Disconnecting means for the machine, main controller, and individual motors
NEC 675.8 The main disconnect for an irrigation machine must sit at the power connection or in sight of the machine, be readily accessible and lockable open, and match the main controller's rating — but individual motor disconnects don't need to be readily accessible.
Q1 NEC 675.8
Under 675.8(C), the disconnecting means for an individual motor and controller on an irrigation machine is not required to be:
- A Rated for the motor's horsepower
- B Located per Article 430, Part IX
- C Capable of disconnecting all ungrounded conductors simultaneously
- D Readily accessible
Show answer & explanation
Correct: D — Readily accessible
675.8(C) specifically states the disconnecting means for individual motors and controllers is not required to be readily accessible, unlike the main disconnect in 675.8(B). It must still disconnect all ungrounded conductors simultaneously and be located per Article 430, Part IX.
Sizing and protecting collector rings
NEC 675.11 Power, control, and grounding collector rings on irrigation machines are all sized at 125% of the largest device's full-load current plus the FLC of every other device served, and all must sit in a suitable enclosure.
Q2 NEC 675.11
Which statement correctly describes the current-rating requirement for a collector ring used for control and signal purposes on an irrigation machine?
- A It must match the ampacity of the feeder supplying the irrigation machine
- B It must have a rating not less than 100% of the sum of all connected loads, since control signals draw negligible current
- C It must have a rating not less than 125% of the largest device's full-load current plus the FLC of all other devices served
- D It may be sized the same as a standard 15 A branch circuit regardless of connected load
Show answer & explanation
Correct: C — It must have a rating not less than 125% of the largest device's full-load current plus the FLC of all other devices served
675.11(B) requires control and signal collector rings to be rated at not less than 125% of the largest device's full-load current plus the FLC of all other devices served — the same formula used for power collector rings. Sizing to only 100% of connected load, to a generic 15 A rating, or to match the feeder ampacity all skip this required margin.
Calculating equivalent current ratings for intermittent-duty machines
NEC 675.7 Irrigation machines with multiple motors on intermittent duty use special equivalent continuous-current and locked-rotor formulas instead of straight Article 430 motor sizing.
Q3 NEC 675.7
A center-pivot irrigation machine has several motors that cycle on and off rather than running continuously. Which article governs determining equivalent current ratings for its conductors and overcurrent protection?
- A Article 675, but only when the machine has a single motor
- B Article 430, but only for the largest motor on the circuit
- C Article 675, using the equivalent continuous-current and locked-rotor formulas
- D Article 430, applied exactly as for any continuous-duty motor
Show answer & explanation
Correct: C — Article 675, using the equivalent continuous-current and locked-rotor formulas
Per 675.7, where irrigation machines have inherent intermittent duty, the equivalent current rating determinations in 675.7(A) and (B) apply instead of straight Article 430 sizing. Article 430 alone applies only where intermittent duty is not involved, not as a blanket rule for irrigation machines.
Low-voltage control/signal circuit allowances (multi-source energy, connectors)
NEC 675.16 A 30-volt-or-less control circuit meeting Article 725 Part II skips the extra disconnect and the 250.124(A) plug/connector construction rule.
Q4 NEC 675.16
Equipment in an irrigation machine enclosure receives power from a second source in addition to the main feed. Under what condition does 675.16 waive the requirement for a separate disconnecting means for that second source?
- A The second source is 50 volts or less and labeled as a control circuit
- B The second source is disconnected automatically when the main feed is de-energized
- C The second source is fused separately from the main feed
- D The second source is 30 volts or less and meets Part II of Article 725
Show answer & explanation
Correct: D — The second source is 30 volts or less and meets Part II of Article 725
675.16 waives the extra disconnecting means only when the additional source is 30 volts or less and meets Part II of Article 725. A 50-volt threshold, separate fusing, or automatic de-energization with the main feed are not the standard this section sets.
Multiple small motors on one protected branch circuit
NEC 675.10 An irrigation machine circuit protected at 30 A or less can feed several small motors without individual branch-circuit short-circuit protection, as long as each motor is ≤2 hp, ≤6 A full-load, and has its own overload protection.
Q5 NEC 675.10 Code lookup
An irrigation machine's motor circuit is protected at 30 amperes, 480 volts, and feeds several small motors. Each motor's full-load current is 5 amperes and it does not exceed 2 hp. Which section lists the conditions that must all be met to use several motors on this one protected branch circuit?
