Can you work on an intrinsically safe circuit while it is live in a hazardous area?
Abstract
Yes, within limits. IEC 60079-17 allows live maintenance on intrinsically safe circuits in the hazardous area: disconnecting and replacing devices, calibration, plug-in parts and suitable test instruments. Site permits apply, and the loop must stay as documented.
Yes, within defined limits. IEC 60079-17 allows live maintenance on intrinsically safe installations, because the energy in a correctly installed IS circuit is too low to ignite the gas even when wires are disconnected or shorted. The permitted work is restricted: disconnecting, removing or replacing devices and cables, adjusting for calibration, swapping plug-in parts, and using test instruments that do not compromise intrinsic safety. Site permits still apply, and the circuit must match its documentation afterwards.
Short answer
- Allowed live, in the hazardous area (IEC 60079-17, 2007 text): disconnecting, removing or replacing equipment and cabling; adjusting controls needed for calibration; removing and replacing plug-in components or assemblies; using the test instruments named in the documentation, or otherwise only instruments that do not affect the intrinsic safety of the circuit; any other activity the documentation specifically permits.
- After the work the person doing it must make sure the IS system still meets its documentation (same device type and parameters, correct connections, screens and earthing).
- In the safe area, associated apparatus that is still connected to hazardous-area circuits may only be worked on in the same limited ways. Other work needs the hazardous-area circuits disconnected first.
- Barrier earths must not be removed while hazardous-area circuits are connected, unless the earth is duplicated and only one conductor is lifted for testing.
- Only IS circuits qualify. A non-IS circuit in the same enclosure, an Ex d instrument head or a mains-powered device does not.
Why live work is acceptable on IS circuits
An intrinsically safe circuit is designed so that opening, shorting or earthing its wiring cannot produce an incendive spark, with the faults allowed for its level (two for ia, one for ib). Disconnecting a transmitter under power is exactly the kind of event the ignition tests simulate. That is the main practical advantage of intrinsic safety: instruments can be calibrated, checked and replaced without a gas-free certificate for every task.
IEC 60079-17 defines live maintenance as maintenance carried out while the associated apparatus, the intrinsically safe apparatus and the circuits are energised, and the current edition (2023) keeps a dedicated clause for it next to the rules for isolating other equipment. For non-IS equipment the default is the opposite: it must be isolated before an enclosure is opened, with narrow exceptions: essential live work under a safe work procedure (IEC 60079-14 gives guidelines for one), or, in Zone 2 only, work justified by a documented safety assessment.
What the conditions mean in practice
| Task | Live in the zone? | Watch out for |
|---|---|---|
| Disconnect and replace a failed transmitter | Yes | Same model and certificate, or redo the loop check before connecting |
| Calibrate or trim a transmitter, zero a sensor | Yes | Use the adjustments provided; do not open non-IS compartments |
| Connect a handheld communicator or calibrator | Yes, if it is certified for the purpose | It adds its own parameters to the loop; check its certificate and instructions |
| Measure with an ordinary multimeter | Only if it cannot affect intrinsic safety | Many sites require an IS-certified meter |
| Insulation resistance test | Only with a tester specifically approved for IS circuits | Lifting a common barrier earth for the test needs gas-free conditions or all dependent circuits de-energised |
| Work inside an Ex d head containing IS and non-IS parts | No | The non-IS parts need isolation and a permit |
The test instrument rule matters most. A handheld communicator or loop calibrator connected to a live IS loop becomes a second source of energy. Instruments intended for this carry their own IS certificate and parameters, and IEC 60079-25 notes that certified apparatus with simple-apparatus-like outputs, such as some test equipment, can be added to a loop with only a minor documentation change. An ordinary multimeter or insulation tester has had no such assessment.
Example: A pressure transmitter Ex ia IIC T4 Ga in Zone 1 fails. The technician obtains the permit for instrument work, confirms the replacement is the same model with the same certificate, disconnects the live loop at the transmitter terminals, fits the new unit, reconnects with the screen arranged as before, and checks the output with a certified IS calibrator. No gas test or isolation of the loop is needed for the IS work itself; the permit decides about access, tools and the area.
What does not change
- Site permit-to-work rules still apply. Many sites require a permit or work instruction for any instrument work in a zone, and some require gas testing even for IS work.
- Mechanical and process hazards (pressure, toxic fluids, heights) are unaffected by intrinsic safety.
- Hot work such as grinding or welding near the instrument is a separate activity with its own permit.
- Level ic circuits (Zone 2) have smaller safety margins than ia and ib (a safety factor of 1.0 instead of 1.5). Where a manufacturer specifies live maintenance procedures, IEC 60079-11 requires that they do not invalidate intrinsic safety; follow those instructions and the current IEC 60079-17 text.
Common mistakes
- Treating every instrument as IS. Check the marking: an
Ex dborEx ebdevice on a 24 V loop is not covered by these rules. - Fitting a "similar" replacement. A different model may have a lower Ui or higher Ci and break the loop calculation.
- Using a non-certified meter or communicator on the live loop in the zone.
- Lifting the barrier earth bar to test it while circuits are connected and there is only one earth conductor.
Related on excodex
- Intrinsic safety (Ex i): ia, ib and ic and the energy limitation principle
- Inspection of Ex installations under IEC 60079-17: initial, periodic, visual, close and detailed
- Hot work permits in hazardous areas
- Can you open the cover of an Ex d enclosure while it is energised?
- Standards spaces: IEC 60079-17, IEC 60079-11
Standards and further reading
- IEC 60079-17, electrical installations inspection and maintenance (edition 6, 2023; EN IEC 60079-17:2024), live maintenance on intrinsically safe installations.
- IEC 60079-11, intrinsic safety "i" (edition 7, 2023), live maintenance procedures in manufacturers' documentation.
- IEC 60079-25, intrinsically safe systems.
- IS/IEC 60079-17:2007, the Indian adoption of IEC 60079-17 edition 4 (superseded), with the text of the live maintenance conditions: law.resource.org
- IEC 60079-17:2023 redline preview with contents and the definition of live maintenance: cdn.standards.iteh.ai
- IEC 60079-11:2011 text (edition 6, superseded): law.resource.org
This article is general technical information prepared by the excodex editorial team. It does not replace the applicable standards, the equipment certificates and instructions, national regulations or the assessment of a competent person.