I read up on the current transformers on the website and noticed it said to never open circuit the CTs once installed. I assume that they are open circuited as soon as you disconnect them from the emonTx V3? The website also mentions that the default CTs (which I am using) have some protection build in. Does this mean that I can safely remove the emonTx V3 if I want to attach a temperature sensor/change the batteries? Or will the power build up still damage the emonTx V3 when I would plug it back in?
(Sorry for the basic question. I am new to the electrical tinkering world and still trying to get my head around it :))
Re: Disconnecting emonTx V3 from CTs and safety
The YHDC 100 A CT does have a pair of 20 V zener diodes internally that are probably good enough to protect you and the CT, and the short to GND in the emonTx's socket should protect the input, but it's never a good idea to rely on protection. If possible, slip the CT off the cable instead, or ensure the circuit remains under zero load while the CT is unplugged.
The mechanism is: the CT is a current source, so in the absence of any load ('burden') it will attempt to generate whatever voltage is necessary to drive the current into an open circuit. A large CT will flash over, having reached several kV, and destroy itself. A smaller CT, even if it does not flash over, if it has an iron core will become permanently magnetised and useless until demagnetised. It is always safe to short-circuit a CT.