Interview Questions.

Question 1. What Is A Hazardous Area?

Answer :

A unsafe place class is one wherein concentrations of flammable materials are present or may be expected to be present. These concentrations are at a degree which requires particular safety requirements and precautions to be taken within the construction, set up and upkeep of all electrical gadget.

A “hazardous location” is described as an area wherein the surroundings carries, or may additionally include in enough portions, flammable or explosive gases, dusts or vapours. In such an ecosystem a hearth or explosion is viable whilst three basic situations are met. This is often known as the “unsafe location” or “combustion” triangle.

In order to guard installations from a potential explosion a way of analysing and classifying a probably risky place is needed. The purpose of this is to ensure the precise selection and set up of equipment to in the long run save you an explosion and to make sure protection of lifestyles. The methods used to categorise an set up can range depending upon which part of the sector it's far placed, but usually there are two primary varieties of classification. In nations that have followed the IEC (International Electro technical Commission) philosophy this is called Zoning even as in North American installations are classified by using Classes, Divisions and Groups to check the extent of protection required.

Question 2. How Hazardous Area Classified?

Answer :

A Hazardous Area is defined by using three predominant criteria, these being:

The form of chance (agencies).
The auto-ignition temperature of the risky cloth (temperature or “T” rating).
The likelihood of the chance being present in flammable concentrations (zones).
Electrical and Electronics Engineering Interview Questions
Question three. Explain About Type Of Hazard (agencies)?

Answer :

The form of hazard can be in the shape of both a gas or vapour or a dust or fibre.

The class of these hazardous is on the whole divided into two groups relying on whether it is in a mining or above floor industry.

These are described below:

Group I – electrical equipment to be used in mines and underground installations at risk of firedamp Group II and Group III -electric gadget to be used in surface installations
Groups II & III are further sub-divided relying upon the hazard. Group II gases are grouped collectively based upon the quantity of energy required to ignite the maximum explosive combination of the gas with air. Group III dusts are subdivided consistent with the character of the explosive environment for which it's far supposed.
Question 4. Explain About Auto Ignition Temperature Or “t” Rating?

Answer :

The threat level of the gases increases from gas group IIA to IIC with institution IIC being the maximum extreme. Substances on this group may be ignited very without problems with Hydrogen being the maximum at chance to ignition. The temperature elegance is based totally on the car-ignition temperature of the gasoline.

If a unsafe is gift the system used in the installation need to receive the proper “T” class for you to hold the integrity. If that hazardous is, say, hydrogen, then all system used need to meet the “T6” score. This manner that each one equipment used ought to not have a surface temperature of greater than eighty five?C. Any system used that could generate a warmer surface temperature of greater than eighty five?C must not be used as this can then boom the probability of an explosion by means of igniting the hydrogen within the environment.

Question five. Classification Of Hazardous Locations?

Answer :

Hazardous locations are classified into zones on the way to facilitate the choice of an appropriate electrical apparatus and to make certain that the electric design and set up meets the required necessities for use in unique areas. The zone classification is primarily based at the chance and the length of an explosive ecosystem.

The region classification for gases is split into 3 zones, particularly Zone zero, Zone 1 and Zone 2 and for dusts Zone 20, Zone 21 and Zone 22.

Definition of dangerous vicinity zones (AS/NZS 60079.10):

Zone zero:

“Place in which an explosive ecosystem which include a aggregate with air of flammable substance inside the form of gas, vapour or mist is present constantly for lengthy periods or regularly”
As per experts revel in that a Zone zero condition is rarely encountered and is restrained in particular to restricted areas (along with the vapour space of closed manner vessels, closed garage tanks and closed boxes), despite the fact that it could occur in larger rooms, inclusive of chemical plants. From the Institute of Petroleum (IP 15) an publicity exceeding a thousand hours in line with 12 months is regularly used.
Zone 1:

“Place in which an explosive surroundings which includes a combination with air of flammable materials inside the form of fuel, vapour or mist is likely to occur in ordinary operation now and again”
A Zone 1 category generally consists of places wherein volatile flammable liquids or liquefied flammable gasses are transferred; gas generator rooms; inadequately ventilated pump rooms for flammable gases or for volatile flammable beverages; and maximum different locations wherein dangerous concentrations of flammable vapours or gases can occur inside the path of everyday operations. IP 15 stipulates between 10 hours and a thousand.
Zone 2:

“Place wherein an explosive environment consisting of a aggregate with air of flammable materials inside the form of gasoline, vapour or mist is not in all likelihood to arise in regular operation however, if it does arise, will persist for a quick length best”

Generally, for a place to be labeled as a Zone 2 place the following situations shall typically be regarded because the minimal requirements for the region:

The region is so properly ventilated that if an atypical situations arises, ignitable concentrations of the fuel or vapour are unexpectedly dispersed; and
Complete segregation from Zone 1 locations is ensured.
In this example an expose to flammable vapours or gases of much less than 10 hours according to annum is prescribed in IP 15.

