In a wye system, the line-to-line voltage is the phase voltage multiplied by √3. This comes from the geometry of three vectors 120° apart. If phase-to-neutral is 120V, line-to-line is 120 × 1.732 = 208V.
208V. This is a wye system where the phase-to-neutral voltage is 120V. The line-to-line voltage is 120 × 1.732 (√3) = 208V.
480V between phases (277V phase-to-neutral in a wye configuration). Common for commercial and industrial motor loads.
You can't easily — use a hand bender. Place the arrow at the mark, put your foot on the footrest, and pull up while maintaining downward pressure. The goal is a smooth 90° with no kinks or wrinkles.
AC (alternating current) reverses direction 60 times per second in North America. DC (direct current) flows in one direction only. AC is used for power distribution because it can be transformed to different voltages easily. Batteries and electronics run on DC.
An Arc Fault Circuit Interrupter detects the electrical signature of arcing — caused by damaged wire insulation, loose connections, or staples through cables. Regular breakers can't detect these; they only trip on sustained overcurrent, by which point a fire may have already started.
Aluminum is much less expensive and lighter than copper. At large sizes (1/0 and above), the cost difference is significant. The tradeoff is that aluminum requires larger conductors for the same ampacity and needs antioxidant compound on connections.
The maximum current a conductor can carry continuously without exceeding its temperature rating. Exceed it and the insulation breaks down.
Aluminum oxidizes when exposed to air, forming a layer of aluminum oxide which is a poor conductor. Antioxidant paste inhibits this oxidation and helps maintain a good electrical connection.
An electrical apprentice who learns to install, maintain, and repair electrical systems under the direct supervision of a licensed journeyman or master electrician. The core duties include assisting with installations, reading blueprints, maintaining safety, and helping diagnose electrical issues under supervision.
An arc flash is a violent release of energy from an electrical arc — it produces a fireball of superheated plasma, intense light, pressure waves, and molten metal. It can cause severe burns or death even without direct contact.
An engineering study that determines the incident energy at each piece of equipment so that the correct PPE can be selected. The results are posted on equipment labels. Required by NFPA 70E before working on energized equipment.
The maximum current that would flow in a dead short at a given point in the electrical system. It's determined by the utility transformer size, conductor impedance, and system configuration. Highest at the service entrance, decreasing downstream.
American Wire Gauge. The larger the AWG number, the smaller the wire. 14 AWG is smaller than 10 AWG. Above 4/0 (0000), wire is sized in kcmil (thousand circular mils) and gets bigger as the number increases.
When a motor spins, its rotating conductors generate a voltage that opposes the supply voltage (back electromotive force). This limits running current. When a motor first starts or is stalled, back-EMF is zero, so inrush current is very high.
To bring conduit over an obstruction — two 45° bends facing each other with a straight section between them, forming a U shape that rises over and comes back down on the other side of whatever is in the way.
Equal loads on all three phases. This minimizes neutral current, reduces losses, and keeps voltage stable. Large systems try to keep loads balanced for efficiency.
Bonding means connecting all metal parts of a system together so they're at the same voltage potential. This prevents a voltage difference between metal surfaces that could shock someone who touches two things at once.
Water pipes can become energized if a fault occurs in equipment connected to them. Bonding them to the electrical system ensures they remain at the same potential as all other grounded metal — so touching two metal surfaces doesn't shock you. If present, metal water pipes are required to be included in the grounding electrode system.
Briefly energize it for a second to check the direction of rotation before full startup. Allows you to correct rotation by swapping leads if needed without running equipment backwards.
A rigid conductor (copper or aluminum bar) used in panels, switchgear, and busways to distribute power. More efficient than wire for high-current applications.
A prefabricated metal duct containing copper or aluminum busbars. Used for high-current distribution where running large conductors in conduit would be impractical. Common in industrial facilities and large commercial buildings.
A U-shaped staple that secures cable to wood framing. Never drive a staple so tight it deforms or cuts into the cable jacket — this can damage insulation and cause faults.
An open support system — like a ladder or mesh tray — that runs cables in commercial or industrial settings. Unlike conduit, cables lie in open trays and can be accessed without pulling through a pipe. Requires cables listed for cable tray use.
