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newSchoolWorks.com › VoTechWorks › Building & Construction › Elevator Mechanic (pre-apprentice) › Elevator Controls: Circuits, Controllers, and Signal Systems › Lesson 1
BLD-ELEV10-04 · Lesson 1 · 12 clock hours · theory

Electrical Fundamentals and Control Vocabulary for Elevator Systems

Objective. Students will explain Ohm's Law, series and parallel circuit behavior, and the meaning of at least 20 standard elevator control schematic symbols accurately enough to pass a written symbol-identification quiz at 80% or higher.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed professional engineer or master tradesperson or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

Why Electrical Fundamentals Matter in the Elevator Machine Room

Every elevator system—traction, hydraulic, or MRL—depends on electrical circuits to move the car, hold it level, open doors, and protect passengers. Before you can read a controller schematic, troubleshoot a fault, or pass either the NEIEP/IUEC entry assessment or the NAEC CET exam, you must have a solid grip on the basic electrical quantities and the symbols used to represent them on drawings. This lesson builds that foundation.

Voltage, Current, Resistance, and Power

Voltage (V) is electrical pressure—the force that pushes electrons through a conductor. It is measured in volts (V). In an elevator machine room you will encounter several voltage levels: low-voltage control circuits (commonly 24 V DC or 115 V AC), single-phase 120/240 V AC for lighting and outlets, and three-phase 208 V, 240 V, or 480 V AC for the hoisting motor.

Current (I) is the rate of electron flow, measured in amperes (A). A large hoisting motor draws many amperes; a small relay coil may draw only milliamperes.

Resistance (R) opposes current flow and is measured in ohms (Ω). Conductors, contacts, coils, and resistors all have resistance. Poor connections add unwanted resistance and create heat—a common cause of elevator faults.

Power (P) is the rate of doing work, measured in watts (W). In DC circuits, P = V × I. In AC circuits, true power also depends on the power factor, but for pre-apprentice work the basic formula is your starting point.

Ohm's Law

Ohm's Law states the relationship among voltage, current, and resistance:

If you know any two quantities you can find the third. This is the tool you will use every day to check coil voltages, calculate expected current draw, and verify that a circuit is behaving correctly.

Series and Parallel Circuits

Series circuits have only one path for current. All components share the same current; voltage is divided among them. Total resistance equals the sum of all individual resistances (R_total = R1 + R2 + R3 …). If any component opens (breaks), the entire circuit stops. Elevator safety strings—chains of normally-closed safety contacts—are wired in series. One open contact removes power from the entire safety circuit.

Parallel circuits provide multiple paths for current. Each branch has the same voltage across it; current divides among branches. Total resistance is less than the smallest individual resistance. If one branch opens, others continue to carry current. Door operator circuits and lighting circuits in a car are typical parallel arrangements.

Most real elevator control circuits are series-parallel combinations: safety contacts in series feeding a parallel arrangement of relay coils, for example.

AC vs. DC and Single-Phase vs. Three-Phase

Direct current (DC) flows in one direction only. Elevator control logic, microprocessor boards, and many signal circuits use DC—often 12 V, 24 V, or 48 V—because it is stable and easy to regulate.

Alternating current (AC) reverses direction periodically at the supply frequency (60 Hz in the United States). AC is used for power distribution because it is efficient to transform to different voltages.

Single-phase AC uses two conductors (plus ground). It supplies lighting, convenience outlets, and small motors in the machine room.

Three-phase AC uses three conductors and is required for the large induction motors that drive traction elevators. Three-phase power is smoother and more efficient than single-phase for heavy motor loads. Losing one phase (a condition called single-phasing) can damage a motor; phase-monitoring relays protect against this.

Standard Elevator Control Schematic Symbols You Must Know

Schematic drawings use standardized symbols so that any qualified mechanic can read any drawing. The following are among the most common you will encounter:

Study these with your card set until recognition is instant.

Safety Points

Before working near any elevator controller or wiring, lockout/tagout (LOTO) procedures must be followed in accordance with OSHA requirements and the authority having jurisdiction. Verify that all energy sources—electrical, hydraulic, and gravitational—are isolated and dissipated before touching circuits. Always wear appropriate PPE: safety glasses and insulated gloves rated for the voltage level present. Never assume a circuit is de-energized; use a calibrated meter to verify. NFPA 70 (National Electrical Code) sets minimum wiring standards that apply throughout the machine room. Know the voltage levels present before you probe any terminal.