- A 675.7(A)
- B 675.10(A)
- C 675.8(C)
- D 675.9
Show answer & explanation
Correct: B — 675.10(A)
675.10(A) sets the conditions (2 hp max, 6-amp full-load rating max, individual overload protection, tap sizing) for putting several small motors on one 30-ampere-or-less protected circuit. 675.9 covers branch-circuit conductor sizing generally, not the multi-motor conditions, and 675.7(A) and 675.8(C) address current ratings and individual disconnects, not this permission.
Sizing center pivot irrigation circuits using equivalent current ratings
NEC 675.22 Center pivot circuits use two equivalent-current formulas — one for conductors and devices, one for locked-rotor withstand — instead of the usual motor-circuit sizing rules.
Q6 NEC 675.22 Code lookup
A center pivot irrigation machine has one 10 A drive motor (the largest) and three additional 5 A drive motors all on the same branch circuit. Which NEC section provides the formula for calculating the equivalent continuous-current rating used to size the branch-circuit conductors?
- A 675.10(A)
- B 675.9
- C 675.22(B)
- D 675.22(A)
Show answer & explanation
Correct: D — 675.22(A)
675.22(A) gives the formula (125% of the largest motor FLC plus 60% of the sum of the remaining motors' FLC) for the equivalent continuous-current rating used to select branch-circuit conductors and devices. 675.22(B) instead covers the equivalent locked-rotor current calculation, a different rating used for a different purpose.
Irrigation cable construction and listed alternates
NEC 675.4 Irrigation machine cable needs stranded conductors, moisture/flame-resistant core, a metallic overlay, and a tough outer jacket — or a listed cable that meets those same specs.
Q7 NEC 675.4
Per 675.4(A), what minimum operating temperature rating must the conductor insulation in irrigation machine interconnecting cable have?
- A 75°C
- B 60°C
- C 90°C
- D 105°C
Show answer & explanation
Correct: A — 75°C
675.4(A) requires conductor insulation listed in Table 310.4(1) for an operating temperature of 75°C (167°F) or higher, and for use in wet locations. 60°C is too low to meet the minimum, while 90°C and 105°C are higher-rated options not specifically required by this section.
Supporting and terminating irrigation cable
NEC 675.4(C) Irrigation cable must be strapped every 4 ft with fittings made for it, and every termination point needs a fitting designed for that cable and its service conditions.
Q8 NEC 675.4(C)
Per 675.4(C), what is the maximum spacing between supports for irrigation cable?
- A 1.2 m (4 ft)
- B 3.0 m (10 ft)
- C 2.5 m (8 ft)
- D 1.8 m (6 ft)
Show answer & explanation
Correct: A — 1.2 m (4 ft)
675.4(C) sets the maximum support interval for irrigation cable at 1.2 m (4 ft). The longer spacings listed are common intervals for other wiring methods but do not apply here.
Ground-fault protection for pier feeders & branch circuits
NEC 682.15(B) Feeder and branch-circuit conductors on piers need ground-fault protection at 30 mA or less, aimed at equipment protection, not personnel.
Q9 NEC 682.15(B)
Under 682.15(B), what is the maximum ground-fault protection level required for feeder and branch-circuit conductors installed on piers?
- A 5 mA
- B 30 mA
- C 100 mA
- D 6 mA
Show answer & explanation
Correct: B — 30 mA
682.15(B) sets the threshold at 30 mA for feeder and branch-circuit conductors on piers. The 5 mA and 6 mA figures are personnel-protection GFCI levels used elsewhere in the Code, not the equipment-protection level required here.
Bonding the equipotential plane: parts, equipment, and walking surfaces
NEC 682.33(C)(1) Equipotential plane bonding conductors must be solid 8 AWG copper minimum, and the plane extends to qualifying outdoor equipment and the walking surface within 36 in. of it.
Q10 NEC 682.33(C)(1)
Per 682.33(C)(1), what type of conductor is required to bond the parts of an equipotential plane together?
- A Insulated copper, stranded or solid, not smaller than 4 AWG
- B Stranded copper, insulated or bare, not smaller than 6 AWG
- C Solid aluminum, not smaller than 8 AWG
- D Solid copper, insulated, covered, or bare, not smaller than 8 AWG
Show answer & explanation
Correct: D — Solid copper, insulated, covered, or bare, not smaller than 8 AWG
682.33(C)(1) requires solid copper conductors, insulated, covered, or bare, sized no smaller than 8 AWG. The stranded 6 AWG option matches perimeter-surface bonding rules elsewhere in pool wiring, not this equipotential plane requirement, and aluminum isn't a recognized material here.
