emonTx V4, emonVS in North America

I mentioned the 300 V stuff simply because it’s a very common rating for electrical
wiring used in a typical US residence.

But, as long as its rating is at least 240 V, it’d be OK for use over here.

The cable & connectors looks like this: 3m RJ12 6P6C 6 Core Straight Wired White | Cablenet - but there’s absolutely no useful information on that website.

This from RS https://uk.rs-online.com/web/p/telephone-cable/0561940 is 150 V, so I’d guess this applies to ours. The dimensions over the cover are about right, also from the look and feel of the cable.

Around these parts at least, stuff installed inside the fuse box needs to withstand higher voltages than stuff hanging off an outlet… maybe 5kV instead of 2kV (but don’t quote me on the numbers). The EmonVS has been through some safety tests, but exactly what that involved isn’t clear.

Let me summarize this idea to make sure I’m caught up.

  1. Install the emonVS-PSU inside the breaker box.
  2. Connect L1, L2 to a 2-pole breaker and the neutral bus (as @dBC posted in the video above).
  3. Connect E to the ground bar.
  4. Run the RJ12 cable out one of the knock-outs to the emonTx V4, similar to what most of us have been doing with the CT cables going to our emonTx V3 all these years.

Seems tidy. Anything I am missing?

Wouldn’t be a bad idea to line the knockout hole with a bushing to give the wire
jacket some protection from the sharp edge the knockout is going to leave.
Code says they’re required, so if you want to keep it to code…

Something like this:

or this:

Don’t forget to keep the LV and HV wires/cables separated from each other. :wink:

Other n’ that, looks good.

The bit about ensuring the EmonVS and the RJ12 cable are all rated as suitable for use in that environment (the CTs and their cables are)

If you already have a 2-pole breaker in your load center, depending on the guage of the wire
attached to it, you might be able to add the wiring for the emonVS directly to the breaker.

If the wire in the breaker is a lot larger than the emonVS wiring, you can add a short pigtail to the breaker, then use wire nuts to attach the emonVS wire to the pigtail.

(code says it’s OK to have two wires attached to one breaker)

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Regarding the emonVS-PSU in North America (both the currently-available 1-input version, and the likely future version with two inputs for split-phase voltage): my understanding is that the CM choke and filter are there to meet EMC standards. I asked about it and Glyn replied here. Earlier in the same conversation, Trystan attached the test results showing the EN standards met.

My question now is, are these components necessary in a US configuration of the emonVS-PSU?

Do they have any impact on the accuracy or function of the emonVS-PSU, or are they there exclusively to meet EMC standards? (Since there is a CM choke and filter both before and after the PSU in the current configuration, my question applies to all four compenents.)

I don’t know whose EMC standards are “tighter” (I suspect it’s the UK’s)
but the US has similar requirements.
(you’ve probably seen the mark pictured below on your electronic devices)


All components in a circuit affect circuit operation to some extent.
How much the EMC components affect circuit operation depends on how well the circuit designer did their job. In a properly designed circuit, the undesireable effects from those components
are kept to a minimal/negligible amount.

AIUI, the components you are asking about are present to meet EMC standards.

I’m seeking confirmation regarding wiring the US NEMA 5-15P cable as the UK labeling differs from what I’m used to in North America.
L1 to black (hot)
N to white (neutral)
E to green (ground or earth)

I appreciate the help. Thank you.

Welcome, Gordon, to the OEM forum.

This looks OK to me. If you have a second ZMPT101B voltage transformer fitted in your emonVs, then the second Line conductor (red) should be wired to L2 (obviously not available when using this particular connector), and you’ll then be able to monitor the voltage of both legs of your supply. You can then pair each c.t. with the appropriate voltage which will give you the most accurate power data.

Power for the emonTx4 is taken between L1 & N, any voltage in the range 100 - 255 V, 50 or 60 Hz.

Question: Is it worth the effort of monitoring both L1 and L2 in the US split-phase system? It seems to me that the typical user that is not adjusting the firmware on their own would not be able to specify which CT goes with which voltage signal.

Since I last visited this thread, the emonPi2 board has replaced the emonTx4 board, but the schematics for the two are almost identical, and for the purpose of this question, they are both designed to read the input(s) of the emonVs.

I appears from the configuration instructions (image below) the CT Type and Phase Correction of each channel can be configured, but not the voltage input.

We could have a much simpler installation in the US if users could use a NEMA 15-5 cable with the emonVS (image below), rather than have the installation inside their breaker panel we discussed above.

