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Are you using the sketch that was loaded in your emonTx V3 when you received it, or have you loaded a different sketch?

Where do you read the 270-330W - is it using the programmer and Arduino IDE serial window, or is it on emonCMS?

Are you using the ac adapter?

hello, thank you for the interest.
I'm using the original sketch that was pre-loaded, i don't changed it.
The value ranging from 270w-330W I read both on the input page of emoncms, and on the log file of RFM12Pi.
Yes I am currently using the AC adapter 9v.

I have never heard of anyone with this problem until now.

The emonTx should be sending, in this order, Power1, Power2, Power3, Power4, Vrms and Temperature. Powers are in Watts, Vrms is × 100, and temperature is deg.C × 10.

Is that what you are seeing, and do the other values look correct? (I want to be certain that you are interpreting the transmitted data correctly.)

What should happen is, when there is no plug in the CT4 socket, the ADC input is grounded. When the sketch starts, it senses that and it should not write a value into Power4. Even if that ground connection has failed, you should not see that much "current".
If you are seeing a power of approx. 300 W, that represents a current of about 1.3 A, or a voltage at the ADC input of approx. 80 mV. I think that the only way that could happen is if there is a bad connection between the input circuit (the bias resistors and burden resistor) and the input pad of the RFμ328, and it is picking up a voltage from an adjacent track.

Do you have a programmer that you could use to load a test sketch?

Sorry for the delay, i was outside home.
With the CT4 connected to sensor, but with the sensor free ( no cable passing the sensor ) today i measure "240-244".

I restart service with log option:

sudo service rfm12piphp restart log
cat /var/log/rfm12piphp.log

MESSAGE RX:> 15i
BASEID SET CORRECTLY
DATA RX:
MESSAGE RX:> 8b
FREQUENCY SET CORRECTLY
DATA RX:
MESSAGE RX:> 210g
GROUP SET CORRECTLY
DATA RX:
DATA RX: 10 204 1 255 255 218 1 240 0 85 90 0 0
DATA RX: 10 171 1 253 255 185 1 243 0 89 90 0 0
DATA RX: 10 179 1 0 0 194 1 244 0 72 90 0 0

As you can see the mistake come from Emontx, emoncms seems to be correct. 

Yes i have a FDTI adapter to load sketch, where can I find a test firmware?

Attached there is a photo of emontx, i removed from the case to photograph it.

following this schema
http://openenergymonitor.org/emon/sites/default/files/emontx-v3.png

with a tester can i measure something ?

Thanks in advance

I see 12-13 W only when I connect the SCT-013-000 to CT4 AND I put it on top of the ac adapter.

Is your CT a long way away from any other pieces of electrical equipment, especially a large transformer or motor? What do you read when the CT is unplugged from the socket?

You could try one of Robin Emley's test sketches here. Probably RawSamplesTool_4ss_2 will be the most useful, but you will need to change "byte voltageSensorPin = 2;" and "byte currentSensorPin = 1;" to 0 and 4 respectively. You should see the letter 'V' tracing out the voltage wave, and with the CT connected a line of 'C's down the middle, perhaps you will see a small sine wave. With the CT disconnected, the 'C's should be at the left-hand edge.

If you have a multimeter and a spare 3.5 mm plug, insert the spare plug and measure the resistance between the two pads at the ends of R18. It should be the 120 Ω of the burden resistor. If you don't have a spare plug, insert the CT plug and you should then see approximately 50 Ω, which is the burden resistor and CT winding resistance in parallel.