How to add energy monitoring to an old panel

Adding energy monitoring to an older electrical panel is one of the most valuable upgrades you can make for a local-first smart home. Unlike cloud-dependent energy monitors, the options below keep your data local and controllable through Home Assistant, Hubitat, or Apple HomeKit.

The good news: for the easiest options you don’t need to touch your panel at all. Here are your real choices, from easiest to most involved.

Smart meter integration (easiest path)

If your utility meter has a P1 port (common in the Netherlands, Belgium, and parts of the EU), you’re in luck. The HomeWizard P1 Meter reads your entire home’s consumption directly from the meter’s P1 data port. It requires zero panel work — no rewiring, no CT clamps, no electrician.

Setup takes about 15 minutes: connect the P1 cable to your meter, power the reader, and enable the Local API in the HomeWizard app. The official HomeWizard integration then creates power and energy sensors in Home Assistant over a fully local API. You’ll get whole-home import/export data.

The tradeoffs: you only see total consumption, not a per-circuit breakdown. If you want to know whether your HVAC or your server rack is driving the bill, you’ll need a panel meter. Also, P1 availability depends on your meter — many EU smart meters have it, but North American utility meters generally do not.

A complementary option for individual devices is the HomeWizard Energy Socket, which meters whatever is plugged into it (within the outlet’s rating).

Per-circuit monitoring with a CT-clamp panel meter

For a breakdown by circuit, you need a dedicated panel meter with CT (current transformer) clamps around individual wires. The Shelly Pro 3EM is a DIN-rail three-phase energy meter that ships with CT clamps and reports per-phase voltage, current, and energy locally — a good fit for whole-panel or multi-circuit monitoring.

Installation means opening your panel and clamping the CTs around the hot conductors you want to track (mains, HVAC, dryer, etc.). This is work inside a live panel, so if you’re not comfortable and qualified, hire an electrician.

In North America, where the P1 route above is generally not an option, the usual circuit-level answer is the Emporia Vue 3: a main-CT plus a set of branch CTs in 8- or 16-circuit kits, which is far more granular than a three-phase DIN-rail meter for a typical split-phase residential panel. It runs through Emporia’s own app out of the box, but for local-first use you can flash it with ESPHome and it becomes a fully local Home Assistant sensor with no cloud. One practical warning: both the Gen 2 and Gen 3 use an ESP32 and need a one-time wired serial flash inside the case, with a USB-to-TTL adapter on the board’s UART pads (do not connect the Vue’s own power lead while flashing). Only later updates go over Wi-Fi.

Note on the inline Shelly relays: the Shelly Plus 2PM has built-in metering on its two switched channels (no external clamps) and is designed to control and monitor a specific load — not to clamp around panel busbars. The Shelly Plus Plug S gives simple plug-level metering for devices near an outlet, but no circuit-level data.

Z-Wave plug options from Zooz also exist for plug-in loads — Zooz’s energy-monitoring smart plugs report consumption — but they only cover what’s plugged into them, not hardwired circuits.

When you need dedicated, higher-accuracy monitoring

If you want voltage, current, and power-factor data per phase with good accuracy (useful for solar or generator setups), a dedicated panel meter like the Shelly Pro 3EM is the practical local choice. For homes with solar you’ll want monitoring on both consumption and production; confirm your meter and CT placement capture bidirectional flow before you buy.

Integration and local control

These devices all work locally with Home Assistant: Shelly devices over their local API / MQTT, and HomeWizard over its own local API. None require a cloud account for basic functionality, though initial setup uses the manufacturer’s app.

For Hubitat users, Z-Wave metering devices integrate directly, and you can bridge them into Home Assistant. Apple HomeKit support is more limited — Eve Energy offers native HomeKit plug-level metering but no circuit-level data.

Bottom line

Start with the HomeWizard P1 Meter if you have a P1 port and want instant whole-home visibility with zero panel work. Step up to a CT-clamp panel meter like the Shelly Pro 3EM when you need per-circuit detail. It’s well worth it for finding phantom loads and trimming your bill.