Most compact CT clamps for 20A?


I recently purchased an IoTaWatt unit with some of the default 100A clamps.

However, the distribution board I’m working in is very small, and the space is quite restricted.

Also, this is for a small apartment, and the breakers are all rated at 20A. (I suspect usage will be a lot less than that as well).

Does anybody know the most compact CT clamps (split preferred - unless the solid’s are much smaller) design that will work for 20A breakers?


Hello Victor,
You bought 50A CTs, and those are the smallest available from the store. There are smaller solid core on the market but you would need to add a longer cord, 3.5mm jack and optionally a TVS diode. Search this forum and you will see some discussions about various models.

Thanks for getting back so quickly =).

Ah got it - you’re correct, sorry, the default ones are 50A, not 100A.

I did see these two 20A ones on a local (Australian) site:

However, from searching the forum here, it doesn’t seem these are a straight drop-in replacement, and will need to be converted. Something about voltage output vs current output:

Are solid cores generally more compact/smaller than the split core ones?

I saw this thread which mentioned a AZ-0500 - and also this thread which discussed using them.

@overeasy did you end up getting the samples from @Automate? I would also be happy to send you a couple as well, if you think this model is a good fit.

I also saw this thread, which mentions the [ECOL09](https://ww

Also, saw a forum thread about the HWCD-004.

My main driver is getting something as compact as possible, to fit within a cramped space.

Second, I have a preference for ready-made units, with the plugs, diodes etc. already wired in. Is there such a thing?

Or if not, is anybody able to share some newbie-suitable notes for how to wire them up?

The SCT013 is larger than the accuCT 50A. Only the SCT013-000 (50mA output) is compatible with IoTaWatt.

No, I did not.

Hose are a bit smaller, solid core. They are available directly from Echun. I don’t carry them anymore because with shipping to USA and 25% tariff they are too expensive.

They are good, but you need to add a cord and jack.

Can you PM me your details? I’ll try to get a AZ-0500 (or a couple) to you.

The ECOL09 seems like the next best option - however, do I need to add things to this as well?

And for the HWCD-004 - what do I need to add to this, and how do I assemble?

These are the smallest CTs:
Micro-40 Donut Style CT - Brultech Research Inc.

I have many of them (that I bought with the ECM-1240 I bought over a decade ago). I have been meaning to send a couple to Bob to get numbers for them. I use the following numbers with them:
Model: generic
Turns: 1525 (sometimes 1528)
Phase lead: 1.2 to 3

Clearly, I need to get the samples to Bob, since my numbers are all over the place :wink:

They are plain wire, so need a TVS diode (when not connected) and a connector. I have been using these to connect them: Billmill 3.5mm 4 Pole Stereo TRRS Male to AV 4 Screw Terminal Female Phoenix Block Balun Headphone Earphone Solderless Connector Adapter (4-Pack): Industrial & Scientific
(don’t need to be TRRS, TRS would work fine since only the Tip and Sleeve are used). They are too big to fit next to each other in the IotaWatt, so I use a short extension if they have to be next to each other. I found the quality of the solder on connectors to be really bad and hard to use. I tried cutting extension cords, but I couldn’t find any that used real copper wire that I could solder. This why I ended up buying a lot of the 50A CTs from the store. They work well and are more accurate and don’t require a bunch of time to get the connector and TVS diode on them.

But, if you REALLY, REALLY, REALLY need tiny CTs, the ones I linked do work well.