get mad and tell them she was not going to be tricked into unnecessary repairs. The punch line was when she rolled away and the hidden camera recorded the looks on the faces of the mechanics. Michael |
Dipole-2 different wire sizes?
"Boomer" wrote in message
... On 7/14/2012 3:33 AM, Ian wrote: "J. C. Mc Laughlin" wrote in message .. . Some 110 responses have been made to the fellow who may, or may not, be in Poland. This does not count a similar number of messages from the fellow, as those are blocked. Why, oh why, do you continue to be the mechanics described so well by Mr. O'Nella? Stop feeding the fellow. 73, Mac N8TT Hello Mac. As I've said before, it is fun and we do have some interesting discussions amongst ourselves about aerials. I've a feeling that Szczepan is looking for the engine and we're telling him that he is looking at a trolley and not a car. Please don't push the analogy too far; some of us may say that we rolled the car downhill and Szczepan can't understand that gravity moved the car so an engine wasn't needed at all. 73 Ian. Don't forget, this stunt was done later with a much more effective punch line. They installed an electric motor in the rear and had batteries in the trunk. She would hear that her engine could not be fixed because it was missing. She would get mad and tell them she was not going to be tricked into unnecessary repairs. The punch line was when she rolled away and the hidden camera recorded the looks on the faces of the mechanics. Michael I like it. 73, Ian. |
UK earthling - was: Dipole-2 different wire sizes?
Dear Jeff: Many thanks.
It is especially interesting to learn that the expectation of encountering a floating (no earthing) system is zero. Expanding a bit on what you have communicated: It appears that the transformer used between one phase of a HV 3 phase line and distribution "wires" is 440VAC, center tapped. The distribution "wires" to a house (or the like) are one side of the aforementioned transformer's secondary and the transformer's center tap, which is labeled as neutral. It is expected that another house (or the like) is fed from the other side of the transformer's secondary and its center tap. At the service entrance: one scheme connects the neutral to an earthing. An alternative (called 'protective multiple earthing' (PME) ) does not connect the neutral to an earthing, but connects exposed metal in the house to an earthing. Wow! The latter scheme is expected in new construction. It is not immediately clear what the advantage of the PME scheme might be. Your caution about RF grounds is well placed. In the North American scheme, for the last 60 or more years, a third wire is involved - the green wire that is connected to an earthing only at the service entrance and then to touchable surfaces of an appliance. The green wire maintains what a human can touch at ground potential without relying on anything else. In sub distribution boxes, the green wire is isolated from neutral so the green wire provides a straight path for current to an earthing. Please correct any errors that have crept into my restatement. I once had a G5 license and, in my radio astronomy days, spent a brief time at U. of Manchester. Warm regards, Mac N8TT "Jeff" wrote in message ... On 15/07/2012 10:10, Jeff wrote: On 15/07/2012 03:20, J. C. Mc Laughlin wrote: OK Gentlemen: I am now more wise. Entertainment comes in multiple forms. A question that is indirectly related to antennas: I was explaining to an attorney how the common North American 60 Hz electrical system is configured for residences (240 VAC, center taped secondary, with the neutral connected to earth and to the green wire [only] at the service entrance) He observed that in the UK he was told that schemes for supplying 240 VAC 50 Hz had earthling being done, if at all, several different ways. So, educate us please: when we travel to the UK what are the schemes we will find. I always used an isolation transformer that was only connected while equipment was being used. The UK distribution and home installation systems are paranoid about earthing, true it can be done in several way but it it *always* done. The primary distribution is 3 phase, the last leg being 3 phase at 440V with 220V between each phase and neutral, normally only 1 phase is feed to domestic premises. Earthing is normally done locally by an earth stake at the home (or formally bonding to water pipes, or the sheath of the incoming supply), the neutral is bonded to earth at the sub-station and at other intervals on the feed. Another system is where the incoming neutral conductor is used as the earth, with no earth stake, BUT all exposed metalwork in the home such as taps, water pipes etc have to be bonded to the earth connection. There is a problem with this system if there is a break in the supply neutral then the 'earth' will float to supply voltage. This is not a problem as long as there is no connection to a real earth and there is no path to earth hence no shock danger, and is why all exposed conductors have to be bonded together. HOWEVER, this does pose a problem for antenna earths as they would be a dangerous connection to a 'real' earth with 230V between it and the local protective earth in the event of a fault. Also if the rf earth has any sort of connection to the mains earth there is a fire risk as that connection could carry the current for every home between it and the neutral break. This system is commonly known as 'protective multiple earthing' (PME) and is common in new installations. It is imperative that you know what system is in use before any additional rf earths are added. Jeff Forgot to add that except in very rural locations the feed to premises from the sub-station is nearly always underground. Jeff J. C. Mc Laughlin Michigan U.S.A. Home: |
UK earthling - was: Dipole-2 different wire sizes?
