Selecting Compenents/O.E.M. Build Questions

AWG 4 or 4/0?

I double checked, it is AWG 2.

So, back to what I think was the original question!

If you put a 240 V ac adapter across the two legs of the well feed, you’ll measure the L-L voltage (obviously!). If you put a CT on each leg, you will measure different currents while the heater is on (presumably it’s thermostatically controlled - but that makes no real difference). Using the voltage and the current in the non-heater leg, your emonTx can calculate real and apparent power in your well pump. Using the difference between the two currents, and a constant - the heater resistance - you can do I2R to give you the real power in the heater, with a small error. The error will be due to the thermal coefficient of resistance, and for nichrome (the likely material), it is 0.4 × 10-3 per degree C. If the working temperature is 350°C, that means the resistance will increase by 14% at the working temperature (or more to the point, the current, hence the power, will be 14% higher at switch-on and fall to the nominal value as it reaches operating temperature).
You can program those sums into your emonTx, or do them in emonCMS.

[Edit]
I got the 0.4 × 10-3 per degree C value from Engineeringtoolbox. Kaye & Laby gives 0.00006 per degree C. There’s a huge difference between those values, and a wire manufacturer gives a factor of 1.028 at 300°C, which is a little higher than Kaye & Laby. Either of those gives the resistance change at around 2%, not the 14% of Engineeringtoolbox.

[Edit 2]
Measuring a 250 W convector heater, I got 202.8 Ω cold, 212.3 Ω hot, so about 4.7% change. From memory, the wire in that heater is a very dark red, only visible in complete darkness, so maybe 600 °C, which is much nearer Kaye & Laby’s value.

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You’re right there. What I see there would be completely unacceptable in the UK, for many reasons. First, even though it is TN-C-S, neutral and the protective earth connections would be made on completely separate busbars and the busbars would be linked at only one point, at the supply authority’s fuse and neutral link. Second, all bare earth conductors must be sleeved in green/yellow, those (presumably twisted) joints covered with a thimble are a definite no-no. I would expect the incoming terminals to be shrouded, and I would expect the unused MCB positions to be shrouded too.

But the spider’s nest is completely normal!

Thank you, thank you! The mportant part is being able to adjust emoncms (which I wasn’t sure how capable it was with handling math);
Now I’m just curious for the sake of being inquisitive, in theory, could I use the 240-9vac transformer, and use one CT on one hot wire and a CT on the neutral wire, and assume, all power going through the second hot is the same as the first minus the current flowing through the neutral to obtain my power readings?
and in the end I’m going to have to do some tests with values, because right now I’m using a ceramic forced air space heater; but that will most likely change next year when I re insulate all the plumbing and then I’ll use heat trace.

If the heater is the only thing connected to the neutral - and there’s no parallel earth path - then measuring the neutral will give you the heater current directly, which should remove the inaccuracy of measuring two nearly equal (maybe ?) currents and subtracting.

I would like to apologize for the wiring standard in my area. :-p This panel was installed just a few years ago due to horse damage (don’t ask) An electrician put it in; and the wire nuts were used to extend the length because the physical box size was bigger and the original wire would not reach; and I would have had a several thousand bill because of the distance to rerun two underground electrical feeds. However, there should really be no flow of electricity in the grounding circuit.
Also, every electrical panel (to my knowledge) has the ground bonded to the neutral; not just the utility transformer.
I also had the protective panel cover removed to identify the circuits and their connections better. You normally would not see the wiring, or the blanks for open spaces for the circuit breakers. That’s why I have three unused breakers, because the knockouts were missing from the cover.

The heater is not grounded; it’s double insulated - whether it is or not, it’s only a two pin plug.
If that’s the case, then holy crap that might make this a lot simpler.
Now; can one use a UK 240 transformer in the US despite the 50hz vs 60hz? I’m just wondering if I can keep the parts and line losses to a minimum instead of having two transformers; use one or is it possibleI used a domestic HVAC 30VA transformer and use 24vac to supply the voltage to the emontx or is that too much?

I take it you’re using the ac input as the power supply for the emonTx, not a separate 5 V USB? In that case the choice of transformer is fairly critical. The normal no-load voltage of our ac adapter is 11.6 V, so a transformer that gives you that or slightly above should be OK, but you must not go above 15 V rms on no-load.
Our UK ac adapter is specified for 50 Hz only (and the plug is integral), and the US one is 120 V only, so it looks as if you’ll need to source a transformer to fit the bill.

I haven’t decided that as of yet for the outdoor unit. If there is a complexity/makes more sense to use separate supplies, I will.

Wait, if I’m basing my power measurements on one hot and a neutral, couldn’t I use a 120 xfmr and specify in cms to double the measured power or am I missing something?

I thought you said that there was a 5 - 10 V difference between the two legs? That’s a 5 - 10% error. Therefore you must need to measure the 240 V Line - Line?

(I intended to point out earlier that you can’t have the emonTx inside that metal box - or if you do, the aerial needs to be on the outside.)

Oh right… thanks for the reminder… okay. Yeah, I’ll just find a low VA 240-120 xfmr and use the offered plug in transformer to do the rest.
BTW the differential varies depending on whats on in the house; but yes there can be and often is a differential of voltage between L1 - N and L2 - N

You are absolutely correct; and I do not plan on placing it inside the main electrical panel; and will install a PVC weatherproof box for the TX unit and electrical power supplies. I’ll only have the CTs inside the panel.

You’ll need to beware the additional phase shift if you’re going to be using two transformers in series.

One source you might check is control transformers like those commonly found in HVAC units.
I managed to find a 40VA unit that had primary taps for 120, 208 and 240V and secondary taps for 2.5.12 and 24V. Cost was ~$16. Source was ebay.

40 VA is more than plenty, and the 12 V tap should be OK, unless the regulation is appalling (which at 40 VA, should not be the case).

I thought about those; albeit the standard 24vac unit as I was an HVAC tech in my former life so I had a few of those but not one with the 2/5/12 volts.
Can the 5v or 12v be used with the TX units to power them as well?

Here ya go Don. 2.5/12/24V secondary. 40VA. $15.