QUE-ANS: 10-30 words

[1]        What is understood by ‘dead front’ switchboard?

Dead front switchboard is one with insulated switches and no exposed terminals.

[2]        What is an electric shock?

Electric shock is due to flow of current through the body. This is often from hand to hand or Hand to foot. A shock current of l5ma ac or dc may be fatal.

[3]        Which system of supply is more lethal, ac or dc?

Ac supply is more lethal than dc supply at similar voltages. On no account should work of Even the simplest nature be undertaken on live ac apparatus without the operator being fully protected.

[4]        What is space heater?

Small resistance heater units mounted in a motor, that are energized, during motor shutdown. To prevent condensation of moisture on the motor windings.

[5]        What is the most serious hazard at sea?

The most serious hazard at sea in electrical systems or caused by electrical systems is fire.

[6]        Above what voltage must special precautions be taken?

Special precautions must be taken in voltages over 55V.

[7]        What is meant by the Term, Type Ex’e’?

Ex’e’ = Increased Safety Equipment.

Increased Safety Equipment is based primarily on the elimination of “open sparking”, i.e. equipment that does not have contacts.

[8]        What is meant by the Term, Type Ex’i’?

Ex’i’ = Intrinsically Safe.

Equipment with circuits that do not generate enough heat to ignite a gas.  This generally means limiting circuits to less than 30V, 50mA.

[9]        What is meant by the Term, Type Ex’p’?

Ex’p’ = Pressurisation.

[10]      What minimum current can be regarded as Fatal?

A shock current as low as 15mA ac or dc can be fatal.

[11]      What is the maximum voltage of electrical systems in tanker cargo areas?

The maximum voltage of electrical systems in tanker cargo areas is 3 phase 440V.

[12]      What must be ensured when replacing lamps or tubes?

When replacing lamps or tubes, it must be ensured that the supply is off.

[13]      What can arc flash cause personnel?

Arc flash can cause personnel blindness, burns and can cause fires.

[14]      What can happen if a higher rated light is fitted in a lamp fitting?

If a higher than rated light is fitted in a lamp fitting, it can cause overheating and fire.

[15]      What must be remembered when changing fluorescent tubes?

When changing fluorescent tubes, it must be remembered the capacitor in the circuit may retain a charge and should be discharged before handling its terminals.

[16]      What should be checked with portable cargo lighting?

With portable cargo lighting, it should be checked that cables and supply plugs are in good condition.

[17]      What will corrosion cause in flameproof light enclosures?

Corrosion in flame proof light enclosures can reduce its strength.

[18]      What should be done if the lamp glass is cracked in a flameproof enclosure?

If the lamps glass is cracked in a flame proof light fitting, a complete new lamp glass assembly should be fitted immediately.

[19]      What could happen if bolts are over tightened?

If bolts are over tightened in a flame proof fitting, it could cause distortion of the flame path, damage seals and cause excessive stress on lamp glasses.

[20]      What is the maximum voltage regarded as reasonably safe for portable power tools?

The maximum voltage regarded as reasonably safe for portable power tools is below 60V.

[21]      What is the maximum shock voltage to earth for a centre tapped 110V tool transformer?

The maximum shock voltage to earth for a centre tapped 110V tool transformer is 55V.

[22]      What is the first thing that must be done when finding a victim of electric shock?

The first thing that must be done when finding a victim of electric shock is to detach them from the live conductor.

[23]      Give two methods of how this is done?

Two methods of how to do this are, switch off the supply or remove the victim using a dry non conducting material.

[24]      Where can details of the first aid to be carried are found?

Details of first aid to be carried out in the event of electric shock can be found on switchboards, high voltage equipment etc.

[25]      What is the range of welding current?

The normal range of welding current is from 50 – 600 Amps.

[26]      What are the two main non-electrical safety precautions to protect welders?

The two main non-electrical safety precautions to protect welders are protective clothing and visor.

[27]      What stops an earth fault at a transformer?

An earth fault is stopped at a transformer by the air gap between the windings.

[28]      Why must an earth return path have low impedance?

An earth return path must have low impedance so all of the earth fault circuit has low impedance.

[29]      At what value of earth currents are earth leakage breakers set?

The value that earth fault leakage breakers are set to trip, are at currents as small as 40 –50mA.

[30]      What is used to protect operators from indirect electrical shock?

To protect operators from indirect electrical shock, the work piece should be well earthed.

