CT Sensor Amps Question(s)

@overeasy,

Once again thank you for the detail and extra input. I really like the clamps on the ECS25200-C2 you have listed and think I will go that route for the two mains when there are a few IoTaWatt units also in stock in the near future. I like when something is set to Plug and Chug! :slight_smile: I also like how you can break out the mains and it is quite revealing how they are used when you have visibility into them with the product. What we miss when we just do not know. I’m almost scare to install one of these as it will show just how spoiled we are.

We will be having solar installed in the next month or two, and I do not think what the circuit will be install for that (research says about 40A for 7.1kw system). I also understand how important it is for the direction of the CTs as the solar will be a supply and the grid will be consumption. I would like to get the product in and running prior to solar to see the difference. I’m a numbers guy and love the charts and graphs. Too awesome.

Sounds like you have some great knowledge of the bigger systems out there. We have 200A to the house and I believe a pole transformer feeing our house and two others. We are also on what I believe is a 1350 line (?) so it is a major feed to the rest of our smaller town.

So, you would recommend 100A on the two mains, and the same for anything 30A or above in the panel? I know on Aliexpress, YHDC sells various rated models such as 20A (not recommended by anyone), 30A, 50A, 75A, 100A and 200A. Sounds like @overeasy recommends going with the models he have available for obvious quality concerns. And for the smaller stuff, just get a few 20As and done.

Thanks for taking the time and your feedback.

By way of example, here are six CTs
ECS1050 - 50A max
SCT013-000 - 100A max
SCT019-000 - 250A max
ECS24200 - 150A max
ECS25200-C2 - 150A max
ECS16-100 - 100A max

There is no special calibration. Just plugged them in a few minutes ago.
image
They are all around a single conductor hooked up to a light bulb array with one each 100W, 75W, 60W. Stepping through the combinations:

imageimageimageimageimageimage

So even at very low current of 0.5A - 2A, the “mains” type CTs are just as accurate and have equal resolution to the 50A “branch” type CT. The SCT019 quickly goes to about -1% from the others, but that is calibration, not resolution. The QC is maybe not as good on those as the Echun, plus they are 6000:1 vs 4000:1, 2000:1, 1000:1. But in any event, excellent results could be obtained using any of these, even on 20A branch circuits.

The accuracy is due to the IoTaWatt having a precision 0.2% voltage reference onboard, as well as sampling at nearly 10 times the rate of some older technologies with 12 bit ADCs. That was the design goal: Get away from the nitty-gritty of custom firmware, burden resistors, and calibration factors.

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@overeasy, wow that is amazing and so cool. Just to bounce it off you, below is an image of what I would be looking at for a set of CTs. I was not really sure of the difference of the two lower (solid core or Not), but I would think for 20A circuits one could use the non-solid and for the 30A-50A use the solid. Hope this is the correct thinking. Always looking for good, but if I can save on some of the smaller circuits it may not matter going cheaper.

Thoughts on the below?

First, for the obvious reasons, I must recommend that you have a qualified electrician install these, especially the solid core that require actually disconnecting and reconnecting high voltage circuits. At the same time, I can only go by the typical usage of these appliances. An electrician would be able to examine the nameplate rating and insure proper capacity. In particular the sub-panels, the A/C is impossible to guess at, and the an electric furnace would certainly exceed the 20A capacity so I’m assuming it’s gas or oil and the primary load is the blower.
Mains are fine.

Barn Subpanel:
Typically, a sub-panel is 240V, so you would either need two ECS-100, or you would have to clamp it around both the red and black conductors in opposite directions. Sounds complicated but actually pretty easy. When you say barn I have to wonder if it’s high current, because if the total of both sides can exceed 100, you would be advised to use an ECS24200.

Garage sub-panel: Same logic as the barn.

Solar: ECS10-50 should be fine for 7.5kW.

Range: Electric ranges require the same treatment as sub-panels because they typically use both 120V and 240V.

