Mixed Deck — All 309A Topics Flashcards

What type of cable is designated TECK90 used for in Canadian electrical installations?

Answer: Exposed industrial wiring in wet or dry locations

TECK90 cable is an armoured cable widely used in Canadian industrial installations. It can be used in wet or dry locations, exposed or concealed, and its interlocking armour provides mechanical protection.

What is the maximum ambient temperature rating for standard NMD90 cable insulation?

Answer: 90°C

NMD90 cable insulation is rated for a maximum temperature of 90°C, as indicated by the '90' in its designation. However, ampacity is typically limited to 60°C terminal ratings.

What does a motor's nameplate 'code letter' indicate?

Answer: The locked-rotor kVA per horsepower

The NEMA code letter on a motor nameplate indicates the locked-rotor kVA per horsepower, which determines the inrush current when the motor starts. Higher code letters indicate higher inrush.

According to the CEC, what is the minimum size of a copper grounding electrode conductor for a 100 A service?

Answer: No. 6 AWG

CEC Table 17 specifies a minimum No. 6 AWG copper grounding electrode conductor for services up to 100 A, ensuring adequate capacity to carry fault current to the grounding electrode.

What is the maximum permitted ground resistance for a single ground rod according to the CEC?

Answer: 25 Ω

CEC Rule 10-702 requires a maximum ground resistance of 25 Ω for a single grounding electrode. If this cannot be achieved, additional electrodes must be installed.

According to CEC Rule 26-710, what type of receptacle is required in a bathroom within 1 m of a sink?

Answer: Ground fault circuit interrupter (GFCI) protected receptacle

CEC Rule 26-710 mandates GFCI protection for receptacles installed within 1.5 m of sinks and in bathrooms to protect against electric shock in wet locations.

When installing conductors in a vertical raceway, at what height intervals must they be supported?

Answer: According to CEC Table 12-18 based on conductor size

CEC Table 12-18 specifies support intervals for conductors in vertical raceways based on conductor size. Larger conductors require more frequent support due to their greater weight.

What type of raceway is most suitable for a corrosive chemical processing environment?

Answer: PVC conduit (Schedule 40)

PVC conduit is highly resistant to chemical corrosion and is the preferred raceway material in corrosive environments such as chemical processing plants.

What is the purpose of a reduced-voltage autotransformer (RVAT) motor starter?

Answer: To reduce starting current by applying reduced voltage through an autotransformer

An RVAT starter uses an autotransformer to apply reduced voltage (typically 65%, 80%, or 100% taps) during starting, reducing inrush current proportionally while maintaining higher torque than resistor starters.

What happens to current flow when the resistance in a circuit is doubled while voltage remains constant?

Answer: Current is halved

According to Ohm's Law (I = V/R), if resistance doubles and voltage stays constant, current is reduced by half. Current and resistance are inversely proportional.

What is the capacitive reactance of a 50 µF capacitor at 60 Hz?

Answer: 53.05 Ω

Capacitive reactance XC = 1/(2πfC) = 1/(2 × 3.14159 × 60 × 0.00005) = 1/0.01885 = 53.05 Ω.

A 75 kVA, 480/120 V single-phase transformer has what full-load secondary current?

Answer: 625 A

Secondary current = kVA × 1000 / V secondary = 75,000 / 120 = 625 A. The lower the secondary voltage, the higher the current for the same kVA rating.

What does a PLC (Programmable Logic Controller) replace in a modern motor control system?

Answer: Hardwired relay logic and timing circuits

PLCs replace hardwired relay logic, timers, and counters with programmable software, offering greater flexibility, easier troubleshooting, and the ability to modify control sequences without rewiring.

What type of motor protection device uses a bimetallic element that bends when heated?

Answer: Thermal overload relay

Thermal overload relays use a bimetallic strip that bends when heated by motor current. When the current exceeds the set point for a sufficient time, the bending trips the relay contacts.

According to the CEC, what is the minimum bonding conductor size for a circuit protected by a 60 A breaker?

Answer: No. 10 AWG

CEC Table 16 specifies the minimum bonding conductor size based on the overcurrent device rating. For a 60 A circuit, a No. 10 AWG copper bonding conductor is required.

What is the purpose of a cable tray system in a commercial or industrial installation?

Answer: To support and route cables in an open, accessible manner

Cable tray systems provide an open, accessible method of supporting and routing power, control, and communication cables in commercial and industrial buildings, allowing easy maintenance and additions.

What is the CEC requirement for tamper-resistant receptacles in dwelling units?

Answer: Required for all 15 A and 20 A receptacles

The CEC requires tamper-resistant receptacles for all 15 A and 20 A, 125 V receptacles in dwelling units to protect children from inserting objects into receptacle slots.

What test is performed on a transformer to determine its core losses (iron losses)?

Answer: Open-circuit test

The open-circuit (no-load) test is performed with the secondary open and rated voltage applied to the primary. The measured power represents core losses (hysteresis and eddy current losses).

What is the primary purpose of a Ground Fault Circuit Interrupter (GFCI)?

Answer: Protecting people from electric shock caused by ground faults

A GFCI detects ground fault currents as low as 4–6 mA and quickly opens the circuit to prevent lethal electric shock.

What is the purpose of paralleling transformers in a distribution system?

Answer: To increase capacity and provide redundancy

Paralleling transformers increases the total available capacity of the system and provides redundancy — if one transformer fails, the other(s) can continue to supply the load at reduced capacity.