Wiring and Protection (Minnesota Journeyman)

Learning Objectives

Apply Article 120's calculation framework, unit loads, and demand factors, including the rule that load calculations do not apply the 125 percent continuous-load multiplier.

Calculate branch-circuit, feeder, service, farm, and health care loads from the standard tables and optional methods.

Select branch circuits under Article 210 for rating, voltage, GFCI, AFCI, receptacle, and lighting-outlet requirements.

Size and locate feeders, outside circuits, services, and disconnecting means under Articles 215, 225, and 230.

Protect conductors under Article 240 with the small-conductor limits, the 800-ampere hinge, and the tap rules.

Size grounding electrode conductors, bonding jumpers, and equipment grounding conductors from the correct Article 250 table.

1.1 Article 120: Framework and Branch-Circuit Loads

120.1, 120.4. Eight parts cover branch circuits, feeder and service loads, farm loads, health care facilities, marinas, and vehicle parks; Table 120.4 sends motors to 430.24 and air-conditioning equipment to Article 440 Part IV.

120.5. Nominal voltages run from 120 and 120/240 through 480Y/277 and 600 volts; fractions under 0.5 ampere may be dropped; floor area excludes detached garages and open porches for dwellings.

120.5(E). Load calculations shall not require continuous loads to be calculated at 125 percent.

120.6, 120.7. Use the single largest of noncoincident loads; power control systems are set no higher than 80 percent of the monitored OCPD rating.

120.10, 120.11. Dwellings route to 120.13, other loads to 120.14, additions to 120.16; the load cannot exceed the circuit rating, and motor equipment over 1/8 hp with other loads takes 125 percent of the largest motor plus the rest per 430.24.

120.13, 120.41. Dwelling branch circuits use 3 volt-amperes per square foot; the dwelling feeder and service use 2 volt-amperes per square foot.

120.14. Dryers 5000 watts or nameplate; heavy-duty lampholders 600 volt-amperes; signs 1200 volt-amperes; show windows 200 volt-amperes per linear foot; multioutlet assemblies 180 volt-amperes per 1.5 m (5 ft) or per 300 mm (1 ft).

120.14(I), 120.16. Receptacles 180 volt-amperes per yoke, or 90 volt-amperes per receptacle on a device with four or more; office receptacles take the larger of that load or 1 volt-ampere per square foot; added dwelling loads follow 120.14.

1.2 Feeder and Service Calculations, Demand Factors, and the Neutral

120.40, 120.41. The load is at least the sum of branch-circuit loads after demand factors; the dwelling load already includes receptacles rated 20 amperes or less, the circuits of 210.11(C)(3) and 210.11(C)(4), the outlets of 210.52(E) and 210.52(G), and the lighting outlets of 210.70.

120.42, 120.43, 120.44. Non-dwelling occupancies use Table 120.42(A) unit loads, such as 16 volt-amperes per square meter (1.5 volt-amperes per square foot), with 120.42(B) energy-code values needing power monitoring; offices follow 120.43 and hotels and motels 120.44.

120.45, 120.47. Table 120.45 demand factors adjust general illumination but never reduce the number of circuits, and 120.47 covers receptacle loads.

120.46, 120.51, 120.52. Show windows take 200 volt-amperes per linear foot and track lighting 150 volt-amperes per 600 mm (2 ft); space heating counts at 100 percent of connected load, and each 2-wire small-appliance circuit of 210.11(C)(1) counts 1500 volt-amperes.

120.82, 120.83, 120.84. Optional dwelling method: 100 percent of the first 8 kVA plus 40 percent of the remainder; Table 120.83 takes 40 percent of existing load above 8 kVA, 80 percent for new electric vehicle supply equipment and central electric resistance heating, and 50 percent for other new loads.

120.102, 120.103, 120.110. Farm loads take 100 percent of simultaneous loads or 125 percent of the largest motor, 50 percent of the next 60 amperes, and 25 percent of the remainder; Table 120.103 takes 100, 75, 65, and 50 percent; health care facilities take 100 percent of the first 10,000 volt-amperes and 20 percent of the remainder.

120.61. A 70 percent factor applies to the unbalanced load above 200 amperes on 3-phase 4-wire and similar systems, but 120.61(C) prohibits reducing neutral capacity for nonlinear loads on a 4-wire, wye-connected system.

1.3 Branch Circuits, GFCI, AFCI, and Outlets (Article 210)

210.4, 210.6. Each multiwire branch circuit needs a means that simultaneously disconnects all ungrounded conductors at the origin, with single-pole breakers allowed per 240.15(B).

