I’m planning the installation of an emonVs (3 phase) and emonTx (v4) to monitor a three phase supply. I can get easy access to two phases and earth through a (2P+E) socket. Otherwise significant work is required to get at the three phases and neutral. Will the emonVs work with two phases and earth? If so, I’d be grateful for advice on how to connect with the emonVs terminals.
Yes - but you won’t be able to use c.t’s (and get meaningful power values) on the third phase - even if the appropriate software exists, which it doesn’t at present. If you look at a circuit diagram, it comprises 3 ZMPT101B transformers and their multiplier resistors wired in star, the star point being neutral. The emonTx’s power supply is wired L1 - N, in parallel with the first transformer. So all three phases are available (if wired) to the emonTx for power calculations against any one of the c.t’s, each pair of c.t. + v.t. is treated as a single phase wattmeter. The current required for the 2nd & 3rd phases is 4 mA - essentially zero, the multiplier resistor value is 60 kΩ.
Do you need to have a socket, or can you permanently wire it into something like a 5-module garage consumer unit (40 A RCD + 3×6 A MCBs), for example, then run a single cable (e.g. https://uk.rs-online.com/web/p/power-cable/2537017, in 5 m or 10 m cut lengths) into the emonVs. This should be OK provided you have a label on the emonVs clearly indicating where to isolate the supply.
Thanks - great suggestion. The installation uses a Henley blocks to isolate the phases and neutral. I can wire from the Henley blocks to the consumer unit. The phases are not in balance. Installation is in a Parish Church with an attached Church Hall. One phase is terminated (L1), one (L2) is connected to the Church Hall which is like a domestic load, but with solar panels (3kW) and a heat pump (15kW thermal) too. L3 serves the Church with lighting, gas boiler and some light electrics. So I think a consumer unit and four MCBs one for each phase and neutral?
No - Henley blocks DO NOT PROVIDE ISOLATION. They are purely connectors allowing the incoming supply to feed several different switchboards/consumer units.
What do you mean? Not used?
NO! That is dangerous. You NEVER have a MCB or a fuse in the neutral. If the neutral MCB trips or the fuse blows, then the circuit appears to be dead - nothing ‘works’ - but all the wiring is live. The only time you can have a switch of any sort in a neutral is when it is mechanically linked to the line side, so that all the line conductors and neutral are switched at the same time. So a 4-pole linked MCB is fine, as is a 4-pole isolating switch, as is a 3-pole or two or three separate MCBs switching the line side only and leaving the neutral permanently connected.
The reason for a 5-module CU was the main isolator/RCD takes up 2 slots, leaving 3 for the MCBs feeding each line to the emonVs - and in this case those should be linked too, as the emonVs will have a live wire inside when any one or more line is live.
So going back to the original question, as you appear not to be using L1, then wiring the emonVs L1 to any line and either L2 or L3 to the other line will be fine. Phase rotation isn’t a concern like it was with the emonTx V3.