UNIT 4 & 5: Ex e Ex n Flashcards
1.
The minimum IP rating for Ex e equipment is?
IP64
IP6X
IP44
IP54
IP54
2.
Which one of the following descriptions represents equipment marked Exe?
Intrinsically safe
Increased safety
Flameproof
Enhanced safety.
Increased safety
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.
EPL Gc (Cat 3G) locations only
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.
nA, nC, nL, nR.
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
Ex d or Exe
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.
Fit gland
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.
Uncertified plastic.
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.
The disconnection time limit when stalled after starting from hot
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.
Certified as meeting the requirements of IEC60079-0
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
An uncertified gland which meets the IP and impact requirements
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
Fit gland, external IP washer, internal serrated washer and locknut
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.
Lamps using non-conducting end-caps or pins with a conductive coating unless tested with the equipment
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.
All gas groups
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
prevent the ingress of dust and moisture
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.
Fit gland, earth tag, external IP washer and internal locknut.
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.
If the motor stalls it must be disconnected by its control gear within 10 seconds at its normal operating temperature.
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.
An uncertified gland complying with the IP and impact requirements for Ex e
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.
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.
Ex e motors
Time Versus Current Ratio graph.
What is the definition of Current Ratio
Current Ratio =
Locked rotor current / motor nominal ruining current
Ex e motors
Define Te in terms of an Ex e motor …
What is limiting temperature of an Ex e motor?
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
PLASTIC Ex e ENCLOSURES
What are the requirements for construction of a plastic Ex e enclosure?
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
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
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.
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
As approved by the manufacturer.
Ex e Glands
After which year were certified Glands required for Ex e enclosures?
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
