Questions about Another Siemens 200a Panel Install

I’ve got the same 200a panel as this installation: https://community.iotawatt.com/t/ct-installation-on-200a-siemens-panel/856. I’ve spent quite a bit of time researching in the forum but I still have some questions as I plan out the install.


The first challenge, as in the other post, are the mains. Here’s a pic looking up into the meter at the lines in from the city and the four mains out to the panel:

I think I have 3 not-ideal options for the mains:

  1. 2 CTs on the lines in from the city. There will some loss through the meter but it will be minimal?
  2. 4 CTs on the 2 black and 2 red mains. Probably no enough room to fit 4.
  3. 2 CTs on the 2 black and 2 red mains. I would need at least 30mm openings in the CTs.

The 400A CTs with 36mm openings are currently out of stock. Are there other CTs, perhaps from other suppliers, I could look at for option #3?

My other 2 questions are about breakers. The first is a breaker to the AC in the master bedroom addition. It has one red and one black, circled in yellow:

Normally in this situation I think I could use 1 CT and double the value. But in this case since there are 2 different sources do I need to use 2 CTs?

The second question is kinda the inverse. I have a subpanel near the pool for the pool pump and sweep. At the main panel 2 40a black wires go the subpanel, one to the pool pump and the other to the sweep:


From what I’ve read in the forums, normally when you have a subpanel you want to read both wires from the main panel. But in this case since both wires are black and I’m only interested in monitoring the pump, can I just put a CT on the wire to the pump-side of the sub panel?

Sorry if some of these questions are obvious. I’m a noob learning as I go. Thanks for the help!

Hi bkgeig,

In the thread that you referenced, the lower left cover was sealed. Since you appear to be able to remove it you can just install 200A CTs on the two mains from the street. There is no loss through the meter.

In general, 240V circuits require 2 CTs or passing both wires through one CT if there is a neutral wire. 50A should be fine.

The bedroom AC is probably two-wire, but you need to verify. If it plugs in, then look at the plug. Does it have three or four prongs? (one is ground).

The picture of the pool sub-panel shows that the circuit is three-wire. The neutral is a black conductor wrapped with some white tape. There are 120V circuits in the panel, a sure tipoff. So the subpanel requires that both lines be monitored. Monitoring just the “pump-side” is not an option as it appears to be 240V (as expected) and uses both sides.

Many thanks, Overeasy. This is a big help. The bedroom AC is a roof-mounted unit (common here in SoCal) and I can’t easily access it. I’ll plan to use 2 CTs on that. For the pool subpanel I’ll run both black wires through 1 CT. The only thing I regularly use on the subpanel anyway is the pool pump.

The other somewhat tricky bit is that the panel is semi-recessed and all the access holes on the right side are used. I’ll have to go in through the left bottom, drill a hole into the right side and then run the CTs. I’m working with an electrician and will post some pics of the install.

It’s a big relief that the mains aren’t complicated, as I feared.

Understand that one must be reversed.

Hey bkgeig, I was the one who posted the original thread you referenced. I wound up having the CTs installed on the 2 mains from the street in the lower left corner. There is just not enough room anywhere else in the panel to get CTs on mains. Technically reading the power consumed by the meter as well, but it’s so small compared to the use of the house that it’s negligible.

Thanks for the reminder on reversing the CT; I probably would have forgotten.

Nice to hear from you, brgr. Wasn’t sure whether you were watching posts. I hope to get mine installed in the next couple of weeks. Had to move some poorly installed coax cables this morning. Now I can fully open the panel to access the breakers.

To be clear, it’s one of the conductors that must be passed through the CT in the reverse direction. Looking at the pictures, that may be very difficult unless there is some slack in one of them. See this in the documentation.

Yes, my plan was to splice in a short piece of wire to give enough slack to reverse the direction. I’ll probably use solid-core CTs since space is tight.

For the solar feed at the top of the panel, is it still OK to use one CT and double the value?

All of the inverters I’ve seen are two-wire, 240V, so yes, you can use one CT and check the box to double the voltage reference.