Digital Electronics Interview Questions
Question 6. Explain Ex I Intrinsic Safety?

Answer :

A protection concept in which the electrical electricity within the system is constrained to a stage that's below that what may cause an ignition or to restrict the heating of the floor of the device. There are  foremost sub kinds to Ex i safety, these being “ia” and “ib”.

Type “ia” safety lets in for the occurrence of two faults at some point of operation.
Type “ib” safety allows for the prevalence of 1 fault in the course of operation.
Question 7. Explain Ex D Flameproof?

Answer :

The system which could cause an explosion is contained inside an enclosure that can withstand the pressure of an explosion and save you transmission to the outdoor unsafe surroundings. This approach of safety also prevents the dangerous ecosystem from coming into the enclosure and entering contact with equipment.

Electrical Engineering Interview Questions
Question eight. Explain Ex M Encapsulation?

Answer :

A safety idea in which via device that might doubtlessly reason an ignition is encapsulated within a compound or resin so one can save you touch with the explosive environment. The concept additionally limits the surface temperature of the system under everyday operating situations.

Question 9. Explain Ex E Increased Safety?

Answer :

Precautions are implemented to the set up to make certain extended protection towards the opportunity of excessive temperatures and sparks from electrical gadget. Equipment that generally reasons sparks is excluded from use within this method of safety.

EDI (digital facts Interchange) Interview Questions
Question 10. Explain Ex P Pressurized?

Answer :

One manner guarantees that the pressure inside an enclosure is enough to save you the doorway of a flammable gas, vapour, dirt, or fibre and prevent a possible ignition. Another method continues a constant fl ow of air (or an inert fuel) to dilute to dispose of any potentially explosive ecosystem.

Question 11. Explain Ex O Oil Immersion?

Answer :

All equipment that has the capability to arc and probably cause an ignition is immersed in a protecting liquid or oil. The oil affords an insulating technique to save you ignition.

Analogue electronics Interview Questions
Question 12. Explain Ex Q Powder Filling?

Answer :

All system that has the capacity to arc is contained inside an enclosure full of quartz or glass powder debris. The powder filling prevents the opportunity of an ignition.

Electrical and Electronics Engineering Interview Questions
Question 13. Explain Ex N Non-sparking?

Answer :

A form of safety where precautions are taken in order that electric gadget that has the ability to arc isn't always able to igniting a surrounding explosive surroundings. This may be similarly categorised as follows: Ex nA -Where components used in production are non-sparking Ex nC -Where components used in creation are non-incendive Ex nR – Where additives used are tightly enclosed to limit the respiration and save you ignition Ex nL -Where components utilized in production do not include enough strength to purpose an ignition.

Question 14. Explain Ex S Special?

Answer :

This method of safety, as its name suggests, has no precise parameters or creation policies. In essence it's miles any approach of safety that can provide a pre-determined level of protection to make sure that there is no capability for an ignition. As such it does now not fall beneath any precise safety approach and can in reality be a mixture of a couple of.

Question 15. Explain Operational Temperatures?

Answer :

All device used within hazardous areas has an operational temperature band or restrict. This is regularly known as the “Tamb” and defines the higher and lower ambient temperatures of which the device is authorised for use in. As described in IEC 60079-0 the same old limits are – 20?C to +40?C. Where the operation temperatures of the system fall between those parameters no additional marking is needed. However, if they're out of doors those parameters than the specific temperatures need to be recognized.

Electrical Machines Interview Questions
Question sixteen. Explain Marking Of Hazardous Area Equipment?

Answer :

All system for use in risky regions should be marked as prescribed in 60079-zero. As a general rule this includes, where appropriate, such facts as:

Company/Manufacturers call and cope with
Hazardous vicinity certificate number(s)
Protection concept -Gas institution(s)
Temperature elegance
Ambient temperature variety
Product identification
Serial quantity and 12 months of manufacture
Electrical parameters
CE marking and ATEX notified Body ID range
ATEX coding -IP code
Question 17. Explain Basic Ul / Csa / Nema Enclosure Types?

Answer :

Type 3: An enclosure that is meant for out of doors use mostly to offer a diploma of protection in opposition to windblown dust, rain, sleet and harm from external ice formation.

Type 3R: An enclosure that is intended for out of doors use mainly to provide a degree of protection against falling rain and harm from outside ice formation.

