[RFI] Wiring practices to minimize emissions

nm8rmedic nm8rmedic at rocketmail.com
Wed Jul 13 10:27:27 EDT 2016


Thank you for well considered input.

1) Mention was made of using twisted pair. Is that practical for 40 horsepower motors?

2) I recall from past board discussions the necessity of minimizing the distance between, and area encompassed by, power carrying conductors to reduce emissions.  Would someone please expound on that.

3) The motor controllers will be soft-starts rather than VFD's . Are there any special EMI considerations regarding soft-starts?

Thank you,

Sent via the Samsung Galaxy Note® II, an AT&T 4G LTE smartphone

<div>-------- Original message --------</div><div>From: Jim Brown <jim at audiosystemsgroup.com> </div><div>Date:07/12/2016  8:34 PM  (GMT-05:00) </div><div>To: rfi at contesting.com </div><div>Subject: Re: [RFI] Wiring practices to minimize emissions </div><div>
</div>On Tue,7/12/2016 11:13 AM, James Gordon Beattie, Jr. wrote:
> im, et al,
> Breaking DC paths with optical interfaces reduces inductive and 
> radiated emissions.

How do you use an optical interface in a circuit carrying 30A DC? Or 
even 30A AC?

> Further, twisted pairs are good, shielded twisted pairs properly 
> bonded and grounded are better.

That is NOT universally true. It depends greatly on shield construction. 
If the shield is a robust copper braid, it can improve isolation. If, 
however, the shield is foil with a drain wire twisted at the same rate 
as the signal pair and closer to one of the signal conductors than the 
other, the shield CAUSES differential-to-common mode conversion, which 
causes the cable shield to radiate the differential signal.  Nearly all 
currently manufactured "rack" cable has this defect, including those 
made by Belden.

See Neil Muncy's landmark paper in JAES, June 1995. The essence of his 
work is on my website, and I've contributed several papers of my own 
extending his work.

73, Jim K9YC

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