Where equipotential planes are required vs. not required
NEC 682.33(A) An equipotential plane goes around outdoor service equipment or disconnects that control equipment in or on the water, extending at least 36 in. from where a person could stand and touch it — but not around the controlled equipment itself.
Q11 NEC 682.33(A)
An outdoor disconnecting means with a metallic enclosure controls a pump located in a pond, and its controls are accessible to personnel. Per 682.33(A), what is required?
- A An equipotential plane extending at least 900 mm (36 in.) from the equipment in all directions a person could stand and contact it
- B No equipotential plane, since the disconnect is outdoors and not submerged
- C An equipotential plane extending 900 mm (36 in.) only on the side facing the water
- D An equipotential plane only around the pump itself in the water
Show answer & explanation
Correct: A — An equipotential plane extending at least 900 mm (36 in.) from the equipment in all directions a person could stand and contact it
682.33(A) requires the equipotential plane around outdoor service equipment or disconnects that are metallic-enclosed, personnel-accessible, and control equipment in or on the water — extending not less than 900 mm (36 in.) in all directions a person could stand and contact it. The pump itself doesn't need its own plane per 682.33(B), being outdoors alone doesn't exempt it, and the requirement isn't limited to one side.
Electrical connection height & sealing above/below datum plane
NEC 682.12(A) Connections belong at least 12 in. above the deck and at or above the electrical datum plane; anything lower must be a submersion-rated sealed system.
Q12 NEC 682.12(A)
An electrician is installing an electrical connection on a fixed pier structure that is not intended to operate while submerged. Per 682.12(A), where must it be located?
- A At least 300 mm (12 in.) above the deck, with no restriction relative to the datum plane
- B At least 300 mm (12 in.) above the electrical datum plane only, regardless of deck height
- C At least 300 mm (12 in.) above the deck, and not below the electrical datum plane
- D Anywhere above the waterline, as long as it is in a wet-location box
Show answer & explanation
Correct: C — At least 300 mm (12 in.) above the deck, and not below the electrical datum plane
682.12(A) requires both conditions on a fixed structure: at least 300 mm (12 in.) above the deck AND not below the electrical datum plane. The option dropping the datum-plane limit and the option dropping the deck-height requirement each capture only half of the rule; the wet-location-box-only answer confuses this with the floating-structure splice allowance.
Disconnecting means for marina/boatyard equipment
NEC 682.14 Submersible and floating equipment needs a marked, land-mounted disconnect within 750 mm of its receptacle, set back 1.5 m from shore and 300 mm above the datum plane.
Q13 NEC 682.14
A floating fountain at a marina is connected by a cord-and-plug to a shore receptacle. Which statement about the required disconnecting means is correct?
- A The plug must be removed from the receptacle to isolate the fountain
- B A breaker or switch must isolate the fountain without requiring the plug to be pulled
- C The disconnect only needs to be marked if more than one receptacle is present
- D Only a circuit breaker qualifies; a switch is not acceptable
Show answer & explanation
Correct: B — A breaker or switch must isolate the fountain without requiring the plug to be pulled
Per 682.14, the disconnecting means must isolate the equipment from its supply without requiring the plug to be removed from the receptacle. 682.14(A) permits a circuit breaker, a switch, or both, and it must always be marked to designate the receptacle or outlet it controls — not just when multiple receptacles exist.
Cord-and-plug connections for submersible/floating equipment
NEC 682.13(C) Submersible or floating marina equipment must connect by cord and plug, using extra-hard usage cord listed with a 'W' suffix.
Q14 NEC 682.13(C)
Per 682.13(C), how must submersible or floating equipment at a marina receive electrical power?
- A Cord-and-plug connection using extra-hard usage cord
- B Direct burial cable rated for wet locations
- C Cord-and-plug connection using standard hard usage cord
- D Hardwired directly using liquidtight flexible metal conduit
Show answer & explanation
Correct: A — Cord-and-plug connection using extra-hard usage cord
682.13(C) requires cord-and-plug connection using extra-hard usage cord listed with a 'W' suffix — hardwiring or a lesser-duty cord type doesn't meet the rule.
GFCI protection for marina outlets
NEC 682.15(A) Outlets at marinas and boatyards fed at up to 150 volts to ground and 60 amperes, single-phase, must have personnel GFCI protection, on top of any 210.8 requirement.
