MA Electrician cheat sheet

NEC Chapter 1 applies generally; Chapters 2-4 cover wiring and equipment, Chapter 5 special occupancies, Chapter 6 special equipment, Chapter 7 special conditions, Chapter 8 communications, and Chapter 9 tables.

In the NEC, 'shall' is mandatory, 'shall not' is prohibited, and 'should' is advisory rather than enforceable.

Equipment must be approved and installed in accordance with its listing and labeling instructions under 110.3(B).

Working space for 600 V or less is at least 30 in wide, 6.5 ft high, and 3 ft deep for 0-150 V; 151-600 V uses 3, 3.5, or 4 ft based on condition.

Dedicated electrical equipment space above and around switchboards, panelboards, and similar equipment must be kept clear.

Overcurrent devices must have an interrupting rating not less than available fault current, and equipment must have adequate short-circuit current rating.

Boxes and conduit bodies containing splices or terminations must be accessible without removing building finish.

Electrical work generally requires a permit and inspection by the local authority having jurisdiction unless specifically exempted.

NM cable is permitted in dry locations, must be protected from physical damage, and is secured every 4.5 ft and within 12 in of boxes.

EMT must be supported at intervals not exceeding 10 ft and within 3 ft of boxes or termination fittings.

Conduit fill limits are 53% for one conductor, 31% for two conductors, and 40% for three or more conductors.

Box fill counts conductors, clamps, devices, and equipment grounding conductors using Article 314.16 volume allowances.

Minimum cover for direct-buried cable is 24 in; PVC raceway is 18 in; rigid metal conduit is 6 in.

Parallel conductors must be 1/0 AWG or larger and identical in material, size, insulation type, and length.

Splices and terminations must be made in accessible boxes or conduit bodies with adequate volume.

Receptacles in wet locations require weatherproof enclosures with while-in-use covers.

Continuous loads are calculated at 125% for branch circuits, feeders, and services, then added to noncontinuous loads.

Standard overcurrent device ratings include 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, and 100 A.

Dwelling kitchens require at least two 20 A small-appliance branch circuits; laundry and bathroom receptacle circuits are also 20 A.

Wall receptacle spacing in dwellings uses the 12 ft rule and the 6 ft rule so no wall point is more than 6 ft from a receptacle.

Countertop receptacles must be installed so no point along the countertop is more than 24 in from a receptacle.

The optional dwelling calculation method uses the first 10 kVA at 100% and the remainder at 40%, plus other loads per Article 220.

Dwelling lighting demand is first 3 kVA at 100%, next 117 kVA at 35%, and remainder at 25%.

Informational voltage-drop recommendations are 3% maximum on a branch circuit and 5% maximum total from service to load.

The grounding electrode system must include all available electrodes, and those electrodes must be bonded together.

A ground rod must be at least 8 ft long and have 25 ohms or less resistance; otherwise a supplemental electrode is required.

The grounding electrode conductor is sized from Table 250.66 using the largest service conductor.

The equipment grounding conductor is sized from Table 250.122; common copper sizes include 12 AWG for 20 A, 10 AWG for 30-60 A, 8 AWG for 100 A, and 6 AWG for 200 A.

Small conductors are protected at 15 A for 14 AWG, 20 A for 12 AWG, and 30 A for 10 AWG unless specifically permitted otherwise.

GFCI protection is required for receptacles in bathrooms, kitchens, outdoors, garages, unfinished basements, and other specified wet or hazardous areas.

AFCI protection is required for specified 120 V, 15 A and 20 A branch circuits in dwelling units.

Bonding creates a low-impedance fault path so overcurrent protection operates quickly during a ground fault.

Ohm's law: V = I × R; power: P = V × I = I²R = V²/R.

Single-phase power: kW = V × I × PF ÷ 1000; three-phase power: kW = √3 × V × I × PF ÷ 1000.

Apparent power: kVA = V × I ÷ 1000 single-phase; kVA = √3 × V × I ÷ 1000 three-phase.

Impedance: Z = √(R² + (XL - XC)²); inductive reactance XL = 2πfL; capacitive reactance XC = 1/(2πfC).

Power factor equals true power divided by apparent power, PF = P/S, and equals cosine of the voltage-current angle.

Series circuits have the same current and add voltages; parallel circuits have the same voltage and add currents.

Balanced wye: line voltage = √3 × phase voltage; balanced delta: line current = √3 × phase current.

Transformer turns ratio: Vp/Vs = Np/Ns; current ratio is inverse; 1 horsepower equals 746 watts.

Motor branch-circuit conductors are sized at 125% of motor full-load current from the Code tables, not the nameplate current.

Motor overload protection is sized from the motor nameplate current and is separate from short-circuit and ground-fault protection.

Motor short-circuit and ground-fault protection is selected from Article 430.52 percentages and the motor full-load current.

A motor disconnecting means must be within sight of the motor and controller or capable of being locked open.

Single-phase and three-phase motor full-load currents are found in Tables 430.248 and 430.250.

Air-conditioning and refrigeration equipment requires a disconnecting means within sight and readily accessible from the equipment.

Motor control circuits are classified as Class 1, 2, or 3 under Article 725 and must be protected accordingly.

Motor starting current can be several times running current, so voltage drop and conductor sizing deserve careful checking.

Class I locations contain flammable gases or vapors; Class II contains combustible dust; Class III contains ignitable fibers or flyings.

Division 1 is a normal hazardous condition; Division 2 is an abnormal condition, and Class I locations may use zones instead.

Swimming pool installations require equipotential bonding of metal parts and equipment and GFCI protection for specified receptacles.

Health care facilities use essential electrical systems with critical and equipment branches to maintain power for patient care.

Photovoltaic systems on buildings require rapid shutdown to reduce conductor voltage for emergency responders.

Temporary wiring on construction sites requires GFCI protection for receptacles and proper support and protection.

Assembly occupancies are covered by Article 518; theaters and similar locations by Article 520.

Agricultural buildings are covered by Article 547 and require attention to dust, water, and equipotential planes.

The Massachusetts Electrical Code is 527 CMR 12.00, which adopts the NEC with Massachusetts amendments.

The Board of State Examiners of Electricians administers licensing under 237 CMR 12.00.

A Massachusetts master electrician is licensed to perform electrical work and obtain electrical permits; journeymen work under a master's supervision.

The local wiring inspector enforces the code in the municipality, issues permits, and inspects installations.

Board regulations govern license types, qualifications, renewal, and disciplinary action.

Massachusetts amendments can add to or modify NEC requirements; the stricter applicable requirement controls.

Concealed electrical work must be inspected before it is covered, and services must be inspected before energization.

Electrical work must be performed by properly licensed individuals as required by Massachusetts law and board rules.

NFPA 70E establishes safe work practices for shock and arc-flash hazards, including approach boundaries and PPE.

The limited approach boundary restricts unqualified persons; the restricted approach boundary is for qualified persons with proper protection.

Lockout/tagout isolates energy sources, and the qualified worker verifies absence of voltage before work begins.

Test before touch: use a meter with the correct CAT rating and confirm the tester on a known live source.

Arc-rated clothing, voltage-rated gloves with leather protectors, and face protection are selected for the hazard.

GFCI protection is required for temporary receptacles on construction sites and for assured grounding programs.

De-energize equipment before work when feasible; treat conductors as energized until verified otherwise.

For electrical injury, call 911, use CPR or an AED as needed, and do not touch a victim who may still be energized.