Very new and lost :)

Hi all,

I feel a bit overwhelmed with all the information available on your site and need some assistance.

I would like to order an EmonPi, but I'm confused on how to install the CT sensor. Where exactly do I clip this? My goal is to monitor all electricity on one particular plug...

Sorry for the dumb question. I just need to be sure before buying.


Robert Wall's picture

Re: Very new and lost :)

The emonPi is not designed for monitoring a single socket outlet, so there are two reasons why you might want to reconsider. First, the current range is 0 - 100 A, which is suitable for monitoring the whole house, but a single socket is unlikely to draw much more than 10% of that, and accuracy will suffer. The second problem is the cable from the plug will be a 2-core or 3-core one, and no current transformer will work on that - you will need to make up an extension cable using two or three separate wires, and clip the current transformer on the line conductor only.

By using various tricks or by using a different current transformer to the one we normally recommend, and altering the calibration of your emonPi, you will be able to reduce the maximum current and improve the accuracy at lower currents, but whether you can do that successfully or not depends largely on your IT skills and whether you can work safely with electricity.

AnovaXT's picture

Re: Very new and lost :)

Hi Robert,

Thank you so much for the detailed response.

The current situation shouldn't be a problem. The plan is to use this to monitor server equipment which generally pulls between 30 and 40 Amps.

Option1: At the cable level. The current setup is that there is an extension wire running from the mains to a plug. My understanding is that the cable contains live, neutral and earth components. Are you recommending to clip only around one of these 3 components? Which one is the conductor?

Option2: At the main board. Is this the normal place where everyone installs their emonPi? Well, I suppose at the main board or any subDB board. In this case to which wire do you connect the CT sensors?

Kind Regards,


Robert Wall's picture

Re: Very new and lost :)

As you appear to be in a commercial environment (i.e. it is not your house), then Option 2 is what I would follow. I can't give you exact details because I've no idea which country you are in and what you local regulations are. In general, in your distribution panel you will have an overcurrent protection device - a fuse or more likely an MCB - feeding the circuit that supplies your servers. You clip the CT on the cable that comes from that. (You can use either line or neutral conductor, but the line from the MCB will be easiest to identify.) You also need give the Pi a sample of the voltage on the same phase (assuming yours is a multi-phase installation) to measure via the ac adapter, and you need to power the Pi separately from a convenient source.

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