Surge / Ground / Lightning
in [Home Built PC]
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From: Tony Hwang on 4 May 2008 09:51 Michael A. Terrell wrote: > Tony Hwang wrote: > >>Hi, >>Is he a ham? What is his call sign? >>Mine is VE6CGX. > > > > It's in his sig file: KA9WGN > > Hmmm, That is sign format of novice class.
From: bud-- on 6 May 2008 13:00 w_tom wrote: > > But when a plug-in protector is sold to maximize > profits (not for protection), then grossly undersized protectors also > create another problem - scary pictures: > http://www.hanford.gov/rl/?page=556&parent=554 w_ can't understand his own hanford link. It is about "some older model" power strips and says overheating was fixed with a revision to UL1449 that required thermal disconnects. That was 1998. There is no reason to believe, from any of these links, that there is a problem with suppressors produced under the UL standard that has been in effect since 1998. But with no valid technical arguments all w_ has is pathetic scare tactics. For reliable information on surges and protection read the IEEE and NIST guides. (Both say plug-in suppressors are effective.) -- bud--
From: phil-news-nospam on 6 May 2008 12:57 In alt.engineering.electrical Eric <me(a)nomail.com> wrote: | I can attest to vhf/uhf content in lightning strikes. I worked for a | communications outfit. We owned and maintained a number of comm sites | with towers and antennas. One strike on an antenna destroyed the LDF rf | cable all the way to the polyphaser at the bottom of the tower. It had | blowouts at about 1 foot intervals all down it's length suggesting a | 1/2 wave of about 1 foot or approx 460 mhz. That's one hell of a lot of | energy at that frequency.. Apparently you had some kind of resonance involved. Maybe the antenna itself can cause that. Or the output tank circuit in the transmitter. Once you have the resonance to narrowband the energy, it would only take a reflection back up the line and you turn a propogating surge into standing waves. -- |WARNING: Due to extreme spam, I no longer see any articles originating from | | Google Groups. If you want your postings to be seen by more readers | | you will need to find a different place to post on Usenet. | | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |
From: phil-news-nospam on 6 May 2008 20:12 In alt.engineering.electrical nicksanspam(a)ece.villanova.edu wrote: | Mike Tomlinson <mike(a)jasper.org.uk> wrote: | |>... This is an important principle of the UK wiring code. It's |>referred to as "equipotential bonding." | | I wonder if "ring mains" (an extra wire from the last outlet to make | a loop back to the fusebox) are legal in the US. Seems like a nice way | to improve voltage regulation with a little extra wire, and if the ring | wire only breaks in one place, all the outlets keep working. It is not legal in the US. It is also considered technically unsafe. You could wire a ring circuit with AWG #14 CU rated at 15 amps and protect it with a 30 amp breaker under the theory that the current would be split across the 2 paths between the source (breaker) and the load. This is the most unsafe configuration because if one of the wires breaks, the breaker will not detect it, and you won't notice until a fire starts. You could wire the same circuit to two separate 15 amps breakers. In this case it is somewhat safer because if one wire breaks, you can't get any use via one of the breakers, effectivly reducing the current that would trip the circuit via the remaining breaker. This is still unsafe because the broken wire could merely be loose, and shutting off one breaker would leave the circuit potentially live via the other breaker as the wire could come back in contact. There could also be confusion with separate breakers. The breakers have to be on the same pole (phase), an issue not present in the single pole single phase home wiring most homes have in UK. The USA, however, has two pole single phase wiring. One way around that would be a "tandem" breaker with the two handles fused together. The safest case would be wiring both ends of the ring into the same breaker rated for the current capacity of the wire as if used in a regular branch circuit. Even this would have a safety issue. If the wire became loose at one point in the ring, it would still be a potential hot spot that would be not as easily noticed as a similar loose wire in a branch circuit. That hot spot could then start a fire. So far I have only described issues with the hot wiring. There are issues with the neutral wiring as well. In all the above configurations, a neutral would have to be wired in from both ends of the ring, and each be wired in a separate hole (not doubled up) in the neutral bus bar. A loose neutral in all these cases would go unnoticed just like a hot wire. But in cases where the total current available (either the 30 amp single breaker, or tandem 15 amp breakers, described above) exceeds the wiring (when neutral is AWG #14 CU) a wiring overheating problem exists. The grounding wire would also have to be wired correctly from both ends. An even greater double hazard potential exists when the neutral on one end is broken while the hot on the other end is broken (or shut off at the breaker). This creates a large inductive loop which can energize other wiring and cause various problems with many metallic constructions. Very little is gained by doing this over direct branch circuits. The issue of voltage stability is addressed by keeping branch circuits short. It is my understanding that UK ring circuits tend to be longer and run all around the portion of a house (often an entire floor). Branch circuits in the USA tend to be shorter. Very long circuits can have voltage issues. An example is a home with a 1000 foot long driveway into the property, and a string of many lights along the way. The more distant lights would be dimmer. This can be addressed to at least balance out the dimming by using a loop-back circuit, which is still a branch circuit. This is a more expensive circuit that is done by having an extra hot wire run with the circuit in the same cable or conduit. Each lamp is connected between the extra wire and the neutral. The extra wire is then connected to the fed hot wire at the last lamp in the string. There is no other connected to the fed hot wire other than the last lamp and the source controlling switch. With this loop-back circuit, each lamp has the same circuit length, and thus will have the same voltage drop. The above technique was discussed on electrical-contrator.net a while back, but they have since changed web site software, and my old links do not work. -- |WARNING: Due to extreme spam, I no longer see any articles originating from | | Google Groups. If you want your postings to be seen by more readers | | you will need to find a different place to post on Usenet. | | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |
From: phil-news-nospam on 6 May 2008 20:24
In alt.engineering.electrical VWWall <vwall(a)large.invalid> wrote: | I had a microwave oven that had a MOV across the 120V line ahead of the | power switch. The other side of the 120/240 20A circuit supplied a | refrigerator. The loss of the neutral applied a good part of the 240V | across the MOV when the refrigerator attempted to start. | | The MOV didn't last long! It would probably have been OK on the load | side of the switch. | | I know that refrigerators should be alone on a "home run" circuit, and | neutrals shouldn't be connected with wire nuts, but that wasn't how it was! How would you connect a neutral? Doubled up on a receptacle device screw? The usual practice is to wire the neutral in a wire nut so it can feed the device in that box, as well as connect up and down stream, even if the device is removed. OTOH, I don't like wire nuts. I've seen them come loose even when wired together well. Maybe it was a defective nut. I definitely will try to avoid them when my new house gets built (a lot of bad electrical things will be avoided in it). | My only complaint with some plug-in protectors is that the MOVs are | often much too small. I've also seen some with only a line-line MOV. You had a plug-in protector for a double line (240V) circuit? Or are you just referring to the neutral as one of the lines? I'm still on the hunt for a plug-in surge suppressor power strip for 240V with NEMA 6-15P plug and NEMA 6-15R outlets. The MOVs between each line and ground need to be the ones appropriate for 120V (330V clamp rated) and the ones between the two lines appropriate for 240V (660V clamp rated). -- |WARNING: Due to extreme spam, I no longer see any articles originating from | | Google Groups. If you want your postings to be seen by more readers | | you will need to find a different place to post on Usenet. | | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) | |