J. C. Mc Laughlin wrote:
Dear Jeff: Many thanks. It is especially interesting to learn that the expectation of encountering a floating (no earthing) system is zero. Expanding a bit on what you have communicated: It appears that the transformer used between one phase of a HV 3 phase line and distribution "wires" is 440VAC, center tapped. The distribution "wires" to a house (or the like) are one side of the aforementioned transformer's secondary and the transformer's center tap, which is labeled as neutral. It is expected that another house (or the like) is fed from the other side of the transformer's secondary and its center tap. This is not what a 3-phase system is. What you describe is a 2-phase system. A 3-phase system has 3 live wires, a neutral, and possibly a ground. The 3 phases are 120 degrees apart, not 180. Each phase has a voltage (230V here), and there is sqrt-3 times that voltage between the phase wires (400V here). All three phases are used in some electrical motors and in highpower applications like electrical heating, and one of the phases is sufficient for a normal house connection. At the service entrance: one scheme connects the neutral to an earthing. An alternative (called 'protective multiple earthing' (PME) ) does not connect the neutral to an earthing, but connects exposed metal in the house to an earthing. Wow! The latter scheme is expected in new construction. Why "Wow!" ? It is the only safe system. Here in the Netherlands we have the same situation. Power is distributed over 4 wires (3 live phases plus neutral) and a 5th wire is locally distributed for safety ground. It is connected to the safety ground connections of all reeceptacles and to metal structures in the house, like water and central heating pipes. The neutral is only connected to ground at the substation, and usually has a couple of volts on it when measured at the receptacles. |
UK earthling - was: Dipole-2 different wire sizes?
Dear Rob: Of course I know what a three phase system is. In North
America, most high voltage (HV) is distributed using three phase. In a residential area, a transformer's primary is connected to one of the phases (with secondary producing what you call a 2-phase, 120VAC - 240VAC system). At the next house, or group of houses, down the road another transformer is connected to a different phase - and so on. Because the net power factor of a residential area is inductive, periodically one will see a platform on a pole holding three sets of capacitors each connected to a phase. However, some businesses, farms, and essentially all industrial sites receive all three phases mostly to avail themselves of the certain torque and efficiency of three-phase-motors. [I told my students that the first rule of 3-phase is never to lock the shaft of a new motor until one verifies which way the shaft actually turns - because it will turn.] It is most interesting to learn that in the Netherlands it is common to deliver three phase to a residence. That is a surprise. My dormitory at university distributed three phase with outlets on facing walls in some rooms being on a different phase. This facilitated fast heating of hot-dog sausages - not that I ever did such a thing. I have known about sqrt-of-3 for a very long time. The use in the Netherlands of a fifth grounding wire - the green wire in North America - is truly a good idea. The "Wow" is prompted by the less than belt-and-suspender nature of a house distribution system not using a green (earthing) wire. Steve pointed out that things can go wrong. The system you described being used in the Netherlands, while at 240 VAC, does not rely on all of the bonding staying effective - and that is good. It also has the advantage of being able to provide 3-phase to the few motors expected in a house. Rob - many thanks for expanding my knowledge. Every engineer from the Netherlands with whom I have worked has impressed me most favorably. Can not say that for engineers from some countries. 