Archived Forum

Have you restarted the emonTx since connecting the CT's to it?

The emonTx only tests for CTs at startup if none are found it won't check again.

The correct way would be to plug in the CT's to the emonTx, then attach the CT's to the respective power cables and lastly start (or reset) the emonTx.

​Paul

Yes I did. Well in fact I didn't use the "reset" button, but I unplugged the power (with CTs connected), waited a few secs, then plug it back. I tried many combination and still not getting data.

How have you fitted the CTs to the wires? Like this?

Yes of course.

It was worth asking - quite a few people who report nil current readings have put it on a 2-core or 3-core flex.
Have you got a programmer, can you see what the emonTx prints to the serial output on start-up?
It should tell you what it thinks it's seeing, in terms of connected hardware.
Another (hopefully stupid) question - are the CT plugs fully home?
If you have a multimeter that reads mA ac, can you see a current direct from the CT (connect tip & sleeve). The calibration is 50 mA per 100 A.

What do you mean, by 2 cores or 3 cores. All cables in my house have 3 wires, 1 ground 1 black and 1 white. So I put the clamp on the 3 wires cable.

What is a programmer? I can use minicom to my RFM12Pi and reboot the emontx. Would that work?

What do you mean by fully home? you want to know if the clamp is full clipped, or the 1/8 jack plugged into the emontx? I verified both and they are correctly plugged. 

I'm about to receive my multi-meter that supports AC (clamp multi-meter), i should be able to check that in a few days.

You must only clamp one of the 2 ac cores. by clamping both (plus the ground) you are measuring current flow in both directions eg on a 3Kw kettle you measure 3Kw going one way and (minus) -3kw going the other way. 3Kw - 3Kw = 0Kw.

ok, I'll try attaching the clamp to only 1 of the core. Should I use the black or white?

Is it possible to attach a clamp to a 240V cable even if the emontx is plugged into a 120V outlet? If yes, how would I need to plug it? 

it doesn't matter much as long as you follow a theme so that when you start adding kettle one to kettle two you don't get the same cancellation.

There is an arrow on the clamp to indicate the direction of flow, you can "flip" a clamp to get it to read the other way (pos or neg).

Jean-Sebastien, You did not put the CT on the cable as shown - that picture shows very clearly a single core cable, whereas you have said all the cables in your house are 3-core. A CT works on the magnetic field surrounding the cable. If you have two cores carrying current in opposite directions - as indeed must be the case - then the magnetic fields cancel and the current transformer picks up nothing. Which is exactly what you found. The third core is a protective earth and should not be carrying any current under normal conditions, so plays no part in this.

If you were to do that to your fixed wiring in the UK, it would fail to comply with BS7617.

[Edit:]
This comment applied to a picture, since removed, showing the sheath removed from a 2-core and earth cable, the 3 conductors separated and a CT clipped around one core.

Whilst valid for illustrative purposes, and for testing under controlled conditions, this practice is not safe for a permanent installation. The reason is the insulation, the brown, blue, red, yellow, black, white or green plastic immediately next to the conductor is electrically good but mechanically poor, and thus susceptible to mechanical damage. The outer sheath though is the reverse: electrically poor but mechanically strong in order to withstand the rigours of installation, etc.

Thank you all. I now understand and you were right as I misunderstood how to plug the clamp. So I opened my electric panel and put the clamp only around 1 core of the cable I wanted to monitor and now it works well. I get data into emoncms.

Thanks again.