Type 3S: An enclosure that is intended for outside use frequently to provide a diploma of safety towards rain, sleet, windblown dirt, and to offer for operation of external mechanisms whilst ice encumbered.

Type 4: An enclosure that is intended for indoor or outside use often to provide a degree of protection against windblown rain and dirt, splashing water, hose directed water and damage from external ice formation.

Type 4X: An enclosure that is meant for indoor or out of doors use more often than not to provide a diploma of safety towards corrosion, windblown rain and dirt, splashing water, hose directed water and harm from outside ice formation.

Type 6: An enclosure that's intended for indoor or out of doors use mainly to offer a degree of safety towards falling dust, hose directed water, the entry of water all through occasional transient submersion at a unique intensity and harm from external ice formation.

Type 6P: An enclosure that's supposed for indoor or out of doors use to commonly to provide a degree of protection towards falling dust, hose directed water and the access of water all through extended submersion at a designated intensity and harm from outside ice formation.

Electrical Power System Interview Questions
Question 18. Why Perform Electrical Equipment In Hazardous Areas Inspections?

Answer :

Perhaps you've got heard the expression ‘if it’s now not broken don’t repair it’. The equal may be stated for Electrical Equipment in Hazardous Areas (EEHA) inspections and there is usually a first rate deal of resistance from engineering and production managers to perform electric inspections which can also involve the isolation positive device or partial plant shutdown. It is a reality that if the electric inspector lacks the vital enjoy, the EEHA inspection ought to indeed do more harm than proper, ensuing in harm to electric equipment, tripping of electrical circuits or extended isolations. For this purpose simplest capable personnel need to be employed for the motive of performing EEHA inspections. Using a able electrical inspector will offer the proprietors or users of the plant with a situation evaluation of the electrical set up in unsafe areas to make certain that it's far maintained in a quality circumstance. It is likewise a demand of AS/NZS 2381.1:2005 Section four that EEHA inspections be achieved on a regular periodic foundation or underneath non-stop supervision by using able personnel.

Before embarking upon an inspection of electrical device inside a unsafe area, the risks associated with the flammable gasoline or vapour must be understood and the quantity of the hazardous sector should be certainly defined. It is a fruitless exercise to begin an EEHA inspection without a clean definition of the dangerous zones. Internationally, the classification of unsafe regions has historically been done by way of people representing the prison proprietors/users of the plant. Often those men and women lack knowledge in dangerous regions classifications as well as the particular understanding of the properties of the flammable substances. As a end result, inconsistencies may additionally exist within the limits of the risky zones. However, in greater latest times hazardous regions classification has tended to be achieved by way of expert multidisciplinary engineering consultancies that specialize in unsafe locations classifications. The electric inspector acting the EEHA inspection need to confirm that the present vicinity class remains correct and that there have been no changes to plant or tactics which can have an effect on the hazardous zones.

Digital Electronics Interview Questions
Question 19. Does All Electrical Equipment For Use In Hazardous Areas Have To Be Submitted To A Test House For Certification?

Answer :

No, electrical gadget in category 1, i.E. Suitable to be used in Zone zero,1 and a pair of must be submitted to a take a look at residence (now known as a notified frame) for EC Type Examination Certification. This also applies to category 2 system (i.E. Suitable to be used in Zone 1 and 2) . Equipment in category three, i.E. Appropriate handiest for use in Zone 2 want best be challenge to self certification through the producer. For all electrical system for use in hazardous areas, the producer need to issue an EC Declaration of Conformity together with his product.

Question 20. If An Enclosure Is Marked Ii 2 Gd And Also Eexd 11c T5 T100 Ip sixty six, What Is The Meaning Of The Upper Case And The Lower Case‘d’s?

Answer :

The upper case D is a part of the ATEX labelling and indicates that the device is for use in areas in which the explosion risk is Dust (the G indicates Gas Hazard). The decrease case d indicates the approach of Ex safety, in this situation flameproof (d from the German Druckefest Kapselung meaning stress evidence enclosure).

Electrical Drives Interview Questions
Question 21. I Have An Eexe Electric Motor Which Is Labelled As T3, I Understand This To Mean That The Temperature Reached By Any Part Of The Motor Will Not Be Any Greater Than 200°c. Is This The Case And Do I Need To Consider Ambient Temperature Effects?

Answer :

This is proper and if there is no ambient temperature range marked at the system then the T rating is primarily based on a number -20°C to +forty°C. Any different variety need to be marked on the label. Q. A flameproof EExd enclosure has a 32mm access and we want to apply it for a 20mm cable gland, is it permissible to use two reducers to attain this? A. No, EN 60079-1, the usual for flameproof device states that for any access most effective one reducer can be used, also that reducers or adapters cannot be used at all with stopping plugs.