EmonLibDB is designed to allow individual adjustment of both amplitude and phase error compensation of every input, both voltage and current. If this is the library that’s being used, there’s no reason why each input device cannot be individually calibrated if a suitable comparison standard is available. Equally, a current input can be paired with any voltage input for the purposes of calculating the power and energy. Unfortunately, it’s not clear to me which sketch, hence library, might be used in the emonPi2.

In answer to the initial question, if there’s a significant difference in the voltages between the two legs (of the same phase), then there is good reason to measure both voltages.

The firmware for the emonPi2 uses the EmonLibDB library. It looks to be almost identical to the emonTx4 firmware.

There are two flavors of firmware available for both emonPi2 and emonTx4 – single phase and 3-phase.

In the single phase versions we have the number of voltage inputs hard-coded to 1.

#define NUM_V_CHANNELS 1                                   // SET TO 1 FOR SINGLE PHASE

In the 3-phase version of the firmware for each board, the number of voltage channels is hard-coded to 3.

All the above (1- and 3-phase) have the same code block for setting up the relationship between the power-monitoring channels and the voltage inputs.

  #if NUM_V_CHANNELS == 3
    EmonLibDB_set_pInput(1, 1); // Phase 1
    EmonLibDB_set_pInput(2, 1); // Phase 2
    EmonLibDB_set_pInput(3, 1); // Phase 3
    EmonLibDB_set_pInput(4, 1); // Phase 1
    EmonLibDB_set_pInput(5, 1); // Phase 2
    EmonLibDB_set_pInput(6, 1); // Phase 3
    EmonLibDB_set_pInput(1, 1, 2);               // CT1 between V1 & V2    
    EmonLibDB_set_pInput(2, 2, 3);               // CT2 between V2 & V3  (etc)
    EmonLibDB_set_pInput(3, 3, 1);  
    EmonLibDB_set_pInput(4, 1, 2);  
    EmonLibDB_set_pInput(5, 2, 3);
    EmonLibDB_set_pInput(6, 3, 1);
    for (byte ch=0; ch<NUM_I_CHANNELS; ch++) {
      EmonLibDB_set_pInput(ch+1, 1);

My thought is that an experienced/technically-inclined user in the US could use an emonVS 3-phase, installed as discussed above, and modify the firmware to use 2 voltage inputs, and change the channel setup code to something that matched their setup, such as

  #if NUM_V_CHANNELS == 2  //one channel for each leg of split-phase US voltage
    EmonLibDB_set_pInput(1, 1); // Leg 1 -- modify these to match the leg used by the monitored circuit
    EmonLibDB_set_pInput(2, 2); // Leg 2
    EmonLibDB_set_pInput(3, 2); // Leg 2
    EmonLibDB_set_pInput(4, 1); // Leg 1
    EmonLibDB_set_pInput(5, 1); // Leg 1
    EmonLibDB_set_pInput(6, 1); // Leg 1

That said, all the recommendations for US users I have seen in the forum and in the docs seem to suggest the single-channel emonVS. This makes sense for the non-technical user for sure, I think. For those that take this route, they only need to connect the device to one leg. It strikes me that they could use the NEMA 15-5 cable mentioned above and plug it into a standard household near the breaker panel.

In the later setup, I would think that some error would be introduced by the fact that voltage can actually vary between the legs. There is also the fact that the phase angle is 180° different than between the legs, but a motivated non-technical user could compensate using the Phase Correction tool in the configuration utility.

Am I on the right track with these two paths? (Technical path: 3-phase tools stepped down to 2-channel, split-phase configuration. Non-technical path: 1-phase tools with phase correction and some loss of accuracy due to voltage difference between the legs.)

This is exactly the intention and why the library calls are provided the way they are. There’s no fundamental difference between a single phase UK setup, a split-phase N.American setup and a 3-phase UK or elsewhere setup, as far as the emonLibDB library is concerned, they’re handled most of the time as one, two or three single-phase channels. With a 3-phase emonVs and two or three phases, you can specify the line-line voltage rather than the (implied) line-neutral voltage.
So to the library (I had no control over the sketches that have been uploaded or appear on Github) all you suggest is catered for.

However, I would suggest adding a 180° phase “error” is a bad idea, far better to use a negative amplitude calibration or point the c.t. in the other direction.

I suggest you download and look at the emonLibDB documentation published on this forum.

Apart from the firmware, the emonTx4 replacement (an emonPi2 without the Pi) and the original emonTx4 both use a 433MHz band radio to communicate with the emonPi2 or emonBase.

