Split core vs solid core - accuracy


I know this topic comes up from time to time, but I haven’t seen specifics in any of the threads.

Specifically to accuracy, is there a graph or stats on the accuracy between split core and solid core, across the current range? Eg are they within N% at 20-80% of rated current, and N+3% outside of that?

I understand there’s differences in price, convenience, etc., but I’m focused specifically on accuracy. Is there any manufacturer datasheets that reference this, or user-generated empirical evidence by comparing a solid core and split core CT on the same circuit or load?

IoTaWatt appeals to my OCD nature, as I’m sure it does for many, and understanding the accuracy potential between the two would be super.


In theory, solid-core has the potential to be the more consistently accurate. In practice, it depends on the particular CT.

The ECOL09 carried in the stuff store is 1% linearity. The AccuCT 50A split core is rated 0.5%.

Another metric is phase shift. Again, the solid-core has the potential to outperform the split-core, but phase-shift is a complex topic and less phase shift doesn’t necessarily contribute to greater accuracy. Moreover, IoTaWatt does dynamic phase correction so as long as the CT and VT have modestly low shift, it’s all good.

The last consideration is not a performance metric. The solid core CTs come from China, and importing the relatively low quantities that are sold is becoming prohibitive.

The Trump tax of 25% is a huge problem.
The Corona pandemic has introduced uncertainty in supply.
Shipping small orders by air-freight has become expensive and slow.

Bottom line is that the landed-cost is double the manufacturer’s price.

There are currently about 33 50A x 9mm solid core CTs in stock. There are no more on order for the above reasons. So if you want some, get em while they last.

Thanks for the quick response, and robust detail.

Having read a number of your replies here on the forum, it’s clear to me that you are passionate about the product and the user experience, and I both appreciate and admire that. (You also get kudos for incredible patience. I assume you have a dozen children.)

I just recently placed an order, and had intended to order solid core CT’s. Apparently my bleary eyes did not make out that the bundle only includes split core. I’m having my panel replaced in two days time, so it’s a perfect time for the solid core CTs, IF they’d produce an improvement in accuracy. (There’s also a size issue to a lesser degree, but I’m hoping I’ll be okay on that front.)

From your comment, the AccuCT 50A split core - according to the specs - should read more accurately than the solid core; the only benefit to the solid core would be smaller size. Is that correct?

I may still order some solid core, but my understanding is I’d either need to remove the split core CT’s, or short them at the audio jack - tape some bare wire along the plug? - to remove the IoTaWatt control unit for bench testing.

As you indicated, about to become a moot point in the near future, and I’m asking here only because I was completely stumped by finding guidance that wasn’t written by a Marketing dept anywhere else. Seems the OCD camp is limited to hobbyists in this regard.

I recognize that the price points aren’t enough for you to be doing this to get rich, so your taking the time to reply and share is because you care, and I appreciate that a lot.

All of the CTs in the store have TVS diodes that will limit the voltage that they can produce to safe levels when disconnected. That said, belt and suspenders, I do recommend physically shorting them If unplugged for more than a short time. Wrapping a strip of aluminum foil tightly around the jack work.

I would not use solid core unless it were a space issue. Accuracy is a purely academic consideration. As a practical matter there is no other advantage (except I suppose slightly lower cost).

Im guessing these are long gone?