⚡ Stuff Every Electrician Should Know: Training Guide

Ohm's Law and Simple Circuits

Resistance is measured in ohms. One ohm means a voltage of one volt pushes a current of one ampere through the conductor. Ohm's law states that the current through a resistor is directly proportional to the voltage across it.

In a series circuit, there is only one path, so the current is the same through every resistor. The voltage from the source splits among the resistors, and their resistances simply add.

In a parallel circuit, each branch connects across the same two points, so the voltage is the same across every branch. Adding parallel paths lowers total resistance because current has more ways to flow.

For two equal resistors in parallel, the total resistance is half of one resistor. Two 10 ohm resistors in parallel give 5 ohms.

Kirchhoff's Rules

Kirchhoff's junction rule says current entering a connection point equals current leaving it. This follows from conservation of charge, since charge cannot pile up at a junction.

Kirchhoff's loop rule says the voltage changes around any closed loop add to zero. The energy a source supplies is used up by the loads in that loop.

AC Power and Effective Values

Household AC voltage is usually quoted as an rms value. For a 120 volt AC outlet, the waveform actually peaks at about 170 volts. The rms value is the DC value that would heat a resistor the same amount.

Electric power in watts equals current in amps multiplied by voltage in volts. Energy used over time is measured in kilowatt-hours, which is power multiplied by time.

Utilities send electricity long distances at very high voltage because higher voltage means lower current for the same power. Lower current greatly reduces power loss in the lines.

In an AC circuit with only a resistor, voltage and current rise and fall together, in phase. A resistor turns electric energy into heat, while a capacitor stores and releases electric energy.

In an AC circuit, capacitor current leads its voltage by a quarter cycle, and inductor current lags. Power factor compares real watts with apparent power, volts times amps.

Three-Phase Systems

A three-phase system has three voltages that are 120 degrees apart in time. Their overlapping peaks make the total power delivery smoother than single-phase power.

In a wye system, line-to-line voltage is about 1.73 times line-to-neutral voltage. That is why 120 volts to neutral becomes 208 volts between phases.

In a balanced three-phase wye system, the three currents are equal and 120 degrees apart, so they cancel and essentially no current flows in the neutral. Unbalanced loads leave a leftover current on the neutral.

Voltmeters and Ammeters

A voltmeter measures voltage across two points, so it connects in parallel with the device. A voltmeter in series would block the circuit.

An ammeter measures current, so it must connect in series with the device. In a single loop, the ammeter reads the same anywhere in that loop.

A good voltmeter has very high resistance compared with the circuit. That way it draws almost no current and does not change the voltage it is reading.

Clamp Meters and Voltage Detectors

A clamp meter reads the magnetic field around a wire, so enclose a single conductor inside the jaws. If hot and neutral are both inside, their fields cancel and the reading is near zero.

Before and after each use, check a voltage detector on a known live source. This proves the tool is working and protects against false negatives.

Resistance and AC Voltage Measurements

Before measuring resistance, turn the power off to the circuit. The meter supplies its own small test current, and live voltage can give false readings or damage the meter.

For AC voltage measurements, plug the black lead into the COM jack and the red lead into the V input. Connect the black lead first and red second.

Never measure voltage with the leads in the A or mA inputs. Those inputs have almost no resistance, so you create a near short in the measurement circuit.

Meter Safety and Verifying Power Off

Fluke assigns meter categories based on available fault energy. Feeders and branch circuits fed from distribution panels are CAT III, while CAT IV covers service entrance and primary overcurrent protection.

If your meter or test probe has cracked insulation, stop using it until it is replaced. Never work alone near exposed and energized equipment.

Seeing an open disconnect switch does not prove the circuit is dead. The handle can be wrong, someone else could close it, or internal parts could still be live. Always test for voltage.

Lockout and Tagout

OSHA's lockout/tagout standard prevents unexpected energization or release of stored energy while someone services equipment. Locks and tags keep the power source isolated.

Normally the employee who applied a lockout or tagout device removes it. An employer can override only under specific, documented procedures, and affected employees must be told before restart.

Lockout/tagout procedures must be inspected at least annually by an authorized employee who is not the one using the procedure being inspected.

A lock is stronger than a tag because a tag is only a warning, not a physical restraint. Tags must never be bypassed or ignored.

