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COMPEX > UNIT 7: Ex i > Flashcards

UNIT 7: Ex i Flashcards

1
Q

1.
Which one of the following locations may· Ex ib equipment be used?

EPL Gc (Cat 3G) only

EPL’s Gb, Gc (Cat’s 2G,Cat 3G)

EPL Ga (Cat 1 G)

EPL’s Ga, Gb, Gc (Cat’s 1G, 2G ,3G);

A

EPL’s Gb, Gc (Cat 2G, Cat 3G)

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2
Q

2.
The comparison between Ex nL and Ex ic is correctly stated by which one of the following statements?

Both may be used in zones 0, 1, and 2

Both may be used in zone 2 only

Ex nL may be used in zones 0, 1 and 2 and Ex nL in zone 2 only

Ex ic can be installed in zones 0, 1 , 2 Ex nL in zone 2 only.

A

Both may be used in zone 2 only

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3
Q

3.
The maximum resistance of the cables connecting a zener barrier earth bar and the main earth should not exceed?

1 ohm

10 ohms

1M ohms

100 ohms

A

1 ohm

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4
Q

4.
Which one of the following colours is recommended for the identification of IS cables?

White

Yellow

Light blue

Red

A

Light Blue

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5
Q

5.
The minimum cross-sectional area of a single IS earth conductor is?

  1. 0 mm2
  2. 0 mm2
  3. 5 mm2
  4. 0 mm2
A

4.0 mm2

Note: two separate earth conductors with minimum cross-sectional area of 1.5mm2 was listed in previous editions and notes, however two x 1.5mm2 copper conductors is not listed in current editions And instead only list Minimum size as 4mm2 copper earth conductor. ASET training Center still list 2 x 1.5mm2 copper conductors as acceptable (as few when Course done 19-Nov20)
With maximum impedance of 1.0 ohms. The provision of two earth conductors
Should be considered to facilitate testing.

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6
Q

6.
The equipment in the hazardous area which may be connected to the output of a zener barrier is which one of the following?

Equipment specified in the documentation and simple apparatus;

The apparatus specified in the documentation only

Any equipment

Any IS certified equipment and simple apparatus

A

The apparatus specified in the documentation only.

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7
Q

7.
Which one of the following statements indicates the correct requirements for an installation comprising both IS and non-IS circuits?

IS and non-IS cables may be installed side-by-side

IS and non-IS cables must be run on sparate cable trays

Non-IS cables must always be screened, armoured or metal sheathed

Either the IS or non-IS cables need only be armoured, screened or metal
sheathed.

A

Either the IS or non-IS cables need only be armoured, screened or metal sheathed.

Methods of Segregating IS and Non-IS circuits.

a. Adequate separation between IS circuits and non-IS circuits. Example: IS and Non-IS cables on different cable trays.
b. Positioning of the IS circuit cables such as to guard against the risk of mechanical damage. Example: IS and Non-IS cables on the same cable tray but separated by either an insulated or earthed partition.
c. The use of armoured, metal sheathed, or screened cables for either the IS or Non-IS cables, then separation with this method is unnecessary. Example: IS and Non-IS cables in the same tray but segregation is afforded by one of the cable types being armoured, screened or metal sheathed.

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8
Q

8.
The minimum clearance between different adjacent IS circuits is?

50mm

3mm

5mm

6mm

A

6mm

Minimum clearance between IS circuit, bare-conductor, and earth is 3mm.
Minimum clearance between different IS circuits, bare-conductors is 6mm.
Minimum clearance between IS and Non-IS circuits is 50mm.

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9
Q

9.
The maximum permitted supply voltage (Um) at the non-IS terminals of an IS
installation is?

250V

28V

As specified in the documentation

115V.

A

As specified in the documentation

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10
Q

10.
An appropriate workshop test for a faulty zener barrier with a possible blown fuse would be?

Disconnect output and measure voltage

Check the incoming supply voltage after suitable safety precautions have been applied

Place barrier in a test rack and measure the current

Disconnect and measure the resistance between the barrier input and output terminals.

