On 03/16/2015 07:33 PM, Greg Bentzinger wrote: > Pardon my ignorance... > > But is there a significant difference between use of shielded cable > between VFD and motor vrs lines in hard or flex metal conduit which > makes a complete ground at each end?
Both cable-shield and a conducting cable-pipe will work the same for most practical purpuses. The trick for effective shields is that it should not carry the ground (current) from one side to the other. If the shield is grounded on both sides, then you most probably leak the signal at the shield (the signal is no longer contained). The *real* difference is that a (properly) shielded cable has tightly controlled impedance and coaxial properties, which is an important attribute and a requirement for most application. Using a pipe will have "an impedance" at some level and is not guaranteed to be the same over the entire length. The result is that you may introduce signal reflection when using a pipe(*). Usually, the shield is connected at one (!) star-point connection to earth where all earth and shield connections come together. It may then be connected from there to ground using a parallel RC 100..1000k//[email protected] (may need to experiment with values for best suppresion). The resistor is to level any potential (static) buildup and the capacitor shorts the AC components. It is a lot cheaper to use a pipe and run some wires in there. But, as said before, you need to measure the exact impact of doing so. You may end up worse if you do it wrongly. (*) With high power signals, such as motor driving lines, reflections can overload the drivers or the feeding PSU. High-power lines should always be as short as possible and tightly impedance controlled. -- Greetings Bertho (disclaimers are disclaimed) ------------------------------------------------------------------------------ Dive into the World of Parallel Programming The Go Parallel Website, sponsored by Intel and developed in partnership with Slashdot Media, is your hub for all things parallel software development, from weekly thought leadership blogs to news, videos, case studies, tutorials and more. Take a look and join the conversation now. http://goparallel.sourceforge.net/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