De-energizing and Energized Work

OSHA says live parts must be deenergized before an employee works on or near them, unless deenergizing creates added hazards or is infeasible. Lockout or tagging keeps parts off while exposed.

The path to ground from circuits and equipment must be permanent, continuous, and effective. A missing or broken ground path is a common cause of electrical injuries.

On construction sites, OSHA accepts either GFCIs or an assured equipment grounding conductor program. The program is a written plan for inspecting and testing cords, receptacles, and equipment regularly.

Portable ladders used near energized parts must have nonconductive side rails. Before work near overhead lines, the lines must be deenergized and grounded or otherwise protected.

Only qualified persons may work on electric parts that have not been deenergized. A qualified person can identify exposed live parts, find nominal voltage, and apply clearance distances.

Insulating Gloves and PPE

Rubber insulating gloves must be electrically tested before first issue and every 6 months afterward. Rubber insulating sleeves and blankets get a longer interval, every 12 months.

Along with a visual check, insulating gloves need an air test before each day's use. Trap air in the glove and look for leaks too small to see.

Leather protector gloves go over rubber insulating gloves. The leather protects the thin rubber from cuts and punctures.

Arc Flash and Shock Dangers

An arc flash can reach temperatures up to about 35,000 degrees Fahrenheit, hot enough to vaporize metal. Distance and arc-rated clothing reduce the danger.

The arc flash boundary is the distance where incident energy equals 1.2 calories per square centimeter. Inside that boundary, arc-rated PPE is needed.

Voltage-rated gloves are required inside the restricted approach boundary for exposed conductors at 50 volts or higher. Using a handheld meter on a 120 V circuit can put you inside that boundary.

It is current through the body that causes harm. Currents above about 10 milliamps can make muscles lock up so you cannot let go, extending the shock.

Grounding and Bonding

In NEC terms, grounding connects a system or equipment to the earth through an electrode. Bonding permanently joins metal parts into a conductive path.

To trip a breaker during a fault, current needs a low-impedance path back to the power source, not to the earth alone. Soil is too poor a conductor to carry enough fault current.

A ground rod by itself does not lower touch voltage on unbonded metal parts to a safe value. Metal parts must be bonded together to keep touch voltage low.

A ground rod electrode must have at least 8 feet in contact with the earth. A single rod needs a supplemental electrode unless its earth contact resistance is 25 ohms or less.

GFCI Protection

A GFCI compares outgoing and returning current and trips when current leaks at about 6 milliamperes. That protects people from shock before a standard breaker would trip.

GFCIs address shock hazards. AFCIs address fire hazards by recognizing dangerous arcing in damaged or loose wiring.

Test a GFCI at least once a month using its test button. CPSC also advises a portable GFCI for electrically powered garden equipment.

OSHA requires GFCI protection for receptacles in bathrooms and on rooftops, among other wet or exposed locations. A Class A GFCI trips at 6 milliamperes; a special-purpose GFCI for circuits over 150V to ground trips at 20 milliamperes.

AFCI Protection

An AFCI is a device that recognizes characteristics unique to arcing and de-energizes the circuit. Standard breakers only trip on overloads and short circuits, not small arcs.

Damaged cords and loose connections can arc without ever overloading a standard breaker. An AFCI detects that arcing pattern and shuts off the circuit. In 2003, CPSC engineers estimated AFCIs could address about half of home wiring fires.

AFCI rules started with bedrooms and grew over time. The 2014 NEC added kitchens and laundry rooms.

Under the 2023 NEC, AFCI protection covers 120V single-phase 10A, 15A and 20A branch circuits feeding outlets or devices in listed areas. Extending an existing circuit less than 6 feet with no new outlet or device does not trigger the rule.

Protecting Small Conductors

Section 240.4(D) caps the overcurrent device size for small conductors by AWG size and material. For 14 AWG copper the maximum is 15A, and for 12 AWG copper it is 20A.

If a conductor's ampacity does not match a standard breaker size, the next size up rule in 240.4(B) may allow the next higher standard rating. This works only at 800A or less and only when specific conditions are met.

Box Fill

Box fill calculations assign a volume to each conductor. Table 314.16(B) gives 14 AWG conductors 2.0 cubic inches and 12 AWG conductors 2.25 cubic inches.

