ME Electrician cheat sheet

NEC Article 100 defines key terms: branch circuit, feeder, service, GFCI, AFCI, and "qualified person" (one who has skills and knowledge related to the construction and operation of electrical equipment and installations and has received safety training).

NEC 90.4 grants the authority having jurisdiction (AHJ) responsibility for approving equipment and materials; in Maine the AHJ is typically the municipal or state electrical inspector enforcing the adopted NEC edition.

Maine's electrical installation rules appear in 02-031 CMR Chapter 120 (Electricians' Examining Board rules), which adopts the NEC by reference with Maine amendments, so always check the edition adopted and any state amendments before citing a section.

Table 310.16 ampacities apply to not more than three current-carrying conductors in a raceway or cable at an ambient of 30 degrees C; correction factors for ambient temperature (310.15(B)) and adjustment for more than three conductors (310.15(C)) must be applied.

Conductor sizing: continuous loads are calculated at 125 percent (NEC 210.19(A), 215.2(A)); the standard OCPD sizes are 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200 amperes (240.6).

Box fill is computed under NEC 314.16: each 14 AWG conductor counts 2.00 cubic inches, 12 AWG 2.25, 10 AWG 2.50; one equipment grounding conductor counts as one conductor, and each device (receptacle, switch) counts as two of the largest conductor in the box.

Working clearance at electrical equipment is Table 110.26(A)(1): 3 ft for 0-150 V to ground, 3.5 ft for 151-300 V, 4 ft for 301-600 V (conditions 1 and 2), with 30-inch width minimum and 6.5 ft headroom.

Receptacle spacing (NEC 210.52): in dwelling units, no point along the floor line of a wall space may be more than 6 ft from a receptacle outlet; kitchen countertop receptacles are required so no point is more than 24 in. from one.

Maine electrician licensing is administered by the Electricians' Examining Board within the Department of Professional and Financial Regulation, Office of Professional and Occupational Regulation; the governing statute is 32 MRSA Chapter 17.

Maine license categories include Master Electrician, Journeyman Electrician, and Helper (apprentice-type) licenses, plus a limited license for specific work scopes; each category has its own experience and examination requirements.

Master Electrician applicants must document qualifying experience (typically years of supervised electrical work, with substitution of approved training allowed) and pass the master examination; a master may supervise and perform all electrical work and may employ or supervise journeymen and helpers.

Journeyman Electrician applicants must document required supervised experience and pass the journeyman examination; a journeyman works under a master's supervision and may not contract for electrical work independently.

Licenses are renewed on a fixed cycle (commonly biennial in Maine) and renewal requires continuing education hours set by Board rule; failing to complete CE by the deadline can result in a lapsed license and late fees.

Unlicensed electrical work is a violation subject to Board discipline and civil penalties; the Board may investigate complaints, hold hearings, suspend or revoke licenses, and impose fines.

A license is not transferable, and licensees must display or provide their license number as required; acting outside the scope of the license class (for example, a journeyman contracting directly with a homeowner) is grounds for discipline.

Maine requires a permit and inspection for most electrical installations through the municipal or state electrical inspector; the licensed electrician of record is responsible for the work performed under the permit.

Ohm's law: E = I x R; power: P = E x I, with P = I squared x R and P = E squared / R for resistive loads; single-phase power in watts equals volts times amperes times power factor.

Three-phase relationships: line-to-line voltage equals 1.732 times line-to-neutral; three-phase power equals 1.732 x E(line) x I(line) x power factor; apparent power in kVA equals E x I / 1000 (single-phase).

Voltage drop: single-phase VD = 2 x K x I x L / CM, three-phase VD = 1.732 x K x I x L / CM, where K is the resistivity constant (about 12.9 for copper, 21.2 for aluminum), L in feet, CM in circular mils; NEC 210.19 and 215.2 informational notes recommend keeping total drop within about 3 percent on branch circuits and 5 percent overall.

Conductor resistance rises with temperature and with smaller circular-mil area; aluminum has roughly 1.6 times the resistance of copper for the same size, which is why aluminum terminations require proper connectors and anti-oxidant.

