Do intrinsically safe cables have to be blue?

No. Intrinsically safe (IS) cables must be identified as such, but a light blue sheath is only one way of doing it. Where colour is used for identification, the convention under IEC 60079-14 and the NEC is light blue, and in IEC practice other cables in the vicinity must then not be light blue; marking or labelling is an acceptable alternative.

Short answer

• The requirement is identification, so that IS circuits are recognised and not mixed up with other circuits during installation, testing and maintenance.
• Light blue is the convention where colour is used: IEC practice allows the sheath or core insulation of IS cables to be light blue, and the NEC permits light blue for IS conductors.
• Colour is not mandatory. Labels, sleeves, marking at both ends and clear segregation can do the same job, for example where an armoured cable with a black sheath is used.
• If you use light blue for IS, keep it for IS: other circuits near IS circuits should not be light blue, or the colour loses its meaning.
• Terminals and junction boxes of IS circuits also need identification. On IS apparatus, IEC 60079-11 requires the IS connection facilities to be clearly marked and, where a colour is used for this, it must be light blue; colour itself remains optional.

Why identification matters more than the colour

An intrinsically safe circuit is safe because the energy it can deliver is limited. That protection fails if a non-IS circuit is connected to it, if its conductors are terminated next to higher-voltage conductors, or if someone treats it as an ordinary circuit and adds an uncertified device. Most of these errors happen during later changes, not during the original installation.

Identification lets the electrician, the instrument technician and the inspector see at once which cables and terminals belong to IS systems. A consistent colour is the quickest way to do that, which is why light blue became the common convention. But the rule is about being recognisable, not about a particular dye.

What IEC practice and the NEC say

IEC 60079-14. The installation standard has a clause on marking of cables in its section on intrinsically safe circuits. As described in the guidance of the Health and Safety Authority (Ireland), the sheath or core insulation of IS cables may be coloured light blue, light blue cables must not be used for other circuits in the vicinity, and where IS and non-IS circuits share an enclosure the IS cores can be grouped in a light blue harness, labelled, or arranged and spaced so they are clearly separate. The guidance also points to the risk of confusion with a blue neutral conductor in the same cabinet, which is one reason labelling matters in mixed panels. Enclosures containing IS circuits used as junction boxes must be marked to show this.

NEC Article 504. The NEC requires IS terminals to be marked so that the marking is not disturbed during testing and servicing, and raceways and other wiring methods to carry permanent labels identifying intrinsic safety wiring. Light blue colour coding of IS conductors appears in section 504.80 as an option, not an obligation, as the code commentaries listed below explain.

Light blue does not make a cable intrinsically safe

A light blue sheath says nothing about the cable's capacitance, inductance, insulation or construction. The cable still has to meet the requirements for IS circuits (insulation strength and parameters within the loop calculation), and multi-core cables carrying several IS circuits have their own construction rules. It also does not change segregation: IS and non-IS circuits must still be separated by distance, partitions or screened or armoured construction, and they may not share a multi-core cable.

Common mistakes

• Using light blue cable for a non-IS circuit because it was on the drum, which tells the next technician the circuit is safe to work on.
• Assuming any blue cable is IS and connecting it to an IS barrier without checking the loop documents.
• Leaving black IS cables unmarked in a panel full of non-IS wiring.

Related on excodex

• Intrinsic safety (Ex i): ia, ib and ic and the energy limitation principle
• Ex installation basics under IEC 60079-14
• Can intrinsically safe and non-IS cables run in the same cable tray?
• Can you work on an intrinsically safe circuit while it is live in a hazardous area?
• Standards spaces: IEC 60079-14, NEC 500 to 506

Standards and further reading

• IEC 60079-14, design, selection and installation of electrical installations (intrinsically safe circuits, marking of cables).
• IEC 60079-11, equipment protection by intrinsic safety "i" (marking of connection facilities; light blue where a colour is used). The 2011 text is public: law.resource.org; the current edition is 2023.
• NFPA 70, National Electrical Code, Article 504 (intrinsically safe systems), section 504.80 (identification).
• Health and Safety Authority (Ireland), instrumentation and control apparatus in explosive atmospheres: hsa.ie
• IEC 60079-14:2024 preview (table of contents): standards.iteh.ai
• EC&M, intrinsically safe systems and NEC 504.80 labels: ecmweb.com
• Electrical Contractor, conductor colour rules including NEC 504.80: ecmag.com

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.