210.11(C). Two or more 20-ampere small-appliance circuits with no other outlets; a laundry circuit; and one or more 120-volt, nominal, 20-ampere bathroom receptacle circuits including countertop receptacles.

210.20, 210.21, 210.23. The OCPD is the noncontinuous load plus 125 percent of the continuous load; Table 210.21(B)(2) caps a 15-ampere receptacle at 12 amperes, a 20-ampere receptacle at 16 amperes, and a 30-ampere receptacle at 24 amperes, while Table 210.21(B)(3) allows 40 or 50 amperes on a 40-ampere circuit.

210.8. GFCI protection covers 125-volt through 250-volt receptacles on single-phase circuits at 150 volts or less to ground in dwelling bathrooms, garages, outdoors, crawl spaces, basements, kitchens, sink areas, and laundry areas, plus appliances rated 150 volts or less to ground and 60 amperes or less under 210.8(D).

210.12. AFCI protection is required for 120-volt, 10-, 15-, and 20-ampere branch circuits in dwelling kitchens, family rooms, dining rooms, living rooms, bedrooms, sunrooms, recreation rooms, closets, hallways, laundry areas, and similar rooms.

210.52, 210.63, 210.70. No point along a wall space may be more than 1.8 m (6 ft) from a receptacle, with (B) kitchens and dining, (C) countertops, (D) bathrooms, (E) outdoors, and (G) basements and garages covered separately.

1.4 Feeders and Outside Branch Circuits and Feeders (Articles 215 and 225)

215.4. Feeder ampacity is the noncontinuous load plus 125 percent of the continuous load unless listed for 100 percent operation, and a feeder grounded conductor is no smaller than the 250.122 equipment grounding conductor for the feeder OCPD.

225.6, 225.10, 225.12. Open conductors in spans up to 15 m (50 ft) are at least 10 AWG copper or 8 AWG aluminum; festoon lighting is at least 12 AWG unless supported by messenger wires over 12 m (40 ft) spans; any Chapter 3 wiring method is permitted on buildings, with 225.12 setting support rules.

225.18. Clearances are 3.0 m (10 ft) over pedestrian-only areas, 3.7 m (12 ft) over residential property and driveways up to 300 volts to ground, 4.5 m (15 ft) there above 300 volts to ground, and 5.5 m (18 ft) over public streets and truck-traffic areas.

225.24, 225.25. Pendant outdoor lampholders need staggered connections, insulation-puncturing types attach only to stranded conductors, and outdoor lamps stay below all energized conductors unless relamping safeguards exist or the equipment is lockable open per 110.25.

225.30, 225.31, 225.33, 225.36, 225.41. Only one feeder or branch circuit supplies a building unless 225.30(A) through (F) permits otherwise, with a multiwire branch circuit counting as one.

1.5 Services: Conductors, Clearances, and Disconnecting Means (Article 230)

230.4. One service per building unless additional services are permitted for fire pumps, emergency systems, standby systems, power production sources, or capacity requirements over 2000 amperes at 1000 volts or less.

230.6, 230.7. Conductors count as outside a building under not less than 50 mm (2 in.) of concrete, in a raceway encased in 50 mm (2 in.) of concrete or brick, in a vault, under 450 mm (18 in.) of earth, or in RMC or IMC through an eave.

230.9, 230.23(B), 230.30(B), 230.31(A). Service conductors clear building openings; overhead conductors are at least 8 AWG copper or 6 AWG aluminum, with 12 AWG hard-drawn copper for a single-circuit service; underground methods include RMC, IMC, NUCC, HDPE, PVC, RTRC, Type IGS, USE, MV or MC for direct burial, and protected MI.

230.24, 230.26. Grade clearances are 3.0 m (10 ft) at the entrance and pedestrian-only areas, 3.7 m (12 ft) over residential property and driveways, 4.5 m (15 ft) above 300 volts to ground, 5.5 m (18 ft) over public streets and truck-traffic areas, and 7.5 m (24 1/2 ft) over railroad tracks, with the point of attachment at least 3.0 m (10 ft) above finished grade.

230.40, 230.42, 230.51. One set of service-entrance conductors is allowed per drop or lateral, with Exceptions 1 through 5; ampacity is the noncontinuous load plus 125 percent of the continuous load and at least the 230.79 rating; spacing follows Table 230.51(C), such as 150 mm.

230.54, 230.68. Conductors of different potential leave through separately bushed openings, the service head sits not more than 600 mm (24 in.) from the point of attachment, drip loops form below the head, and meter sockets are covered by 230.68.

230.70, 230.71, 230.72, 230.76. A means must disconnect all conductors; one- and two-family dwelling disconnects are marked EMERGENCY DISCONNECT per 110.21(B) with red background, white text, and 13 mm (1/2 in.) letters.

