Are some sort of cable clamps required for low voltage wiring to enter into the electrical panel? I'm looking at the type of system like IotaWatt, which is an energy monitor. The current transformers are all low-voltage. Do I need to run the current transformer wiring in a conduit, and then use the traditional conduit terminations? Or can I simply open a knock-out in the box and run all of the low voltage wiring through that? (seems like I probably can't do that, right?)

  • Does the IotaWatt itself (the box you are connecting the current transformers to) have its own box, or does it mount into a wall box? Aug 5, 2020 at 0:18

1 Answer 1


You can't use this product in the US. It is not approved (NEC 110.2). Unfortunately this guy chose a design approach which was seemingly incompatible with UL approval, and got pinched as a result.

You don't enter a service panel with low voltage wiring.

That's because low voltage wiring is not allowed in the same raceways, gutters or boxes as AC mains wiring.

If every single conductor of the entire low voltage system is contained entirely within class I mains wiring, that is an exception. Basically if there is a problem and AC mains finds itself on the low voltage system, then everywhere it could possibly go is inside Class I wiring enclosures, so no harm can be done.

Indeed, every product of this type has the smart module, its power supply and the current transformers — all of it - living entirely inside the service panel. That is the normal approach to this. The only thing that sticks out of the panel is a waveguide for a WiFi antenna.

The only other exception is if the manufacturer found a way to make that intrinsically safe, and convinced UL of this to their satisfaction. Indeed, that type of approach is done by the "no neutral" smart switch makers, who bootleg ground with UL approval. They have satisfied UL that no harm could possibly occur.

That is how competitors get UL to let them stick a WiFi antenna out of a knockout.

You don't do anything with this, since it's not UL approved.

The maker talked a big game about UL approval, but choked on actually doing it. So not approved. The person got CE approval, but you can find that in the bottom of cereal boxes. The maker carries on a great deal about how the components are approved, and sells it like the whole thing is approved. It's not.

It cannot be used in a US installation, unless you can convince your AHJ (local authority) to approve it. NEC 110.2 requires every piece of electrical equipment be approved by the AHJ. In practice, AHJs don't want to be running testing labs, so they defer to UL and the other NRTLs. They can approve other stuff (say you're one stick short on Rigid conduit so you use some Sched 80 black pipe) at their discretion, so it's up to them whether to accept this.

I suspect the biggest hangup with UL listing* was the system design of mounting the unit outside and then having a bunch of CTs running their cords inside the panel. That was always a non-starter I suspect, but this person was very inexperienced at building hardware and getting AC mains products through UL listing. And did not even understand the scope of the process, being blindsided by the next step.

The person openly admits being a "software guy" and not really into the hardware except to get the software done. That person and everybody else: we see lots of manufacturers and consumers get caught up by this.

As a result it appears the owner was able to get the module proper "Recognized" as a component (with no CTs attached), but was not able to get it "listed" as a product, because opened the can-of-worms of what to do about the CT problem. So don't count on that product picking up a UL listing anytime, now or in the future.

Anyway, the person/company is brazenly selling them as components with the admonishment to use the hub with a UL component-recognized power supply, and the company supplies UL component-recognized CTs.

As such, there are NO instructions that have been UL approved. That creates an interesting 110.3(B) problem since you must follow the UL approved instructions.

It appears many/most users are simply installing the whole kaboodle inside the service panel - module, power brick and all (substituting a power brick with leads rather than a wall-wart with a plug). Just like every other product of that type installs normally. I don't know what it provides for a WiFi antenna.

I also suspect most people are doing this under the table without AHJ approval. I can't recommend that, especially when similar units from UL-approved vendors are readily available.

*(Or equivalent NRTL such as ETL)

  • It looks to me like the best/only way to use this is to install it outside the box with a clamp around each cable as it leaves the box. This would involve opening the wall to get access to all the wiring outside the box, installing the clamps, running all the wiring to a 1-gang box, covering all the wiring back up, installing a std NEMA 1-15 plug in a box next to it, then have all the "bits" in the 1-gang box as a convenient storage spot. Barring some minor details, would that be workable?
    – FreeMan
    Aug 5, 2020 at 12:56
  • @FreeMan that would work if clamping whole cables worked, but unfortunately the very thing Code requires - balanced/equal currents to make EMFs cancel out - would also make the CT ineffectual. Aug 5, 2020 at 14:39
  • Got it. I wasn't sure how those worked. thanks.
    – FreeMan
    Aug 5, 2020 at 15:00

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