Excellent post, Kenneth. I've been involved in EMC for more than 25
years as Vice-Chair of the EMC WG of the Audio Engineering Society
Standards Committee, largely composed of members from the UK and North
America. We first became aware of serious RFI issues from variable-speed
motor controllers for elevators in buildings with large performance
spaces, and all of the issues were the result of massive failures by
system designers. We learned then that controllers were usually widely
separated from their motors, and wiring practices were ignorant of the
fundamentals of preventing both magnetic and electromagnetic coupling.
The same failings are present in consumer products like HVAC systems,
and in industrial control systems. I'm encouraged that you and your
colleagues are doing your part to educate designers of these systems.
One of the most important principles that we learned is that avoiding
the creation of the fields is at least as important as shielding. For
example, all current-carrying conductors MUST be twisted pair, and
circuit layout, including board layout, is critical. In the NJ
Performing Arts Center, where Neil Muncy first encountered the issue
with elevator motors, it was the magnetic field that was coupling into
audio system wiring. Since current-carrying conductors are nearly always
bypassed to "ground," it is critical that ground conductors be run WITH
and tightly couples to current carrying conductors so that they function
as transmission lines.
In his lectures, Henry Ott has emphasized this principle, noting that
when "ground" layers on boards are interrupted under signal, the traces
no longer form transmission lines, wreaking all sorts of havoc. He also
observes the invisible schematic hiding behind the ground symbol.
73, Jim K9YC
On 2/14/2023 12:20 PM, Kenneth Wyatt via RFI wrote:
Steve is correct that it’s possible to purchase large appliances that are designed with EMC
in mind (mostly for the European market). As an EMC consultant for the past 15 years, I’ve
helped several appliance clients with their washing machines, air conditioning systems, etc. achieve
EMI compliance. The problems I’ve seen include EMI mains filters located too far inside the
works, which allows noise coupling directly into the mains wiring. Also the VS drive electronics is
not fully enclosed with shielding. But the biggest problem is that the internal cable routing is
haphazard, allowing multiple coupling between noisy circuits and mains wiring, which can lead to
both radiated and conducted emissions.
I, and a handful of others, in the world also teach product design for
compliance to EMC and product safety, but these topics are largely ignored in
college and university. The result is that designers end up learning the hard
way about EMC and the end users bear the consequences.
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