Which CTs for tight spaces on mains

Dear IoTaWatt folks,
I am brand new to the subject of energy monitoring (using unconnected kill-a-watt doesn’t count). Want to get and install iotawatt in my distribution board. But the placing seems to be quite tight and I am afraid stock “Current Transformer 200A x 24mm split-core” which is a part of the North American bundle wouldn’t fit:


is there a smaller factor CTs which you could recommend instead in my case?

Thank you in advance!

PS any discounts to Debian developers and otherwise good FOSS folk? :wink:

You may be able to get a couple of ECS25200 clamps in there. The cross section of the clamp portion is 14mm x 15mm. If the space between the cables is, or be made to be, greater than 14mm (~9/16"), they could fit. To stack two in the space would require that the 9/16" space be about 1.25" long. I think there’s enough space on the right for one clamp, the left would depend on how much space is under the neutral.

If an electrician could coax those two cables 3/4" apart for 2" you could fit a pair of SCT023R in there. You would need to get the 300A/80mA model to match the entry in the IoTaWatt configuration tables.

Note: ECS25200 should be back in stock soon.

Thank you for the quick reply! 9/16" between might work at the bottom but not yet sure if for 1.25" long since they start “converging” pretty rapidly. Here are photos with the ruler (forgot to dig under neutral to check spacing there heh - I guess will need to dig in again):


BTW – would you recognize those “clamp style” CTs in this nice iotawatt review https://quellareviews.wordpress.com/2018/09/16/iotawatt-energy-monitoring-device-review/

No model was listed but they were chosen to replace ECS24200 for this tight fitting. Although they are bulky in width, from the picture they seems to not require much separation between wires, so I wonder if those might fit.

crazy idea came to mind: if there were 3d models true to size/shape of the CTs, I could have printed those to try the fit before purchasing! :wink:

Those are ECS24200, which is currently standard with the US bundle. What’s not apparent in the photo is that when installed that way, they extend about 1.1" from the face of the cable, so you need that much clearance to install the panel cover. It doesn’t look to me that you have that much clearance, but possibly you do.

Regardless of whether you went with the clamps or the ECS24200, you would need at least 1/2" clearance between the cables for up to 2". I think that’s doable, but can’t recommend that you manipulate those live cables to make it happen. I have to recommend you get an electrician to possibly slit the gray cable jacket as far as possible, and persuade the two conductors apart with a non-metallic tool like a wooden wedge. It’s probably not possible to shut down the feeds unless you have an outdoor disconnect, but at least shutting down the mains would insure there is no current through the connectors as they are disturbed. An electrician may also see a way to feed more cable into the box, and could also disconnect the neutral to install a clamp while the main is off.

Thanks again! I will entertain an idea to invite electrician at some point. May be meanwhile I will just establish monitoring of the specific loads, and look into ingesting our total consumption from our power provider – https://greenmountainpower.com/ – which provides .csv (or a fancier Green Button initiative compliant XML dataset) at 15 minutes interval.

edit: I do not think there is a conveniently available outside mains disconnect

I can say that the image you showed is my install and yes as @overeasy said they are the standard 200 amp clamps. After this install, as it was tight even in my panel, I instead paid a bit more and went with the clamp style CT he sells which allowed more room near the mains, but they have a bit more bulk below where the sensor cable comes out. So I had to clamp them around the main and swing where the cable came out towards the back of the panel so I could close things up. The picture was taken prior to me making the change to the different style. Just so you are aware.