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COMPEX > UNIT 4 & 5: Ex e Ex n > Flashcards

UNIT 4 & 5: Ex e Ex n Flashcards

1
Q

1.
The minimum IP rating for Ex e equipment is?

IP64
IP6X
IP44
IP54

A

IP54

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2
Q

2.
Which one of the following descriptions represents equipment marked Exe?

Intrinsically safe
Increased safety
Flameproof
Enhanced safety.

A

Increased safety

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3
Q

3.
Which one of the following locations may Ex n equipment be installed?

EPL Gb (Cat 2G) locations only

EPL Gc (Cat 3G) locations only

EPL Ga (Cat 1G) locations

EPL’s Gb, Gc (Cats 2G, 3G) locations.

A

EPL Gc (Cat 3G) locations only

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4
Q

4.
Four variations of Ex n equipment are available, which are?

Na, Ne, NL, Nr

nA, nB, nC, nD

px, py, pz

nA, nC, nL, nR.

A

nA, nC, nL, nR.

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5
Q

5.
Installed in 2009, an Ex d motor has an Ex e terminal box. Which one of the following gland options may be used on a SWA cable?

Uncertified E1W

Ex i

Ex d

Ex d or Exe

A

Ex d or Exe

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6
Q

6.
A steel Ex e enclosure has a threaded entry 10mm in length. Which one of the following options achieves the minimum installation requirement when fitting an Ex e cable gland?

Fit gland

Fit gland, external IP washer and internal serrated washer

Fit gland, external IP washer and internal lock nut

Fit gland, earth tag, serrated washer and internal lock nut.

A

Fit gland

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7
Q

7.
For Ex e equipment installed in 2005, which one of the following glands is not acceptable?

Ex e certified

Uncertified

Ex d certified

Uncertified plastic.

A

Uncertified plastic.

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8
Q

8.
The te time of an Ex e motor indicates?

The disconnection time limit when stalled after starting from cold

The disconnection time limit when stalled after starting from hot

The run-up time to full speed

The minimum time interval between re-starts.

A

The disconnection time limit when stalled after starting from hot

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9
Q

9.
The requirements for cable glands entering Ex n equipment after 2007 are?

Ex d barrier gland

Ex e certified gland

Certified as meeting the requirements of IEC60079-0

Ex d certified gland.

A

Certified as meeting the requirements of IEC60079-0

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10
Q

10.
An Ex de motor, with an Ex e terminal box, was installed in 2005. Which one of the following cable glands .achieves the minimum installation requirements:

An E1W. Exe gland

An E1WF Ex d gland

An uncertified gland which meets the IP and impact requirements

An Ex d gland

A

An uncertified gland which meets the IP and impact requirements

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11
Q

11.
A steel Ex e enclosure has clearance entries. What is the minimum requirement
for installing an SWA cable :

Fit gland, internal IP washer, serrated washer and locknut

Fit gland, earth tag, serrated washer and internal locknut

Fit gland, external IP washer, internal serrated washer and locknut

Fit gland, external IP washer and internal locknut

A

Fit gland, external IP washer, internal serrated washer and locknut

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12
Q

12.
Which one of the following restrictions apply to Ex e and Ex n light fittings?

Lamps using non-conducting end-caps or pins with a conductive coating unless tested with the equipment

Lamps using conducting end-caps or pins are prohibited

Lamps with screwed connections are prohibited

Fluorescent lamps must be bi-pin.

A

Lamps using non-conducting end-caps or pins with a conductive coating unless tested with the equipment

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13
Q

13.
An increased safety enclosure is marked Ex e II T6. The absence of a letter after ‘II’ indicates the enclosure may be used in: Group IIC gases only

iGroup IIA gases only

All gas groups

iv In combustible dusts only.

A

All gas groups

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14
Q

14.
The purpose of seals at the joints of Exe enclosures is to:

prevent the ingress of dust and moisture

prevent the ingress of flammable gases I vapour

insulate the parts from one another

contain an internal explosion

A

prevent the ingress of dust and moisture

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15
Q

15.
A plastic Ex e enclosure has clearance entries and no internal continuity plate.
Which one of the following arrangements achieves the minimum requirements
when installing an Ex e cable gland

Fit gland and external IP washer

Fit gland, earth tag

internal locknut and external shroud

Fit gland, external IP washer and internal locknut

Fit gland, earth tag, external IP washer and internal locknut.

