Glossary · Ex i
What is Intrinsic safety (Ex i)?
A protection concept that limits the electrical energy in a circuit so it cannot produce an igniting spark or heat, even under fault conditions.
Defined in IEC 60079-11 with levels ia (two faults, suits Zone 0), ib (one fault, Zone 1) and ic (Zone 2). Very common for 4-20 mA instruments.
It needs a barrier or isolator in the safe area, and a check that the cable and device capacitance and inductance stay within the permitted limits.
Related terms
- 4-20 mA signal
- The most widely used analogue signal in industrial measurement: 4 mA is the bottom of the range and 20 mA the top, and current, unlike voltage, is not affected by cable length.
- Equipment Protection Level (EPL)
- The equipment protection level states how safe a device is as an ignition source, and maps directly to the zones where it may be used.
- Flameproof protection (Ex d)
- A protection concept that lets an explosion happen inside the enclosure, which withstands it and cools the escaping flame through its gaps so the surrounding atmosphere does not ignite.