Red Seal Industrial Electrician flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Test-before-touch procedure

Confirm the voltage tester on a known live source, test the isolated conductor, then re-test the source; a single zero reading does not prove the circuit is de-energized.

Arc flash boundary

The distance at which a person without arc-rated protective equipment would receive second-degree burns, defined as an incident energy of 1.2 cal/cm².

Class A GFCI trip level

Personnel-protection ground-fault circuit interrupters trip at 5 mA plus or minus 1 mA and must be tested before each use on construction sites.

Rule 8-104 continuous load

Continuous loads are limited to 80% of the rating of the conductor or overcurrent device unless the assembly is approved for 100% loading.

Rule 8-102 voltage drop

The maximum permitted voltage drop is 3% on a branch circuit and 5% total measured from the service entrance to the load.

Table 16 bonding conductor

Used to size the bonding conductor from the ampere rating of the overcurrent device protecting the circuit, expressed in square millimetres or AWG.

Three-phase power formula

Real power equals the square root of three times line voltage times line current times power factor for a balanced three-phase load.

Inductive reactance formula

Reactance in ohms equals two pi times frequency in hertz times inductance in henries; it rises with frequency and opposes changes in current.

Transformer turns ratio

Primary voltage divided by secondary voltage equals primary turns divided by secondary turns, and the current ratio is the inverse of that value.

Capacitor power factor correction

The required capacitive kVAR equals real power P times the difference between the tangents of the original and target power-factor angles.

Conduit fill percentage

A raceway may be filled to 53% of its interior area with one conductor, 31% with two conductors, and 40% with three or more.

360-degree bend rule

No more than four quarter bends, totaling 360 degrees, are permitted between pull points in a single raceway run.

TECK90 cable use

Armoured cable with a moisture-resistant jacket, approved for dry, damp, and wet locations and for direct burial where so listed.

Percent impedance and fault current

Bolted fault current equals full-load current divided by the per-unit impedance, so a 5% transformer delivers about 20 times rated current.

Transformer inrush current

Energizing a transformer can draw 8 to 12 times rated current for several cycles, so time-delay overcurrent protection is normally used.

Delta-wye phase shift

A delta primary with a wye secondary shifts the secondary voltage by 30 electrical degrees relative to the primary voltage.

Synchronous speed calculation

Synchronous speed in rpm equals 120 times frequency in hertz divided by the number of poles; 60 Hz with four poles gives 1800 rpm.

Motor slip percentage

Slip equals synchronous speed minus rotor speed, divided by synchronous speed and multiplied by 100; rotor frequency equals slip times line frequency.

Motor overload sizing

Overload protection is normally set at 115% to 125% of nameplate full-load current, the exact value depending on service factor and temperature rise.

Overload relay class

The class number is the maximum trip time in seconds at six times rated current: Class 10 for standard loads, Class 20 or 30 for high inertia.

Wye-delta starting torque

Wye-delta starting applies 58% of line voltage to each winding during start and delivers one third of direct-on-line starting torque.

VFD volts per hertz

Below base speed a drive holds voltage proportional to frequency to keep motor flux, and therefore available torque, essentially constant.

PLC scan cycle

The processor reads input status, executes the ladder program from top to bottom, then updates outputs; the total elapsed time is the scan time.

Sourcing versus sinking input

A sourcing PNP sensor supplies positive voltage to the input terminal, while a sinking NPN sensor switches the input terminal down to common.

Retentive timer instruction

An RTO accumulates time while its rung is true and retains that accumulated value when the rung goes false, until a reset is executed.

Live-zero 4-20 mA signal

4 mA represents 0% of span and 20 mA represents 100%; a reading of 0 mA indicates an open loop or a lost supply.

Pt100 RTD resistance

A platinum resistance detector reads 100 ohms at 0 degrees Celsius and rises about 0.385 ohms per degree Celsius, giving a nearly linear output.

Thermocouple cold junction

The reference junction temperature must be measured and compensated because the output voltage depends on the difference between hot and cold junctions.

RS-485 termination resistor

A 120 ohm resistor is placed across each physical end of the bus to prevent signal reflections; the bus supports up to 32 unit loads.

Online double-conversion UPS

The load runs continuously from the inverter, so transfer to battery is immediate and the output is isolated from input sags and transients.

Inverting amplifier gain

Voltage gain equals the negative of feedback resistance divided by input resistance; the minus sign indicates a 180 degree phase inversion.

Diode bridge ripple frequency

A full-wave bridge rectifier fed from a 60 Hz supply produces 120 Hz ripple, which a filter capacitor smooths into a steadier DC voltage.