Used to correct power factor where high inductive loads are present. Capacitors provide reactive power locally, reducing the reactive current that has to flow from the utility, which reduces losses and can lower utility demand charges.
A single-phase motor that uses a capacitor in series with a start winding to create the phase shift needed to produce a starting torque. The capacitor and start winding are disconnected by a centrifugal switch once the motor reaches running speed.
Long wire runs, undersized wire, high current loads, or high resistance connections. Fix it by using larger wire or reducing the run length.
It's an automatic switch that opens (trips) when current exceeds its rating, protecting the wiring from overheating. It protects the wire, not the equipment. Reset manually after the cause is corrected.
So that the right circuit can be de-energized for maintenance, others aren't accidentally turned off, and the system can be understood by anyone working on it. Poor labeling is a safety hazard.
A clamp meter measures current by clamping around a single conductor. The changing magnetic field from current flow is detected without breaking the circuit. Use it to check motor current, verify circuit loading, or troubleshoot imbalances.
A series of concentric rings in an electrical enclosure that can be removed to create different hole sizes — without a knockout punch, by using a hammer and screwdriver to knock out the rings.
When multiple current-carrying conductors are bundled together, they generate heat that can't dissipate as easily. We derate (reduce) the allowable ampacity to prevent insulation damage.
The maximum temperature the insulation can withstand without degrading. Using a conductor in an environment hotter than its rating will break down the insulation, creating a shock and fire hazard.
Unsupported conduit can sag, stress fittings, and pull connections loose. Unsupported cable can be physically damaged. Support spacing requirements ensure the installation remains stable long-term.
A hand tool used to bend conduit. Has an arrow, star, and degree markings. The arrow is used for stub-up bends (mark where the end of the 90 will be), the star is used for back-to-back bends.
A fitting that provides access to conductors in a conduit run for pulling and splicing. Common types: LB (90° with cover at the back), LL (left 90°), LR (right 90°), C (straight through), T (tee).
Conduit fill is how much of the conduit's interior space is taken up by conductors. Overfilling makes pulling impossible and generates excess heat since conductors can't dissipate heat properly.
The path from one pull point to another, including all the conduit sections, fittings, and bends in between. Planned before installation to minimize bends and make wire pulling as easy as possible.
EMT must be supported within 3 feet of every box or fitting and at least every 10 feet along the run. Exact spacing varies by conduit type.
Continuity testing checks if a complete path exists between two points. A continuous path (low resistance) means the conductor is unbroken. Open circuit means the path is broken somewhere.
The flow of electrons through a conductor, measured in amps. Like the flow rate of water in a pipe.
Current decreases. More resistance restricts the flow of electrons, just like a smaller pipe restricts water flow.
A fuse that clears a fault so quickly it limits the let-through current. Used in high fault-current applications where the let-through current could damage equipment even before a regular breaker opens.
The primary is connected in a delta (triangle) configuration and the secondary in a wye (star). This is the most common utility and commercial transformer configuration because it provides a neutral on the secondary for 120V loads while blocking some harmonics.
A utility billing charge based on the peak power demand during a billing period, not just total energy used. A brief high demand event can significantly increase a bill. Industrial facilities manage this carefully.
Reducing the allowable ampacity of a conductor when conditions cause excess heat — such as high ambient temperature, conduit fill with multiple conductors, or installing in a hot location. Look up the correction factors in the ampacity tables.
A dimmer reduces voltage to a light to reduce brightness. Must be matched to the load type — incandescent dimmers don't work on LED or fluorescent fixtures. Use LED-compatible dimmers for LED lighting.
A switch that de-energizes equipment so it can be safely worked on. Motors and equipment must have a disconnecting means within sight of the equipment. Some are fusible (contain fuses) for additional protection.
Check for electrical, plumbing, and structural elements with a stud finder, wire tracer, and inspection. Drilling through a live wire creates a shock hazard and a potential fire.
The service conductors loop below the weatherhead attachment point before rising in. Water runs off the loop and drips away rather than following the wire into the conduit.
A transformer cooled by air circulation rather than oil. Common in buildings because they don't pose a fire or spill risk. The core and windings are exposed to air.
Has two elements: one that blows instantly on short circuits and one that delays on moderate overcurrents. Allows motor inrush to pass without blowing while still protecting against overloads and faults.
