CT Sensor installation

I just got one of the kits with a CT sensor.

The sensor has an inner diameter of 13 mm.

The line I am trying to put it around is 16mm.

Am I attempting to install it in the right place?

If yes, my options seem to be replacing the line with something that the sensor will fit around, which I believe I would have to pay someone to do, or buy a new sensor with a larger hole.

Are there other options, and what seems like the cheapest?


Robert Wall's picture

Re: CT Sensor installation

That does indeed look like the correct place. I think the explanation is the c.t. you have is rated at 100 A, and your main circuit breaker, and presumably the cables feeding it, is rated at 200 A. No responsible electrician will replace that main feeder with a thinner, lower rated one, so your only option is a different current transformer. I suggest you should try to get a reasonable estimate of the maximum current you are likely to draw, (which might of course be less than 200 A) and we'll take it from there. I assume you're using an emonTx in a kit from the OpenEnergyMonitor shop?


antony.trupe's picture

Re: CT Sensor installation

Correct, I have the emonTx kit, with the 100A ct sensor that is sold in the OEM shop.

The label on the breaker says it is 200 A, and my understanding is that that is split between the two feeder mains, but I could be completely wrong about how that works.

Regardless, it seems clear that getting a right sized ct sensor is a better option then replacing existing wiring.

How would I go about getting an estimate on the maximum current draw?

Is there a significant cost difference between different rated current transformers?

This looks like it would work, and is reasonably priced, but I don't know if there are things to consider about making it work with the emonTx.

Robert Wall's picture

Re: CT Sensor installation

Sorry, I didn't see your post until now. I haven't tested that c.t. of course so no guarantees, but I can't see why it should not work. You will need to calculate a value for your burden resistor - the Building Blocks articles on CTs and calibration should guide you. All you can do for maximum current is make a list of all appliances that you are likely to have in use at any one time, and list the currents from the rating plate. You can't ever be totally accurate, all you need is a good estimate and if your c.t. is rated at that or up to about 1.5 x above, it should be fine. But I'd be concerned about accuracy at the low current end if your normal current was (say) only 10 - 20% of the c.t's rated current.

tbilan's picture

Re: CT Sensor installation

Did you ever choose a CT that worked with the emontx?  I too have 200A service and the same problem.



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