Question about Shelly Pro 3EM 120A

The power cables are approx. 60cm long. Extension cables are available (link removed, but the article is called "Extension cable for Shelly Pro 3EM / Pro EM 50A / EM Gen3") but I would be careful with this, as an extension cable always increases the resistance.

The length of the cord is 50 cm. I don't know the answer regarding the extension

The cables of the power terminals are without cable, you have to put it in and you decide the length. As far as the current clamps are concerned, they are 60 cm, and if I am not mistaken they cannot be extended because otherwise the measured data will not be correct.