BOM and design advice sought (AU, 3-phase)

New to this field, but have some experience with monitoring tools.

Am looking for some feedback on my assumptions and kit-out plans.


I’m in Australia (240v) with a 3-phase supply coming into a meter box which has a feed-out to a small cabin, daisy-chaining to the shed, and then one phase extending up to a small granny flat. Distances are ~ 10-20 metres between each

Main meter box has ONE standard power outlet, which we use to feed an always-on septic system fan / pump.

Cabin has a basic set of circuit breakers, no apparent access to wiring, I believe single phase take-off for this structure, including two hard-wired split-system air-conditioners (both 500W units, I believe).

Next in daisy-chain is the shed, which has 3-phase present (but unused). Hot water (basic element system) I believe is an 1800W element, we have it on a timer arrangement next to the circuit breaker. The switchboard here also feeds in a 10kW solar panel inverter - AIUI it splits feed to each phase equally. We can access the rear of this panel, so TCs will be easy here.

Finally, one phase from the shed up to the granny flat, that feeds domestic devices (1 x air-con, stove/oven (32A), etc). In there we have just another basic circuit-breaker board with no easy access to actual wiring.

I currently obtain 5-10 minute interval figures for solar power (via Modbus).

We’re using more grid power than I feel we should (20-40 kWh / day), but struggle to reconcile these against solar power, and utilising some wall-plug devices I’ve moved around and run in place for a few days (fridge, computers, etc) to get some average consumption figures.

We get very poor data from our energy provider (1-2h granularity figures, several days lag on availability, manual downloads of xls files).

I manually record daily readings at the meter box for the 3 phases, but it’s pretty unsatisfying / ambiguous of course.

Line drawing of power distribution at the site follows:

Following photos show things better. I’ve had to merge photos as new users can’t embed > 3 images total.

Top - the main incoming meter’s front panel.

Sorry it’s a bit fuzzy - I can update later if needed.

Yellow extension lead at bottom to septic - that’s the socket I’d use for the reference DC adapter.

Middle - this shows the rear of the main incoming meter - from top, incoming from transformer - 4 x black wires (neutral + 3 x phases).

Outbound (bottom) goes to cabin.

Lower - shows the reverse of the main meter board:

Next we have the shed sub-board.

Top – show the front panel - 3 phases, HWS (hot water system) + timer for same. Couple of circuits for 15A and lights within the shed.

Reasonably confident the HWS is the only thing on one of our phases (what the main meter calls #3).

Far-right, the circuit up to the granny flat (‘Roost’ shown here - converted chicken shed).

Middle - the rear of box - showing orange (left, lower, coming up) from solar inverter, and then an insane mess, but at least it looks relatively easy to locate space for CTs

Lower - a slightly better view of the rear of that panel.

Assumptions / questions

I emailed recently and received no response - but I gather from other threads that they are indeed still active (as recently as April 2024) and their online store’s stock availability is accurate, so I’ll proceed with purchase via them.

I am thinking I will get two x Iotawatt monitor devices - one to be installed at the main meter, and another in the shed at the sub-board.

I don’t believe there’s a convenient way to measure any of the air-con units, or the single-circuit stove / oven, and am resolved to working out their usage mathematically from other data.

Reference (9V DC adapter) – is this fine to come off the same powerpoint (in main meter box) used to power fan/pump in septic (periodic cyling)?

Do I need a reference DC adapter at both meter boxes (both iotawatts)? I assume yes.

Would it help significantly / much / not at all - to get two more power outputs wired in the main meter box, one per phase, for more reference adapters?

Similarly, with the shed meter box? only have 100W TC’s on stock but I’d been assuming I’d use exclusively those anyway - mostly for the ability to repurpose in the future.

I gather I don’t lose any significant accuracy with those over the 50W versions (which are out of stock here, and no hint on if / when they may be available again).

Number of TC’s needed - I’m thinking:
4 for the incoming (3-phase + neutral)
4 for solar (ditto)
2 for HWS
6 (2 each) for the 2 x shed internal circuits (‘Power’ & ‘Lights’), and the granny-flat / Roost circuit

Do I need or want TC’s on ‘both sides’ of the incoming meter?