No issues having an electrician do the work, yet I have also bee in my panel quite a bit (mains off) and previously ran some of my own circuits. Each of the devices I have listed are the actual circuit breaker rating on the listed items. Would you recommend using something that does not requite the removal of the wires. I was not sure if the main differences between the two models apart from solid core and not.

The Garage sub panel is a 50A where the previous owner did some auto repair work and had an electric heater; now removed. The only thing fed from the panel today apart from outlets are two garage doors (1/2 HP) and a mini-split A/C for the lower part of the house. This is a single run like a range, so it sounds like for anything that is 240v I would need to either double the connectors or join them as you suggest to have a single sensor pickup for both.

The Barn sub panel was a new install when we had our barn remodeled and they pulled 100A circuit for lighting, some networking gear and security cameras (POE), yet in the winter we do have to run two heated water buckets which I think will pull some extra Amps (but I’m sure a 50A would have supplied our needs. 100A may be just a safer option for a new install. I agree, I will need to add a 100A for the other side of the barn to make things easier.

You are correct on the “furnace” as it really is an oil burner for both the boiler and one for the Hot Water. So the current is only needed to get it started things started. I will have to go back and though through the 240V is this could impact the number of devices or CTs now. Thanks for checking.

Looks like the following would be 240V in my configuration: Range, Clothes Dryer, Barn, and Garage. I may do the turn around option for these so I can have more sensors then less. Nothing else I can think of is 240V. Is a typical Solar install 240v I would have to assume?

Lastly (I think), I assume you can combine two lower amp circuits that are really the same device such as the A/C unit which has a 15A for the blower in the Attic and a 30A for the outside condenser. If I put a single CT around them, we could be able to bind the used current for the one device, correct?

Looking more like this may be a better option and give me flexibility:

Here are a few images for my panel at 240V items and an image/question on twisting one leg of the cable around in the CT.

When you say turn around one of the wires in a 240v circuit (sub panels, dryer, AC) do you mean like the below? Do you not get both negative and positive values in the configuration? Maybe I’m missing something as I thought they were directional sensors and such a configuration would show positive current for one flow and negative current on the other leg.

Is the reason you cannot do the below is that you only get 1/2 the current measured do to the 120v reference current?

I also saw this article from the learn section of OpenEnergyMonitoring.org, but it is not as clear on the aspects of monitoring a US 240V circuit using a single CT. Use in North America — OpenEnergyMonitor 0.0.1 documentation

Anyone else have anything they can find on this?

I know this is hard to understand. Consider this: when you install CTs on single 120V breakers, they should be oriented in one direction for circuits on one leg of the split phase, and the other direction for circuits on the other leg. This is because there is only one voltage reference transformer and the voltage on the two legs is exactly opposite. So when you reverse the CTs on the other leg, you reverse the current signal as well and it now matches the voltage reference from the other leg.

So when you run the conductor for one leg backwards through the CT for 240 volts, it’s like reversing the CT on that leg. If you did not reverse one of the conductors, one would yield positive current and the other negative, cancelling each other out. What you would be left with is any difference in current between the two. In the case of a balanced load, that would be zero. In the case of a branch panel with various 120V circuits, it would be the amount of unbalance between the two legs.

There are other ways to handle the branch panel. You can put an individual CT on each leg, reversing one, and combine them with a headphone splitter before inserting into the IoTaWatt input. That would be the same as using the single CT with a reversed conductor, except that now, the CTs only need to be rated for the maximum capacity of the one conductor rather than the total combined load.

Thanks again @overeasy for the feedback and details. I assume that one needs to do this turn for any 240v circuits or only for the subs? Something like the well, dryer, etc would also have a single CT but one phase reversed, correct?

I’m not sure my panel will be able to add more CTs (it is older and cramped already). So I would rather get some close info than do the double CTs. If you go the way of the splitter, do you get the same resolution or lose anything?