230.79, 230.80, 230.82, 230.90, 230.91, 230.94. Ratings are at least the calculated load and 30 amperes for two 2-wire branch circuits, 100 amperes for a one-family dwelling, and 60 amperes for all others, with the combined rating of multiple disconnects meeting that requirement; only listed equipment may connect ahead of the disconnect, and no device may sit in a grounded service conductor except a breaker opening all conductors.

230.95. Solidly grounded wye services over 150 volts to ground with a 1000-ampere or larger disconnect need ground-fault protection set at 1200 amperes maximum with a one-second maximum delay at 3000 amperes and above, tested on site by primary current injection.

1.6 Overcurrent Protection (Article 240)

240.4(B), 240.4(C). At or below 800 amperes, the next higher standard rating from Table 240.6(A) is permitted, with adjustable trip devices allowed under restricted access per 240.6(C); above 800 amperes, conductor ampacity must equal or exceed the OCPD rating.

240.4(D). Unless 240.4(E) or 240.4(G) applies: 14 AWG copper 15 amperes, 12 AWG copper 20 amperes, 10 AWG copper 30 amperes, 12 AWG aluminum 15 amperes, and 10 AWG aluminum 25 amperes, after correction factors.

240.4(F), 240.6. Transformer secondary conductors of single-phase (other than 2-wire) and multiphase (other than delta-delta 3-wire) transformers are not considered protected by the primary OCPD; Table 240.6(A) ratings add 1, 3, 6, and 601 for fuses.

240.21. A tap up to 3 m (10 ft) long stays within the enclosure of the equipment it supplies with ampacity at least one-tenth of the feeder OCPD rating, and a tap up to 7.5 m (25 ft) long needs ampacity at least one-third of that rating with a single breaker or fuse set limiting the load.

240.22, 240.24. No OCPD may be in series with an intentionally grounded conductor unless it opens all conductors with no independent pole, or it is required by 430.36 or 430.37; the handle grip center stays not more than 2.0 m (6 ft 7 in.) above the floor, with ready access for each occupant.

240.50, 240.51, 240.53. Plug fuses are limited to 125 volts between conductors or 150 volts line-to-neutral on a grounded-neutral system; Type S fuses are classified at not over 125 volts in ranges 0 to 15, 16 to 20, and 21 to 30 amperes.

240.67, 240.83. Fuses rated 1200 amperes or higher need documentation and a method to reduce clearing time to 0.07 seconds or less at the available arcing current; breakers with an interrupting rating other than 5000 amperes must be marked with it, and breakers switching fluorescent lighting are marked SWD or HID.

240.85, 240.86. A slash-rated breaker applies only where the voltage to ground does not exceed the lower value and the phase-to-phase voltage does not exceed the higher; series ratings are barred where motor circuits draw more than 1 percent of the interrupting rating of the lower-rated breaker.

1.7 Grounded Conductors, System Grounding, and Electrodes (Articles 200 and 250)

200.6, 200.7. Grounded conductors of 6 AWG or smaller need a continuous white or gray finish or three continuous white or gray stripes on other than green insulation; conductors of 4 AWG or larger may be marked white or gray at their terminations.

200.8. White or gray is limited to the grounded circuit conductor unless otherwise permitted; a reidentified conductor in switch loops may serve only as the supply to the switch, not as the return to the outlet.

250.4, 250.6. Systems need a low-impedance circuit able to carry the maximum ground-fault current, and the earth is not an effective ground-fault current path; grounding connections causing objectionable current may be discontinued, relocated, or interrupted, but fault currents are not objectionable current.

250.20, 250.21, 250.26. Ac systems of 50 volts to 1000 volts are grounded where the voltage to ground would not exceed 150 volts and where a 3-phase, 4-wire, wye-connected system uses the neutral as a circuit conductor; the neutral of a single-phase, 3-wire system is grounded.

250.24, 250.28. The grounding electrode conductor connection is made from the load end of the service conductors to the terminal or bus at the service disconnect, with an extra connection at or near an outdoor transformer unless the system is impedance grounded under 250.36 or 270.36.

250.30, 250.32. Separately derived systems need a supply-side bonding jumper to the first disconnecting means enclosure and the building grounding electrode system as their electrode, with a common grounding electrode conductor not smaller than 3/0 AWG copper or 250 kcmil aluminum.

