What is the difference between a barrier and a isolator?

In the field of explosion protection, intrinsic safety (Ex-i) is an important protection type. In the event of a failure, energy limitation in the circuit in potentially explosive areas plays a decisive role in ensuring protection.

Both the barriers and the isolators are interfaces between the sensor or the actuator in the Ex-i area and the controller. The energy limitation can be achieved with help of a circuit design with Zener diodes and resistors.

Barriers and isolators are installed in a non-explosive area if other safety measures have not been taken . Only protected circuits are routed in the Ex-zone.


Barriers, also known as "safety barriers", must be connected to the equipotential bonding system of a system along the shortest possible route.

This means that the circuit cannot be grounded at another point in the Ex-i- circuit in order to prevent voltage equilization currents.

Structure of an Ex-barrier
Structure of an Ex-barrier


Circuit of a device with 3-way electrical isolation
Circuit of a device with 3-way electrical isolation
Colloquially, the term "isolator" is also used for an intrinsically safe isolation amplifier and a measuring transducer, which as opposed to the barrier, have preconnected electrical isolation in addition to the energy limiting circuit.

This isolation is also known as buffer stage or electrical isolator. Equipotential bonding is not necessary in an Ex-i isolator and the connected field devices may be grounded during the operation.

Electrical isolation should be preferably used for circuits of the field devices in Ex-zone 0 (EN 60079-14).

In case of a 3-way isolation, input and output as well as the power supply are electrically isolated. This enables a flexible installation design. The devices can be connected with different potentials since there is no unintentional potential transfer in this case.

Module with intrinsically safe input or output circuit
Module with intrinsically safe input or output circuit

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