Hi, I just ordered a nanodeRF and emonTX and looking forward to start the installation at my house here on Lantau Island, Hong Kong. As I am very new to this, just wanted to get some advice before i receive the hardware and switch anything on, so here goes my first post.
Attached is a picture of the meter box of my house; mains come in at the bottom, split in two in 4 henley boxes, then 3 meters. My house has 3 floors and each floor has a separate meter (left and centre are 3-phase, right is 1-phase).
- To monitor the power consumption of the entire house, i assume i should put 3 CTs (connected to 1 emonTX) on the red/yellow/blue mains below the henley boxes, right? I'd like to start with 'current only' (emonTX_CT123 firmware), as there is no AC plug near my (outdoor) meter box. Voltage here is 220V, i will configure that in the firmware.
- If i decide to add voltage, i understand i only need to measure voltage once, so 1 emonTX would be enough, right? Would you recommend me to also use voltage or will i get decent results with current only?
- I don't think i'm allowed to put an AC socket in my meter box, and other sockets are far away. Would it be technically feasible to collect the voltage data at the emonBase level (indoor)? Maybe not, as i seem to understand that the power calculations are made inside the emonTX.
- At a later stage, i would consider monitoring the 3 meters to get a better understanding of consumption; i would need 3 emonTX's for that, and could i use 1 AC/AC adapter and split the output into the 3 emonTX's?
Thanks for your advice, hope to contribute my results soon.
Re: CT positioning on 3phase mains
1. Correct.
2. It depends. If the voltage is relatively constant, and if the voltage on all 3 phases is always the same (i.e. the loads on all 3 phases are balanced) then you should get reasonably accurate "apparent power" values by reading one voltage. If the voltages are balanced and you want "real power", you can shift that voltage in software to again get reasonable, but not totally accurate, values. But in reality, that is unlikely to be the case, so for accurate power you need 3 emonTx's and 3 voltages, one per phase.
3. No, you need to feed both the voltage and current into the emonTx when you are measuring real power. But if apparent power is good enough, then yes, you can send current and voltage separately to the base and multiply them there.
4. I think you'd need 3 emonTx's and 3 voltage feeds - you'd use one emonTx per phase and feed one phase of the 3 flats into each input.
What about the single phase meter on the right?
Re: CT positioning on 3phase mains
Thanks a lot Robert for the feedback. I understand now that i will need 3 voltage measurements, and where i need to measure them: i need the voltage of each phase (red/yellow/blue) and thus need to look into my fuse box to know in which circuit i need to plug in each of the 3 adapters to measure the relevant voltage (and it does not matter behind which of my 3 meters i measure this voltage, only phase is important). I need one emonTX for red CT and red voltage, and one for yellow, one for blue.
Re: CT positioning on 3phase mains
That all looks correct. You can still measure each flat separately of course, as you have 3 current inputs available on the emonTx (so 9 c.t's, 3 emonTx's, 3 voltage monitors and one (big) 5 V power supply in total for the sensors side). I guess you're looking at a Raspberry Pi and RF module to collate and save the data?
Re: CT positioning on 3phase mains
Thanks Robert. In fact i want to start with a nanodeRF to upload the data to emoncms.org so i have access from anywhere. But i'll have to see how it goes with my internet connection here; if that does not work well enough, i'll hook it up to a Raspberry Pi local server with emoncms.
Re: CT positioning on 3phase mains
I am a Master Electrician and have done a few things but I have never wired anything in China.
From your picture though, it looks like if you want to monitor the entire house you would place your CT's on the wires coming in the very bottom of the cabinet into the modular connectors. The one on the right would be the neutral of a wye connection.They appear to be using black for a neutral and the other colors as you say for the 3 phases.
To get the voltage readings you could connect to the phase conductors your fusebox as you say. I don't know exactly how the emon sensors work just yet as I am new to this device but the voltage for each phase would be taken between that phase and the neutral wire. Here in the US that would be a 120/208 volt system. So, to get proper power readings (P=I*E) you would need to get the current on each phase and the voltage between each phase and the neutral.
Rule #1 is NEVER connect anything while it is energized. ALWAYS shut the power off first. If in doubt, hire an electrician that knows these systems. Safety first!
Thanks for the picture, I will use this in my training classes for an example of how things are done in other parts of the world.
Happy day from the USA!
Re: CT positioning on 3phase mains
A note on the safety points that ArchonOSX raises:
The emonTx is designed as a non-invasive system, the standard ac adapter is CE approved and can be safely plugged in to a live socket, and the output at around 10 V is quite safe to handle. The c.t. clips over the insulated and sheathed cable and there is no galvanic connection to the main conductor, though the c.t. must be plugged in to the emonTx first and never unplugged while the main conductor is carrying current.
From time to time, the question is asked, directly or indirectly: "Can I make a direct connection to the mains?" The answer is a firm NO. As soon as you make any connection, either to the line or the neutral conductor - both of which are regarded as live conductors - the whole emonTx and anything connected to it must be regarded as live, and potentially lethal.