Flexible CT Sensor

I have an older panel with very limited room in it. There is no way I can get any type of CT sensor on the mains lines other than a flexible Rogowski type. Without doing too much homework I purchased the Emproia one, thinking it would work since it has a built in integrator, but now I see others asking about it and being told it will not work. It DOES pull in information to IotaWatt, but it’s just not accurate, and I’m not sure what custom settings I would use for it.

Anyway, true question, is there any Rogowski sensor that can be used with IotaWatt? Any at all?

I think it’s technically possible, but I have not tried to do it. It’s all open source, so if anyone wants to do the R&D, have at it.

I would love to do that, but unfortunately that is well beyond my abilities. If Rogowski sensors won’t work today, do you know of any sensors that are compatible and are smaller than the slim one that is currently out of stock on the store? I would really like to monitor my mains but as you can see in the picture, space is very limited. This flexible sensor was barely able to squeeze behind the line as it is.

How much room is there between the cables and back of the box. It looks like you might be able to put a CT on the left cable. Can you post a picture of the neutral conductor?

Less than 10mm. Probably 7mm, and there’s a bolt head on the left of the left wire that takes up some room too.

It’s hard to get a picture of that neutral wire behind the other wires as they are quite stiff, but there is very little room to the side or behind it due to the black plastic, and up top where it turns (behind the black wire is pictured) there is no room due to the clamps (black and purple) on the incoming line .

Doesn’t appear possible then.

That’s really unfortunate. I really liked the IotaWatt and was hopeful I could get this to work with my fairly limited skills.

Looking into this a bit more and reading all I can, from these labels on the Emporia sensors’ integrators, do these look like VT sensors instead of CT? If so, would it make sense that IotaWatt is able to get a date reading when configured as a CT sensor? Or am I way off base here?

It won’t work as a VT, but if it looks like a 333mV CT, there is hope. If the burden resistor is removed from an input, it will become a 0-1V input instead of a 0-50mA input. The RC output is only 1/3 of scale, but that may give satisfactory results.

If you want to give it a go, remove the burden on one of the inputs, plug in the RC using a 3.5mm jack wired to tip and sleeve, change the burden value in setup to 6.67 ohms and configure as an AcuCT-H100-200.

OOOooo this gives me hope!! The RC already has a 3.5mm jack on it.

Could I use the ports 13 and 14 (the extra ones) instead of modifying the IotaWatt? If so, what are the dimensions of that barrel connector so I can look for a 3.5mm adapter?

Thanks so much for all the help.

You can use any input, but it must be through the 3.5mm jack and you would need to remove the internal burden resistor. That’s pretty easy actually. If you are going to order one, I can remove the resistor, but no guaranty it is going to work. Another approach is to send me the RCs and I’ll try to make it work at the bench.

I sent you a PM to discuss this further. Hopefully we can get it working - if so this would be a great opportunity for others, as I have seen similar questions on the forum.

Got the package today. Bench tested at various amperage from 8-30 and output was as expected. Connected to an IoTaWatt with burden removed and was plenty accurate. I installed on my mains alongside Echun 200A clamps. Seems to be within 1% but will let it run overnight to get a better sample.


After 24 hours the rogowski coil has shown to be as accurate as the Echun clamp. They are within 0.4% of each other. I’ll be writing this up and adding to the docs.

Basically what is involved is buying a set from Emporia ($59.99 right now), remove the burden resistors from two iotawatt inputs, install the rogowski coils and plug them into the IoTaWatt, configure as generic with 12,000 turns.

I am curious… What are the two circled devices on the incoming MAINS in the picture below? If these are some sort of ‘tap’ devices, feeding another panel/device, wouldn’t the CTs need go go above them in the panel to measure the total load on each leg? :thinking: Unless a solar system is involved in some way…

[UPDATE] After doing a little research, I am guessing they are Supply Side Taps for a solar system, used when the electrical panel is full and cannot handle the addition of a backfeed breaker for the solar energy. Can anyone confirm?

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That was my assumption.

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Yes, those taps are for the solar supply. I have separate CT sensors on the solar lines.

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Looking at the emporia website, the rogowski requires its own power supply?

Yes, but the power supply is included. It doesn’t have a power plug - just 2 wires they expect you to wire in your breaker box. It’s a single transformer with 2 barrel connectors (one for each coil)