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" <wd8dsb@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 <jim@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
>>
>>
>>
>>
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