4th Class Power Engineering lighting, water supply and drainage practice questions (4B).

Five free practice questions on lighting, water supply and drainage: unit B8 of paper B (4B) of the 4th Class Power Engineer certificate exam, written to the SOPEEC syllabus. They are in the exam's format: four options, one correct answer. Answer each one before opening the explanation. No account, no email.

01The questions

1. Procedural · Explain the various methods of lighting control

   Operators in a boiler room complain that the ceiling occupancy sensor turns the lights off while they stand still at a control panel writing up the log. The sensor is a passive-infrared type. Which change best fixes the problem?

   1. Move the sensor to the doorway so it sees everyone enter
   2. Fit a photocell so the lights stay on whenever it is dark
   3. Fit a dual-technology sensor and lengthen its time delay
   4. Replace the lamps with a type that restarts instantly
   Show the answer

   C. Correct. A passive-infrared sensor sees warm bodies moving across its zones, so a person standing still is missed. A dual-technology sensor adds ultrasonic or microwave detection of small movements, and a longer delay rides through quiet spells. A boiler room is no place to be left in the dark at a panel.

   Why not the others

   A. At the doorway the sensor would see people come in but would see even less of someone standing still at the panel; the lights would still time out on the operator.

   B. A photocell responds to daylight, not to people. In a windowless boiler room it would either hold the lights on all the time or do nothing about an operator standing still.

   D. Lamps that restart instantly would shorten the dark spells but would not stop the sensor switching the lights off while the room is occupied.

2. Recall · Describe the construction and operation of building system hot water heaters, including temperature regulation

   A storage water heater is heated by a steam coil. A self-acting temperature regulator has its valve in the steam line to the coil and its sensing bulb in the tank. When a large draw brings cold water into the tank, the regulator

   1. opens the steam valve fully and holds it until reset
   2. closes the steam valve until the draw has ended
   3. holds the steam valve at a fixed opening
   4. opens the steam valve further as the water cools
   Show the answer

   D. Correct. The bulb's fill contracts as the incoming cold water cools it, and the valve opens further to admit more steam; as the water nears its set point the valve throttles back. The heat input follows the load and holds the stored water near its setting.

   Why not the others

   A. Locking in a position until someone resets it is how a limit or safety device behaves. The regulator opens in proportion to the temperature fall and closes back as the water recovers.

   B. Closing the steam valve on a draw would let the tank go cold just when demand is highest. The regulator responds to a falling water temperature by opening, not closing.

   C. A fixed opening would overheat the tank at light load and fall behind at heavy load. A self-acting regulator modulates: its opening changes with the water temperature it senses.

3. Recall · Describe storm water drainage systems for buildings

   In a city with separate sanitary and storm sewers, a plant's roof drains must be piped to the storm sewer, not to the sanitary sewer. Why?

   1. Rainwater passing through would wash the water out of the traps.
   2. Storm flows would overload the sanitary sewers and treatment plant.
   3. Storm sewers are vented to the roof, while sanitary sewers are not.
   4. Roof water would cool the sewage too much for it to be treated.
   Show the answer

   B. Correct. A heavy rain can deliver far more water than a building's fixtures normally do. Sanitary sewers and treatment plants are sized for sewage, so roof water in them can surcharge the pipes, back sewage into basements and force untreated overflows. The storm sewer takes rainwater, which needs little treatment, to a watercourse or a pond.

   Why not the others

   A. Trap seals are lost by siphonage, back-pressure or evaporation, not by clean rainwater passing through. The problem with roof water in the sanitary sewer is the volume it adds.

   C. Sanitary drainage is the system vented through the building's roof; venting has nothing to do with where roof water goes. The issue is the volume of storm flow.

   D. Temperature is not the reason; the problem is the sheer volume of storm water arriving all at once at sewers and a plant sized for sewage.

4. Procedural · Describe the general requirements and criteria for emergency lighting in buildings

   A boiler plant's standby generator takes up to 10 s to start and pick up the emergency lighting panel after a power failure. The chief engineer wants light at the boiler fronts and exits with no dark period at all. What provides it?

