Don, you should request that the technician install the new conduit runs using compression couplings and connectors instead of the more common setscrew type. Compression couplings make a much better electrical connection between sticks of conduit which will be better to keep the conduit acting as a proper shield.
The manufacturer of the motor drive will likely specify a maximum wire distance between the drive and the motor. It sounds like you're lucky and have a tech that wants to help! Bill KB8WYP Presently in Dayton and hoping it doesn't rain all weekend. Sent from my iPhone On May 14, 2015, at 10:32 AM, "Don Kirk" <wd8...@gmail.com> wrote: > Hi Jim, > > Thanks, and I have shared a lot of documents with the folks that cover the > major points your section on variable speed drives covers, but found that I > still had to make a recommendations list for them (taking into account > simplicity of install, cost, and highest probability of success), while at > the same time telling them that I was not liable for anything they opted to > do. > > Actually sounds like the technician is now trying to get approval to move > the drives up into the attic which would put them very close to the motors > (which are roof mount) and at the same time he would do a much better job > on the conduit run between the drives and the motors. Currently the drives > are around 50 feet away from the motors with very questionable conduit runs > (and the current conduit runs are impossible to access). > > Note : Previously one simple option I suggested was the use of common mode > cores on the output of the drives (similar to what George AA7JV suggested), > but the original technician that was working on the job did not contact me > for assistance and he installed the cores incorrectly which caused drive > faults, so they abandoned that approach (I'm giving them some time and > space before I bring up the common mode cores again). I also want to > develop a better working relationship with the current technician (I have > offered to be onsite with him when he makes changes, but he has yet to take > me up on my offer). > > I would like to make one comment about your section on VFDs. It does not > mention shielded cable that is now available specifically for use on the > output side of variable speed drives, and these cables offer some major > advantages over the use of metal conduit (but at much greater expense). > > 73, > Don (wd8dsb) > > On Wed, May 13, 2015 at 2:41 PM, Jim Brown <j...@audiosystemsgroup.com> > wrote: > >> On Wed,5/13/2015 11:14 AM, Don Kirk wrote: >> >>> The local technician is now planning on additional changes since the input >>> line filters have not totally mitigated the problem (but they sure >>> helped), >>> and will provide an update when I have new information to share. >> >> Hi Don, >> >> You might want to refer the people working on the problem to this Power >> Point for a tutorial workshop that I've taught to pro audio and video >> people. The principles are no different when the interference is at RF. >> >> http://k9yc.com/InfoComm-Grounding2012.pdf >> >> Henry Ott's excellent text on EMC includes a sub-chapter on these very >> nasty RFI sources. His book is widely used as an EE text, and considered >> "the EMC bible." >> >> >> http://www.amazon.com/Electromagnetic-Compatibility-Engineering-Henry-Ott/dp/0470189304 >> >> 73, Jim K9YC >> >> >> >> >> _________________ >> Topband Reflector Archives - http://www.contesting.com/_topband > _________________ > Topband Reflector Archives - http://www.contesting.com/_topband _________________ Topband Reflector Archives - http://www.contesting.com/_topband