Q15 NEC 682.15(A)
At a marina, an outlet is supplied by a branch circuit rated 120 volts to ground and 50 amperes, single-phase. Per 682.15(A), what protection is required?
- A No GFCI protection because the circuit exceeds typical receptacle ratings
- B GFCI protection only if the outlet is within 6 ft of the water's edge
- C Personnel ground-fault circuit-interrupter protection
- D Equipment ground-fault protection instead of personnel GFCI protection
Show answer & explanation
Correct: C — Personnel ground-fault circuit-interrupter protection
Under 682.15(A), any outlet supplied by a branch circuit not exceeding 150 volts to ground and 60 amperes, single-phase, requires GFCI protection for personnel — this circuit fits that description exactly. There is no exception based on distance to water, and equipment ground-fault protection is a different, higher-current concept not what this section requires.
Equipment grounding conductor requirements for natant wiring
NEC 682.31 In natant (floating) wiring, boxes, equipment frames, and receptacle grounding terminals must all tie to an insulated copper EGC sized per 250.122 but never smaller than 12 AWG.
Q16 NEC 682.31
What type of conductor must be used as the equipment grounding conductor for natant wiring per 682.31(B)?
- A Insulated aluminum conductor not smaller than 12 AWG
- B Bare copper conductor sized per 250.122
- C Insulated copper conductor not smaller than 8 AWG
- D Insulated copper conductor sized per 250.122, not smaller than 12 AWG
Show answer & explanation
Correct: D — Insulated copper conductor sized per 250.122, not smaller than 12 AWG
682.31(B) requires an insulated copper conductor sized under 250.122 with a 12 AWG floor. A bare copper conductor is the equipotential bonding style used elsewhere for pools, not this circuit's EGC; aluminum isn't permitted here; and 8 AWG is not the minimum this section sets — 12 AWG is.
Electrical Datum Plane for Bodies of Water
NEC 682.5 Every clearance rule near water starts from the electrical datum plane, not the water surface you see on install day.
Q17 NEC 682.5
A dock is built on a lake with no tidal influence. Per 682.5, where is the electrical datum plane established?
- A 300 mm (12 in.) above the level of the deck
- B 750 mm (30 in.) above the water level at the structure
- C 600 mm (2 ft) above the highest high tide for the area
- D 600 mm (2 ft) above the highest normal water level for the area
Show answer & explanation
Correct: D — 600 mm (2 ft) above the highest normal water level for the area
682.5(2) sets the datum plane for non-tidal land areas at 600 mm (2 ft) above the highest normal water level. The highest-high-tide option applies only to tidal areas under 682.5(1), and the 750 mm / 300 mm figures are the floating-structure rule, not the fixed-land rule.
Ungrounded DC and control circuits for orderly shutdown
NEC 685.12 Article 685 lets two-wire DC circuits and low-voltage control circuits stay ungrounded so a fault doesn't force an uncontrolled shutdown.
Q18 NEC 685.12
Under 685.12, which dc circuits are permitted to be ungrounded?
- A Three-wire dc circuits with a grounded neutral
- B Dc circuits supplying receptacle outlets only
- C Two-wire dc circuits
- D Any dc circuit under 600 volts
Show answer & explanation
Correct: C — Two-wire dc circuits
685.12 specifically permits two-wire dc circuits to be ungrounded. It does not extend this permission to three-wire systems, all circuits under 600 volts generally, or circuits defined by receptacle use.
What qualifies as a large-scale PV electric supply station
NEC 691.4 Article 691 only applies to non-utility-controlled PV stations that meet all seven 691.4 criteria, including a minimum 5000 kW inverter capacity and no siting on buildings.
Q19 NEC 691.4
A PV site has an inverter generating capacity of 3000 kW and operates as a standalone facility with no ties to other sites. Does it qualify as a large-scale PV electric supply station under Article 691?
- A Yes, because any utility-interconnected PV site is automatically covered by Article 691
- B No, because Article 691 only applies to sites installed on buildings
- C Yes, because 691.4 sets no minimum capacity for standalone sites
- D No, because it falls below the 5000 kW threshold and is not part of a group reaching that total
Show answer & explanation
Correct: D — No, because it falls below the 5000 kW threshold and is not part of a group reaching that total
691.4(7) requires at least 5000 kW of inverter capacity, or membership in a group of facilities whose combined capacity exceeds 5000 kW. A standalone 3000 kW site meets neither condition, so it doesn't qualify. Article 691 in fact prohibits building-mounted installations per 691.4(5), the opposite of the last option.
