UK CT Advice and Suppliers

Hello all,

I am looking to get started with Energy Monitoring in my home and I’ve been reading all the documentation but I’ve hit a bit of a block.
I have two issues I’m hoping someone can help with; supported/recommended CTs and where to get them.

I have a couple of split-core CTs for purely sizing purposes and I have consulted with my electrician who has stated that we are going to struggle to get these into the consumer-unit (the standard UK consumer unit is not very big). We have talked about a double-length/height unit but these are expensive and obviously a significant cost to install (including a full part-P check once installed).

Having been reading the documentation (both IotaWatt and others), i wonder if I would be able to fit solid-core CTs into the existing unit as they look a lot smaller, however I notice that these are not available in the store and I am struggling to find anywhere that sells these with the jack-plugs required to fit to the IotaWatt system. The USB power supply and voltage reference transformer should not be an issue.

Is there anyone here from the UK that has managed to set this up and if so, how did you fit the CTs into the consumer unit (and which ones did you use).
I need to double-check what rating CTs I require (I assume I need 1 for each individual ring main - 12 - and 2 to cover the main cables coming into the unit); I can post a photo on the inside of the consumer unit if it helps.

I appreciate that this is a bit vague, so I appreciate any advice.

Finally, I appreciate that stock has recently been an issue, but will the individual units still be sold in the future? I can only see bundles at the moment.

I would recommend that.

Assuming you mean the base unit alone, yes, that will be available in the near future. Right now just trying to service the backlog.

Apologies for the delay; here is a picture of the inside of the consumer unit.

For reference, the dimensions are approximately 450mm x 230mm

It seems like the standard US electrical boxes are quite a bit bigger than ours in the UK; they seem to try to cram it all in such a small space here.

I faced the same problem when I tried to add energy monitoring in my home which is also an UK-style electrical box. Here is the electrical box in my recent IotaWatt installation.

I ended up using the solid core CT - “DL-CT08CL2" (1000 turns). The IotaWatt unit comes with burden resistor value of 24 ohms, which translates into around 48.6 Amps of maximum RMS current. If you know a little bit of soldering skills, you may change the burden resistor to increase the sensitivity.

Also, the DL-CT08CL2 does not have the input jack, and you may need to extend the wire and add a input jack by yourselves.


Thanks so much for this; I’ll have a read and have a chat with my electrician.

You might also look into smaller split core CTs. While I’m not a fan of the SCT006, they are OK for up to about 15A. I see they are currently out of stock in the OEM shop but you could ask when they might be available. They are supported in IoTaWatt and OEM is in your backyard.

I’ve had a look at the CTs on alibaba and the DL-CT08CL2 might do the trick if they did a 50A rated one but they only seem to be available in 20A versions (unless I’m missing something; definately a possibility). As you can see from my picture, i have 6 x 32A and 1 x 40A.

To be brutally honest, I work in IT and I am not an electrical engineer. While I could probably have a go at extending the cables and fitting the input jacks I’d be nervous of fitting these to my mains power supply for safety reasons; I’m not sure my electrician would approve of something I’d assembled myself either.

For now, I may return to the previous plan suggested by the electrican, namely a wider consumer unit to allow more space for the split-core CTs (available ready-made from the store). This will increase the overall cost, but both he and I will probably be more comfortable with the fitting; 2 x 100A and 12 x 50A CTs should cover everything.

I do really appreciate the advice on offer however, and when I next speak to my electrcian I’ll float the idea of he and/or I constructing the CTs ourselves; he may be able to source suitable CTs himself via trade avenues.

If I’m missing something obvious, please do correct me. I am keen to set this up, but I’m just not confident (or qualified) to mess about with mains power. I’m beginning to suspect that this isn’t going to happen.

Many products from China have poor documentation, and I think the product description of 20A / 20mA is just for illustrating the current ratio between primary and secondary windings, instead of the maximum supported current . I can find another image from the China online store mentioning that it can support up to 60A / 60mA. The Chinese words “以下规格都可使用” in the image means “The following specification can be used”.


Frankly, with the primary current of 50 amps, it only induces 50mA in the secondary windings. 50mA is just a little current and should not be problem. I am using it for all my 32A circuit breakers, and another post in the forum (Solid core CTs no more? - #2 by fermulator) also mentioned that it should be capable to support 50A. I have already using more than twenty DL-CT08CL2 for myself, and this product is in good quality given its low price.

Nevertheless, I am just a hobbyist and you may wish to obtain second opinion from your electrician.

I’m in the UK and I managed to squeeze 11 ways of the standard 50A CT into my consumer unit, it’s a new build so the unit was pretty well organised (albeit with a fair bit of slack squeezed into the back of the unit) and all my circuits are RCBO so I had to work around neutral wires. It’s not tidy by any stretch of the imagination but it works and I was able to run all the CT wires around the edge and out the bottom to a seperate enclosure I mounted the Iotawatt into. I’m afraid I didn’t take any before shots.

From your photo it looks like you’ve got a similar size consumer unit but with a lot more cabling crammed into the top area because it’s a dual RCD board rather than RCBOs,

I wouldn’t bother with putting CTs on your mains incomers, if you need your total consumption you can just add the draw from all your circuits together in software. This is unless you’re not monitoring all of your circuits, if that’s the case then go ahead and do it, you only need one though as the current in the line and neutral incomers should be identical.

Thanks, I appreciate the reply.

I have had to put this on the back-burner for now.
I had conversations with my electrician and his plan of a double-width unit and replacing everything with RCBOs was going to cost well over £1000 (the unit alone was ~£600), plus the additional cost of all the CTs and the IotaWatt itself was getting a bit excessive for essentially an enthusiast view of my usage.

I just couldn’t justify the cost to the wife; although with raising energy prices, maybe this will change in the future.

Thanks again