Key terms8

Ohm's LawThe mathematical relationship V = I × R, stating that voltage equals current multiplied by resistance; used to find any one of the three quantities when the other two are known.
Series circuitA circuit with only one path for current; all components share the same current, and an open in any component breaks the entire circuit—the basis of elevator safety strings.
Parallel circuitA circuit with multiple current paths; each branch shares the same voltage, and an open in one branch does not interrupt the others.
Normally open (NO) contactA switch or relay contact that is open (no current flows) in its rest (de-energized) state and closes when actuated.
Normally closed (NC) contactA contact that is closed (current flows) in its rest state and opens when actuated; used extensively in elevator safety circuits.
Three-phase ACAn alternating-current supply using three conductors whose voltages are offset by 120 degrees; required for large elevator hoisting motors because of its efficiency and smooth power delivery.
Lockout/Tagout (LOTO)A federally required safety procedure for isolating and securing all energy sources before performing maintenance or inspection on equipment, preventing unexpected energization.
Schematic symbolA standardized graphical representation of an electrical component used on wiring and control diagrams so that any qualified technician can interpret the drawing.

Worked examples4

1. A relay coil in an elevator control circuit has a resistance of 240 Ω and is connected across a 24 V DC supply. What current flows through the coil?
  1. Identify the known values: V = 24 V, R = 240 Ω.
  2. Select the correct form of Ohm's Law to find current: I = V / R.
  3. Substitute: I = 24 / 240.
  4. Calculate: I = 0.1 A (100 mA).
Answer: I = 0.1 A (100 milliamperes)
2. A door operator circuit runs on 115 V AC. You measure 2.3 A of current flowing to the operator motor. What is the effective resistance of the motor at that operating point?
  1. Identify known values: V = 115 V, I = 2.3 A.
  2. Select the form of Ohm's Law for resistance: R = V / I.
  3. Substitute: R = 115 / 2.3.
  4. Calculate: R = 50 Ω.
Answer: R = 50 Ω
3. Three safety-string resistors are wired in series: R1 = 10 Ω, R2 = 15 Ω, R3 = 25 Ω. The supply is 48 V DC. Find total resistance and total current.
  1. For a series circuit, R_total = R1 + R2 + R3 = 10 + 15 + 25 = 50 Ω.
  2. Apply Ohm's Law for current: I = V / R_total = 48 / 50.
  3. Calculate: I = 0.96 A.
Answer: R_total = 50 Ω; I = 0.96 A
4. Two parallel branch resistors represent two indicator lamps in an elevator car: R1 = 120 Ω and R2 = 120 Ω, both connected across 24 V DC. Find the current through each branch and total current drawn from the supply.
  1. In a parallel circuit each branch sees the full supply voltage: V = 24 V for both branches.
  2. Current in branch 1: I1 = 24 / 120 = 0.2 A.
  3. Current in branch 2: I2 = 24 / 120 = 0.2 A.
  4. Total current: I_total = I1 + I2 = 0.2 + 0.2 = 0.4 A.
Answer: I1 = 0.2 A, I2 = 0.2 A, I_total = 0.4 A

The math in this lesson2

Learners compute total resistance and current for series and parallel control circuits.
A-SSE.1A-CED.4
Brush up in the math halls at newSchoolWorks.com:
In class: Instructor-led lecture using NEIEP Module 1 and NFPA 70 reference materials; students take guided notes on voltage, current, resistance, power, AC vs. DC, and single-phase vs. three-phase supply as they apply to elevator machine rooms. · Symbol-matching card sort: each student receives a set of 30 cards (one side shows the schematic symbol, the other shows the component name) and practices until they can match all 30 without error; pairs quiz each other and record scores. · Short written exercises: students redraw three simple series-parallel circuits from written descriptions, calculate missing values using Ohm's Law, and label each component with its correct schematic symbol before exchanging papers for peer review.
Materials: NEIEP Electrical and Controls curriculum materials, NFPA 70 (National Electrical Code) reference copy, whiteboard/projector, schematic symbol card sets, graph paper, scientific calculators
Check: Symbol-identification quiz of 25 items (multiple-choice and matching) plus three Ohm's Law calculation problems; pass = 80% combined score; instructor reviews any missed symbols individually before next lesson.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Electrical theory and calculations
1. A control circuit has a voltage of 120 V and a resistance of 60 Ω. What is the current in the circuit?
Elevator safety systems and circuit theory
2. In an elevator safety circuit, six normally closed contacts are wired in series. What happens when any one of those contacts opens?
Schematic symbol identification
3. Which schematic symbol represents a normally open pushbutton?
Electrical power systems
4. What is the primary reason large elevator hoisting motors use three-phase AC power rather than single-phase AC?
Schematic symbol identification
5. On an elevator controller schematic, you see a solid dot where two conductor lines cross. What does the dot indicate?
Safety and LOTO procedures
6. Before probing any terminal in an elevator machine room controller, which action is required first?
Electrical theory and calculations
7. Two resistors, 30 Ω and 60 Ω, are connected in parallel across a 120 V supply. What is the current through the 30 Ω resistor?
Schematic symbol identification
8. A schematic shows a circle with an X drawn inside it connected to a control line. This symbol most likely represents which component?
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