A safety mechanism that prevents two things from happening simultaneously — like two sources from being connected at the same time, or a motor from running without a safety guard in place.
The EGC is the green or bare (typically copper) wire in a circuit. It connects metal parts of equipment back to the panel so that if a live wire touches metal, fault current flows back and quickly trips the breaker instead of energizing the enclosure and shocking someone.
Connecting all metal surfaces in an area so they're all at the same voltage. Critical in wet areas like pools and bathrooms where contact with multiple surfaces is likely. Prevents voltage differences from causing shock.
De-energize the circuit. Use an ohmmeter between hot and neutral (or ground). A reading close to zero ohms confirms a short. Then isolate sections of the circuit to narrow down the location.
Use a voltmeter. Start at the panel where you have voltage. Work downstream, testing at each point. The point where voltage disappears is beyond the break. Or use a continuity tester on a de-energized circuit to find the open.
A stiff flat metal or fiberglass tape coiled in a reel, used to route through walls, conduit, or ceiling spaces to pull wire. Sent through first, then wire is attached to the hook on the end and pulled back.
Usually a loose connection somewhere — at the fixture, switch, outlet, or panel. Could also be a utility problem (transformer issue) or an overloaded circuit causing voltage drop. Investigate by checking all connections in the circuit.
A neutral that's lost its connection to ground, causing the neutral point to shift. In a 3-phase system, this causes voltage unbalance across phases. Dangerous and must be repaired immediately.
Used to control a light from three or more locations. Goes between two three-way switches. It has four terminals and swaps the traveler connections each time it's toggled.
A fused disconnect contains fuses for overcurrent protection. An unfused disconnect simply breaks the circuit. Fused disconnects are common on motors and equipment where overcurrent protection is needed.
A transfer switch disconnects the building from utility power before connecting the generator. Without one, backfeed from the generator can energize the utility lines and electrocute utility workers.
A Ground Fault Circuit Interrupter monitors the difference in current between hot and neutral. If more than ~5 milliamps flows where it shouldn't (a ground fault path), it trips in 1/40th of a second — fast enough to prevent electrocution.
A GFCI receptacle protects only itself and any outlets connected downstream. A GFCI breaker protects every outlet and device on that entire circuit.
Flexible Metal Conduit — a spiral metal armor without conductors. Used for final connections to motors and equipment where vibration isolation or movement is needed.
When a hot conductor contacts a grounded metal surface or the earth — current takes an unintended path to back to its source. This can energize equipment enclosures and create a shock or fire hazard.
A conductive object embedded in the earth that provides the connection between the electrical system and earth ground. Examples: ground rods, water pipes, concrete-encased electrodes (Ufer grounds).
Harmonics are currents and voltages at multiples of 60 Hz (120 Hz, 180 Hz, etc.) created by non-linear loads like computers and drives. They cause neutral conductors to overheat (even in balanced systems), overheat transformers, cause motor vibration, and interfere with equipment.
A connection that's loose, corroded, or improperly made. It creates resistance at that point, generating heat under load. Left unchecked, it can melt insulation, start fires, or fail completely.
The main bus bars in a panel are always live unless the utility has disconnected power — the main breaker only controls what comes after it. Working near the service entrance of a panel means working near always-energized conductors.
Use an infrared thermometer or thermal camera under load — hot spots glow relative to surrounding material. Also look for discoloration, melted plastic, or burned insulation.
The total opposition to current flow in an AC circuit, including both resistance and reactance (from inductors and capacitors). Measured in ohms.
Using a thermal camera to scan electrical equipment under load and identify hot spots from loose connections, overloaded circuits, or failing components. Done as part of preventive maintenance — finds problems before they become failures.
The large spike of current a motor or transformer draws when it first starts up, before it reaches operating speed. Can be 6–10x the normal running current. This is why breakers are sized larger than the motor's running current.
The maximum fault current a breaker or fuse can safely interrupt. If the available fault current exceeds the AIC rating, the device may explode or fail to clear the fault safely. Must be matched to the available fault current at that point in the system.
A breaker that trips faster as the overcurrent increases. Small overcurrents require more time to trip; large overcurrents trip nearly instantly. This allows normal inrush currents to pass without nuisance tripping while still protecting against faults.
It must be in place and accessible. An open junction box is a shock hazard. A buried or painted-over box is a code violation — you must be able to access all splices.