Just let me (Us) know when they are ready as I’ m ready fro you to take my money for CTs and the IoTaWatt device (power plug, etc.). :slight_smile:

For dryer, well pump, probably A/C, you only need to put a CT on one leg and then double the value using the output “calculator”. I am also adding the ability to specify that the basic input should be doubled in an upcoming release.

In a past life, when I was wiring a 240V panel, I ran allof the conductors to the bottom of the panel and then turned them up to the appropriate circuit breaker.


In this way, there is flexibility to move circuit breakers around within the panel. This is common practice among many electricians. I bring it up because it really facilitates connecting a CT to a 240V circuit with one conductor reversed:

The CT is an ECS10-50 and fits pretty well into the space.

I can confirm that most of the wiring in the panel does have a decent loop and pushed to the one side, so like you have shown, it looks like for the sub-panes (barn/garage) I will have one CT and reverse one of the legs as shown above. For the other 240v services such as the dryer, pump, etc. I just put it around the one and double the reference voltage in the UI.

Sound just too easy, again, take my money. I’m sold. Not just on the product, but the great service and consulting services as well!

For a dryer and stove, you either should put both conductors through one CT or use two CTs. Dryer motors are typically 120V, so you would either not count it or double count it with only one CT and one wire. Stoves vary in terms of how they use power, but can and do only use 120V some of the time. Pumps and water heaters generally don’t get wired to the neutral, so a single wire, single CT works fine for them.

Thanks Frogmore for the info. Sounds like it is something that is trial and error or if you have access to the appliance it may tell you. So for a Dryer, is it often the motor on 120v and the heater on the other leg of the 120v? Our dryer connection is a three-wire 240v connection and 30A double sized circuit in the breaker. In my drawings above, all the appliances are 240v (dryer, A/C, Pump, Range, and I assume future solar). I would assume I could also join the two A/C objects into one as one is the air handler in the attic and the other is the condenser outside. Both have a 240v connection to the box, yet they are a single object. That way I could potentially save on CTs if I could combine these two.

Wherever possible, I recommend placing the CTs of 240V circuits as diagrammed with one conductor reversed. There is no downside, it takes away the guesswork of whether there is a 120V component, and the input will show true power without the need to double it in the IoTaWatt.

So, there are two options based on your previous feedback where (not for sub panels) you can place one CT on one leg of the 240v circuit and double it, or you recommend the same with all 240v and sub panels to use the turn-around one leg option and no need to double based on reference voltage? I just want to make sure that I’m clear from the previous input above.

The best option in your opinion is to go with reversed leg (twist one phase) in the CT for all 240 based circuits in the panel?

It takes away any guesswork as to whether there is a 120V component. I don’t expect users to have the fundamental understanding of how these circuits and appliances operate, and I don’t think it should be necessary. So yes, On balance I think this is the best universal recommendation.

That said, an electrician would know whether any particular circuit is true 240, and there could be circumstances where measuring just one leg could be useful. For example, if the CT available is not rated for the full current of both legs, or if the panel is wired in such a way that it would require modification to add the reversed leg.

Consider a 10Kw solar inverter. The nominal output would be about 42Amps per leg at full output. Inverters are true 240V so you could use an ECS1050 on one leg and double it. To monitor both conductors would require an 82Amp CT like an ECS16-100 or SCT013-000.

I often over think things and I like that there are options that a little troubleshooting would not solve. Tweak a few things here, change a few things there. I was hoping to limit the number of CTs installed in my panel (being from the 1970s) it is quite tight in places and rather full. I wanted to get the most number of circuits monitored with the lest number of CTs.; as I’m sure everyone is wanting to do.

My thoughts are to use up 4 of the 14 to monitor mains (2x) and solar inverter (2x) as these are the more important items to have good numbers on. Consumption of energy and suppling of energy (via solar).