Wikipedia says that the 433.05 - 454.79MHz ISM band is legal in ITU Region 1 i.e. mostly Europe & Africa. The Americas (ITU Region 2) use 902 MHz-928 MHz.
Wikipedia says that the 433.05 MHz - 434.79 MHz ISM band is legal in ITU Region 1 i.e. mostly Europe & Africa. The Americas (ITU Region 2) use 902 MHz-928 MHz.
[Corrected by post no.59 below]
Hence the 915MHz versions of the RFM69.

This might be worth considering?

My advice for US users would be to use the 433MHz radio that is currently offered by the OEM shop.

I’ve always used the 433MHz radios in my US installation. I started in 2015 with an emonTx, an RFM69Pi board on a Pi, and three emonTH sensors. I’ve since added on a second emonTx and several homegrown boards with 433MHz radios. I’ve had no issues. I asked a radio expert I know and he told me HopeRF, the maker of RFM69 transceivers, has an FCC part 15 grant for the 433MHz band. https://fccid.io/2ASEORFM380F32

The OEM shop doesn’t currently seem to offer the emonPi2 with the 868-915MHz option. If you have never tried to desolder one of these transceivers from a board let me tell you - it gets ugly. Felix Russo from LowPowerLab once described to me how he does so with a pair of chisel tips and a Metcal power supply that together cost more than a couple emonPis.

If someone did want the 868MHz option on an emonPi, I’d recommend checking with the OEM folks to see if they could make one that way or provide one without a transceiver. Felix Russo’s shop sells the transceivers and he has some online tutorials about soldering them in place, which is relatively easy. Transceivers

I’d like to recap this thread, including the timeline of what happened between April 2023, when I started the thread, and now (March 2024) as I look at all the new things that have been released in that span. This is to make sure I understand where we now sit.

Nov 2022

emonTx v4 (emonTx4) becomes available in the OEM Shop along with emonVS PSU single-phase. The 3-phase version is available as a hidden option in the Shop. There is not yet firmware that supports 3-phase monitoring. emonLib and emonLibCM are available, both of which are designed for one voltage input channel.

AVR-DB: emonTx V4, new hardware in progress - Hardware - OpenEnergyMonitor Community

April 2023

I started this thread and we envisioned two types of North American users of the new emonTx4+emonVS. The non-technical user could use the single-phase emonVS with NEMA 5-15P cable and a single-phase firmware available for emonTx4. The technical user interested in monitoring both legs of their split-phase power did not yet have an option, but they soon would.

May 2023

3-Phase Support came to OEM courtesy of Robert Wall’s emonLibDB.

EmonTx4 3-phase support with emonLibDB - Hardware / emonTx - OpenEnergyMonitor Community

The technical user could now use the 3-phase emonVS (or a 2-phase through special request?) mounted inside their breaker panel and an emonTx4 with 3-phase firmware configured for split-phase US power and the specific circuits monitored.

But this was only the case for a few months, because the emonTx4 was soon supplanted.

Dec 2023

The emonPi2 was released and the emonTx4 was discontinued. The next generation of emonTx will be based on this board but is not yet available per se as I write this.


Non-technical users would continue to use the single-phase emonVS with NEMA 5-15P cable but would use the emonPi2 with single-phase firmware instead of an emonTx4.

Technical users would continue to use the 3-phase emonVS (or perhaps a 2-phase emonVS through special request) mounted in their breaker panel, and would now use the emonPi2 with 3-phase firmware configured for split-phase US power and the circuits being monitored.

These are high-level outlines, of course. There are various flavors of the plan for each type of user, as we’ve discussed above. My intent is to summarize what devices would be used with what firmware and high-level configuration. Again, my hope is to make sure I understand where we now sit.

To correct my previous post:

Wikipedia says that the 433.05 MHz - 434.79 MHz ISM band is legal in ITU Region 1 i.e. mostly Europe & Africa. The Americas (ITU Region 2) use 902 MHz-928 MHz.

Sorry for the typo!

My advice has always been - don’t try. I have considered getting a piece of copper busbar or equivalent, about 6 mm thick and bending it into a ‘U’ shape with the legs just wide enough to span the RFM, and the same length as the RFM, and attaching an insulated handle - to make a soldering iron capable of reaching and melting all 14 joints at the same time. It would need heating with a gas blowtorch or similar, and even then, I think it would be very tricky to pull off without damaging something.