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COMPEX > UNIT 6: Pressurization EX p > Flashcards

UNIT 6: Pressurization EX p Flashcards

1
Q

1.
For an area requiring EPL Gc (Cat 3) equipment, which one of the following options may be used if the pressurised enclosure contains an ignition source?

No protection required

Ex py

Ex px

Ex px or Ex pz.

A

Ex px or Ex pz.

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2
Q

2.
Where a pressurised enclosure contains no ignition source, which one of the following will suit an area requiring EPL Gb (Cat 2) equipment?

Ex py

No protection required

Ex px

Ex px or Ex pz.

A

Ex py

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3
Q

3.
Where a pressurised enclosure contains no ignition source, which one of the following will suit an area requiring EPL Gc Cat 3) equipment?

Ex py;

No protection required

Ex px;

Ex px or Ex pz.

A

No protection required

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4
Q

4.
Protection types for pressurised enclosures are?

Ex p1, Ex p2, Ex p3

Ex px, Ex py, Ex pz

Ex pG, Ex pD

Ex pa, Ex pb or Ex pc

A

Ex px, Ex py, Ex pz

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5
Q

5.
Which one of the following statements represents the type of protection Ex p:

The internal pressure has to be greater than 0.5 Bar

The air used for pressurisation shall be taken from a specified non-
hazardous area

Pressurisation of the enclosure is intended to contain explosive gases

Switching on is only permitted after the enclosure has been pressurised for
at least 15 minutes.

A

The air used for pressurisation shall be taken from a specified non-hazardous area

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6
Q

6.
The interior of a pressurised control room - in a location requiring EPL Gc(Cat 3), is ‘safe’ provided the pressurisation is maintained and there are no gases released internally.

What action is required if the pressurisation fails and the
internal equipment does not meet EPL Gc (Cat 3) requirements?

Alarm sounds and all flameproof equipment must be isolated

On operation of alarm, automatic disconnection of all equipment

No action

On operation of alarm, immediate action taken to restore

A

On operation of alarm, immediate action taken to restore

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7
Q

7.
Ex p equipment is permitted in which one of the following areas?

Main area needing EPL Gc (Cat 3G) only

An area needing EPL Ga (Cat 1 G) only

An area needing EPL Gb (Cat 2G) only

An area needing EPL’s Gb or Gc Cats 2G or 3G) only

A

An area needing EPL’s Gb or Gc Cats 2G or 3G) only

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8
Q

8.
A pressurised enclosure, containing ignition capable components, is rated EPL Gb (Cat 2). Which one of the following options may be used?

No protection required

Ex py

Ex px

Ex px or Ex pz.

A

Ex px

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9
Q

Ex i

When the zener diode fails, does in normally fail open circuit open circuit or short circuit?

A

Test show that diodes always test to a short circuit condition.

Zener diodes can only be considered infallible when 2 or more diodes are connected In parallel.

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10
Q

Ex i capacitance vrs inductance.

How is capacitance and inductance of an IS circuit influenced by IS circuit Voltage!

A

At lower voltages (say 5 volts) inductance will be predominant

At higher voltages (say 28 volts) capacitance will be predominant.

[affects of stored energy in a circuit as a result of circuit inductance and capacitance]

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11
Q

IS earth

What are the maximum allowable resistance between Barrier Earth and the main earth point?

A

The maximum resistance between barrier earth and the main earth point should not be greater than 1 ohm.

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12
Q

IS earth

What is the minimum allowed cross sectional area of an IS earth conductor?

A

The minimum cross sectional area allowed is

Two separate 1.5nm2 copper conductors

One 4mn2 copper conductor.

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13
Q

IS Earth.

What are the requirements when two separate Earth conductors are installed as a Barrier Earth?

A

Where two earth conductors are installed, each earth conductor to be secured at separate points at each end to connect the Barrier Earth Bar to the Main Earth Point.

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14
Q

IS Earth Conductor

When installing an IS Earth what must be considered in terms of short circuit currents?

A

The IS earth conductor must be rated and capable of carrying maximum fault current of the IS Circuit.

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15
Q

IS Earth Conductor

What is the insulation requirement on the IS conductor?

A

The IS Earth conductor must be insulated and Undamaged along its entire length, to prevent contact with any exposed metal work in the plant

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16
Q

IS Circuit

What is the minimum requirement of an IS Circuit in terms of insulation resistance test voltage to Earth.

A

The IS Circuit in the hazardous area must be able to withstand a 500 volt insulation resistance test to Earth.

IS cable screens will have sheathing capable of withstanding 500vac or 750Vdc

17
Q

Ex pxb

What is the definition of Ex pxb?

A

Ex pxb pressurisation reduces the equipment protection level within the pressurised enclosure from Gb to Non-Hazardous

Minimum overpressure of 0.5 mBar required.

Non-Ex components can be installed inside the pressurised enclosure.

Approved for use in EPL Gb and Gc. (Zone 1 and Zone 2)

18
Q

Ex pzc

What is the definition of Ex pzc?

A

Ex pzc pressurisation reduces the equipment protection level within the pressurised enclosure from Gc to Non-Hazardous.

Minimum overpressure of 0.25 mBar required

Non-Ex components can be installed inside the pressurised enclosure.

Approved for use in EPL Gc. (Zone 2)

19
Q

Ex pyb

What is the definition of Ex pyb

A

Ex pyb pressurisation reduces the equipment protection level within the pressurised enclosure from Gb to Gc.

