Glossary · Process instrumentation and analytical measurement
Intrinsically safe circuit
Also known as: IS circuit, Intrinsically safe loop
German: Eigensicherer Stromkreis
In explosion protection, an intrinsically safe circuit is a circuit in which any spark or thermal effect produced under the normal and specified fault conditions is incapable of causing ignition of a given explosive atmosphere.
- Process instrumentation
- Standards
- Process industry
In one sentence
An intrinsically safe circuit cannot ignite a given explosive atmosphere by sparks or heat, even under specified fault conditions.
Example
The loop from an isolating barrier in the safe area to a temperature transmitter in zone 1, including the cable, forms one intrinsically safe circuit.
How it applies
- Engineering: Verify each circuit: the associated apparatus's output parameters must not exceed the field device's input parameters, and the cable capacitance and inductance must stay within the permitted values.
- Installation: Keep intrinsically safe circuits separated from non-intrinsically safe circuits in cabinets, cable trays and terminals, and mark them.
- Maintenance: Modifications, such as a different cable length or replacement devices with other parameters, require re-verification.
- Documentation: Document each circuit's verification with the devices, parameters and cable data. Loop diagrams and terminal plans should identify intrinsically safe circuits unambiguously.
Intrinsically safe circuit vs. intrinsically safe device
A device can be certified for use in intrinsically safe circuits, but the circuit is only intrinsically safe when the combination of all devices and cables has been verified.