Creates clean round holes in electrical enclosures for conduit fittings. A punch and die are threaded together through a pilot hole, and a wrench or hydraulic unit draws them together to cut a clean hole.
Liquidtight Flexible Metal Conduit — like FMC but with a plastic jacket for use in wet locations and outdoors. Common for final connections to outdoor equipment, compressors, and machines.
Heavy-duty pliers with a cutting edge and flat gripping faces. Used to cut, pull, and twist wire — a core tool of every electrician. The flat jaws twist wire nuts and the cutters handle large conductors.
A device that generates a controlled electrical load, used to test generators and UPS systems under realistic load conditions without using actual building loads.
Essentially the same thing — load center is the residential term, panelboard is commercial. Panelboards are typically more robust and handle higher loads.
Selectively turning off non-critical loads during high demand or emergencies to reduce total electrical load. Used in large facilities to prevent exceeding demand limits or during generator operation.
The high current a motor draws when it's energized but not yet spinning — the rotor is 'locked.' It can be 6–10x the full load current. Normal starting condition, but sustained locked rotor current will destroy a motor.
The connection between the neutral and the grounding electrode system at the main service panel. It's what ties together the neutral conductor, equipment grounds, and earth connection. Only installed at the service equipment.
It's the single disconnect for the entire panel — turns off all branch circuits at once. Also provides overcurrent protection for the panel's main bus.
Strip the conductor ends to the correct length, connect them to the device terminals properly, fold the conductors neatly, and seat the device into the box without pinching wires.
Metal-clad cable — conductors in a flexible metal armor. More durable than NM, used where physical protection is needed. The metal armor can serve as the equipment ground in some types.
Resistance is the opposition to current flow. MUST be measured with the circuit de-energized. Place the ohmmeter probes across the component or conductor being tested.
Voltage is the electrical pressure between two points. Measure it with a voltmeter set to the correct range: place one probe on each point and read the result. Always measure voltage in parallel — never in series.
Tests insulation resistance of cables and motor windings by applying high voltage (500–5000V) and measuring resistance in megohms. Low insulation resistance indicates damaged or wet insulation. Critical for commissioning motors and troubleshooting cable failures.
Metal is conductive — if the ladder contacts an energized conductor or you contact a live part while on a metal ladder, the ladder becomes a conductor to ground. Always use fiberglass ladders when working near electricity.
The utility-owned enclosure that houses the kilowatt-hour meter. The electrician installs it per utility specifications; the utility installs the meter. Power flows from utility through the meter to the service equipment.
A heavy-duty relay designed to switch motor loads. It uses a small control voltage to energize a coil, which magnetically closes the main power contacts. Contactors handle the high inrush current of motors without burning up.
A rack of motor starter cubicles in a central enclosure. Each cubicle contains a contactor, overloads, and disconnect for one motor. Allows centralized control and maintenance of many motors.
Applying high DC voltage between each winding and the motor frame to test insulation resistance. Low readings (below 1 megohm) indicate degraded insulation that may fail in service. Used to evaluate motors before installation and as part of maintenance.
The amp rating marked on the motor nameplate — the current the motor draws at rated voltage when delivering rated horsepower continuously. Used to set overload protection.
Overloading, high ambient temperature, poor ventilation, single-phasing, voltage unbalance, low voltage, excessive starts per hour, or dirty windings that can't dissipate heat.
A circuit breaker protects the wiring from overcurrent. Overload protection protects the motor from sustained overcurrent that would cause overheating. The breaker responds to shorts and large faults; the overload responds to sustained loads that exceed the motor's rating.
Overloading, high ambient temperature, low or high voltage, voltage unbalance, single-phasing, too many starts per hour, blocked ventilation, or accumulated dirt preventing heat dissipation.
A number on the nameplate (e.g., 1.15) indicating the motor can operate safely at that percentage above rated load. A 10 HP motor with SF 1.15 can handle 11.5 HP loads for limited periods. Doesn't mean it should run there continuously.
The difference between synchronous speed and actual rotor speed. Induction motors always run slightly slower than synchronous speed — the slip creates the relative motion that induces current in the rotor and produces torque. Typically 2–5% slip at full load.
