Safety — Safe by Design

rbAmp is built so that mains never reaches the board. The module itself is entirely low-voltage — there is no high-voltage measurement circuit on it. Current is read by a CT clamp that never touches the wire, and the only mains reference at all (on voltage-sensing variants) is a galvanically isolated tap. Everything you wire — the I²C bus to an ESP32, Arduino or Raspberry Pi — is never at mains potential.

This page collects, in one place, the isolation architecture, what you may safely touch, what belongs to a qualified electrician, and how an isolated design differs from the shunt-based meters common in DIY energy monitoring.

The architecture: an all-low-voltage module

The module itself carries no high-voltage measurement circuit. Both ways it senses power keep mains away from the board you touch:

• Current — a contactless CT. The clamp closes around the outside of an insulated conductor. A current transformer couples magnetically — there is no electrical contact with the mains wire, and nothing at line potential ever enters the module. The CT hands the board only a small, isolated signal.
• Voltage (UI* variants) — an isolated tap. The one place mains is referenced at all is the L–N terminal on voltage-sensing variants, and it feeds a galvanically isolated sensing divider behind an isolation barrier. Ampere-only variants have no mains connection whatsoever.
• The side you wire — pure LV. Five pins: VCC (5 V), GND, SDA, SCL, DRDY. Logic runs at 3.3 V (an on-board low-noise regulator derives it), the lines are 5 V-tolerant, and the module's GND is your host's ground, not mains neutral.

So there is no user-accessible high voltage anywhere: the current sensor never contacts the wire, the voltage reference is isolated, and the bus rides your own ground. Wiring the module straight to your ESP32/Arduino/Pi carries no shock risk and no short-circuit-through-ground risk.

Never open the enclosure — it voids the factory calibration.

What you touch — always the safe side

• The four I²C wires (VCC, GND, SDA, SCL) and the optional DRDY line — isolated, low-voltage, safe.
• The CT clamp, which closes around the outside of an insulated conductor. A current transformer couples magnetically — there is no electrical contact with the wire it measures. rbAmp's SCT-013-style clamps carry an internal burden, so there's no open-secondary hazard.

That's the whole of the user's job on a current-only build: bus wires to your controller, clamp on an insulated conductor.

The voltage connection (UI* voltage-sensing variants)

Modules that measure voltage (the UI variants — real active power, not just current) need a reference to the line: connect L and N to the module's L–N terminal. The sensing side is galvanically isolated* inside the module — feeding L/N to the terminal keeps your I²C side just as safe as before. There are two ways to bring L/N in:

1. The simple, user-safe way — a plug into a socket. Use a ready-made L–N pigtail (a short cable with a proper mains plug) from the module's L–N terminal, and plug it into a wall socket — exactly like plugging in any appliance. You never handle bare conductors; the plug and socket do the mains connection for you. This is the recommended path for a desk or single-outlet setup.
2. The permanent way — an electrician. For a panel install or a hardwired feed, a qualified electrician connects L/N at the panel to local electrical code.

⚠️ The isolation protects the measurement side — but the L/N feed itself is still mains. Use a proper plug, or a qualified electrician. Never connect bare mains conductors yourself unless you are qualified to do so.

Who does what

Isolated by design vs a non-isolated shunt

Much of DIY energy monitoring — and many single-chip meter ICs — measure current through a shunt resistor placed in series with the load. That approach puts the measurement circuit (and, on many boards, the whole logic side) at mains potential, with no galvanic isolation. The consequences:

• The board is not safe to touch while live, and a stray contact between it and your grounded controller can be hazardous.
• Getting the readings to an MCU or Raspberry Pi safely means adding isolation yourself — opto-isolators, an isolated supply, careful enclosure — or accepting the risk.

rbAmp measures the opposite way. Its current path is a CT that clamps around the conductor and never touches it — no galvanic connection to the mains at all, so nothing on the module sits at line potential from the current side. On voltage-sensing variants the single L–N reference goes through an isolated divider. There is no shunt in the mains path and no live logic board: the side you wire, handle and debug is low-voltage by construction. That's what "safe by design" means — not a sticker, an architecture.

(rbAmp is designed for isolation as described here; it is not a substitute for following your local electrical code, and it is not sold as a certified metering instrument.)

In short

• The module is all low-voltage — the CT clamps the wire without touching it, and voltage (UI variants) comes in through an isolated* tap; the side you touch is never at mains potential.
• Current is sensed by a CT (no contact); voltage (UI variants) via an isolated divider — bring L/N in with a plug into a socket*, or an electrician.
• Don't open the enclosure. For panel work, kill the main, verify dead, and use a qualified electrician.
• Isolation is in the design — unlike a bare shunt meter, the side you handle is never live.

Related

• 01 · Hardware Connection — pinout, wiring, CT install.
• FAQ — Is the rbAmp module isolated from mains?
• Three-Phase Energy Monitoring in Home Assistant — panel-level safety in a real build.