emonTx V4, emonVS in North America

Here is the latest entry to the recap given above in March, which provided a timeline of what happened between April 2023, when I started the thread, and March 2024.

June 2024
emonTx5 was introduced to the OEM Shop. A new “N. American split-phase” option for the EmonVs was introduced to both the emonTx5 and the emonPi2 ordering options. This option provides the components for the “technical user” configuration discussed above: an emonVs with 2 input channels and firmware for monitoring both legs of North American split-phase power. Here is the announcement topic.
emonTx5 transmitter node & emonPi2 (12 CT expansion) available in the shop - Hardware - OpenEnergyMonitor Community

In that announcement topic @Bill.Thomson pointed out that we still may not have solved the question of what a safe, up-to-code installation will look like for this split-phase monitoring.

The National Electrical Code (NEC 725.136A) specifically excludes any low voltage wiring from being installed in an electric panel, raceway, or box used for high voltage (120/240V) circuits.

Low voltage in this context, means less than 50 Volts.

I suggested in that topic the shop could offer a “non-technical” configuration like the one we discussed in this topic, and @TrystanLea said he would discuss it with @Gwil.

I would like to further discuss here the safe, code-compliant installation of a split-phase-monitoring emonVs.

My next thought would be to run a length of Romex (residential branch wiring) from a 2-pole breaker, out of the electric panel, and into the emonVs, so that the emonVs would be outside the electric panel but have each input connected to a leg inside the panel.

A 4-pole connector was mentioned earlier in this thread.

That would be an option if a user has an unused 4-pole receptacle near the electrical panel already.

The majority of users will not. Those receptacles will be in the garage (EVSE), behind the dryer, behind the oven, and so on, and typically they will already be in use.

One could be installed by a technical user (AKA “electrician”). The receptacle part costs about $13 US, and the plug with cable at least $32 US. I would personally prefer to have my electrician run the Romex directly to my emonVs without the bulky intervening receptacle, plug, and cable. But if the experts on US code (looking at you @Bill.Thomson) tell me I have to have the receptacle, so be it.

That’ll work as long as it’s in a conduit.
(this is where something like flexible PVC - often sold under the name “liquid tight” - works really well. (much easier to install compared to metallic conduit)

It doesn’t even have to be Romex. As we’re speaking of running the wiring in conduit, individual wires are OK and cost quite a bit less than Romex.

You will need some sort of enclosure. It can be as simple as a junction box or as elaborate as you wish.

AFAIK, it can be hardwired. i.e. no receptacle needed.

In the UK, the emonVS can be permanently connected - either the single-phase or the 3-phase version, but will of course need a 2-pole or 4-pole isolator and appropriate over-current protection in the form of a single-pole or 3-pole linked mcb, and connected following normal wiring practice.

Could the conduit (for example Liquid Tight) connect directing to the emonVs enclosure by replacing the M20 cable gland ( Cable glands for emonVs-PSU - Hardware - OpenEnergyMonitor Community) with a conduit fitting? (Something like this: Liquid Tight Conduit Straight Fittings (flexiblepvc.net).)

I should’ve mentioned the fact I was speaking of a US installation.
That said, It’ll need overcurrent protection (can be a circuit breaker or fuses) and although not required, it’s never a bad idea to use some form of disconnect device. (US term for isolator.)

It should work OK. Although the fit would be a little “sloppy.” The thread diameter of the gland you linked to is 20 mm and the threads of a 3/4 inch gland should measure ~19.1 mm
(a difference of about 0.035 inches)

Fuses? That surprises me, because the fuse on one leg could operate, leaving the other leg live and the emonVs would still be live to one leg. In the UK, fuses would not be acceptable for that reason – a linked circuit breaker would be required.

Double pole fusing was normal in the UK in the dim and distant past, and was made illegal for exactly the same reason - the neutral fuse could operate while still leaving the apparatus live though the line fuse and thus potentially dangerous.

As an example, both the WattsOn and WattNode specify circuit breakers or fuses as OCP for their mains inputs.

I did give some incorrect info about the need for a disconnect device. (I forgot about the rules regarding permanently connected equipment.)

The use of a disconnect is required when a device is considered permanently connected. i.e. hardwired. That’s mentioned in the CCS WattNode manual excerpt shown below.

The WattsOn wiring is shown below. Note the use of a dead-front fuse block.

Elkor Technologies is a Canadian company.
The WattNode is made by Continental Control Systems, a US company.

Thanks, Bill. I contacted Continental Control Systems, described the use case (and provided a link to this topic) and asked if they could recommend a package for North American users that would include an enclosure and circuit breakers. Something like this: WattNode Meter Enclosure Brochure (ctlsys.com)

In the meantime, as I was searching, I noticed that Sense suggests users can install their unit inside the electrical panel. My search found many images of people having done so. Are they non-compliant?
Installation – Sense.com

It’s a nice enclosure, but they’re mighty proud of that bad boy.
As it’s a UL 508 listed assembly, from what I’ve read, the NEC does not apply.
However, there are rules specific to 508 type devices.


The cost for that item alone will more than likely be a showstopper for most users.

WRT the Sense device being installed inside of a load center…
There must be something in the NEC that allows them to do that with a device that
uses a radio link vice a wired connection. (the NEC is a large document)
As a retail company, they have too much to lose if it wasn’t legit to install their
device in a load center.