Noise from one device bleeds to another?


I’m getting everything set up the way I like pushing metrics to an Influxdb and Using Grafana for the graphs. One question I have for example when my dryer comes on at the same time there will be a much lower wattage mimicking the dryer wattage at the same time frame on another device. Is this normal or one device receives interference from another? Please see picture. …Well I don’t see and option to upload a picture…



While barely significant, that is interesting, and if you want to work with me we could try to figure out where this is coming from. Yes, it’s possible that there is some communicative effect inside the IoTaWatt that cause this to happen. I kinda doubt it, but easy enough to narrow it down. First, I’d like to see the configuration and what kind of CTs are used by both circuits.

I’d like to see you move this circuit to a different input on the IoTaWatt, preferably on the other side so it is using a different ADC. If the problem moves with the CT to the new input, then I would look at something going on in the panel like the CT for this circuit being right next to the CT or wiring for the Dryer.

If it doesn’t move, then I’d like to see another CT plugged into the original input and see if it does the same thing. If it does, then I would agree that it could be one input effecting another.

Either way, I think it’s amazing that you are getting that resolution on the outdoor light channel to record 1.75 watts in such sympathy with the dryer. My money is on an external factor.


I will will get this info for you and try moving the input to the other side and post that result this evening.



Here is the config where we see the dryer and outside lights next to each other resulting in the above graph. Second picture I switched input 10 (dryer) with input 4 Well…I will let it generate some data and see what happens now. Thanks.



Unrelated, you might want to review the documentation on 120/240 Volt circuits. Just doubling the value for the range, and probably the dryer, will probably not be completely accurate. Those appliances use both 120 and 240 Volts, so both conductors must be monitored. You can do it by passing both through the same CT if you observe polarity. Read the discussion referenced above.


Thanks. I knew the range this was needed and had to order another CT because the wire is 4 ga. (to large) I will get a two into on adapter as explained in document to connect. I didn’t know the dryer was like this as well and just fixed it. Thanks for your help.


Okay, Here are some pictures of today with he dryer moved like suggested. As you can see the riffle is on other branches as well even the barn in a diff sub-panel. I’m not complaining or seeking support, I think the IoTaWatt is amazing and what I’ve been looking for. I’m going to try flipping the hot water heater off and see if the dryer affects it like that. Notice the outside lights are smooth no affect at all. Strange.


It looks like it may be something going on in the ADC. I took a close look at my data with the dryer running and I can see something similar. Funny I never noticed it before. Like you, some circuits seem to be immune. One twist with my system is there’s one that appears to be negatively effected:

Then I’ve got another that seems to be effected several times as much as the others, and that one has three circuits running through the CT. So It may be inductive cross-talk or it may be in the ADC. I’m going to open up my panel and take a closer look at the CT and wire paths.


The negatively effected circuit maybe explained by the voltage drop in your mains associated with turning on a large load. Lower voltage means other circuits will show lower power consumption. Depends on the impedance in the utility network upstream from your board. In my case the LV mains are long and the effect is quite noticeable as you can see below when the hot eater heater turns on.


Well, there’s your problem. You probably should have something that gives up heat not takes it in for a heater :wink:.

But, good point on the lower voltage causing a difference. I see a change of less than half a watt on some circuits that are basically nothing (less than a W) when water heater turns on 2.5-3k to 1 difference, ie close to 1 bit out of 12.


Voltage drop does not explain where the shape is in sync across two circuits. That is if they both go up and down at exactly the same time then it looks more like some sort of lack of signal separation whether at the CT, CT leads on in the Iotawatt.

Yes the “hot eater heater” is an interesting concept.


Flying purple people eater


I actually have one of those. The hot eater water heater that is. It is a heat pump water heater and it eats the heat of the surrounding area and gives it to the water. I have had it for over a year and it does appear to save a significant amount of energy, but I have it set so it runs 16 hours a day.


I’m thinking there may be some current leakage in the TVS diodes. IoTaWatt uses 4 channel rail-to-rail TVS ICs, so groups of 4 (0-3, 4-7, 8-10, 11-14). My dryer is on 6. I see this on 4 and 7, but not on 3 and nowhere on the other ADC (where the drop was). I’ll be doing some experiments.


and @frogmore, @Giraffe,

I did some experimenting this afternoon, and narrowed this down a lot.

First, I focused on my oven/stove circuit which measures 2 240V circuits by passing all of the conductors (black one way, red the other) through an SCT013-000 (been there for years). This CT comes in port 7 with the dryer in port 6.

When I start the dryer, the oven/stove goes from 6 watts to 16-17 watts. I tried it in multiple inputs on both ADCs. Same thing.

So I dragged the oscilloscope down there and hooked the probes up to a 3.5mm jack with a 22 Ohm burden. With the dryer off, I saw a little under 1mV at 60Hz. When I turn on the dryer, the value jumps by about 1mV.

Lets do the math. The SCT has a calibration of 100, which means that 1 Volt across the burden is 100 Amps primary. So 1 mV = .001V x 100 = .1 Amps. .1Amps x 120V = 12 Watts - just about the increase I’m seeing.

My conclusion is that the problem is external to the IoTaWatt. It’s reporting what the CT is telling it. I tried removing the CT from the cables but leaving the CT cord running through the load center and the problem went away, so I don’t think it is anything with the cord. The two (4) CBs for the oven/stove circuit are in the upper right of my load center and the dryer is in the upper left. The cables do not come anywhere near each other, although they do run near the mains, which also carry the dryer load.

My main panel has been running these CTs for years. There is an eclectic mix of CTs - SCT013-000, CR3110, HWCT-004. I have been meaning to redo it with Echun CTs. Maybe that will have an effect on this issue.

I intend to try various turns ratio CTs to see if it’s actually current in the wire or the CT. In the meantime, there’s nothing that can be done in the IoTaWatt.


Thanks for sharing this information. Like I said this isn’t a problem. I was just curious. Thanks again.


I’m glad you brought it up and that I was able to resolve it. Had it been something inside the IoTaWatt, I would have considered it a problem.