That is possible. If there is no current input to your emonTx, then you might measure some small power due to electrical noise. 240 W is about 1% of the maximum that you can measure, I would expect the noise to measure less than that.

I have the sketch running here, with only one CT which is not near a cable, and I am seeing a small current and very small real power (3 samples):

`Voltage: 249.62 Phase 1: 0.00 A, -0.01 W, 1.14 VA, PF=-0.006 Phase 2: 0.00 A, 0.00 W, 0.00 VA, PF=nan Phase 3: 0.00 A, 0.00 W, 0.00 VA, PF=nan Input 4: 0.00 A, 0.00 W, 0.00 VA, PF=nan Temperatures: 26.80 27.10 20.30 Pulses=1 `

`Voltage: 249.58 Phase 1: 0.03 A, 0.28 W, 6.93 VA, PF=0.041 Phase 2: 0.00 A, 0.00 W, 0.00 VA, PF=nan Phase 3: 0.00 A, 0.00 W, 0.00 VA, PF=nan Input 4: 0.00 A, 0.00 W, 0.00 VA, PF=nan Temperatures: 27.10 27.30 20.30 Pulses=1`

`Voltage: 251.34 Phase 1: 0.00 A, -0.01 W, 1.15 VA, PF=-0.011 Phase 2: 0.00 A, 0.00 W, 0.00 VA, PF=nan Phase 3: 0.00 A, 0.00 W, 0.00 VA, PF=nan Input 4: 0.00 A, 0.00 W, 0.00 VA, PF=nan Temperatures: 27.20 27.50 20.30 Pulses=1 `