A

Fit gland, earth tag, external IP washer and internal locknut.

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16
Q

16.
An Ex e motor rating plate indicates a tE time of 10 secs for a T4 temp class. What
does the 10 second tE time indicate

Full speed is reached by the motor in 10 sees at a T4 ambient temp

Restarting of the motor not permitted within 10 sec to avoid the temperature
exceeding the T 4 temperature class

The motor insulation has been tested for 10 sees at the T 4 temp

If the motor stalls it must be disconnected by its control gear within 10 seconds at its normal operating temperature.

A

If the motor stalls it must be disconnected by its control gear within 10 seconds at its normal operating temperature.

17
Q

17.
An Ex d motor has an Ex e terminal box and was installed in 2005. Which one of
the following meets the minimum requirement for the cable gland?

An uncertified gland complying with the IP and impact requirements for Exe

An E1WF cable gland

An EEx d cable gland

An EEx i cable gland.

A

An uncertified gland complying with the IP and impact requirements for Ex e

18
Q

18.
The number of cores of different cross-sections that may be connected to any one
terminal in an Ex e enclosure is?

Two, if the cores are fitted round the terminal screw in the shape of a “U’

Dependent on the size of the core

One

One, unless the certification permit otherwise.

A

One, unless the certification permit otherwise

Ex e Ex n enclosures
Unless permitted by the certification, two wires of different cross-section should not be connected into one terminal unless first secured with a single compression type ferrule.

Single conductors in single screw type saddle clamp should have the U-shaped around the screw to permit proper clamping.

19
Q

Ex e motors

Time Versus Current Ratio graph.

What is the definition of Current Ratio

A

Current Ratio =

Locked rotor current / motor nominal ruining current

20
Q

Ex e motors

Define Te in terms of an Ex e motor …

What is limiting temperature of an Ex e motor?

A

Te is the time taken for motor temperature to rise from maximum temperature at rated current to limiting temperature for locked rotor current

Te limiting temperature

Current Ratio = Ia / In

Ia  = locked rotor current
In  = nominal rated current
21
Q

PLASTIC Ex e ENCLOSURES

What are the requirements for construction of a plastic Ex e enclosure?

A

Hawke PL615 / PL620

Constructed from anti-Static GRP material

insulation resistance less than 1 G ohm

highly resistant to corrosion.

Resist impact up to 20 Nm

22
Q

RESTRICTED BREATHING TYPES

Ex nA Non-Sparking
Ex nA has now been replaced with Ex ec

Ex nC Enclosed Break
Sparking where the contacts are suitably protected other than by types R, L, or Z
Sparking Contacts are enclosed within Hermetically Sealed enclosure.
The seal maybe soldering, brazing, welding, or fusion of glass to metal.
External connections are usually by flying leads or terminals.
Encapsulated (enclosed device)
Arcing component sealed in glass
No contact with explosive gas.

Ex nL Energy Limiting
Ex nL has now been replaced with Ex ic

Uses zener diodes and series resistors
Internal volume must be less than 0.1 litres (100 cm3).
To be replaced by Ex Ic

Ex nZ enclosure with pressurisation
Ex nZ has now been replaced with Ex pz

A

Ex nR Restricted Breathing
Mainly used on light fittings.
Good seal at joints and cable entries.
Suitable for Zone 2 only EPL Gc (Cat 3G)

Does not totally prevent the entry of gases.
Main use of Ex nL is for luminaries.
The position of restricted breathing enclosures may need careful consideration, particularly in sunlight.

Cable entry requirements include correct IP washer (steel and rubber)
Periodic Testing required.
Gaskets and seals to be replaced when re-lamping.

23
Q

Ex n lamps

Mono Pin, Bi-Pin, Screw Connection.

Caps made from non-conductive material with conductive coating are not permitted unless tested with the equipment

A

As approved by the manufacturer.

24
Q

Ex e Glands

After which year were certified Glands required for Ex e enclosures?

A

After 2007

Prior to 2007
Uncertified Glands were permissible, of 7-joule impact resistance and maintained the IP rating of the enclosure.

Uncertified plastic glands were not permissible

COMPEX (14 decks)

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