Old(er)skool Powermeter wonderings

[xanhoera]

Ages ago, I've been using the original RFXCom LAN including a powermeter to retrieve the power usage for the entire household for my single-phase-wired installation. However, since the introduction of the digital meters, the device has been re-introduced as only a power meter for one specific circuit. With the powermeter clamp around the phase wire of that specific circuit, numbers were showing up in HS3 with the RFXCOM plugin.

However, recently I've upgraded the household to a 3-phase-wired 400V installation, and I noticed the numbers increased massively. I did not expect it to change anything? Is there any calculation that needs to be done to calculate the correct kwh, now that 400V is in order? The wiring of the circuit where the powermeter is connected to, did not change. Consumption habits on that specific metered circuit did not change either.

Does it make sense that I see the numbers changing (for the same usage)? Maybe someone can point me to a single-phase vs three-phase for dummies site?