250.50, 250.52, 250.53, 250.54. All present electrodes of 250.52(A)(1) through (A)(8) are bonded together, and a single rod, pipe, or plate electrode must be supplemented unless its resistance to earth is 25 ohms or less; bonded electrodes include a metal underground water pipe in earth contact for 3.0 m (10 ft) or more, a concrete-encased electrode of 6.0 m (20 ft) of rebar not less than 13 mm (1/2 in.) or bare copper not smaller than 4 AWG, and a ground ring of 6.0 m (20 ft) of bare copper not smaller than 2 AWG.

250.64, 250.66, 250.68, 250.70, 250.94. Table 250.66 ceilings are 6 AWG copper or 4 AWG aluminum for rod, pipe, and plate electrodes and 4 AWG copper for concrete-encased electrodes; interior metal water piping extends a connection only within 1.52 m (5 ft) of the point of entrance, and a 6 AWG or larger grounding electrode conductor exposed to damage needs RMC, IMC, Schedule 80 rigid PVC, RTRC-XW, EMT, or cable armor.

1.8 Bonding and Equipment Grounding Conductors (Article 250, Parts IV through VIII)

250.8, 250.92. Connections use listed pressure connectors, terminal bars, exothermic welding, machine screw-type fasteners engaging at least two threads, thread-forming machine screws engaging at least two threads, or other listed means — never solely by solder.

250.97, 250.100. Circuits over 250 volts to ground use the bonding methods of 250.92(B); hazardous (classified) locations require continuity of metal parts regardless of voltage, with classifications in 500.5, 505.5, and 506.5 and installation rules in 500.30, 505.30, and 506.30.

250.104, 250.110, 250.112, 250.134, 250.136, 250.138. Metal water piping is bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor, or the grounding electrodes, with the jumper sized per Table 250.102(C)(1).

250.118, 250.119. Permitted grounding conductors include copper and aluminum, RMC, IMC, EMT, and listed flexible metal conduit qualifying only with listed fittings, conductors protected at 20 amperes or less, size not over metric designator 35 (trade size 1 1/4), and total flexible and liquidtight flexible metal conduit not over 1.8 m (6 ft) in the same path.

250.122, 250.102. Equipment grounding conductors are sized from Table 250.122 by the OCPD ahead of the equipment — 6 AWG copper for 200 amperes, 4 AWG copper for 300 amperes, and 2 AWG copper for 500 amperes — never larger than the circuit conductors and increased proportionately where ungrounded conductors are increased for reasons other than 310.15(B), 310.15(C), or 310.16.

250.130, 250.142, 250.146, 250.148. A grounded conductor may contact metal parts only on the supply side of or within the service disconnect enclosure, at the main disconnect of a separate building, and at a separately derived system disconnect where 250.30(A)(1) permits, with load-side connections barred except at meter enclosures and under 250.32(B)(1) Exception No. 1; a grounding-type receptacle may replace a nongrounding type through the equipment grounding terminal bar at the circuit origin.

Code Navigation

Topic	NEC Section	What it covers
Terminations and conductor connections	110.14	Connection methods and termination temperature limitations
High-leg marking	110.15	Orange identification of the higher-voltage-to-ground phase on a 4-wire delta system
Field markings	110.21	Durability of markings, including the emergency disconnect marking of 230.70(B)(2)
Identifying disconnecting means	110.22	Permanent marking of what each disconnect controls
Lockable disconnects	110.25	Capability of being locked open, referenced by 225.25 and 230.76
Working space	110.26	Working clearances and egress around electrical equipment
In-sight requirements	110.29, 110.39	Sight-distance rules applied by 230.70(A)(1) and to equipment requiring service
Motor and combination loads	430.24, 430.36, 430.37, 430.52, 430.53	Motor load calculations, overload protection, and short-circuit protection
Transformer protection and vaults	450.5	Transformer overcurrent protection, with Article 450 Part III vaults referenced by 230.6(3)
Single-phase dwelling services	310.12	Conductor sizing for 120/240-volt dwelling services and feeders
Industrial control panel buses	409.102(B)	A, B, C phase arrangement, with B phase the higher voltage to ground
Protection of grounding electrode conductors	250.10	Cited by an approved explanation; see the NEC text for the rule
Decimal value cited by the bank, not a section number	30.5	Cited by an approved explanation; see the NEC text for the rule
Equipotential bonding of pools and similar installations	680.26	Cited by an approved explanation; see the NEC text for the rule

Common Exam Traps

The 800-ampere hinge in 240.4. At or below 800 amperes, 240.4(B) permits the next higher standard rating from Table 240.6(A); above 800 amperes, 240.4(C) requires conductor ampacity to equal or exceed the OCPD rating, so a next-size-up answer on a 1000-ampere feeder fails.

