Can I splice in a second CT to my solar CT

I have 2 solar panel systems. One is old and has sense solar connected to it inside my main panel, the other solar system is new and connected to a sub panel in my garage. There is no dedicated breaker on my main panel for the second solar setup. Can I buy a 3rd CT and splice it into the solar CT to create 2 solar CT pairs? I want to connect them both to solar production but the solar production breakers are in separate panels and not close enough to have them use one pair.

You can parallel 2 CT’s as long as the ratio’s eg 1:1000 and the phases (eg both L1) and the from/to is aligned with the arrow, are the same, up to maximum rating of amps of 1 CT.

So if the original CT is 1:1000 and 400 amp,
you can parallel 2 of 1:1000 as long as the combined amps are not more than 400 amp.


That is great news. The combined amps of both solar breakers would be 50, so that part is ok. Do you happen to know if the accessory they have for sale on their website (the flex add-on sensor”) is the same 1:1000 as the original CT?

Should be the same ratio as original CT’s.
I used 1:1000 as an example.
Afaik it isn’t published what ratio they are using. But as long as you buy their CTt’s you should be fine.

The software does not allow changing ratio’s and there is no way the Sense unit would know by itself what the ratio is.

When you work on CT’s , make sure there is no current flowing through the wires that it is around.
Take them off any wires before you electrically merge them together.
It is (like the name says) a current transformer.

eg with a 1:1000 ratio 40 Amp going through the main wire which it is wrapped around, would be 40 mA what you would measure at the plug side. When it is not connected to anything the voltage will go higher and higher in order to get to that 40 mA and I promise you, you will not like it when you touch both leads.


Hi. I got my new second CT in the mail, but it is a different model than the original. Not sure if it is comparable enough for me to wire it in parallel. What do you think:

The original says:

  • Model CT150
  • 600V
  • 200A
  • 50/60 HZ

The new one says:
Model CTSL

  • Cat IV
  • 250V
  • 200A
  • 50/60 HZ

Thank you again

I am pretty sure they are compatible with regards to the ratio.
That is the only thing that matters with a current transformer.
Each CT is used to measure “only” a 120 volt leg “only”, so doesn’t matter if it is rated 250 or 600 Volts.

Go for it !


Thank you again! When I install it all I will let you know how it works out.


I gave it a try. It works but it’s providing inaccurate data. It seems to cut my production in half. Each inverter is producing nearly double what sense is reporting. I have the CTs all the right direction since I swapped them like a 100 times to be sure. Either I did something wrong that I can’t figure out or it just won’t work. Oh well. Thanks again for your help.

The only other thing I can think of is to match the CTs. Instead of a new and old model I could try using 2 new ones.

Can you give some information from before and after you paralleled the 2nd CT ?
Do you have some photos ?

This is for reference:

Did your 1 CT setup show your 1 inverter correctly ?
after hooking up your 2nd ct, what does it show now ?
Need more context in order to debug.

Don’t waster your money on another pair of CT’s.
It should work [TM]
We just have to figure out why it currently isn’t :wink:

When you disconnect 1 of the parallel CT’s it should behave just like you had in the beginning with just 1 CT attached. Is that still the case ?

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Both the original and new CT register the correct wattage before I did any splicing. I then spliced the extension 18–2 gauge wire from each original CTs to the new ones in my garage. When both were hooked up and clamped around power the wattage was close to half of what it should be. , I then unclamped from power both CTs in my garage panel. Wattage went down. I hooked them back up and then disconnected the original cts in my main panel. Again I saw wattage go down. So clearly I could see the cumulative effect of both CTs on each leg, but the cumulative amount was low. Near 1/2 of what it should be. I wondered if I had cts clamped on the wrong wire (black bs red) or inverted (sun side of CT vs label side), but when I flipped each one around to either black/red or flipped them around I could see that make it worse. Other things I tried. - I removed the extension 18-2 wire from the original solar CTs and put them back together as they originally came (with no extension to a second set of CTs). Wattage went up to normal. So, with the original CTs reconnected alone and showing correct wattage, I then connected one original ct clamp to one of the new ones in the garage (the garage one was not clamped around any power). Wattage dropped. I tried it with different directions and with each seperate garage ct separately. It seems as though the act of connecting one extra CT to the original causes wattage drop even if the second one is not clamped around any power.