Minimum overpressure of 0.5 mBar required

Only components tested for Zone 2, as a minimum, can be installed inside the pressurised enclosure.

Approved for use in EPL Gb and Gc (Zone 1 and Zone 2)

20
Q

Ex pxb

What is the required action in event of loss of pressure in Ex pxb enclosure?

EPL Gb (Zone 1)
EPL Gc  (Zone 2)
A

Ex pxb loss of pressure.

EPL Gb (Zone 1)
Alarm and shutdown.
Alternate gas supply should be available in more dangerous Atmospheres Areas
EPL Gc (Zone 2)
Alarm and requires immediate action to restore the integrity of the system.
21
Q

Ex pzc

What is the required action in event of loss of pressure in a Ex pzc enclosure

EPL Gc (zone 2) only

A

Ex pzc loss of pressure.

Gc (Zone 2)
Alarm and requires immediate action to restore the integrity of the system.

22
Q

Ex pyb

What is the required action in the event of loss is pressure in an Ex pyb Enclosure?

EPL Gb (Zone 1)
EPL Gc (Zone 2)
A

Ex pyb loss of pressure.

EPL Gb (Zone 1)
Alarm and requires immediate action to restore the integrity of the system.
EPL Gc (Zone 2)
No action required.   Ex pyb enclosure only contains equipment that is already rated and approved for use in EPL Gc (Zone 2)
23
Q

Ex ma

Encapsulation apparatus with a protection Level Ex ma must not be capable of causing ignition during what situations?t

A

Ex ma

No ignition in normal operation and installation conditions.

No ignition in any specified abnormal conditions.

No ignition in defined failure conditions.

Must not have an operating voltage in excess of 1kV

Approved for use in EPL Ga, Gb, Gc
(Zone 0, 1, 2)

24
Q

Ex mb

Encapsulation apparatus with a protection Level Ex mb must not be capable of causing ignition during what situations?

A

Ex mb

No ignition in normal operation and installation conditions.

No ignition in defined failure conditions.

Approved for use in EPL Gb, Gc)
(Zone 1, 2)

25
Q

Ex q

What is the minimum IP rating of Ex q apparatus

A

Ex q minimum IP rating of IP54, but apparatus constructed to IP55 must be fitted with a breathing device.

Where used in a clean and dry environment IP rating must be at least IP43 and required to be marked with suffix X

26
Q

Ex q

What is the minimum size of granule filling of Ex q devices?

A

1 mm
The upper limit uses a sieve manufactured from metal wire cloth, or perforated metal plate, with a nominal perforation size of 1mm

0.5 mm
The lower limit, metal wire cloth with a nominal perforation size of 0.5 mm may be used.

The filling material is required to withstand an electric field strength test where the leakage current must not exceed 10 micro-Amps

The upper limit for granule sizes is specified in ISO 565

27
Q

Dielectric Strength Test

What is the electric strength test?

A

The Dielectric Strength Test measures the leakage current of a device under test conditions.

Phase and Neutral are short circuited together across the medium being tested.

The Dielectric Strength Test can be destructive or non-destructive.

Test voltages vary from hundreds of volts to several tens of kilovolts. The test voltage is determined by the standards which apply to the product being tested.

28
Q

What is the minimum IP rating for a pressurised enclosure?

A

IP40

The IEC recommends a minimum enclosure rating of IP40. However, UL Type 4 (IP65) enclosures are recommended as they are robust and provide additional latching points that assist in preventing leakage.

29
Q

How many air changes required during the purge time?

A

IEC/ATEX requires 5 air exchanges prior to pressurization. The volume of air needed for replacement is based on the interior volume of the enclosure (Height x Width x Depth), what type of protective gas used, and the ambient conditions. An exterior label is provided for the system specifying the exact time needed for purging prior to pressurization and powering equipment.

30
Q

Where can you find the minimum purge time required for pressurising an enclosure?

A

In the documentation and certificate for the enclosure

Additionally an exterior label is provided for the system specifying the exact time needed for purging prior to pressurization and powering equipment.

31
Q

Warning notices should be posted with reference to cooling down period in the pressurised enclosure.

What does this mean?

A

Warning notices should be fitted or a timed interlock installed to ensure that hot surfaces have cooled and capacitors have discharged prior to the pressurised door being opened.

32
Q

What is the minimum test pressure requirement for testing the internal over pressure of a pressurised enclosure as factor or percentage in relation to that normal working pressure?

A

The minimum requirement is 1.5 times the working pressure stated by the manufacturer.

The enclosure must be able to withstand the maximum over-pressure, when all ducts are closed. Example minimum over-pressure will be 2mBAR

33
Q

For loss of pressure or flow in a pressurised enclosure. What sensors are used and where are they place to monitor over-pressure and flow?

A

Over-pressure sensor
Is monitored by a pressure sensor or pressure switch.

Flow rate sensor
Is monitored by either flow switch or flow sensor.

Both sensors are located in the outlet duct used to monitor the flow of gas through the enclosure.

If a loss of over-pressure or
or loss of flow rate is detected will either activate a shutdown of the system and an alarm, or raise an alarm dependant on the EPL of the enclosure.

Ex px Zone 1 shutdown + alarm
Ex px Zone 2 alarm

Ex py Zone 1 alarm
Ex py Zone 2 no action

Ex px Zone 2 alarm

COMPEX (14 decks)

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