What Is Galvanic Isolation?

Galvanic isolation means two circuits have no conductive path between them: no shared wire, no common ground. Energy or information still crosses from one side to the other, but by a means that does not carry current, such as light in an optocoupler, a magnetic field in a transformer or an electric field across a tiny capacitor.

The term comes from galvanic current, the direct current that flows when two conductors at different potentials are connected. Isolating two circuits lets each side keep its own ground, even when those grounds sit volts or even kilovolts apart.

Every isolator has a barrier, usually an insulating layer of polymer, silicon dioxide or the gap between transformer windings. How thick that barrier is and what it is made of set how much voltage it can withstand and for how long.

Ground is never quite the same voltage everywhere. On a factory floor, in a substation or on a vehicle, the ground at one end of a cable can be several volts away from the ground at the other, because of heavy motor currents, long earth paths or lightning. Connect the two ends with a signal cable and a ground loop forms: current flows along the shield or 0 V wire, adding noise to the signal or, in the worst case, damaging the port.

Isolation breaks that loop. It is used for four main reasons:

Several technologies cross the barrier. Which one fits depends on whether it carries power or data, how fast the data is and how long it must last.

Optocouplers are cheap and well understood, but their LEDs slowly dim over many years, so designs allow a margin. Capacitive and magnetic digital isolators are faster, use less power and do not wear in the same way, which is why they have replaced optocouplers in most new serial and CAN interfaces.

Datasheets quote several voltages, and they mean different things. The withstand voltage, often 2.5 kV or 5 kV rms, is a 60-second test the barrier must survive, as defined in UL 1577. The working voltage is the voltage the barrier can sit at continuously for its whole life, and is much lower. The surge rating covers short spikes such as lightning-induced transients. For fast digital isolators, common-mode transient immunity (CMTI), in kV/µs, shows how well data survives fast ground shifts.

Standards also grade the insulation. Functional isolation only makes the circuit work. Basic insulation gives one level of protection against shock, and reinforced insulation is equivalent to two. IEC 60747-17 covers magnetic and capacitive isolators, and equipment standards such as IEC 62368-1 set which grade is needed where.

On industrial and embedded computers, isolation is fitted where the computer meets field wiring. Digital inputs are usually optically isolated, so a 24 V sensor or a 4–20 mA current loop shares no ground with the processor. Serial and CAN ports are isolated with digital isolators and an isolated DC-DC converter. Ethernet ports are isolated by their magnetics, which IEEE 802.3 requires to withstand 1,500 V rms. The power input itself is often isolated too, on vehicle and rail computers.

Within the Advantech range we list, the MIC-713 Jetson computers have four optically isolated digital inputs and four isolated outputs on terminal blocks, and the MIC-733-AO Jetson AGX Orin computer has four isolated inputs and four outputs. To add isolated ports to an existing system, our serial I/O modules include opto-isolated RS-232 and RS-485 cards, and our CAN bus modules include isolated CAN adapters.

We fit isolated digital I/O, serial and CAN ports to industrial and edge AI computers as standard, and check the wiring, grounding and isolation needs of your site before we specify the system.