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Physical Size of Current Transformers


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The current transformers that come with the Shelly Pro 3EM are indeed physically a bit too large for installation in typically quite filled distribution boxes in apartments.

The ones that come with the Shelly Pro EM-50 are significantly more suitable. Does anyone know if there is a possibility to install the current transformers intended for the Shelly Pro EM-50 on the Shelly Pro 3EM? And that the calculation of current, power, and energy be accurate?

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Posted (edited)

Both current clamps have a transmission ratio of 1:3000 and are interchangeable - with the only restriction, the 50A clamp will saturate earlier.

Another issue is the type of plug. But the plugs are both MOLEX types (micro fit 3.0), which may be easily interchanged (pins are the same).

Some details:

https://smarthome-forum.eu/thread/19721-einsatz-von-fremdwandlern-an-shellies-der-em-familie/

Edited by thgoebel
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Thank you, thgoebel, for the comprehensive answer. I believe I have all the answers I needed. I will buy an additional 50A CT for the Shelly EM; I already have two from the old EM, which broke. I just need three more MOLEX connectors, and I’ll be all set.

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Posted (edited)

Another remark: The 50A clamp should be calibrated „on site“: Supply the Shelly pro 3EM with one phase only via terminals A to C. Connect original clamp A (120A) at IA, and 50A clamp at IB. Get a consumer with more than 500W (electric kettle or flat iron) and connect it with the same phase. Put both current clamps in correct direction at the live wire to the consumer and start calibration (A to B)…

Edited by thgoebel
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