Hi all.
Have a question which came up in a debate between us tech’s here. Maybe one of you have tried this before. Would it be possible to use one CT to provide measurement to two EM24 smartmeters? Basically the CT would be shunted between the two smartmeters.
Depends on the way the EM24 works and measure currents.
Generally, in order to measure something with a sensor, no matter the type, you need to generate a controlled/constant environment (measurement bridges, constant currents, resonance frequency, etc.) and then the sensor will perturb that controlled/constant environment.
Measuring the perturbation you’ll have the value of the measured item.
Each EM24 may generate such environment and the CT probe will perturb that.
Connecting the CT to both EM24, means that, in a way, you’ll parallelize the measurement environments of the two EM24s and that leads to reference errors.
It may work, but with deviations/errors. Which can be small and you can live with them, or great and it’s unusable.
Or, you may be lucky and the EM24 may have a very high impedance input measurement and the CT to have a too small impedance to matter and all will work just OK.
Try it, you have nothing to loose. Experiment ! 
If with CT you mean a current transformer…then you should be able to connect the two inputs in serial, as the current is measured.
Yes, I mean an external current transformer.
Are you sure of that?
The CT is an inductance and the EM24 measure the voltage induced in that inductance by the current passing through the wire…
Yes, the inputs are low impedance, measure current.
You may read have half the current on each EM24…
Only if you connect them in parallel…
I believe I am missing something…
Isn’t a CT an inductance that is clamped on the wire?
FWIK, it generates a voltage proportional with the current passing the wire.
It’s not a resistor put in series with the wire.
For example, Tektronix characterize CT probes like this: The CT provides 1 mV per milliamp when terminated in 50 Ω.
LE:
You’re right. 
Reading the Tektronix phrase above just hit me that you’re right. Sorry…
I was thinking in terms of voltage and forgot the termination resistor.
Ok, so in theory it should work if we shunted the CT onto the second smartmeter because voltage stays the same no matter how many smartmeters reading it. Right?
Can you put a small drawing on how you want them to be connected?
The two (2) EM24 and the single CT?
Thanks!
No, this is parallel wiring
Yes. Measure the input impedance of the EM24’s CT port.
If it’s closer to 50 ohms, then this is the one.
If it’s high impedance, then try as in your first picture.
Anyway, try… 
If you connect the two meters to one CT in parallel, then the termination resistor’s value will be of the expected value. If you connect them in series then you double the termination’s resistance. Neither is likely to produce an accurate reading.
Also the internal circuitry of each meter may interact with each other. For example if one side of the CT input is connected to ground in each meter there could be ground loops between the grounds in the two meters even if the meters are close to each other physically. Interaction could be even more significant if the input is expected to be floating.
This is what I’ve tried to explain in the 2nd post of the thread.
Still, for the sake of the experiment, he can try.
But, obviously, the current is measured in a single place, because there is only one CT.
An elegant way is that sharing of the current info should be made at the application level, as the meter will be placed in a network and there is no problem that the two “receivers” to be placed in the same network and interrogate, through Modbus or whatever, the same EM24 meter.
Indeed, very good points made! Isn’t modbus address based? I don’t think there can be one meter used by two inverters. Maybe I understand it wrong
I admit, I didn’t use an AC smartmeter until now and I may be wrong, but I don’t see why not two different devices could not interrogate the same smartmeter. If all are on the same subnet, then any device is requesting info from the smartmeter, must be answered.
In the end they are not paired and it’s an IP to IP dialog, over TCP.