The speed the magnetic field rotates in the stator, determined by the number of poles and the frequency: RPM = 120 × frequency ÷ number of poles. A 4-pole, 60 Hz motor has a synchronous speed of 1800 RPM.
A multimeter measures voltage, current, and resistance. When measuring voltage: set to the correct voltage type (AC/DC) and range, insert probes into the meter, touch the probes to the circuit one at a time — never both at once on an energized circuit. Always test the meter on a known source first.
Sloppy wiring is harder to troubleshoot, harder for the next person to understand, and more likely to be physically damaged. Neat work indicates quality installation and makes future maintenance safer and faster.
The neutral bar terminates the white (neutral) conductors. The ground bar terminates equipment grounds. In a main panel they're bonded together. In a subpanel they must be separate — neutral is isolated, ground bonds to the panel enclosure.
The neutral (white or gray) carries return current back to the source to complete the circuit. Under normal conditions it carries the same current as the hot. In a balanced 3-phase system, neutral current is zero.
The neutral carries return current during normal operation. The ground carries current only during a fault. They bond together at the main panel but must be kept separate at subpanels and downstream.
Non-metallic sheathed cable (Romex). Used in dry residential and light commercial construction. Contains hot, neutral, and ground conductors in a plastic sheath. Not for wet locations or most commercial applications.
A pen-style tester that beeps or lights up when near an energized conductor without making contact. Useful for quick checks but not as reliable as a contact tester — always verify with a contact tester before touching anything.
Detects motion to turn lights on when someone enters a space and off after they leave. Saves energy in spaces that are intermittently occupied.
Two bends that shift the conduit horizontally or vertically to align with a different plane — for example, entering a panel that's offset from the conduit run.
Voltage = Current × Resistance (V = I × R). If you know any two of these values, you can calculate the third. It's the foundation of all electrical calculations.
When working near energized parts, keep one hand behind your back or in your pocket. This prevents current from flowing through your chest (heart) if you accidentally contact a live conductor with the working hand.
The enclosure of the equipment is no longer connected back to the panel. If a hot wire contacts the enclosure, the entire enclosure becomes energized. Making contact could provide a current path causing shock or electrocution.
The distribution center for branch circuits. Contains the main breaker (or main lugs), neutral bar, ground bar, and individual circuit breakers. All branch circuits originate here.
Determines the phase sequence (A-B-C) of a three-phase system. Important when paralleling sources, connecting generators, or installing motors where wrong rotation would damage equipment.
Identifying which secondary terminals correspond to which phase and polarity. Critical when paralleling transformers or connecting to an existing bus — wrong phasing creates a dead short.
Verifying that conductors at two ends of a run are on the same phase before making connections. Done with a phase rotation meter or by testing with a voltmeter to ensure A-phase at one end connects to A-phase at the other.
A device that turns lights on at dusk and off at dawn by sensing ambient light. Used on parking lot lights and exterior fixtures.
A short piece of wire used to connect multiple conductors to a single device terminal, since most device terminals only accept one conductor. The pigtail goes to the device; all wires are spliced together at the pigtail.
Indicates whether a load is on or off. Useful when the load is out of sight from the switch location — like a garage light controlled from inside the house.
Programmable Logic Controller — a programmable module used to automate control of machinery and processes. Replaces banks of relays with programmable logic. Common in manufacturing and automated systems.
In data centers, a device that distributes power to multiple servers and equipment. Monitors power usage at each outlet and can be remotely managed.
Power factor is the ratio of real power (doing actual work) to apparent power (total power supplied). A PF of 1.0 means all power is being used. Motors and other inductive loads have a PF less than 1, meaning some power is returned to the source.
Adding capacitors to a system to reduce reactive power demand. Improves the power factor closer to 1.0, reducing line losses and utility charges. The capacitors supply reactive current locally so it doesn't have to come from the utility.
Personal Protective Equipment. Minimum for electrical work: safety glasses. Near energized equipment: rated insulating gloves, arc flash PPE as determined by hazard analysis (NFPA 70E). Eye and face protection for any possibility of arc flash.
In practice they're similar, but a pull box is used when you need a point to pull conductors through a long run, while a junction box is used to make splices. Larger pull boxes are required for larger conduit systems.
Schedule 40 or 80 PVC plastic conduit. Used underground, in wet locations, or in corrosive environments where metal would corrode. Cannot be used as an equipment ground path — must pull a separate EGC.