   1. Self-luminous exit signs mounted at each plant door
   2. LED luminaires fed from the generator's emergency panel
   3. Metal halide luminaires fed from the generator's panel
   4. Battery units that light on loss of normal power
   Show the answer

   D. Correct. A battery unit (or a central battery or inverter system) watches the normal supply and lights its lamps within a fraction of a second when it fails, so there is no wait for the engine. Many plants use both: batteries for the first moments and the generator for a long outage.

   Why not the others

   A. Self-luminous signs mark the exits but give almost no light to walk or work by; they do not light the boiler fronts.

   B. LEDs light the instant they get power, but on the generator panel they get none until the set has started and transferred, up to 10 s here.

   C. Metal halide lamps would wait for the generator and then take minutes to warm up, longer still if they were hot when the power dropped.

5. Recall · Describe the construction and operation of water system protective devices in buildings

   A large storage water heater in a school has a vacuum relief valve on its cold-water inlet piping above the tank. Its purpose is to

   1. let air in when a vacuum forms in the tank
   2. release water when the tank pressure rises too high
   3. absorb the expansion of the water as it heats
   4. vent air out of the tank while it is being filled
   Show the answer

   A. Correct. If the supply main loses pressure, or the tank is drained from below with the inlet shut, the falling water can pull a vacuum. That can siphon water out of the tank and can collapse a thin-walled or lined tank. The vacuum relief valve opens to atmosphere and breaks the vacuum.

   Why not the others

   B. Over-pressure (and over-temperature) relief is the job of the temperature and pressure relief valve. The vacuum relief valve works the other way, admitting air when the pressure falls below atmospheric.

   C. Thermal expansion is taken up by an expansion tank. The vacuum relief valve protects against pressure falling below atmospheric.

   D. Air is let out during filling through a fixture or a vent at the top; a vacuum relief valve is a one-way device that opens inward only when a vacuum forms.

02Answer key

03What unit B8 covers

The building systems around the plant: lighting equipment, light sources and controls, emergency lighting and the link between lighting and air conditioning, cold and hot water supply, water heaters and their protective devices, backflow prevention, maintenance of the water system, and sanitary and storm drainage and run-off.

Part B of the SOPEEC 4th Class syllabus names this unit “B8 Auxiliary Building Systems” and lists three objectives under it (objectives 33 to 35 of 52). SOPEEC does not publish how many exam questions come from each unit, and neither do the ABSA, Technical Safety BC, TSASK or TSSA pages we checked. The right-hand column is how many questions our bank holds on each objective, Standard and Advanced together, not a count from the exam.

04What the questions turn on

Illuminance is lumens over area

Average illuminance is the lumens that actually reach the floor, after fixture, room and dirt losses, divided by the floor area. Lighting in a cooled space is also cooling load, so cutting lighting power cuts the chiller's input too. Battery emergency lights cover the seconds before a standby generator picks up.

Pressure comes from height or from pumps

In a roof-tank downfeed system the pressure at a fixture comes from the height of water above it, about 9.8 kPa per metre, so the top floor is weakest. A hydropneumatic tank on a booster set meets small draws so the pumps do not start for each one.

Protective devices on the water system

A reduced-pressure backflow preventer that drips steadily from its relief port has a fouled check or relief valve and needs a qualified tester. A vacuum relief valve on a storage heater lets air in so the tank cannot be siphoned or collapsed.

Drains need vents and fall

Vents hold the air in the drains near atmospheric so trap seals are not siphoned or blown. A drain relaid almost level carries water but lets solids settle until it blocks. Roof drains go to the storm sewer, since storm flows would overload sanitary sewers.

05The other units

Paper 4B has twelve units, B1 to B12. Each has its own page of free questions:

The 4th Class Power Engineering practice exam (4B) page describes the full question bank; paper A has its own 4A practice exam. How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.