# Minimum Distance between CT?

Is their a recommended distance between CT so that they do not interfere with one another?

Up until now, I have been using Emonpi to measure my solar generation and import/export to the grid. Yesterday I had a PowerVault battery fitted to make use of spare generation rather than send it to the grid. The PowerVault uses CT for calculating the same thing so I don’t want the magnetic fields impacting one another and skewing the readings.

Apologies if this is an overly basic question.

Paul

That isn’t quite the data that I think you’re looking for, but it should give some indication.

I think the way to establish what the interaction (if any) is would be to reverse one of the c.t’s and note the difference in magnitude of its reading. Obviously everything else has to be in steady state while you do that. The ‘crosstalk’ is then half that difference.

I could quite easily test two SCT-013-000 c.t’s, but unless both of yours are that one, it’s of limited relevance to you.

Thanks @Robert.Wall The CT used by the PowerVault appears to be same model but a different version. The company is YHDC and the model is SCT013-RJ45 (100A:50mA) My understanding from the document you provided is that as long as they are not touching and as far away from one another as possible the impact will be no more than a few mA

Paul

I’ve just done some measurements. Here they are:

My test rig is a 20 turns coil with approx 2 A flowing, i.e. equivalent to 40 A. The coil diameter is approx 100 mm.
The two c.t’s are both SCT-013-000, black cable, moulded plug, using emonLibCM and the average of 10 current readings each time. The maths: difference = (1 - I2/I1) × 1000000

The 2 c.t’s diametrically opposite, facing the same way, calibration adjusted to give equal readings: difference 2 ppm (parts per million)
one c.t reversed: -1220 ppm
both reversed: -1056 ppm
both back in original positions: 393 ppm
both facing the same way, touching: 263 ppm
one reversed, touching: -467 ppm
both facing the same way, one c.t. thickness apart: -12787 ppm
both facing the same way, one c.t. thickness apart, repeated: 4242 ppm
one c.t. reversed, one c.t. thickness apart: -3673

The two pairs of measurements that were supposedly the same shows how important it is to seat the core halves accurately, and gives some idea of the error in my technique.

In general, it looks as if the error is ½ % or less.

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