Cutting leaves sharp burrs inside the conduit end. Reaming removes those burrs so they don't damage the insulation on conductors being pulled through.
An electrically operated switch. A small control signal energizes a coil, which creates a magnetic field that opens or closes a separate set of contacts carrying a larger load. Allows low-voltage controls to switch high-voltage loads.
Overloaded circuit (too many loads), a short circuit, a ground fault, or a faulty breaker. Check total load on the circuit first. If the breaker trips immediately upon reset, look for a short or ground fault.
The opposition to current flow in a conductor, measured in ohms. Heat, wire material, and wire length all affect resistance.
Rigid Metal Conduit — heavy-wall threaded steel conduit. Used in areas needing maximum protection, outdoors, and in hazardous locations. Much stronger than EMT but heavier and harder to work with.
Drilling into concrete and masonry. Combines rotation with a hammering impact to break through hard materials. Used to set anchors, drill through concrete walls, and install supports.
Different voltage classes: Class 00 (500V), Class 0 (1000V), Class 1 (7500V), Class 2 (17000V), etc. The rating is the maximum AC proof-test voltage. Always use leather protectors over rubber gloves to prevent physical damage.
A self-resetting overload resets automatically once cooled — dangerous if it resets into an ongoing fault. Manual reset requires someone to physically reset it, allowing investigation before the motor restarts. Manual reset is preferred in most applications.
The conductors and equipment that bring power from the utility into the building. Includes the service drop or lateral, meter, and main disconnect.
Leaving extra wire at each connection point — at a panel, fixture, or outlet — so that the connection can be remade if a wire is damaged or a connection fails. Typically 6–12 inches extra.
A power system with one AC voltage. Residential service is single-phase — actually two hots 180° apart sharing one neutral, giving 120V to neutral and 240V between hots.
A device that gradually ramps up voltage when starting a motor. It reduces the mechanical stress of sudden starts and the inrush current spike, but unlike a VFD, it only controls the starting process — it runs at full speed once started.
A rugged tester with a solenoid that buzzes and a plunger that moves to indicate voltage. Preferred by many electricians for verifying absence of voltage because it actually draws current — it won't give a false reading from induced voltage the way non-contact testers can.
A splice is a connection between two or more conductors. It must be mechanically secure, electrically continuous, and insulated at least to the level of the conductors being spliced. Typically done with wire nuts, push-in connectors, or compression splices.
So they're accessible for inspection, maintenance, and future changes. Buried or concealed splices are a code violation and a maintenance nightmare — if they fail, you can't find them.
Drilling holes in sheet metal, electrical boxes, and enclosures. The stepped design allows one bit to drill multiple hole sizes.
The voltage difference between two points on the ground that a person could straddle during a fault. Current can flow up one leg and down the other. Dangerous near downed power lines or ground faults.
Use wire strippers sized for the conductor. Strip only enough insulation for the connection — typically 3/4 inch for wire nuts, more for terminals. Don't nick the conductor.
A galvanized steel channel used to support conduit, cable trays, panels, and equipment. Bolts, clamps, and fittings attach to the channel without drilling. Very versatile for commercial and industrial support systems.
A device that limits voltage spikes (transients) by diverting excess voltage to ground. Installed at the service entrance (Type 1), panel (Type 2), or point of use (Type 3). Protects sensitive electronics from voltage transients.
A larger distribution panel, typically floor-mounted, that feeds multiple panelboards. Used in commercial and industrial settings where multiple services or large distributions are needed.
High-voltage or high-ampacity distribution equipment in industrial and utility settings. Contains switches, breakers, and protective relays. Much more robust and maintainable than standard panelboards.
Always use a voltage tester to verify a circuit is de-energized before touching any conductors. Never assume a circuit is dead because you turned off a breaker — verify it every time.
Test with a meter. Test the meter on a known live source first to verify it works. Then test the circuit. Test after removing the last fuse or opening the last breaker. This verifies the meter works and the circuit is actually dead.
The most common type of circuit breaker. Has two trip mechanisms: a bimetallic thermal strip that trips on sustained overcurrent (heating up over time), and an electromagnetic mechanism that trips instantly on high-current shorts.
THHN is rated for dry locations at 90°C. THWN is rated for wet or dry at 75°C. Most wire sold today is dual-rated THHN/THWN-2, usable in both environments.