73, Mac N8TT "Rob" wrote in message ... J. C. Mc Laughlin wrote: Dear Jeff: Many thanks. It is especially interesting to learn that the expectation of encountering a floating (no earthing) system is zero. Expanding a bit on what you have communicated: It appears that the transformer used between one phase of a HV 3 phase line and distribution "wires" is 440VAC, center tapped. The distribution "wires" to a house (or the like) are one side of the aforementioned transformer's secondary and the transformer's center tap, which is labeled as neutral. It is expected that another house (or the like) is fed from the other side of the transformer's secondary and its center tap. This is not what a 3-phase system is. What you describe is a 2-phase system. A 3-phase system has 3 live wires, a neutral, and possibly a ground. The 3 phases are 120 degrees apart, not 180. Each phase has a voltage (230V here), and there is sqrt-3 times that voltage between the phase wires (400V here). All three phases are used in some electrical motors and in highpower applications like electrical heating, and one of the phases is sufficient for a normal house connection. At the service entrance: one scheme connects the neutral to an earthing. An alternative (called 'protective multiple earthing' (PME) ) does not connect the neutral to an earthing, but connects exposed metal in the house to an earthing. Wow! The latter scheme is expected in new construction. Why "Wow!" ? It is the only safe system. Here in the Netherlands we have the same situation. Power is distributed over 4 wires (3 live phases plus neutral) and a 5th wire is locally distributed for safety ground. It is connected to the safety ground connections of all reeceptacles and to metal structures in the house, like water and central heating pipes. The neutral is only connected to ground at the substation, and usually has a couple of volts on it when measured at the receptacles. J. C. Mc Laughlin Michigan U.S.A. Home: |
UK earthling - was: Dipole-2 different wire sizes?
J. C. Mc Laughlin wrote:
Dear Rob: Of course I know what a three phase system is. In North America, most high voltage (HV) is distributed using three phase. In a residential area, a transformer's primary is connected to one of the phases (with secondary producing what you call a 2-phase, 120VAC - 240VAC system). At the next house, or group of houses, down the road another transformer is connected to a different phase - and so on. Because the net power factor of a residential area is inductive, periodically one will see a platform on a pole holding three sets of capacitors each connected to a phase. Like in the UK, we don't have low and medium voltage power distribution on poles. All local distribution is underground. Only high voltage is distrubuted (between cities) on overhead cables. It is most interesting to learn that in the Netherlands it is common to deliver three phase to a residence. That is a surprise. It is common, but not everyone has it. However, it is the normal situation to distribute 3-phase power to every residence and then connect only a single phase to a meter, picking another phase at each residence. On request, the connection can be upgraded to 3-phase by exchanging the meter and adding two more fuses to the already present 3-fuse box. |
UK earthling - was: Dipole-2 different wire sizes?
