Larger CT?

I'm new to the forum so hopefully posting this right...

I am happily assembling my first emonTX and emonBase.  My dream is to use several TX's inside a distribution panel, each one measuring a different 3-phase service (240V) to buildings here at the community, and feeding the data into 1 emonBase which I intend to connect directly to a computer rather than to the website.  Your comments welcomed about that.

Unfortunately the SCT-013-000 CT only accommodates wire diameters up to about 12mm, and some of these services are wired with 17mm cables.  Please note I am confident there are no individual phases pulling more than 100A.  Can someone recommend a larger size CT that is compatible with emonTX?

Robert Wall's picture

Re: Larger CT?

Any current transformer that has a sufficient VA rating will work with an external burden resistor. You need to choose the transformer ratio and burden to give about 1.1 V rms at the maximum current you need to measure, and then the transformer VA rating is determined by that.

You could try something like one of these from  but noting the output is 0.333 V rms. You could try contacting the factor/manufacturer to check what the exact effect of increasing the burden resistance will be (if that's possible), and see what they recommend. If you use it only to the nominal output voltage, then you will only be using 1/3 of the input range and you will have significant inaccuracies when measuring low powers.

I believe one of the forum members is successfully using one of these, but not with the standard emonTx kit - he's using it with the Arduino board with a 1.1 V p-p input, which this c.t appears to be designed for.

[Edited - duff link, thanks to Calypso_rae for spotting that, plus some details added]

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