The retrofitted grounded helical shield may be effective if the
windings on the helix are bridged; the shield needs to provide a low
impedance for the noise. Otherwise, the noise current would be forced
to follow, and be impeded by, the windings of the helix, which is
simply an inductor.

If Trane doesn't have a solution within a reasonable amount of time, I
may experiment with such shielding. It would take some very careful
soldering to bridge the windings without damaging the insulation on the
enclosed wires.

I may also try using some very light guage copper sheet (or foil)
folded around the wiring harness and closed with screws and nuts. That
way I wouldn't have to worry about soldering and bridging the turns on
the helix.

Any other ideas?

Smarty wrote:
This comment opens up the possibility that wrapping the existing harness
with a braided wrap as a helix and then bonding the outer braid to a good
earth ground may help the radiated electromagnetic interference (EMI). The
conducted noise will still need to be filtered / trapped before the wiring
enters / exists the furnace. Given that this EMI goes from the AM band
(approx 1 MHz frequency all the way up to VHF or UHF television frequencies,
however, the likelihood of being able to devise a good wideband filter which
substantially reduces the conducted EMI is remote without a lot of expense.
If the motor itself is truly the principal noise source, then getting some
noise suppression right at the motor offers the best solution, either with
shielding, series inductors (chokes), shunt capacitors, or all of the above.
The motor brushes and commutating connections may be creating a lot of
arcing, and a new motor may help if it is constructed differently (from a
different vendor).

Smarty


"MLD" wrote in message news:d6J4h.3603$Ue.2593@trndny03...
Looking back, I now recall that replacing the inducer motor wiring harness
with one that had better shielding did make a significant improvement
although it didn't completely resolve the noise problem.
MLD


"MLD" wrote in message
news:q0J4h.5540$qG.1024@trndny02...

"modelman" wrote in message
oups.com...
Several months ago I had a high efficiency Trane XV90 natural gas
furnace and heat pump installed. Since the weather has recently been
cold enough for the gas furnace to provide heat, I have been
experiencing severe radio interference. The interference wipes out AM
broadcast reception throughout my house. I also see snow on a TV
connected to an external antenna.

The radio noise occurs as soon as the draft inducer motor starts up;
the pitch of the interference is related to the motor speed. The draft
inducer motor is a dc motor driven by a PWM controller on the main
circuit board. It is well known that PWM systems generate strong
harmonics throughout the radio spectrum, resulting in radio
interference. However, properly designed PWM systems include filtering
and shielding to suppress the radio frequency currents from the wiring.

I contacted my installer, who is totally unfamiliar with the problem.
The electrician who was sent to my house to investigate the problem
also doesn't understand what's going on. I had to explain the
difference between an RF ground and dc or house ground to him.
Although everything appears to be well grounded from a dc perspective,
I suspect that portions of the system are radiating RF energy.

Several days ago I emailed Trane about the problem, but haven't
received any response.

Although there has been past discussion in this group about radio/TV
interference emanating from Trane high efficiency gas furnaces, I
haven't seen any definitive fix. Does anyone know if Trane has a fix
for this problem. Do they have a shielded cable and or rf filter kit
to suppress this noise? Since my system is under warranty, I won't
attempt any modiifcations to the system.

Has anyone experienced this problem?

Thanks.


Here's one guy that had the exact same problem. I was a bit luckier that
you in that it didn't bother my AM radio signal but it did screw up my
kitchen TV picture--rabbit ears. It's coming from the inducer motor as
you
surmised. The installer was very cooperative and tried to fix it based
on
input from Trane. Changed out the cable to the motor with one that was
supposed to provide better shielding and when that didn't work changed
the
control board---both without any success. Prior to and after component
replacements I tried grounding everything that I could, again with no
success. Got the local Trane Rep on the phone; he made promises but
never
followed through with a solution. Had a new Trane for about a year that
got
into a problem resulting in it being replaced under warranty rather than
repaired--it was the replacement furnace that had the RF noise problem.
Found out that Trane went to a "new design" inducer motor. I tried to get
the Trane Rep to replace the motor with the same design that was on my
first
furnace. No luck there, was just ignored and yessed to death. If Trane
acts
dumb about the RF noise it's all show-because mine happened about a year
ago. My guess is that you're stuck with the problem. I finally made
mine
going away by putting in a cable line to the TV.
My suggestion in your tussle with Trane or the installer is to go find an
inducer motor from an earlier vintage furnace. Even if it has to be
cannibalized off an older (2yrs or so) furnace.
MLD