The remaining 10 ports could be used to monitor the two subpanels (2x) with one reversed leg (Barn/Garage) which gives me 8 remaining ports for things like the Burner/Hot Water, A/C, Well Pump, Range, Fridge, Dryer, Freezer. So , I would be back at the same plan with the number of CTs to cover the major items from earlier discussions.

Sounds like I would need to look at another unit to pick up all the smaller circuits if I wanted too in the future.

I suppose this discussion could go on forever, but I do think it has been productive and is a really good example of the kinds of decisions many users will face, so I’ll add a little more:

The solar only needs one CT.

Using the two wire method, you need to have a CT that is rated for the sum of the two breakers feeding the 240V circuit. So I’m guessing the Range, Dryer, possibly A/C will need more than 50Amps.

In my house, I monitor what I can with the 14 inputs, and then I have defined an output which is mains minus all of the monitored circuits. It’s remarkably useful. Here is my “unmeasured” usage for the past 24 hours:

The baseload is about 80 watts and is composed of various 24/7 stuff like our Radon fan and some standby battery chargers in the garage. Even with large appliances switching on and off, this doesn’t vary more than 10W or so. What you see on the left is a dehumidifier that I’ve had to run for a couple of days in the basement. It apparently filled up and stopped about 15:30 yesterday. The blip at 17:00 is lights in the basement when I went down to feed the worms. The usage starting at 20:30 is outdoor lighting.

The point is that using this “remainder” method, you can actually see what is not directly measured, and decide if it’s something that needs it’s own dedicated monitoring. I’m of the opinion that most households can get on top of 95% of their usage with 14 CTs.

Here I’ve zoomed in on three hours of that dehumidifier portion:

Bear in mind that this isn’t a direct measurement of the duhumidifier with it’s own CT. It’s my mains with all of the measured circuits subtracted from it. IMO the accuracy of the measurement is awesome. In each cycle of the device, you can see the inrush current and the exact same trend up as it heats up and uses more power. Then when it shuts down, the usage drops right back to my baseline load.

You’ll have to stare at it for awhile to make sense of it, but here’s that same zoom of the dehumidifier with the mains and a few of the more active circuits that are being subtracted from it.

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Yes, taking a look at the remainder is helpful, as is looking at which “phase” it is on, or if it is a 240V load.

Bob, which dehumidifier do you have and how are you controling it?
Most dehumidifiers I have seen turn on the fan before and after running the compressor, which seems like a good idea, but turns out to actually not be one from an efficiency point of view. If you have the dehumidifier in the basement for moisture control (more than comfort) running it with such short cycles is not a good idea. It it the way most/all are setup, but it uses more electricity and stressed the components excessively. My first one lasted a season running like that and made the basement quite hot. My 2nd didn’t even last a season, but I got all my money back on that one :grinning:. I am now on my third one and it has been running since November. I have a custom control system that turns it on and leaves it on for a minimum of 30min. I have the dehumidifier set to keep the humidity at 35%, which it likely could never achieve. I measure the water output with a modified rain gauge and now have an idea of how well things are going. I did this originally to see when the dehumidifier was loosing it’s refrigerant charge, since that was the failure mode of the previous two, and it was visibile in the power utilization. It takes less power to run the pump when there is less/no refrigerant. I first discovered this looking at the remainder signal. Now, I have a Sonoff POW that measures the power of and turns on and off the dehumidifier. I have a sensor on the other side of the room that measures the humidity. I have a flow in NodeRED that gets the power measurement from the POW via MQTT and the humidity from another device and then makes the decision to turn on/off the dehumidifier by sending a command to the POW.

I’m a graph and data guy and I love the images you have attached along with the visibility they provide. Way too cool. So, in your opinion, you would just buy the two 200A CT for the mains and the rest (12) 100A CTs just to be safe and make sure I would not exceed the load? I love the discussion and I agree it could go on for ever, but as you said, this is very helpful to me and I’m sure future readers, etc. Love the interaction and sharing.

Can you PM me when you have time and we can talk about the CTs and a unit when available? Or, if I can get on a list of users when they come available?