Question about adding CTs to a SE cable

Question

Trying to figure out the best location to put some CTs on 2 runs of service entrance cable. I have a 400A main meter panel on the exterior of my house (2 200A main disconnects), one 200A main goes to the sub panel in the basement the other 200A goes to a garage sub panel. The SE for the garage enters the basement as an easier way to access a pair of 3" underground conduits that already breeched the foundation. I want to add CTs to both the sub panel in the basement and on the lines going to the garage for monitoring.

The basement panel I can just open and access the SE above the main lugs on that panel, easy!

The SE that heads to the garage, not so easy :( Can I strip back 6" -1' of the outer insulation to hook my CTs in to the SE cable going to the garage or do I need to access it in the outdoor panel (that has its own set of problems getting the CT wires back inside) obviously I would be wrapping everything in tape except where the CTs are hooked on if this is ok to do by code.

I am trying to avoid if I can having to run the CTs outside to A keep them out of the weather and B I have to drop down the outside of the house about 1.5' to get to where the SE cables enter the basement. I would likely have to run conduit to protect the CT wires from the weather. If I have to run a piece of conduit I will but its not easy to get stuff in to this house (reason I am trying to avoid it). Post and beam construction and the piece I would have to drill through is roughly a 6 x 12 (yikes!)

Answer 1

CTs and supervisory systems follow special rules

Any occupancy (building) on the land is subject to the National Electrical Code (or equivalent), unless it runs on rails. NEC sets out the rules for working with cables and handling supervisory circuits such as CTs and monitoring devices.

Unfortunately, certain individuals manufacture and illegally sell power monitoring system components, and encourage their improper installation. These cannot be used, and you have no recourse but to send them back and seek refund. To spot them, look for (fake) CE marks, or only component approvals such as "RU Recognized" but a notable lack of a full-system UL Listing. These violate NEC 110.2.

Proper systems are UL-approved as a system, and will have the "UL Listed" mark. They come with UL approved instructions, which specify Code compliant installation procedures. UL will not approve a product whose instructions say to violate Code, with very, very narrow exceptions. You must follow the instructions for installing the entire system: NEC 110.3(B).

Low voltage systems that interact with AC power must be entirely inside AC power rated enclosures.

Normally, low voltage systems are forbidden from interacting with AC power systems in any way, or even being in the same enclosure. (Unless there is a physical divider).

However, an exception is made for low-voltage systems where the entire system is housed inside wiring methods and enclosures proper for AC wiring.

The gold-standard way to install a power monitor with CTs is to have the entire system live inside the service panel. With nothing sticking out except a WiFi antenna wave guide.

At least one manufacturer saw this as a "gap in the marketplace" and charged in to fill it, with a hub that lived outside the panel, sent CTs into the panel, and took ethernet and wall-wart power. They got a rude awakening when UL explained the irreconcilable design flaw and how it would never be approved. They sold it anyway, underground, rather than refine it with an interior module and fiber-optic or wireless comms.

Handling multiple panels

So the way we handle this is by keeping all the hardware inside the service panel, and having no comms "through the envelope" except WiFi or fiber-optic.

Now in your case, you need to be in more than one panel. That's not inherently a problem. Remember, the low voltage system can go anywhere as long as it stays entirely within Class 1 (AC power quality) wiring methods. You can lay AC-rated conduit (or share conduit) between the panels and run your CT leads through those conduits to clamp leads in the other panels. That is fine.

Getting data out

The only ways to get data in/out of Class 1 wiring methods are wirelessly, or via fiber-optic. Fiber-optic is an exception to the rule if it is non-conductive. It's a great way to run Internet out to a shed or pool house without trenching another conduit.

All of the (approved) home power monitor products I have seen use WiFi, via an antenna waveguide that sticks out of a "knockout" on the side of the service panel.