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Obviously the noise, when you express it in watts, relates to the maximum current that you've set the calibration to. It also depends on whether or not you are measuring the voltage. If you're working on apparent power because you're not measuring the voltage, then you will get higher noise values in any case because every sniff of noise is rectified by the software and counts towards the rms average current. If you are measuring the voltage, the noise, being random, tends to largely cancel itself out as it does not get rectified.

You can test if it is noise or a genuine magnetic field that the CTs are picking up (if you're monitoring voltage as well), by flipping the CT over - that will reverse the power if it is a genuine magnetic field, or at least change the value if it's a mixture of noise and genuine pick-up. That won't work without the voltage input.

5 W is reasonable for a 100 A CT. 25 W is a bit high.

I flipped the CT's over and got the same response. I then swapped channel and still got the same response, so the noise is not related to the CT, but emontx.

Where should I look possible causes? Cold solder joint? After removing the old resistors and installing the new ones, I plugged in an unused 3.5mm plug and measured the resistance and got the correct ohms.

Or should I just live with it - noise is normal - just look at the US elections...

In my opinion there seems to be something wrong there.

Even I that I'm messing with the firmware have rarely seen such noise.

The worse I've seen was a CT picking about 15W from a near one (about 2cm) that was measuring about 3000W.

When you switched the CTs from on port to the other did the same port kept the same reading or the reading switched with the CT?

Cheers.

The noise did not change channels when I swapped CT's.

I did the following experiments:

1) After the emontx was running, I unplugged CT2 (the one that's reading 20W). It now read zero.

2) I measured the resistance of both CT's and got near 490 ohms +/- 5.

3) I plugged in a spare 3.5mm plug and left it open. It read zero

4) I shorted the plugs and it's now reading 20 W.

5) I measured the resistance of the burden resistor from the open plug and got 39 Ohm, the burden resistor value

From this I either have a cold solder joint, a possibly defective emontx or it's just normal noise. I could try changing the burden resistor to CT3 and see what happens.

How are you powering your emonTx, and which version is it?

And can you say what your calibration is, i.e. what is the maximum power that you are set up for?

1) After the emontx was running, I unplugged CT2 (the one that's reading 20W). It now read zero.
That is expected. The input is shorted to GND with no plug inserted (but not in the emonTx V2).

2) I measured the resistance of both CT's and got near 490 ohms +/- 5.
I don't know what it should be, but that's believable.

3) I plugged in a spare 3.5mm plug and left it open. It read zero

4) I shorted the plugs and it's now reading 20 W.
Taken together, 3 & 4 don't add up. The 'open' plug is in parallel with your burden resistor of 39 Ω, so I'd expect to see almost the same in both cases, as in the circuit you have, there isn't much difference between a short and 39 Ω - it's by far the lowest impedance around at 60 Hz mains frequency. That's puzzling. The only explanation that I can think of at the moment is that particular plug didn't open the break contact in the socket that grounds the input. If the plug tip or sleeve measure 1.65 V d.c. when you do that, I'm wrong and the contact was opened correctly.

5) I measured the resistance of the burden resistor from the open plug and got 39 Ohm, the burden resistor value
So that's good.

2) I measured the resistance of both CT's and got near 490 ohms +/- 5.
I don't know what it should be, but that's believable.

Cross check - 490Ω appears to be correct. The SCT-0750-000 I have, measures 490.8.

I put a burden resistor on CT3 and tried that. That channel is reading up to 1W. Not sure what's up with CT2 but I only have 2 CT's so can use CT1 and CT3. CT1 is still reading around 4-5W noise. This is acceptable. I'm happy.

BTW someone made a comment that appeared to imply that the CT's when attached to the house wires should not be near each other - how close is too close?

Thanks all for your help.

"how close is too close?" There's a line or two in the YHDC test report about that.

Hi, I am also experiencing this, the thing is I'm trying to use only 1 CT so that leaves out the issue that there is some interference between two CT's given a certain distance. I am receiving about 19-21 watts of noise on my CT. If I remove the CT, I get zero reading. I also get a proper reading when an appliance is running but whenever I shut it down, the reading would return to 19-21 watts

Watts is meaningless without knowing your system voltage and maximum current.