A

Disconnect and measure the resistance between the barrier input and output terminals.

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11
Q

11.
From the following statements, which one has equipment that does not require a dedicated IS earth?

Barrier used in circuit installed in group IIC gases

Zener barrier with output connected in hazardous area

24V zener barrier

Galvanic isolation barrier.

A

Galvanic isolation barrier.

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12
Q

12.
What does the marking, [Ex ib] IIC, on an item of IS equipment indicate?

It is intrinsically safe and for use with IIC gases

It is intrinsically safe and can be installed anywhere

It may only be installed in a non-hazardous area

It is equipment associated with IS circuits.

A

It is equipment associated with IS circuits.

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13
Q

13.
The minimum clearance between IS terminals and earth is?

30mm

50mm

3mm

6mm

A

3mm

Minimum clearance between IS circuit, bare-conductor, and earth is 3mm.
Minimum clearance between different IS circuits, bare-conductors is 6mm.
Minimum clearance between IS and Non-IS circuits is 50mm.

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14
Q

14.
The screen of a cable in an IS circuit must be connected to,

The main earth conductor;

The point indicated on the loop (hook up) diagram;

Earth at both ends

Earth at one end only.

A

The point indicated on the loop (hook up) diagram;

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15
Q

15.
Equipment marked Ex d [ia] indicates that?

The flameproof enclosure is deemed ‘simple apparatus’ in an ‘ia’ circuit

The flameproof enclosure contains associated IS equipment

The components inside are all intrinsically safe

Electrical items other than IS items are inside.

A

The flameproof enclosure contains associated IS equipment

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16
Q

16.
IS cables with screens will have sheathing capable of withstanding which one of the following test voltages?

500Vac and 750Vdc

500Vac or 750Vdc

1000V

Double the working voltage. The

A

500Vac or 750Vdc

IR test voltage is
Twice I.S. Circuit Voltage or
500 vac or
750 vdc

On a sample of circuit periodically.

IR testing of IS circuits

IR test of IS circuits is required on Sample Inspections only
(IEC 60079-17 Table 2, B.9)

The IR test instrument for testing IS circuits must be specifically approved for use on IS circuits.

Test voltage 500vac or 750vdc.
The conductors of IS cables are required to be insulated with elastomeric or thermoplastic insulation with a minimum thickness of 0.3mm. The cables must be capable of withstanding a 500vac or 750vdc test voltage between …

conductors and earth
conductors and screens, and
screen to earth.

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17
Q

17.
Power supply modules for an Ex ia circuit are to be located in an area requiring EPL Gc (Cat 3G) equipment. In which one of the following enclosures may the modules be fitted?

Ex e/i

Ex p

Ex e

Ex n.

A

Ex p

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18
Q

18.
Which one of the following statements represent what must be considered when selecting cables for an IS circuit?

The cable inductance and capacitance may be ignored

Only the cable inductance is applicable

The cable inductance and capacitance is applicable

Only the cable capacitance is applicable.

A

The cable inductance and capacitance is applicable

19
Q

19.
Which one of the following components may be considered simple apparatus for use in an IS circuit?

0.1 kW motor

an L.E.D

a 9V battery

an electronic relay.

A

an L.E.D

Description of Simple apparatus.
Device that does not generate more than 1.5 volts, 100mA, 25mW
Simple apparatus not required to be certified
but justification for its use must be included in the system documentation.
be

20
Q

20.
The purpose of a zener barrier in an IS circuit is to?

control capacitance and inductance levels in the hazardous area

permit the use of any certified equipment in the hazardous area

permit the use of both simple and certified apparatus in the hazardous area

limit the level of energy that may pass into the hazardous area equipment.

A

limit the level of energy that may pass into the hazardous area equipment.

21
Q

21.
Equipment with an IS output is installed in a flameproof enclosure. Which one of the following cable glands should be used for the IS circuit?

A standard industrial cable gland

An Ex e cable gland

Flameproof Ex d cable gland

An Ex i cable gland.

