The AM Forum

Guys,
I’ve got an interesting RFI problem. I recently installed electric radiant heating in the upstairs bathroom, while installing the new tile floor. The tile is now toasty warm and the wife loves it! Gotta keep her happy. When I get on 75m, I trip the GFI that’s part of the thermostat.

I’m not tripping the other GFI located next to the bathroom sink, so I believe that the floor heating grid in the floor is acting like a giant loop antenna. Since the wiring is in the wall, installing some homemade ferrite chokes is not that easy. Has anyone had any experience with desensitizing GFI devices to RF?

The radiant heating is shown here:
http://www.thermosoft.com/radiant-floor-heating/

Here’s the thermostat
http://www.thermosoft.com/radiant-floor-heating-products/shop/thermostats/
TH114-AF-GA/U

http://amfone.net/Amforum/index.php?topic=37569.msg287539#msg287539

recently had a similar discussion .... gfci trip on 7 mA differential current .... not hard to do !

The GFI on my back patio was tripping when I was on 80M. I bought a new one at the hardware store and it solved the problem. I think the age of the outlet made it more susceptible to tripping.

Thanks guys! In order to fit the capacitors I think I'm going to switch out the single wall box to a double. I'll have plenty of extra space.

Remember, one 0.01uF capacitor (total of two or three) must be connected between each wire on the protected (load) side of the GFCI, and the safety ground wire. I.e. hot (black) and neutral (white) for 120VAC, or hot (black) and hot (red) for 240VAC with no neutral, or hot (black), hot (red) and white (neutral) for 240VAC with neutral.

This will bypass the common mode RF current around the GFCI's common mode current detector... while still maintaining the normal 60Hz GFCI functionality.  


Stu

My neighbor was having random trips on his spa that's on the patio.

I offered to come over with a clamp on ammeter and check if he had a problem.

I noted that the spa cord is terminated in a "plug end" GFI made by a TOWER INDUSTRIES.
Searching for specs, its rated ground fault sensing is 3-5 ma.

The 120 vac spa was installed and using the 15 amp patio receptacle.

That receptacle is tail ended off the garage outlets GFI.So he had two GFI's in series.
Not what I would think was proper.But, he paid for the installation and I didnt want to void any warranties on his spa.

The spa was drawing 14 amps on peak starting high speed jets and full heat.
It settled back down to 10 amps.
 Although I have little resolution for low reads, I checked the ground and saw no measurable ground current.
Hot leg current and neutral return currents equal.

I looked at how close the east leg of my 80 mtr Inc ver was to his spa.

I hated to suggest it, but I said..

I wonder if my radio is causing the trip.
His problems sounded like they started about the time I hot my T368 operating.

Well, I operate CW 95% of the time, but occasionally check into the 3974 and 3985 military users net.

I tried both modes and three frequencies.

No problems tripping the cord mounted GFI.

He came over to see my latest boat anchor, the T3.His dad was a ham  so he has some interest in radio.

I fired it up and gave a CW on the cw end.He was impressed by all the old gear that had been restored to service.

I told him to call or text me if it shows up again.
5 minutes later. he said it was tripped.

So apparently while he was here at the shack and I keyed the radio..

His SPA TRIPPED!.
We did more tests and EVERY time I keyed cw or AM at over 150 watts....his spa died
:-(

I tried ferrite beads everywhere.No change.

I went to Home Depot to get another plug end GFI.

I found a good LEVITON plug end GFI.

Came back home, swapped put his gfi plug.

We tried it with the Leviton.
Success.
It would not trip at whatever power level or mode I tried.

So, when you have a similar problems.

Get the LEVITON brand and toss anything from TOWER industries.

In my case, it's not that simple. The GFI device is integrated into the thermostat for the electric radiant heating in the bathroom. I've tried everything that's been suggested, with no luck. Tried reaching out to the manufacturer and their only response was that their device meets all applicable specs.

Once the tile floor gets warm, it stays warm for quite a while. I've just got in the habit of resetting it after Ive been on 75m.

I will back Ron on leviton.

I will also add Hubbell branded WP outdoor rated 20A commercial.

When I built out my station and shop I added a GFI from every manufacturer I could find.  I did this by collecting gfi units from homes I worked in for 3 years.

I have about 10 in line.  All parallelled.  Almost all have something plugged in.

Johnson 1kw flashbox with owl about 8 feet from the farthest gfi unit.  MAYBE ten feet.

Leviton I had no problems with

Hubbell I had no problems with.

All off brands and old ones nearly had a problem in one way or another.

And I'll add.  Almost as much as rf nuisance tripping was tripping from equipment with .01 uf caps across the lines leaking!  OMG, I wore a gfi out resetting it in a year that protected the bench.



Another aside.  They do make gfi BREAKERS!   They go in the panel.  These have nice long antennas connected to them.  Keep this in mind in New construction as we have to install them in specific areas now (not just afci)

--Shane
KD6VXI