Double CT Loop - worth it at low loads?

Can someone confirm that its best to double loop the live conductor through the CT where possible for low loads and adjust the burden resistor for double the actual current? The channel concerned is only likely to meet 1500W peak so it already has a lower burden resistor than standard.

I have 2 other channels that measure up to 3Kw, is it worthwhile doing the same with these too?

All 3 have the standard 100A CT

Robert Wall's picture

Re: Double CT Loop - worth it at low loads?

I'm not sure what you're saying there, I think your reasoning is a little mixed up. A current transformer works on currents. Having a two-turn primary winding will double the primary ampere-turns and that will in turn double the current in the secondary winding. Adjusting the value of the burden resistor will change the voltage that is developed across that resistor by the secondary current, and it's that voltage that the ADC converts to numbers. Doubling the primary turns is a better course of action than doubling the burden value, because the CT errors remain roughly constant (i.e. smaller in proportion to the secondary current), but you can do both.

A lower value of burden resistor will reduce the sensitivity of the input.

sheppy's picture

Re: Double CT Loop - worth it at low loads?

Thanks for the reply, currently the input has a burden calculated to allow 6.5A as a maximum current which allows best use of the ADC steps but doesn't allow for CT inaccuracies at low currents. I had room in the spa heater solar divert box to provide a double loop through the CT and I'll now change the burden to be the same as my 13A channels to minimise the low end error

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