CTs Too Small

Okay, I got my emonTX built and my emonCMS going on the Raspberry Pi.  So I went to install the two CTs that I ordered with my kits and found that the SCT-013 (13mm core) just isn't large enough for my mains.  I'm in the US and my home was built in 2004.  I still have 200A service but the mains are huge.  I'll have to measure to see if the SCT-019 will work, but my question is if it's loose, will I still be able to use it?

Or if anybody has any other recommendations I'm open to it.


Robert Wall's picture

Re: CTs Too Small

As long as the (single) supply cable will fit through the core without putting any stress on the ferrite (which is a brittle material and can fracture very easily) then you should be OK. Having an air space between core and cable, and not having the cable exactly in the centre, will make a very small difference that can be corrected in the calibration. So no, it won't really matter if it's loose.

This make has been tried, and if I remember correctly was found to be OK (though which one from which range I can't remember). It was used with an Arduino and might have been used on the 1 V reference range (0.35 V rms absolute maximum), so you could well have sensitivity problems working into an emonTx with a 3.3 V reference (1.15 V rms). I have not measured one of these so I can't give you any indication of the highest value of burden resistor that you can use.


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