[31]      Why is the type B electrode holder better than the type A?

The type ‘B’ electrode holder is better than the type ‘A’ because no live parts are accessible to the standard test finger and when the electrode is fitted, it’’ non-coated end does not protrude from the electrode holder.

[32]      What is the classification of equipment that suffers from interference?

Equipment that suffers from interference is classified as susceptible.

[33]      Give an example of non-electrical equipment giving rise to static?

An example of non-electrical equipment giving rise to static is a shaft on the rubbing face of a bearing.

[34]      Given an example of a very common source of interference which is a steady state condition?

An example of a very common source of interference which is a steady state condition could be from a fluorescent tube, generator or motor.

[35]      What can cause intermittent interference?

Intermittent interference could be caused by erratic connections.

[36]      What is the only guaranteed way of preventing interference?

The only way of guaranteeing the prevention of interference is keeping as far away as possible equipment that causes interference but this is not practical or possible on a ship.

[37]      How are radio receivers and transmitters constructed to reduce interference?

Radio transmitters and receivers are constructed so that their casings form complete electromagnetic screens to prevent interference.

[38]      Where are suppressors fitted?

Suppressors are fitted in power supply lines as close as possible (not more than 150mm away) to the equipment being protected.

[39]      What types of cables should not be run together?

Cables that should not be run together are sensitive and non-sensitive cables.

[40]      What must an emergency generator be provided with?

An emergency generator must be provided with its own IC engine as a prime mover, own fuel supply tank, starting equipment and switchboard, and must be above the water level.

  30-60 words

[1]        What is meant by the Term, Type Ex’d’?

Ex’d’ = Flame Proof Enclosure.

This is an enclosure that will withstand an Internal Explosion of Flammable Gas within itself and dissipate heat from that explosion before reaching outside atmosphere, which could ignite the gas in surrounding atmosphere, i.e. a Ship’s Battery Locker could be classed as Ex’d’.

  60-100 words

[1]        What would you do if you found an Engineer in Electric Shock?

First raise the alarm then isolate or switch off the current.

If this is not possible, pull or push the victim away from the source, taking care not to make electrical contact with the victim or the electrical source, i.e. use something non-conductive.

Once the victim has been removed from the electrical source, if the breathing is feeble or ceased, artificial respiration should be started at once.  Delay in starting artificial respiration can prove fatal.

Note:  If artificial respiration is started at once, 70% of the victims recover.  If there is 3 (three) minutes delay, only 20% of victims recover.

[2]     What is the difference between shock received due to dc and that due to AC?

Current from a steady dc source in passing through the skin, will tend to cause muscular contraction at the initial contact and when the contact is broken. Ac produces continue spasm in the muscles through which current passes, with its change from forward to reverse flow either at 50 hz or 60 hz rate. Ac has the ability to stimulate nerves directly.

[3]    What are the conditions that affect the electric shock?

The size of electric shock current is related to following factors: 1. Applied voltage (2) body Resistance. The size of human body resistance depends on other factors also, like state of health, Degree of contact with live wires, perspiration or dampness of skin. Typical dry full contact Body resistance is about 5000 ohms at 25V, falling to about 2000 ohms at 250V. This indicates that human body resistance goes down as the applied voltage goes up, giving rise to the increased Current at high voltages.

[4]    What is meant by intrinsically safe?

An electrical circuit or part of a circuit is intrinsically safe, if any spark or thermal effect produced normally (e.g. by breaking or closing the circuit) or accidentally (e.g. by short circuit or earth fault), is incapable of igniting a prescribed gas mixture, under prescribed test condition.

An equipment, which cannot released sufficient electrical or thermal energy, under any condition to ignite a particular flammable vapour in its vicinity.

[5]        What are the causes for short circuits?

Short circuit may occur because of breakdown of insulation of equipment due to overheating or ingress of water. Sometimes terminal connections become loose, causing two power supply cables to make electrical contact. Short circuit may also occur in the windings of a transformer because of insulation breakdown due to overheat. Electrical cables exposed to fire, mechanical damage. Cuts etc. can cause short circuit.”

[6]         Why the equipments are earthed on board the ship?

In order to protect against the dangers of electric shock and fire that may result from earth Faults, the metal enclosures and other non-current carrying metal parts of electrical equipment Must be earthed. The earthing conductor connects the metal enclosures to earth (ship’s hull) and prevents such metal parts from attaining dangerous voltage with respect to earth in the event of an earth fault occurring.