Electrical Safety and Earthing Questions and Answers

Answer: B

In domestic house wiring the most commonly used fuse is the rewireable fuse, also called the kit-kat fuse, in which a fuse wire is fitted in a porcelain carrier and can be replaced when it has blown. HRC fuses are costlier and are used in industry, an electromagnetic fuse is not a common type and a residual fuse is not a term used for a fuse. The answer is rewireable fuse, option (B). The fuse wire is fitted in a porcelain carrier and the wire is replaced after each blow, and this is cheap and simple, which is why it is used in houses and small shops.

Answer: A

If it is unavoidable to work on a live circuit, the worker must be insulated from the live parts and from the ground, which is done with rubber gloves and a rubber mat to stand on. Bare hands would give a path for the current through the body, and GI pipes and copper rods are conductors, so they would carry current and could cause a shock or short circuit. The answer is Rubber gloves and rubber mats, option (A). Rubber is an insulator, and so the rubber gloves keep the current from passing through the body, and the mat keeps the feet from the earth.

Answer: D

Safety signs have standard shapes and colours: prohibition signs are circular with a red border, mandatory signs are circular and blue, and warning signs are triangular with a yellow background and a black border. So the shape and colour of a warning sign is triangular and yellow, option (D). Circular and white, square and blue and hexagonal and pink are not the combination for a warning sign. Yellow is the colour used for warning because it is the most easily seen, and the triangle shape separates the warning signs from the mandatory and prohibition signs, which are circular.

Answer: D

The key gives eyes and face protection as the equipment that comes under the PPE5 category, option (D). Personal protective equipment is grouped by the part of the body it protects, such as head protection (helmet), foot protection (safety footwear), hand and arm protection and eye and face protection. The other three options belong to other categories in that grouping. The question is a recall item and the key is followed.

Answer: C

A latching relay has a mechanism, magnetic or mechanical, that holds the contacts in the position they were last moved to, so they stay there even after the power is cut off. An impedance relay and a differential relay are protective relays that return to their rest position when the coil is not energised, and a reed relay also opens when the field is removed. The answer is Latching relay, option (C). Latching relays are used where a state must be held without power being applied all the time, as in lighting control and in some protection circuits.

Answer: A

An electric iron gives a shock when the live part of the heating element touches the metal body, which happens when the insulation of the heating element is weak or has failed. A wrong setting of the thermostat only changes the temperature, a dirty sole-plate affects the ironing, and an open thermal fuse would cut off the supply to the iron altogether. The answer is Weak insulation of heating element, option (A). The shock occurs because the metal body of the iron becomes live, which is why a three-pin plug with an earth connection is used for irons.

Answer: B

Using a screwdriver with a wooden handle while working on electric circuits is a good safety practice. Wood is an insulator, so the handle keeps the worker's hand from the live parts and reduces the risk of a shock. Tools for electrical work should have insulated handles.

A water pipe is a poor earthing path and is not accepted as an earth electrode, because it may be of plastic or have insulating joints and it can carry fault current to other people. Stopping a rotating motor with the hand risks injury from the moving parts, and touching bare conductors can give a shock. So only the second option is a good practice.

Answer: D

The safety sign for the risk of electric shock is a warning sign. Warning signs are triangular with a yellow background and a black border, and they warn of a hazard such as electricity, fire or an explosion. The sign with a lightning arrow tells people of a danger and does not order anything.

A mandatory sign (blue circle) says what must be done, a prohibition sign (red circle with a slash) says what must not be done, and an information sign (green) shows a safe condition such as a first aid point. So the fourth option is the answer.

Answer: B

The meaning of a prohibition sign is that 'it must not be done'. Prohibition signs are red circles with a slash across a picture, and they forbid an action such as smoking, entry or the use of naked flames.

A mandatory sign tells us what must be done (for example wear a helmet), an information sign gives facts such as an exit or first aid point, and a warning sign tells us of a danger. None of these says that something must not be done, so the second option is correct.

Answer: C

'No smoking' is an example of a prohibition sign. It is a red circle with a slash through a cigarette, which forbids an action.

'Risk of explosion' and 'Risk of fire' are warning signs, drawn as yellow triangles, because they warn of a hazard and do not forbid anything. The 'first aid point' sign is an information (safe condition) sign, shown in green. So the third option is the answer.