Phil Brown Presentation Exi SystemsX

After AS2380.7 and AS2381.7

Philip Brown

Principal Engineer

Austdac Pty Ltd

New Ex i Standards� AS2380.7 Equipment standard replaced by AS/NZS

60079-11 ✓� AS2381.7 Installation standard replaced by AS/NZS

2381.1 ✗� AS2381.7 Installation standard replaced by AS/NZS

60079-14 ✗� So where do we look when designing Group I Ex i

systems and installations?

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The Ex i Systems Standard� AS/NZS 60079-25

� Provides information and rules about designing and

assessing Ex i systems using already certified equipment

with entity parameters and simple apparatus.

� Provides information about documenting system designs

and installation requirements.

� Also provides a standard to which a certifying body can

issue a certificate, if required.

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Why a Systems Standard?� The design and installation of Group I Ex i explosion

protected systems is far to important to be left to the

installation phase.

� The system must be carefully designed, assessed and

documented prior to installation, to ensure maximum

safety of the mine installation.

� AS/NZS 2381.1 and AS/NZS 60079-14 do not provide the

required level of rigour for a safe design and installation.

� AS/NZS 60079-14 is mainly a group II standard.

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AS/NZS 60079-25 Procedure� DESIGN – Put system together to suit functional

specification.

� ASSESS – Check system for Ex i safety, conduct risk

assessments on cables and determine their types.

� DOCUMENT – Show all aspects of design including

certified modules, simple apparatus, junction boxes,

entity parameters, cable types and cable parameters.

� INSTALL – Carry out installation in accordance with

documentation, if a change is required, repeat full

procedure, above all update documentation.

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Descriptive System Document� AS/NZS 60079-25 requires that a descriptive system

document or drawing be produced to show ALL aspects of the design and installation.

� It should show all certified equipment connections, the entity parameters for each port, hazardous areas, safe areas, zones, cables with their types, parameters, routes and mechanical protection.

� Satisfies DPI documentation / dossier requirements.

� Change the document then the installation, not the other way around.

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Descriptive System Document

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Multi-core CablesAS/NZS 2381.7 AS/NZS 60079-25

� Required individual i.s. circuit

screens for a system design to

occupy a multi-core cable.

� Did not specify the faults to

be applied between individual

circuits when screens not

used.

� The end user was forced to go

for an individual system

certification.

� Allows individual i.s. circuit

screens for a system design

to occupy a multi-core cable.

� Specifies the faults to be

applied between individual

circuits when screens not

used.

� Allows a risk assessment

approach to which type of

multi-core cable can be used.

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Multi-core Cable TypesAS/NZS 2381.7 AS/NZS 60079-25

� Screened – No faults need be

applied.

� Unscreened – All possible

(unspecified) faults shall be

applied.

� Type A – Screened – No faults need be applied.

� Type B – Unscreened cable with low risk of damage – No faults need be applied.

� Type C – Unscreened cable with high risk of damage –Specified faults applied.

� Type D – Unscreened cable of inferior construction – All possible (unspecified) faults applied.

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Multi-core Cable – Specified Faults

� Four open circuit faults.

� Two short circuit faults.

� These are the minimum number and type of faults

required to cause voltage and current addition between

two independent i.s. circuits.

� Voltage and current addition are the most ignition

capable scenarios that can occur in multi-core cable

damage.

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Simple Intrinsically Safe Circuit

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Type A Cable (screens)

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Type B cable (Risk Assessment - Pass)

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Risk Assessment – Fail

� Cable is now treated as a type C cable.

� Therefore need to apply 2 short circuit faults and 4 open

circuit faults to determine safety of design.

� Apply faults to obtain most unsafe conditions.

� Maximum voltage (voltage addition).

� Maximum current (current addition).

� Take note of infallible connections of power supply

negative terminals – prevents voltage addition.

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Type C Cable (Voltage Addition)

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Permitted Capacitance

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Infallible Common Connections

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Type C Cable (Current Addition)

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Determining Lo/Ro

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Conclusion

� Ex i equipment standard AS/NZS 60079-11. ✓� Ex i system standard AS/NZS 60079-25. ✓� Installation standard AS/NZS 60079-14. ✗� Format of descriptive system document is now specified.

� System designer now has the tools (specified faults) to

conduct an assessment of individual Ex i circuits in cables

without screens.

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The End� Questions

� Thank you

� Contact: [email protected]

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