Software
Phase Peak Guard: understand your 3×25 A connection
A home with a 3×25 A main connection has three phases, each carrying its own load. Total energy use may look normal while one phase is under much greater strain. Phase Peak Guard is an AppDaemon app for Home Assistant that monitors L1, L2 and L3 separately. The app measures and analyses; it does not switch devices off.
Why measure each phase?
With a 3×25 A connection, you cannot treat the supply as a single 75 A allowance. An induction hob, heat pump, boiler, EV charger or another single-phase appliance can load one phase much more heavily than the other two.
Phase Peak Guard calculates the headroom remaining on each phase before reaching the configured main-fuse rating. The default is 25 A per phase, with configurable levels of 17.5 A elevated, 20 A high, 22.5 A critical and 25 A overload. A reading of L1 = 11.2 A, L2 = 18.7 A and L3 = 23.1 A, for example, shows that only L3 is approaching the critical range.
Measurements, trends and forecasts
For each phase, the app tracks current, power, a smoothed reading, one-, five- and fifteen-minute averages, and remaining headroom. Using recent samples, it estimates current 30, 60 and 120 seconds ahead, together with an indication of forecast confidence. A phase drawing 21 A and rising quickly towards 24 A calls for different attention from a steady 21 A load.
The fuse stress value is a heuristic thermal indicator: sustained high current carries more weight than a brief spike, and load is weighted approximately quadratically relative to the configured main-fuse rating. It is not an official fuse characteristic or an IEC fuse-curve model.
Phase imbalance and history
Phase Peak Guard compares the most- and least-loaded phases. It retains historical data and analyses the P95 load over seven and thirty days. This helps reveal whether one phase is consistently more heavily loaded, useful when planning an additional boiler, air conditioner or other substantial single-phase appliance.
Which measurements can it use?
Directly measured phase current is preferred. If that is unavailable, the app can calculate current from apparent power (VA / voltage) or estimate it from active power, voltage and a configured power factor. Units including A, mA, W, kW, VA and kVA are converted automatically.
What appears in Home Assistant?
Through MQTT Discovery, the app creates Home Assistant entities for per-phase current, averages, maxima, remaining headroom, forecasts, trend, fuse stress, energy direction and historical values. General sensors can show the most-loaded phase, lowest headroom, phase imbalance, status and a recommended action. Example action codes include avoid_new_load, reduce_load_l2 and critical_load_l3.
You can use these readings for dashboards, alerts or your own automations. Phase Peak Guard only observes and advises; Home Assistant or a separate control system decides whether to switch anything.