Recommended source of solid core CTs

While clip on CTs are good, would like to know the recommended solid core (I am getting electrician to install) CTs for 20A circuits, with a decent 3.5mm lead length


I’ve been looking for the same! But with a 1m to 1.5m length of cable. A 3.5mm lead length seems very short. Mounting the CT to a circuit board?

And I’d like to find a solid core for a 30 amp circuit breaker. This is for the HVAC compressor and I’m afraid I’d damage something using a 20A CT.

I have had great success with the HWCT-004. I used to be able to get them on eBay for about $2 in lots of 10 or 15. Not so much anymore. They are available from a variety of suppliers on AliExpress for $3 -$5 free shipping from Shenznen. Takes 2-3 weeks. I’ve bought quite a few various items on AliExpress and AliBaba. To me, there’s no difference buying from China via eBay vs AliExpress. I think I’ve said this before - what do you have to lose? Order them today and you’ll have them before Christmas.

I don’t know of any inexpensive small solid core CTs that come with long leads. They all come with a couple 6" wires. I buy cheap 3.5mm male-male audio cords, cut them in half, and solder them to the CTs. Nice little piece-work project.

The HWCT-004’s are good to about 40 amps in an IoTaWatt. They do the 20A circuits fine as well. I’ve got a bunch in my panel. If you come across any DL08CL2’s, they look identical to the HWCT-004 and work the same.

oops, sorry I mean 3.5mm jack

Ive been using the following CT’s without any issues, I solder on my own wires with zenor diodes within the plugs…

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I tested those awhile back with 24 ohm burden. Never found an official datasheet. They are advertised as 0-120A. I tested them to 60A with no sign of saturation. They are available now on eBay for $1.90 each free shipping from China.

Good linearity:

And low phase, typical of solid core:

I found your post from earlier this year. Thank your for the test info and images!

I found very little info about the HWCT-004 on the internet.
• What physical size are the CTs?
• Are any additional components needed to use these (e.g., diode, resistor)?

OD = 26mm
ID = 9mm
width = 14mm

You can add a TVS diode if you want to be able to unplug it while the primary circuit is hot. I don’t have diodes on mine.

The burden resistors in the IoTaWatt (or TX) are fine. Turns = 1000.

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Would be great to get a picture of the zener diode soldered onto the lead,
(I am a real newbie at this) (orientation and specific zener diode specs, would be really nice)
I suspect that with solid core CT, you are more likely to plug/unplug while the circuit is hot,
although I suppose I could just trip the circuit breaker.

Although thinking about this, I want to put a clamp around the main feed into house, so I can
measure import/export (I have Solar PV) as well. And that one is hard to get at, and I supppose
it will always be “hot”

Or is it just safer to power down the IotaWatt when plugging in CTs

Does this pic make sense - I am assuming the CT on the domestic supply will show me import or export, depending on current flow
2017-11-23 20_34_26-panel

Looks good as far as what gets monitored and where. conceptually I might indicate the 20A circuits with a blue arrow going out of the panel. Thee algebraic sum of the red power flow would then equal the blue power flow.

Yes the main can be negative, and you must check the box to “allow negative” when configuring the main.

I don’t have pictures or a source for CT TVS diodes. I’d recommend an sct013-000 for th3 main if it will fit on the cable. They have diodes built in.

Hi Michael
Please see below picture of my home brew CT leads…

I just got 15 HWCT-004’s off AliExpress. Was a but reluctant as they (They being AliExpress) don’t get the most glowing of reviews, but they got here as ordered and DHL delivered on a Sunday to boot (Wasn’t expecting that - DHL driver didn’t seem terribly happy though lol).

Dave, do you have a schematic of how you wire up the diodes and what ‘model’ of Diode you use? Can’t really tell how it’s wired up in the pic. I’m going to need to get these wired since they only have about 5" leads.

I am curious what day you ordered the HWCT-004 CTs? I ordered from AliExpress also (and I am in the US).

I ordered them on 11/15 and they were delivered today. But I also selected their ‘AliExpress Premium Shipping’ for a little more.

Ahhh! I paid the $0.90 to get tracking and I should have paid a few $$ more to get it faster.

HI Dave
I have taken a screenshot of my RS order below, note that the 22v diodes were used for another project.


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Thanks Dave - Is this how you have them wired up? Assuming so, is there any technical reason they couldn’t be wired up closer to the CT, such as where I’ll have to extend the wires (I wouldn’t think so, just checking)?

I have to be honest, I’ve never really looked all that closely into how Zener Diodes work before - so the way they are wired up, I’m assuming they function like an open circuit until 9.1v is reached, at which time they allow current flow and dissipate the built up voltage long before it becomes hazardous to a person or damaging to the CT?


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So I got all f my HWCT-004’s wired up - For grins, I put one on a circuit, and attached my meter to the connector and when I turned the circuit on, it pretty quickly shot up to 4 or 5 volts. Based on further reading, it seems that the Zener diodes don’t just ‘short’ when they hit their limit, but instead ‘regulate’ the voltage at tier breakpoint, so in theory, if they weren’t working right, the voltage I saw should have continued to climb ‘forever’ (or until the circuit was shut off).

Here’s how I wired them up, rather than trying to shove them in the connector at the end (since I had to extend the leads anyway).

Then shrink tubing over each diode to isolate them and larger shrink tubing over the entire package to isolate any part of the diodes from ever contacting something in the panel.

I’m guessing, based on how the Zener diodes work, that the orientation of the diodes don’t really matter for this circuit other than to make sure that the Anode of one is joined to the anode of the other, or cathode to cathode? Either way, unless the voltage hits the breakpoint, which it shouldn’t if it’s hooked up and working as intended, a complete circuit will never be completed to shunt some/most of the voltage.


Thats a great help Dkramkowski