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Top picture shows the original CTs wired back together like they came. The second pic shows one of the extension 18-2 wire I had connected to it to head to the garage.

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To answer your “update” question. - When I disconnect one of the CTs in parallel (unclamp it from power but leave it wired in parallel) I see a drop in wattage. BUT when I unwire (remove the second ct in parallel, leaving me with just one) the wattage reported shoots up to match the read out of my inverter. So, I do see that both CTs in parallel are adding wattage from both systems, but each is reporting close to half of what is really being produced. The only time I see the true wattage is when I do not have them wired in parallel. Basically going back to just one. It makes me think the Sense software can’t understand it, or the 2 different model CT’s don’t play well together.

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For reference:

Normally CT’s are really just the transformer.

That explains something to me.
The CT’s that Sense seems to be using has an integrated resistor per CT.
2 in parallel means 1/2 the resistance = half the value measured :frowning:
So the wires coming out do not carry any current (measured current / ratio) but is put on resistor.
The Voltage over the resistor is then fed through the wires to the PCB of Sense and measured with an ADC.
I am sorry, this is one of the few times you actually can not parallel the CT’s.
Unless you open one of the CT’s up and disconnect the resistor at one end.
The CT’s are now no longer original anyway, might consider that.

Wow. Despite not being able to do it, I actually feel happy that I have an answer. Haha. Much appreciated. Maybe I’ll do exactly what you suggested and see if I can crack open the old CT pair. And see if I can locate and remove the resistor. Do You think I only need to do this to one of the CTs in parallel or both? I can’t thank you enough for helping me.

Yes, only one. and that one without the resistor can not be used on the sense by itself anymore.
That will have the high voltage warning that I wrote earlier about.
Because of the fact that the sense ct’s have that resistor, there will not be high voltage since the current always get absorbed by the resistor.
You will need to have 1 resistor to get the voltage.

Original CT:

CT---------+--------------------- connector to sense unit
CT---------+--------------------- connector to sense unit

When you parallel 2 of those, there will be 2 resistors in parallel meaning 1/2 voltage measured.

Connecting 2 together like this

CT---------+--------------------- connected to 2nd CT and then to Sense
CT---------+--------------------- connected to 2nd CT and then to Sense


CT---------+--------------------- connected to 2nd CT and then to Sense
   This unit without resistor will induce high voltages because of removed resistor
CT---------+--------------------- connected to 2nd CT and then to Sense

That should work [FAMOUS LAST WORDS]
If you are able to open one of the CT’s up, please share some photos

@dannyterhaar, you made me look back through the community forum to find someone who had spliced two Flex Sensors together. Here’s the one case where I found, but they did it in series - that’s what you would do if the monitor uses reference voltages, instead of measuring currents.

@dan_streiffert , you might want to contact @jenkins.robert directly ?

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Please try Kevins suggestion first.
I am still trying to get my head around if that should work.
You are basically adding voltages on top of each other.
If one would be 0 and the other some value, would the total voltage still be correct ?
I have to think about it, but you have nothing to lose to hook it up and try it.

Thanks Kevin!

You, my friend, are a genius. I removed the resistor in both secondary CT’s and it appears to be working correctly. I’m running out of sun on one of my systems but next sunny day I will verify that it is truly working. But when I hooked up the second ct in parallel I no longer saw it go to half. And when I clamped it on it added. The only thing I noticed was that one ct in the parallel is clamped to the red (top) wire on the breaker but on my sub panel it is connected to the black (bottom) wire off the breaker. When I flip one around or put both on Red (top) then it subtracts.