Two devices connected to one CT clamp

I have an awkward electricity meter installation in which the cables feeding and exiting the meter are mostly hidden within the wall. A small part of the supply feed is exposed and has a CT clamp fixed around it to sense import/export for a SolarEdge solar system.

I need to connect a second CT clamp to this cable for an emonTx to read the same cable, but there is not enought cable exposed to do this.

If I were to take the existing CT clamp and split the connection between the SolarEdge device and an emonTX, effectively wired in paralel, are they likely to get an accurate reading, or would it be halved to each unit, or be completely disastrous?

I look forward to any input.

I wouldn’t like to put any bets on the outcome, other than the second option is very much the more likely one.
However, if the clamp c.t. it is one of these

or one of these

and your emonTx is an emonTx4, then, because the c.t. is a 0.333 V output device, you could connect the Solar Edge and emonTx4 in parallel and both would read correctly (after you’d re-calibrated your emonTx4 to 225 A or whatever the c.t. rating is). But you would be connecting the emonTx4 & emonVs ground to the Solar Edge device, so it would still be possible to damage either or both when you make the connection.

You could try asking Solar Edge, but only if you have an emonTx4 or later (emonPi2 etc). You want to know if it is permissible to connect an emonTx4, which has a 333 mV input requirement with one side of the input connected to mains earth, in parallel with your Solar Edge c.t.

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Thank you for the useful advice regarding this.

The solarEdge clamp C.T. is one of the latter ones, it’s a black unit that is attached to a remote sensing unit. That unit is powered by 240v mains current and itself is earthed. My emonTX is a 4. As itself is powered with a transformer and has no earth as such, is this the reason there could be damage once the connnection is made?

I will contact SolarEdge and ask them also.

If your emonTx4 has no connection to either mains neutral or earth, there should be no problem connecting its c.t. input across the SolarEdge c.t. output in parallel with the SolarEdge itself. The problem would have been if the ‘earthy’ side of the emonTx4 input (the sleeve of the jack) connected to a voltage generated inside the SolarEdge. Even if one side of the SolarEdge input was earthed and you linked the two earths, it would be possible for a circulating current to flow and either or both could give false readings. With your emonTx4 ‘floating’, all should be OK.

Hello Robert, thank you for your reply.

I have contacted solaredge and am still waiting for a reply. However I fear your reply might have been in vain as the emonTx is in fact a v3. I apologize.

I have since found an electrician that has helped gain access to the cables and I now have the emonTx CT clamp installed alongside the solaredge CT clamp.

I will next calibrate the emonTx and it will be interesting to see if it differs to the SolarEdge readings.