Chapter 5
Protection concepts: d, e, i, m, o, p, q, n, t
Published
- Ex protection concepts at a glance: d, e, i, p, m, o, q, n and t
The Ex types of protection d, e, i, p, m, o, q, n and t stop equipment igniting gas or dust by containing an explosion, keeping the atmosphere out, avoiding sparks and hot spots, or limiting energy. Overview table with EPLs, typical equipment, standards and how to choose.
- Flameproof enclosures (Ex d): how flamepaths stop an internal explosion
A flameproof (Ex d) enclosure lets gas ignite inside, withstands the explosion pressure and cools the escaping gases in narrow flamepaths so the outside atmosphere does not ignite. Flamepath types, gaps, pressure piling and maintenance rules.
- Increased safety (Ex e): preventing sparks, arcs and hot spots
Increased safety (Ex e) stops sparks, arcs and hot spots from occurring at all, using secure terminals, wide creepage and clearance, IP54 enclosures and strict temperature limits. Terminals, motors and tE, eb vs ec, junction boxes and terminal loading.
- Intrinsic safety (Ex i): ia, ib and ic and the energy limitation principle
Intrinsic safety (Ex i) limits the energy in a circuit so that no spark or hot surface can ignite the gas, even with faults. How ignition curves work, what ia, ib and ic mean, and the roles of simple apparatus, associated apparatus and cable parameters.
- Intrinsic safety loop verification: Uo, Io, Po, Co, Lo and the entity concept
How to verify an intrinsically safe loop with the entity concept: compare Uo, Io and Po with Ui, Ii and Pi, and check that Ci plus cable capacitance and Li plus cable inductance stay within Co and Lo. Rules, cable values, a worked example and FISCO.
- Zener barriers vs galvanic isolators: choosing intrinsic safety interfaces
Zener barriers divert fault energy to a high-integrity earth; galvanic isolators block it with transformer isolation and need no IS earth. How each works, barrier earthing rules, pros and cons, a voltage budget example and when to choose which.
- Pressurisation (Ex p): px, py and pz, purging and protective gas
Pressurisation (Ex p) keeps gas or dust out of an enclosure with air or inert gas at overpressure. Levels pxb, pyb and pzc, purging before power-on, 50 Pa and 25 Pa minimums, leakage compensation vs continuous flow, and when pressure loss must trip the power.
- Encapsulation (Ex m), oil immersion (Ex o) and powder filling (Ex q)
Ex m, Ex o and Ex q stop ignition by burying the ignition source in compound, liquid or quartz grains. How each works, levels ma/mb/mc and ob/oc, EPLs, voltage limits, typical uses such as coils, transformers and luminaire parts, and their limits.
- Ex ec, Ex nA and Ex nR: protection for Zone 2
Ex ec, Ex nA and Ex nR are Zone 2 (EPL Gc) protection types. How type n was split, why nA became increased safety ec, how restricted breathing nR works, sealed and non-incendive nC, typical uses and how to read old and new markings.
- Dust ignition protection by enclosure (Ex t): ta, tb and tc
Ex t protects equipment in combustible dust by a dust-tight or dust-protected enclosure and a limited surface temperature marked in °C. Levels ta, tb and tc, the IP6X and IP5X rules per dust group, T85 °C and T200 320 °C markings, and how to select for Zones 20 to 22.
- Ex d or Ex e? Choosing between flameproof and increased safety for motors and junction boxes
Ex d contains an internal explosion; Ex e stops sparks and hot spots from occurring. How the two compare for junction boxes and motors: cable entries, gas group, tE time, weight, cost and maintenance, with a selection guide.
- Combined protection concepts: Ex db eb, Ex d e terminal boxes and multiple markings
Ex db eb means one product protected by two concepts, typically a flameproof motor or switch part with an increased safety terminal box. How combined equipment is certified and marked, and how to read strings with brackets, slashes and two lines.
- Non-electrical equipment in hazardous areas: Ex h, constructional safety c, control of ignition sources b and liquid immersion k
Pumps, gearboxes, fans and couplings can ignite gas or dust through friction, sparks and hot surfaces. How ISO 80079-36 and -37 assess and protect them (types c, b and k), what the Ex h marking means and how ATEX applies.