Each single-gang device yoke, like a switch or receptacle, counts as two conductor volumes. Multigang yokes count two volumes per gang.

All equipment grounding conductors in a box count together as a single conductor volume. Internal cable clamps also count as one volume total for one or more clamps.

Cables and Raceways

Nonmetallic sheathed cable, often called NM cable, must be secured within 12 inches of every box, cabinet, or fitting. After that, it must be supported at intervals not exceeding 4.5 feet.

Electrical metallic tubing (EMT) is a lightweight raceway that is relatively easy to bend, cut, and ream. PVC conduit is inexpensive and easy to install but brittle in the cold and prone to sag in heat.

Flexible metal conduit is mainly used for the final 6 feet to moving or vibrating equipment. In high vibration, a wire-type equipment grounding conductor is required in the FMC.

Common Wiring Rules

THHN insulation is typically used in dry and damp locations but not wet locations. Wet location types include THWN, THWN-2, THHW, and XHHW. Insulated neutral conductors must be white or gray.

Tamper-resistant receptacles are required in dwelling units, but receptacles more than 5 1/2 feet above the floor are exempt. Receptacles in dedicated appliance space can also be exempt when the appliance is not easily moved.

A dwelling kitchen must have at least two 20-ampere small-appliance branch circuits. Along dwelling unit walls, receptacles can be spaced no more than 12 feet apart so no point along a wall is more than 6 feet from a receptacle.

A bathroom receptacle must be within 3 feet of the outside edge of each basin. A 20A bathroom circuit serving only one bathroom may also feed that bathroom's lighting or fan.

A service can have up to six service disconnects, grouped and marked. Outside one- and two-family dwellings, an indoor service disconnect must be nearest the point of service conductor entry. Equipment is in sight if visible and not more than 50 feet away.

The working space in front of electrical equipment must be at least 30 inches wide or the width of the equipment if wider. It must be clear from the floor up to 6 1/2 feet or the equipment height, whichever is greater.

Motor Circuits

Branch-circuit conductors serving a single motor must have an ampacity of at least 125 percent of the motor's full load current. FLC comes from NEC motor tables, not the nameplate.

Overload protection is sized from the nameplate current. A motor with a service factor of 1.15 or higher can have overload protection up to 125 percent of nameplate current; other motors are limited to 115 percent.

Every motor and controller must include a disconnect. The disconnect must have an ampere rating of at least 115 percent of the motor's full load current.

Swimming Pool Bonding

Pool equipotential bonding conductors can be solid copper no smaller than 8 AWG. The bonding grid reduces voltage differences around the pool.

The pool perimeter surface for bonding extends 3 feet horizontally from the inside wall. Metal parts and surfaces within that area get equipotential bonding, including grass and dirt.

For an unpaved pool perimeter, the copper bonding conductor is located 18 to 24 inches from the inside pool wall and buried 4 to 6 inches below finished grade.

Where no other bonded part touches the pool water, a conductive surface must expose at least 9 square inches to the water. It must stay exposed at all times.

Photovoltaic Rapid Shutdown

Rapid shutdown rules divide PV circuits into inside and outside the array boundary, which is 1 foot from the array in all directions.

In the 2023 NEC, one rapid shutdown option limits conductors inside the array boundary to 80 volts within 30 seconds. The 30 volt limit applies outside the boundary.

2023 and 2026 NEC Highlights

The 2023 NEC requires GFCI protection for all 125V through 250V dwelling unit kitchen receptacles, not just countertop receptacles. It also newly requires GFCI protection for clothes dryers and other appliances rated 150V or less to ground and 60A or less.

The 2023 NEC made kitchen island and peninsula receptacles optional, but provisions to add one later are required. The 2026 NEC bans kitchen receptacle outlets within 24 inches below the countertop surface.

The 2026 NEC requires GFCI protection for outdoor outlets rated 60A or less. A new exception permits a listed Class C SPGFCI for HVAC equipment.

For one- and two-family dwellings, the 2026 NEC requires the service disconnect to be readily accessible and outdoors. It also serves as the emergency disconnect.

The 2026 NEC removed the 1,000 ampere cutoff from the arc flash marking rule, so all non-dwelling service and feeder equipment needs arc flash warning labels.

The 2026 NEC requires panelboards outside one- and two-family dwellings to be field marked with available fault current and the calculation date.