CT Interference/Bleedover?

I’ve got everything moved over to the IoTWatt, and now that I have more than four CT ports, I added in the extra SCT013 that I’ve had laying around clipped on the leads for my A/C unit. Later on, I noticed that the A/C was showing some draw in the EmonCMS graphs - peaking at about 16 Watts, but the A/C was off. Looking at the other charts, it looks like that’s when the electric range was on, and the wires for the range are real close to the CT for the A/C, so I’m guessing that the CT was picking up some bleed from the ranges lines. Assuming that’s the case, is there a certain amount of distance needed between the CT and other lines to prevent this? Any other things that might help?

That seems like a lot of current to be picked up as noise in an SCT013-000, but maybe, lets look into it. First, can you post the chart that raises this suspicion? Also, can you give me a little more detail about you A/C? I’ve got a mini-split heatpump, and when it’s off, it draws 11 watts:

Those 3/4 watt spikes may be induced noise, but I’m very confident that the base draw is accurate. I have an EKM meter on that circuit and it matches exactly with the IoTaWatt kwh usage.

Sometimes HVAC units have 24V transformers that are notoriously bad phantom power suckers.

So show me the data and we’ll go from there.

EDIT: Also, a simple test would be to simply shut off the breaker to the AC. If that’s phantom power draw, it should go away.

Basically, I noticed some power usage when my wife was cooking in the oven, so I looked closer and found a correlation.

Here is the whole house draw from last night:

Here is the A/C draw from the same time period:

Add in the same thing this morning (just a bit less) when I was cooking my breakfast:


And the A/C fro when I put the CT on the lines:

You can JUST make out the little ripple around 1800 and then again all the way at the very right this AM.

The unit is an older one, probably 10 or more years old, and I’m PRETTY sure it doesn’t have a transformer in it - there is one on the side of the furnace that runs it and the thermostat though, and that’s on a different feed.

You’ve convinced me that there is noise associated with the oven. I’d like to narrow that down. Looking at the graph, it looks like the oven draws around 2500 - 3000 watts. That seems to be the incremental change in whole house usage. I’d be curious if you have a CT on just the oven, because the sympathetic reading on the AC seems to go to zero when the oven is off, even though the rest of the house is still using a fair bit of power - like 3500 watts.

So, unless there is a CT bringing just that oven usage into the IoTaWatt, i’m thinking it’s not any kind of crosstalk inside the IoTaWatt, as it would probably wouldn’t go to zero while there is still half as much usage on the main.

That leaves the CT and it’s cable. Can you do anything to change the situation and see what happens? Usually in a US panel, the wires are stripped back to the point of entry, so they are accessible at various points. Some panels are neat and others are a ratsnest. Be CAREFUL. better to shut it down rather than have to gingerely nudge things around. REMEMBER, the mains are still live, even when the breaker is off!

So it looks like I got it sorted out. Both the A/C and range breakers are on the same side of the panel, so I did a little untangling and moving. I got the A/C lines untangled so that I was able to place the CT higher up in the panel and a bit cleaner than it was before, and I moved the breaker for the range down to a spot that I had a 240v breaker that is not doing anything (and in the process I made an interesting discovery - one of the lines for the range was loose and popped out of the breaker when I removed it! Looks like it had been that way for a while and had gotten a tad warm. Maybe that’s why the old stove would trip the breaker when we used the broiler!). After doing this and firing up the stove, not a peep from the A/C feed. So it must have been due to the way the CT was clipped over the lines for the A/C along with the proximity to the lines for the stove.

At the moment, I do not have a CT on the stove, although I plan to put one on it. I was going to put the SCT013 on it, but the CT’s opening isn’t quite big enough to clamp over both wires. The moving of the two breakers also put the stoves wires in a better position to put a CT on them.

Glad to hear it. Thanks for the update.

That’s one of the reasons why I shudder when I think of non-experienced people inside a panel. I have a really BIG screwdriver that I use when I tighten down a breaker connection, and I really go at it, to the point I think I might just bust the thing up. But they can take it and it’s the way I always see electricians do it. So you dodged a bullet without a little arc-fire. Another reason why I always make sure to put the cover back on the panel.

As an aside, have you tried induction cooking? So much of an improvement over electric resistance cooking.

The thing is the panel and that breaker was put in by an electrician! I’m not a pro, but working inside an electrical panel is nothing new to me. Like you, I crank them down good when I install breakers.

Believe me, I wanted an induction cooktop. I really don’t like this one. Takes FOREVER and a year to heat up, not to mention when something boils over or spills, have fun cleaning that up. But, at least when we were looking for the new stove, there weren’t many induction stoves, they were pricey (bot not off the charts) and were pretty much only available in stainless, and my wife ‘hates’ stainless :/. Truthfully, I’d rather have gas, but that would have been a little more involved than wheeling in the new stove and plugging it in.