Do I need two per internal circuit - one for neutral, one for active - as I’ve detailed above - or can I start to share ‘common neutral’?

I have a similar situation, in rural Tasmania, although not quite as spread out. I plan to buy one iotawatt now for the meter box and get another for the house later rather than spend all that money at once. I have different reasons for needing it than you do though.

From my reading of the docs we don’t need a neutral CT; certainly I don’t have one for my zappi EV charger which uses monitoring to direct excess solar into the car.

I’ll need 8x100A at the meter box (grid input, house output, and two for other circuits at the box). Ideally one would be 50A but the $5 difference isn’t worth worrying about. Future plans may involve another 3 so the iotawatt seems perfect for this.

Once I start monitoring the house I will easily fill all 14 inputs of a second iotawatt, but I’d prefer to save $5 per CT and use 50A. Sadly I doubt there’s any way to do that while costing less than the savings.

[update: I asked them and they now only sell 100A.]

Hey Andrew,

Thanks for the response there.

You inspired me to just go and buy some kit and worry about the implementation details later ; )

On that note - sorry to say, but they evidently only had 10 remaining 100A CT’s, as they’re now showing out-of-stock.

I’d read some earlier threads around the accuracy of the 100’s being comparable to the 50’s, so, like you, I reasoned the $5 saving on those now would inevitably just end up annoying me later.

(I think there was a time when one model was clipable, the other had to be installed by a sparky.)

I suspect there’ll be some note-comparing once my kit arrives, and smartguys get some CTs back in stock. (Again, sorry about that!)

I note that smartguys have $30 off their IoTaWatt’s at the moment - poor timing for me!.

Also that you can pick up the same YHDC SCT-013 CT’s for about $20 from ebay (au) (I have another five on order, as I’ve used up the ten I picked up originally).

I’ve got the key bits of my system now instrumented, 3-phase calibrated, and will track & reconcile the figures from this system over my daily meter readings and my solar inverter data for a while to make sure it’s all agreeing with each other.

With my IoTaWatt at the shed sub-board - mid-way between main meter box (primary IoTaWatt) and other structures / power draws, I track ‘incoming’ power there as well as the 3 x Solar feed-ins.

This is a dashboard I’ve had for a while, mostly using prometheus scraped data from a ‘solariot’ exporter for the Sungrow inverter ( GitHub - meltaxa/solariot: Leverage your IoT enabled Solar PV Inverter to stream your solar energy usage data to a real time dashboard. )

I’ve added one panel - top left - using the influx data from the IoTa’s 3 x inverter inputs, and it’s pretty close.

Been a while since I’ve had to use the Influx QL … and remembering now just how awful it is.

So the next priority will be to set up an OpenTelemetry collector that can receive influx v2 data, and emit metrics into my Prometheus / Mimir system.

Was happily surprised that the IoTa down in the main meter box talks to my WiFi – it’s a good distance from the nearest AP, and it has that 1.2mm galv steel case around it. I get occasional drop-outs, and will extend a mesh point down there sometime, but so far so good.

Really, my biggest complaint so far is the American date format of ‘Month dd’ on the built-in graphing tool ; )

That’s from this morning - B & C jumps are my 1400W air-cons cranking up, but then everything trending towards negative as the solar inverter starts feeding back into the grid.

Kit & documentation have been a delight to work with.

I did get caught out briefly after playing with one of the modules on a different wifi when I first picked them up - and not realising I needed to note the device name, as that becomes the password when it’s in standalone wifi-AP mode (I had foolishly not made a note of what I’d called it - ended up having to take the microSD card out and check). But that’s all because I hadn’t read the docs before fiddling.

Thank you for the ebay tip! When I tried searching for them I used the smartguys SKU not the one written on the picture. That makes a lot more sense. Looks like there’s a store in Perth that sells them too!

This store sells both current and voltage types, looking at the iotawatt docs either works but current is the normal one.

The discount is good timing for me, I need to get my first before too much longer. I don’t think I want to drop $1000 on my full setup just yet, so I’ll just get one now and deal with not having a discount later.

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