A

Flameproof Ex d cable gland

22
Q

22.
A test instrument for use on an IS circuit must be?

Approved for use on the IS circuit

Used only via a protective zener barrier

Intrinsically safe

Fitted with a battery having an output lower than 3V.

A

Approved for use on the IS circuit.

The output parameters should not exceed 1.2 volts, 100mA, 25W and not capable of storing more than 20 micro-joules of energy.

It must be remembered there exists the possibility that the parameters, inductance and capacitance, of circuits under test may be large enough to modify the spark energy produced at the test probes of instruments and cause ignition of the surrounding flammable gases.

23
Q

23.
An IS circuit has both Ex ia and Ex ib equipment installed in its loop, therefore, the loop will be deemed?

An Ex ia loop

An approved loop

A non-certified loop

An Ex ib loop.

A

An Ex ib loop.

24
Q

24.
When IS and non-IS terminals are fitted in the same enclosure the minimum
clearance between the live-parts of the two terminal types is required to be?

50mm

40mm

6mm

3mm.

A

50mm

Minimum clearance between IS circuit, bare-conductor, and earth is 3mm.
Minimum clearance between different IS circuits, bare-conductors is 6mm.
Minimum clearance between IS and Non-IS circuits is 50mm.

25
Q

25.
An IS barrier is required to maintain safety even under fault conditions. On
handover of an installation, the permitted number of faults is?

one fault only

two faults

three faults

no faults.

A

No faults

26
Q

26.
The approach for installing Ex nl is?

It cannot be used in an intrinsically safe ‘ic’ circuit

it may be used in an intrinsically safe ‘ic’ circuit

it can be used in any intrinsically safe circuit

it must be replaced with Ex ic equipment

A

It may be used in an intrinsically safe ic circuit.

27
Q

27.
An insulation test on an IS system is only required?

On a sample of circuits periodically.

On all circuits every 10 years:

On all circuits in zone 0

Periodically

A

On a sample of circuit periodically.

IR testing of IS circuits

IR test of IS circuits is required on Sample Inspections only
(IEC 60079-17 Table 2, B.9)

The IR test instrument for testing IS circuits must be specifically approved for use on IS circuits.

Test voltage 500vac or 750vdc.
The conductors of IS cables are required to be insulated with elastomeric or thermoplastic insulation with a minimum thickness of 0.3mm. The cables must be capable of withstanding a 500vac or 750vdc test voltage between …

conductors and earth
conductors and screens, and
screen to earth.

28
Q

28.
Compared to other methods of protection, IS systems have a higher level of documentation because?

It is a low current method of protection

The cable details need to be known

Intrinsic safety is a system concept

It is usually associated with instrument systems

A

Intrinsic safety is a system concept

29
Q

29.
The label on part of an intrinsically safe (IS) system is marked, Um 250V. This
indicates that:

The interconnecting cables to the barrier need to be designed for at least 250V

The barrier has been designed for a 250Vac Supply

The output voltage is a maximum of 250V

testing of the barrier at 250V is required prior to use.

A

The barrier has been designed for a 250Vac Supply

30
Q

30.
Where an IS instrument requires a 3-core screened cable but only cable with screened pairs is available, one pair may be used for two of the cores, but from where may the 3rd core used:

only a three-core screened cable can be used

from a pair where one of the cores is used as the 3rd core for another circuit

one core may used from an adjacent screened pair with the other core left as unused

Any spare core from the opposite side of the cable may be used.

A

one core may used from an adjacent screened pair with the other core left as unused

31
Q

31.
Which one of the following statements specifies the requirement for the selection of cable in an IS circuit?

The use of mineral insulated cable is not permitted

Multi-core screened cable has to be used

The cables are required to withstand a test voltage of 500Vac or 750Vdc

The colour of the cables must be light blue.

A

The cables are required to withstand a test voltage of 500Vac or 750Vdc

IR test voltage is
Twice I.S. Circuit Voltage or
500 vac or
750 vdc

32
Q

32.
Why must the screen of an IS circuit cable be insulated along its entire length when it is normally earthed at one point anyway?

