[RFI] 3" ID core for RFI suppression

[Jim Brown]

Howard,

Before you go around chasing this as RFI, I strongly suggest that you 
look for wiring errors in the AC power system. Yes, the washing machine 
is RF susceptible, but that could be caused by an AC wiring problem.

Things to look for in the AC wiring are: 1)  reversal of phase (hot) and 
neutral; 2) reversal of neutral and ground (green); 3) using phase and 
ground to run 120V appliances (by LAW, ground (green) cannot be used as 
a current carrying conductor; and 4) any connection between neutral and 
green other than the panel (usually the main breaker panel) where power 
enters your home.

Equipment that uses ONLY 240V is properly wired with two phases and 
green, NOT neutral. 240V equipment may be wired with a neutral ONLY if 
some part of it runs from 120V.

Outlet testers will find some of these errors.

Some things can be checked with a voltmeter. By LAW, all grounds within 
a premises must be bonded together, and since ground (green) cannot 
carry power, and because neutral and green may be bonded only at the 
single panel, we should see some small voltage (tens to hundreds of 
milivolts) between neutral and green at any outlet when it is supplying 
power to something (the IR drop from return current in the neutral). If 
we see no voltage, there's likely a bond between neutral and ground 
somewhere. If we see no voltage between neutral and green, an ohmmeter 
check between neutral and green should see that improper short. And if 
there's no improper bond, the ohmmeter should see the resistance of the 
two conductors (neutral and green) back to the main breaker panel. And, 
of course, if we see line voltage (120V) between neutral and ground 
(green), phase and neutral are reversed.

One of the wiring mistakes I found in the home I bought 14 years ago 
here in CA was a string of 120V outlets in the half-kitchen of the 
"mother-in-law" garage apartment that were powered from one phase and 
ground of the 240V dryer circuit! In the house, I found an outlet with 
phase and neutral reversed.

And I saved the worst for last -- power is fed to most homes as 240V 
with neutral, but NOT ground (phase, phase, and neutral), and by law, it 
must be bonded to earth at the entry point. That required bond ran on 
#12 bare copper (later painted) about 30 ft along a wall to an outlet 
for a garden hose -- which was fed by PVC pipe. The only connection to 
earth was a driven rod outside that garage apartment, with about 50 ft 
of (painted) bare #12 to a breaker panel on the other side of that 
building. And that panel was fed from the house, so the ground wire was 
close to 150 ft long. VERY illegal and VERY unsafe.

You can read more about power systems here, in a tutorial I was 
commissioned to write for installers of professional audio and video 
systems. The first link is text, the other two are slides for talks I 
did at trade shows.

http://k9yc.com/SurgeXPowerGround.pdf
http://k9yc.com/InfoComm-PowerSystems2012.pdf
http://k9yc.com/InfoComm-Grounding2012.pdf

73, Jim K9YC

On 12/29/2020 5:07 PM, Howard Lester wrote:
> Very long story short: A particular circuit card (I am guessing so) of my 2-1/2 year-old Maytag HE washing machine is susceptible to RFI from… my propane-fueled furnace! The symptom is occasional: A loud 2-step snapping sound that emanates from parts of the back of the machine’s control panel when the furnace first gets the signal from the thermostat, and then begins its cycling on. It happens just once in a while, and I can prevent it from happening at all simply by unplugging the washer from the AC outlet. What could be easier?
> 
> When the snapping recently occurred when my 16KW Generac generator kicked on for its weekly 5-minute exercising, I got even more suspicious. And when yesterday I transmitted with 75 watts on 20 m SSB, using my MFJ Hi-Q Loop up in the attic about 15-20 feet away from the washer, and I heard the snapping multiple times, I then said, “This means war!”  ;-) (That was the first time I ever heard the washer do that from me transmitting on any band. I rarely use more than 50 watts.)
> 
> The flat AC cord is a bit under 1/2” across and has a large plug. The plug size requires about a 2” I.D. core, but I cannot find anything specifically of Type 31 or 77 or, really, anything — except this:
> 
> https://palomar-engineers.com/ferrite-products/AC-Cable-Noise-Filter-for-Large-Plugs-3-ID-p75172171 <https://palomar-engineers.com/ferrite-products/AC-Cable-Noise-Filter-for-Large-Plugs-3-ID-p75172171>
> 
> But it’s $40+, and I don’t want to spend that kind of money if it’s not the right tool for the job. No, I will not cut the AC cord. The washer is past its 1 year full parts and labor warranty, so I’m out of luck there. (Until last November, well past the 1 year, I thought all along it was the furnace making the snapping sounds.)
> 
> Thanks for any ideas. No, I’m not going to replace the washer. As I said, I can just unplug the thing except for the few times a week I use it.
> 
> Howard N7SO
> 
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