Tap fractions and lengths. The 3 m (10 ft) tap of 240.21(B)(1) uses the one-tenth fraction and must terminate within the enclosure of what it supplies; the 7.5 m (25 ft) tap of 240.21(B)(2) uses the one-third fraction and must terminate in a single breaker or fuse set that limits the load.

Grounded conductors are protected at both ends. Section 240.22 bars an OCPD in series with an intentionally grounded conductor unless all conductors open with no independent pole; 230.90(B) repeats the rule for the grounded service conductor.

The earth is never an effective ground-fault current path. Section 250.4(A)(5)(c) says so, and 250.4(B)(4) applies the same rule to ungrounded systems.

Three Article 250 tables, three different inputs. Table 250.66 sizes the grounding electrode conductor from the largest ungrounded service conductor, Table 250.102(C)(1) sizes main, system, and supply-side bonding jumpers, and Table 250.122 sizes equipment grounding conductors from the OCPD rating.

Distance limits hidden in exceptions. Interior metal water piping extends a grounding electrode conductor connection only within 1.52 m (5 ft) of the point of entrance under 250.68(C)(1); a point of attachment is never less than 3.0 m (10 ft) above finished grade under 230.26, and the AFCI lengths of 210.12(A)(3)(b) are 15.2 m (50 ft) for 14 AWG and 21.3 m (70 ft) for 12 AWG, never 30.5.

Cross-reference slip in the question bank. One explanation prints the 80 percent cord-and-plug rule as ref120.23(B)(1); the governing text is 210.23(B)(1), so treat that tag as a typographical slip for 210.23.

Practical Field Points

Decide the Article 120 part before touching a table: dwellings use 120.13 for branch circuits and 120.41 for the feeder unit load, farms add 120.102(B) and Table 120.103, health care facilities add Tables 120.110 and 120.111, and the optional methods of 120.82 through 120.84 apply only when their conditions are met.

Section 120.5(E) removed the extra 125 percent multiplier from load calculations, but 210.20(A), 215.4(A)(1), and 230.42(A)(1) still apply it when sizing conductors and overcurrent devices for continuous loads.

Count disconnects before ordering equipment: six is the maximum under 230.71 and 225.33, the combined rating must satisfy 230.79 and 230.80, and one- and two-family dwelling enclosures need the emergency disconnect marking with red background, white letters, and 13 mm (1/2 in.) letters.

Plan ground-fault protection early: 230.95 applies at a service disconnect rated 1000 amperes or more with more than 150 volts to ground, allows a 1200-ampere maximum setting and a one-second maximum delay at 3000 amperes and above, and requires an on-site test by primary current injection.

Treat bonding as a physical checklist: prepare surfaces, use listed fittings, install bonding jumpers around reducing washers and oversized, concentric, or eccentric knockouts per 250.92(B), and never rely on a standard locknut or bushing alone.

Document the neutral: 120.61(C) forbids reducing neutral capacity for the nonlinear loads it names, and paralleled service conductors need a grounded conductor in each raceway sized per Table 250.102(C)(1) and not smaller than 1/0 AWG under 250.24(D)(2).

Summary

Chapter 3 links the load-calculation rules of Article 120 to the wiring and protection rules of Articles 200, 210, 215, 225, 230, 240, and 250. Article 120 supplies the unit loads and demand factors: 3 volt-amperes per square foot for dwelling branch circuits under 120.13, 2 volt-amperes per square foot for the dwelling feeder under 120.41, 180 volt-amperes per receptacle under 120.14(I), the first 8 kVA plus 40 percent optional method of 120.82, and the 100, 75, 65, and 50 percent farm factors of Table 120.103. Section 120.5(E) states that load calculations do not require continuous loads at 125 percent.

Article 210 turns those loads into circuits: the voltage limits of 210.6, the required small-appliance, laundry, and bathroom circuits of 210.11, receptacle spacing at 1.8 m (6 ft) in 210.52(A)(1), GFCI and AFCI coverage in 210.8 and 210.12 with the 15.2 m (50 ft) and 21.3 m (70 ft) AFCI lengths, and the 7.5 m (25 ft) equipment-servicing outlet of 210.63.

Article 230 organizes the service: one service per building unless 230.4 permits otherwise, the conductor and clearance ladder of 230.23, 230.24, and 230.26, a disconnecting means rated per 230.79 and limited by 230.71, and ground-fault protection of equipment at 1000 amperes with a maximum setting of 1200 amperes.

Article 250 closes the loop by making faults clearable: it requires a low-impedance path, states that the earth is not one, governs where a grounded conductor may contact metal parts under 250.142, and provides three sizing tables — 250.66, 250.102(C)(1), and 250.122 — that must never be mixed.

Wiring and Protection