To prevent possible incendive stray currents invading the screen

To keep to a minimum the completion time of the circuit

To prevent further connections to the screen in the hazardous area

To ensure both ends of the screen are at the same potential

A

To prevent possible incendive stray currents invading the screen

33
Q

33.
The unused cores of a multi-core cable in an unearthed IS installation should be?

Insulated from earth at both ends

connected to earth in the non-hazardous area only

connected to earth in the hazardous area only

Connected to earth at both ends.

A

Insulated from earth at both ends

34
Q

34.
Equipment marked Ex nL is to be considered for use in an intrinsically safe (IS) circuit. Which one of the following will determine if this is possible?

Can be connected in a ‘level ic’ IS circuit if the electrical parameters are the same

It is not suitable for use in an intrinsically safe (IS) circuit

Can be connected in a ‘level ib’ IS circuit if the electrical parameter/are same

If the electrical parameters are the same it may be used in any IS circuit

A

Can be connected in a ‘level ic’ IS circuit if the electrical parameters are the same.

35
Q

Ex i Levels of Intrinsic Safety.

Define level Ia?

How many allowable faults?

What EPL can Ia be used?

A

Ex Ia has 3 zener diodes in parallel and allows for a maximum of 2 zener diodes to fail to Intrinsic safety.

Two faults are possible.

Ex Ia can be used in EPL Ga, Gb, Gc

36
Q

Ex i Levels of Intrinsic Safety.

Define level Ic?

How many allowable faults?

What EPL can Ic be used?

A

Ex Ic only has 1 zener diode and therefore no faults are considered to maintain Intrinsic safety.

No fault are possible.

Ex Ic can only be used in EPL Gc

Level of protection Ic Will replace energy limiting method used in Ex nL

37
Q

Ex i Levels of Intrinsic Safety.

Define level Ib?

How many allowable faults?

What EPL can Ib be used?

A

Ex Ib has 2 zener diodes in parallel and allows for a maximum of 1 zener diode to fail to maintain Intrinsic safety.

One fault are possible.

Ex Ib Incan be used in EPL Gb, Gc

38
Q

Ex i Cable minimum conductor size.

What is the minimum diameter of individual wire strands?

A

Individual wire strands of finely stranded cables

should not be less than 0.1 mm

39
Q

Where a terminal box contains more than one Intrinsically safe circuit, the enclosure shall meet the requirements of IEC 60079-0.

What does this effectively mean?

A

This effectively means that under these circumstances, the enclosure shall be certified.

40
Q

23.
An IS circuit contains ia, ib and ic equipment, what level should the loop be considered?

An ia loop

An ib loop

An ic loop

An in-certified loop

A

An ic loop

41
Q

What is the minimum IP rating for enclosures of IS circuits?

A

The minimum IP rating for enclosures of IS circuits is IP20

But environmental conditions may require higher rating.

42
Q

What are the requirements for enclosures and junctions boxes containing IS circuits?

A

Regardless if enclosure is certified or non-certified the enclosure or junction box must be marked that they contain IS circuits.

Certified enclosures are required when zener barriers and galvanic isolators are to be installed in the hazardous area, since these components have a non-IS input as well as an IS output. A pressurised enclosure would be a suitable alternative for the purpose.

Where a terminal box contains more than one Intrinsically safe circuit, the enclosure shall meet the requirements of IEC 60079-0. This effectively means that under these circumstances, the enclosure shall be certified.

43
Q

IS test Instruments for testing the IS installations

What is the requirement of test instrument for an IS circuit?

A

The test instruments to be approved for use on IS circuits.

The output parameters should not exceed 1.2 volts, 100mA, 25W and not capable of storing more than 20 micro-joules of energy.

It must be remembered there exists the possibility that the parameters, inductance and capacitance, of circuits under test may be large enough to modify the spark energy produced at the test probes of instruments and cause ignition of the surrounding flammable gases.

44
Q

Is it considered good practice to mount Zener Barriers on the same rail as Galvanic Isolators.

A

No.

It is not considered good practice to mount Zener Barriers on the same rail as Galvanic barriers.

COMPEX (14 decks)

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