The most common industrial motor. Three-phase current creates a rotating magnetic field in the stator that induces current in the rotor, causing it to rotate. Simple, reliable, no brushes or commutators.
Three AC voltages, each 120° apart. More efficient than single-phase for large motors and commercial loads because the power delivery is smoother and motors are simpler and more reliable. Uses conductors more efficiently than single-phase at the same power level.
Two switches that control one light from two locations. Each switch has a common terminal and two traveler terminals. Flipping either switch changes which traveler is connected to the common, completing or breaking the circuit path.
A device that turns loads on and off based on a programmed schedule. Used for lighting, HVAC, and other loads that operate on a schedule.
A fuse with a built-in delay before it blows on moderate overcurrent, but fast response to high-current faults. Used for motor circuits where inrush current is high at startup but sustained overcurrent should blow the fuse.
A small level used to ensure conduit, panels, and boxes are installed plumb and level. Conduit that's obviously out of level looks unprofessional and can affect drainage in wet locations.
Tighten a lug, bolt, or fitting to a specific torque value using a torque wrench or torque screwdriver. Under-torqued connections can loosen and overheat. Over-torqued connections can damage conductors. Correct torque ensures reliable, lasting connections.
The voltage between a person's hand and foot when touching an energized object. High touch potential is dangerous because current flows through the body.
Provides a path for the magnetic flux generated by the primary winding. The core concentrates flux so it efficiently links the primary and secondary windings. Laminated to reduce eddy current losses.
The ratio of primary winding turns to secondary winding turns. A 2:1 turns ratio steps voltage down by half and doubles current on the secondary side.
DC doesn't change direction, so it doesn't create a changing magnetic field. No changing magnetic field means no induction in the secondary winding — the transformer won't transfer energy.
The handle moves to a middle position (between ON and OFF) or falls to the OFF position depending on the breaker design. To reset: push firmly to OFF, then back to ON.
Underground Feeder cable — similar to NM but with conductors embedded in a solid plastic core. Rated for direct burial and wet locations.
At least 20 feet of bare copper wire or rebar encased in concrete footings below grade. One of the best grounding electrodes because concrete has good contact with earth and the rebar or wire has large surface area. Required when a building has a concrete foundation.
A device with a battery backup that provides continuous power to critical loads if utility power fails. Commonly used for computers, data centers, and life safety systems.
Underground Service Entrance cable. Rated for direct burial and exposure to wet conditions. Used for underground service laterals from the utility.
A Variable Frequency Drive controls a motor's speed by changing the frequency and voltage of the power supply. Running a motor at lower speed uses significantly less energy — a motor running at 80% speed uses about half the power.
The electrical pressure that pushes current through a circuit, measured in volts. Like water pressure in a pipe.
Voltage drop is the loss of voltage as current travels through a conductor due to the resistance of the conductor itself. A circuit with too much voltage drop means equipment at the end of the run gets less voltage than it needs — motors run hot, lights dim, electronic equipment can malfunction.
A brief reduction in voltage, usually caused by a large motor starting, a fault on the utility system, or heavily loaded lines. Can cause computers to reboot, contactors to drop out, and drives to fault.
Power (watts) = Voltage × Current (P = V × I). A 1200-watt heater on 120V draws 10 amps.
In a 4-wire delta system, the center tap of one transformer winding creates a neutral. The conductor on the opposite leg has a higher voltage to ground (~208V in a 240V system). This leg must be identified with orange tape and cannot be used for single-phase 120V loads.
A label, tape, or sleeve that identifies conductors at each end of a run. Critical in multi-conductor installations so you know which wire is which without tracing. Standard practice in commercial and industrial work.
Reduces friction when pulling conductors through conduit, preventing insulation damage and making long pulls possible without exceeding the maximum pulling tension of the conductors.
Remove insulation from the end of a conductor without nicking the copper or aluminum. Nicks create weak points that can break under tension or overheat under load.
Strip to the correct depth, insert fully into the lug with no bare copper showing outside, and torque to manufacturer's specification. Insert straight — never fold or bunch conductors.
A sheet metal trough with a hinged or removable cover used to route and protect conductors, usually in commercial and industrial environments where many circuits need to be routed together and need to be accessible.