Sharing CT Clamp Output

Hardware
1

I’d like to share the CT Clamp output from my Sense energy monitor with an emonpi. I was able to get into the provider side of my electrical panel during the initial installation and clamp the L1 and L2 with the Sense CT clamps that came with my Sense kit. The provider side is now locked up tight with a tamper seal.

Is there any way to share/split the output of the CT clamp with both devices? Would I need to share a ground plane for reference?

2

Welcome, Jim, to the OEM forum.

I’m afraid the short answer is probably not. There’s no useful information on the page you linked to, nor on what passes for the manufacturer’s website - what I would need to know is first, what the rated current is and the output at that current, and second, how is that output used inside the main unit? The whole set of circuit diagrams is available for the emonPi, I doubt very much whether the Sense’s manufacturer will divulge that, but it might be worth a try. In any case, the emonPi input is not designed for sharing - and my guess is, not for the likely output of that c.t. anyway, and even if the circuit arrangement of the inputs of the Sense monitor was known, it might still not be possible for the two to co-exist using the same c.t’s; at least not without some add-on electronic wizardry.

I’m sorry to put a dampener on your plans, it might be necessary to break the seals and install two more c.t’s - bearing in mind our standard ones are probably unsuitable for your incoming cable, and you’ll need one from our ‘Learn’ page about using the emonTx (& emonPi) in N.America.

3

Thanks for the quick and thorough reply Robert. I was also unable to find any detail on the CT Clamps and if they have an internal burden resistor or not (I would expect yes, for safety). I suppose I could connect the output to an oscilloscope and look for readings around 0-1v or possibly a DVM to see if I’m getting current instead.

4

I would guess (and it is only a guess) that you’re right about the internal burden, and the output might well be 333 mV - but at what primary current? possibly 200 A. Before installing the c.t, this measurement would have been easy. It’s quite tricky now. But it still doesn’t help with using the Sense monitor and the emonPi in parallel.