RME Board Exam flashcards

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

Ohm's law

Current through a conductor is directly proportional to voltage and inversely proportional to resistance, written V = I × R; it gives any one quantity when the other two are known.

Electric power formula

Power in a DC or purely resistive circuit equals voltage times current, P = V × I, and can also be written P = I²R or P = V²/R.

Series circuit resistance

In a series circuit the same current flows through every element and total resistance is the sum RT = R1 + R2 + R3 + …, so adding loads reduces current.

Parallel circuit resistance

In a parallel circuit voltage is equal across branches and the reciprocal of total resistance is the sum of reciprocals, 1/RT = 1/R1 + 1/R2 + …, giving a total below the smallest branch.

Kirchhoff's current law

At any junction the total current entering equals the total current leaving; the algebraic sum of currents at a node is zero.

Kirchhoff's voltage law

Around any closed loop the algebraic sum of all voltage rises and drops is zero, so source voltage equals the sum of the series voltage drops.

RMS value of sine wave

The root-mean-square value is 0.707 times the peak value of a sine wave; it is the effective value producing the same heating as an equal DC value.

Inductive reactance

Inductive reactance opposes alternating current and rises with frequency and inductance, XL = 2πfL, measured in ohms; it is zero at DC.

Capacitive reactance

Capacitive reactance opposes alternating current and falls as frequency or capacitance increases, XC = 1/(2πfC) in ohms; it is infinite at DC.

Series RLC impedance

Impedance is the vector sum of resistance and net reactance, Z = √(R² + (XL − XC)²) in ohms, and current equals voltage divided by Z.

Power factor

Power factor is the ratio of real power in watts to apparent power in volt-amperes, PF = cos θ = P/(V × I); it equals 1.0 for purely resistive loads.

Balanced three-phase power

Real power in a balanced three-phase system equals √3 times line voltage times line current times power factor, P = √3 × VL × IL × cos θ.

Transformer turns ratio

The voltage ratio equals the turns ratio and the inverse of the current ratio, V1/V2 = N1/N2 = I2/I1; ideal transformer input power equals output power.

One horsepower in watts

One mechanical horsepower equals 746 watts; motor input power in watts is output horsepower times 746 divided by efficiency.

Conductor resistance from dimensions

Resistance equals resistivity times length divided by cross-sectional area, R = ρL/A, so longer or thinner conductors have proportionally higher resistance.

Kilowatt-hour energy

Energy in kilowatt-hours equals power in kilowatts multiplied by time in hours; a 2 kW load running 3 hours consumes 6 kWh.

PEC code basis

The Philippine Electrical Code is the Philippine adaptation of NFPA 70, the National Electrical Code, with local amendments; Philippine supply is 60 Hz, nominally 230 V line-to-neutral and 400 V three-phase.

Small conductor overcurrent limits

Unless a specific article permits otherwise, overcurrent devices must not exceed 15 A for 14 AWG copper, 20 A for 12 AWG, and 30 A for 10 AWG conductors.

Continuous load overcurrent sizing

The overcurrent device must be at least 125% of the continuous load current plus 100% of the noncontinuous load current, using the next standard rating.

Voltage drop limits

Branch-circuit conductors are sized so drop does not exceed 3% of supply voltage, and feeder plus branch drop does not exceed 5% at the load.

Working space depth

Clear depth in front of live equipment is 600 mm for Condition 1, 900 mm for Condition 2, and 1000 mm for Condition 3, with 2.0 m headroom.

Dwelling receptacle spacing rule

In dwelling units no point along the floor line of a wall space may be more than 600 mm from a receptacle outlet, and wall spaces 600 mm or wider require one.

GFCI required locations

Ground-fault circuit-interrupter protection is required for receptacles in bathrooms, garages, outdoors, kitchens, laundry areas, basements, crawl spaces, and near sinks.

Conduit fill percentages

Raceway fill limits are 53% for one conductor, 31% for two conductors, and 40% for three or more conductors, taken from the Chapter 9 tables.

Box fill per conductor

Each 14 AWG conductor counts 2.0 cubic inches, 12 AWG counts 2.25, and 10 AWG counts 2.5; clamps, devices, and grounding conductors add allowances.

Ground rod minimum size

A rod-type grounding electrode must be at least 2.44 m (8 ft) long and 16 mm (5/8 in) in diameter, and must be driven to full depth.

Supplemental grounding electrode rule

A single rod, pipe, or plate electrode must be supplemented by an additional electrode unless it demonstrates 25 ohms or less resistance to earth.

Standard overcurrent device ratings

Standard fuse and breaker ratings include 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, and 200 amperes.

Service disconnect location

The service disconnecting means must be at a readily accessible location, installed outside the building or inside nearest the point of entry of the service conductors.

Ampacity table application

Conductor ampacity is taken from Table 310.16, then corrected for ambient temperature and adjusted for more than three current-carrying conductors in a raceway or cable.

Residential branch circuit burial depth

Residential branch circuits of 120 V or less and 20 A or less with GFCI protection need 450 mm (18 in) burial; other direct-buried cables require 600 mm (24 in).

Equipment grounding conductor sizing

The equipment grounding conductor is sized from Table 250.122 using the rating of the overcurrent device protecting the circuit, not the circuit conductor ampacity.