Wiring methods: NM-B cable is permitted in dwellings and dry interior locations but not in wet locations, exposed to physical damage, or in most commercial occupancies; MC cable and EMT are common in commercial work; rigid metal conduit is required in many hazardous or high-damage areas.

Raceway fill: Chapter 9 tables limit conduit fill (typically 40 percent for three or more conductors); Table 1 gives the percent of interior cross-section, and Annex C gives conductor counts for common raceways.

Support and securing: NM cable must be secured within 12 in. of boxes and every 4.5 ft (334.30); EMT must be supported at least every 10 ft and within 3 ft of boxes (358.30); boxes must be accessible and covers installed.

Motor branch circuits: NEC 430 requires overload protection sized to the motor's nameplate current, branch-circuit short-circuit and ground-fault protection per Table 430.52 (often 250 percent of full-load current for inverse-time breakers), and conductors at 125 percent of FLC.

Grounding and bonding serve different purposes: grounding connects the system to earth (grounded conductor, grounding electrode), while bonding connects metal parts together to ensure a low-impedance fault path (equipment grounding conductor).

NEC 250.32 and 250.50 require a grounding electrode system at each service and at separate buildings fed by feeders; electrodes include ground rods, metal water pipe (10 ft or more in contact with earth), concrete-encased electrode, and ground ring.

A single ground rod must have 25 ohms or less resistance to earth, or be supplemented by one additional electrode (250.53(A)(2)); the two rods must be at least 6 ft apart.

The equipment grounding conductor must be sized per Table 250.122 based on the rating of the overcurrent device protecting the circuit, not the conductor ampacity; it may be increased proportionally when conductors are upsized for voltage drop.

Bonding jumpers are required around water meters, at gas piping (per 250.104(B)), and at service equipment; the main bonding jumper connects the grounded conductor to the equipment grounding bus only at the service, never at subpanels.

Overcurrent protection: the OCPD protects conductors, not the load; conductors must be protected at their ampacity except where the next standard size up is permitted (240.4(B)) for circuits over 800 amperes or where the ampacity does not exceed 800 A and the next size does not exceed 800 A.

GFCI protection (NEC 210.8) is required in dwelling bathrooms, kitchens, garages, outdoors, and other listed locations; AFCI protection (210.12) is required for most 120-volt branch circuits in dwelling units.

Arc flash and shock safety: NFPA 70E establishes approach boundaries (limited, restricted) and requires a risk assessment, appropriate PPE, and lockout/tagout before working on energized equipment; de-energize whenever feasible.

Grounding and bonding serve different purposes: grounding connects the system to earth (grounded conductor, grounding electrode), while bonding connects metal parts together to ensure a low-impedance fault path (equipment grounding conductor).

NEC 250.32 and 250.50 require a grounding electrode system at each service and at separate buildings fed by feeders; electrodes include ground rods, metal water pipe (10 ft or more in contact with earth), concrete-encased electrode, and ground ring.

A single ground rod must have 25 ohms or less resistance to earth, or be supplemented by one additional electrode (250.53(A)(2)); the two rods must be at least 6 ft apart.

The equipment grounding conductor must be sized per Table 250.122 based on the rating of the overcurrent device protecting the circuit, not the conductor ampacity; it may be increased proportionally when conductors are upsized for voltage drop.

Bonding jumpers are required around water meters, at gas piping (per 250.104(B)), and at service equipment; the main bonding jumper connects the grounded conductor to the equipment grounding bus only at the service, never at subpanels.

Overcurrent protection: the OCPD protects conductors, not the load; conductors must be protected at their ampacity except where the next standard size up is permitted (240.4(B)).

GFCI protection (NEC 210.8) is required in dwelling bathrooms, kitchens, garages, outdoors, and other listed locations; AFCI protection (210.12) is required for most 120-volt branch circuits in dwelling units.

Arc flash and shock safety: NFPA 70E establishes approach boundaries (limited, restricted) and requires a risk assessment, appropriate PPE, and lockout/tagout before working on energized equipment; de-energize whenever feasible.