Dear Rob: That is amazing. Very forward thinking. However, it seems to
use a lot of copper, some of which is latent waiting to be used. On the other hand, the cost of running the 3 phase cable underground probably is much more than the cost of the cable. In the North American scheme, most HV and LV cables are "in the air." This tends to minimize the cost of running the cable and, too often, advantage is taken of air-cooling to use what I believe to be wire that is too small. Some newer, crowded residential areas do bury everything. The wires to my house are buried both as a means to provide safety (antennas can not touch wires) and, because of the reduced cooling, as a means to have the right gauge of wire used. I had to pay extra to have the pole to house connection be as I think it should be. Each of the disclosed systems has advantages and costs. It is fascinating to see how different systems value the costs. Thank you for expanding my knowledge. One wonders if you are a radio amateur. 73, Mac N8TT "Rob" wrote in message ... J. C. Mc Laughlin wrote: Dear Rob: Of course I know what a three phase system is. In North America, most high voltage (HV) is distributed using three phase. In a residential area, a transformer's primary is connected to one of the phases (with secondary producing what you call a 2-phase, 120VAC - 240VAC system). At the next house, or group of houses, down the road another transformer is connected to a different phase - and so on. Because the net power factor of a residential area is inductive, periodically one will see a platform on a pole holding three sets of capacitors each connected to a phase. Like in the UK, we don't have low and medium voltage power distribution on poles. All local distribution is underground. Only high voltage is distrubuted (between cities) on overhead cables. It is most interesting to learn that in the Netherlands it is common to deliver three phase to a residence. That is a surprise. It is common, but not everyone has it. However, it is the normal situation to distribute 3-phase power to every residence and then connect only a single phase to a meter, picking another phase at each residence. On request, the connection can be upgraded to 3-phase by exchanging the meter and adding two more fuses to the already present 3-fuse box. J. C. Mc Laughlin Michigan U.S.A. Home: |
UK earthling - was: Dipole-2 different wire sizes?
Dear Jeff: OK No tap on the LV side of the (3 phase) transformer. One
230 VAC wire and neutral wire go to house from the transformer. The non-PME scheme: neutral is "earthed" only at the sub-station AND a local earthing of a separate wire that seems to serve the same function as the North American green wire is provided. The PME scheme: no earthing takes place; at the house entrance, the neutral is connected to what seems to serve as the green wire (the "local protective earth wire"). Thinking now about installing an antenna and radio: with the PME scheme the radio's case is connected to the "local protective earth wire" and yet the outside of the coax is often going to be connected to an actual earthing. I expect some current. When I do the same thing here with the green wire connected to the radio's case and the outside of the coax well attached to an extensive earthing system, nothing happens because all of the earthings are connected together. Most important of all, if I grab an exposed bit of the radio while holding the unattached coax connector, no tickle is felt. It sounds as if a standard part of each radio amateur faced with a PME system is to use an isolation transformer. Thanks too to you Jeff for significantly expanding my understanding of how different people arrive at a solution to the same issue. By the way, are you a radio amateur? 73, Mac N8TT "Jeff" wrote in message ... On 15/07/2012 15:50, J. C. Mc Laughlin wrote: Dear Jeff: Many thanks. It is especially interesting to learn that the expectation of encountering a floating (no earthing) system is zero. Expanding a bit on what you have communicated: It appears that the transformer used between one phase of a HV 3 phase line and distribution "wires" is 440VAC, center tapped. The distribution "wires" to a house (or the like) are one side of the aforementioned transformer's secondary and the transformer's center tap, which is labeled as neutral. It is expected that another house (or the like) is fed from the other side of the transformer's secondary and its center tap. No, there is no centre tapping, the supply is direct from one of the 3 phases at 230V+/- wrt neutral. At the service entrance: one scheme connects the neutral to an earthing. An alternative (called 'protective multiple earthing' (PME) ) does not connect the neutral to an earthing, but connects exposed metal in the house to an earthing. Wow! The latter scheme is expected in new construction. No, one scheme leaves the neutral floating (at the consumer's end, grounded at the sub-station) and provides an additional protective earth wire locally via an earth stake (or in the past bonding to water pipes etc). PME bonds the local protective earth wire to the neutral at the consumer's end, and all exposed metal is bonded to that wire. NO external earths are allowed (without modification of the scheme). It is not immediately clear what the advantage of the PME scheme might be. Your caution about RF grounds is well placed. The claim is that because the earth is provided by the supply company is it more reliable than a local earth stake. Personally I am not convinced by the whole scheme. Have a look at: electrical.theiet.org/wiring-matters/16/earthing-questions.cfm?type=pdf for more info Jeff J. C. Mc Laughlin Michigan U.S.A. Home: |
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