Engineering documentation package for PV supply stations
NEC 691.6 Large-scale PV supply stations run on stamped engineering documentation, not field inspection alone — design, construction conformance, DC voltage calcs, fire mitigation, and fence grounding all get papered by a licensed PE.
Q20 NEC 691.6
Who is authorized to stamp the independent engineering reports required for a large-scale PV electric supply station under Article 691?
- A The electrical contractor performing the installation
- B Any licensed engineer employed by the utility interconnecting the station
- C A licensed professional electrical engineer retained by the system owner or installer
- D The local AHJ's chief electrical inspector
Show answer & explanation
Correct: C — A licensed professional electrical engineer retained by the system owner or installer
691.6 and 691.7 both specify the independent engineer must be a licensed professional electrical engineer retained by the system owner or installer. The installing contractor, the AHJ inspector, and a utility-employed engineer are not what the section calls for — the stamp has to come from a PE retained by the owner/installer specifically.
Fuel cell system disconnecting means
NEC 692.13 A fuel cell system needs a single readily accessible switch or breaker to disconnect all current-carrying conductors, plus a shock-hazard warning sign if terminals stay energized when open.
Q21 NEC 692.13 Code lookup
A fuel cell system power source feeds a commercial building and you need to establish means to disconnect all of its current-carrying conductors from every other conductor system in the building. Which section requires this disconnection of all conductors?
- A 692.61
- B 692.13
- C 692.60
- D 692.17
Show answer & explanation
Correct: B — 692.13
692.13 is the section requiring means to disconnect all current-carrying conductors of the fuel cell system power source from all other conductors in the building. 692.60 covers connection to other systems (interconnection), and 692.61 covers transfer switches — neither addresses the general requirement to disconnect all conductors.
Connecting fuel cell systems to other sources or the grid
NEC 692.60 Fuel cell systems tied to other power sources follow Article 705's interconnection rules, and non-grid-interactive systems with utility backup need an isolating transfer switch.
Q22 NEC 692.60
A non-grid-interactive fuel cell system uses the utility grid as backup power. What does 692.61 require?
- A A transfer switch that maintains isolation from the grid
- B A dedicated disconnecting means only, with no transfer switch
- C A ground-fault protection device sized for the grid
- D An automatic paralleling device between the fuel cell system and the grid
Show answer & explanation
Correct: A — A transfer switch that maintains isolation from the grid
692.61 requires a transfer switch in non-grid-interactive systems that use utility grid backup, and that switch must keep the fuel cell system isolated from the grid. Since the system is non-grid-interactive, it never parallels with the utility, ruling out an automatic paralleling device; a disconnecting means alone doesn't satisfy the isolation requirement.
Marking the fuel cell power source disconnect
NEC 692.50 The fuel cell disconnect must be marked on site with system type, output voltage, output power rating, and continuous output current.
Q23 NEC 692.50
Per 692.50, which of the following must appear on the marking at a fuel cell power source's disconnecting means?
- A Fuel type and tank pressure rating only
- B Output power rating and continuous output current rating
- C Maximum short-circuit current rating of the disconnect only
- D Installer's license number and inspection date
Show answer & explanation
Correct: B — Output power rating and continuous output current rating
692.50 requires the marking to specify the fuel cell system, output voltage, output power rating, and continuous output current rating. Short-circuit current, installer details, and fuel/tank pressure data are not part of this required marking.
Stored energy warning sign at service disconnect
NEC 692.52 A fuel cell system with electrical energy storage devices needs a warning sign at the service disconnecting means, per the 110.21(B) marking rules.
Q24 NEC 692.52
A fuel cell power system on a premises stores electrical energy internally. Where does 692.52 require the associated warning sign to be placed?
- A At the utility meter
- B At the location of the service disconnecting means of the premises
- C Inside the fuel cell enclosure only
- D At the fuel cell system's own disconnecting means only
Show answer & explanation
Correct: B — At the location of the service disconnecting means of the premises
692.52 requires the warning sign at the location of the service disconnecting means of the premises, not merely at the fuel cell's own disconnect, the enclosure, or the meter.
Sizing fuel cell feeder conductors and neutral
NEC 692.8 Size fuel cell feeder conductors to the greater of the nameplate rated current or the overcurrent device rating, and check the neutral for unbalanced load plus fuel cell output.
Q25 NEC 692.8
Under 692.8(B), how is the minimum ampacity of feeder conductors from a fuel cell system to the premises wiring system determined?
- A The sum of the nameplate rated circuit current and the overcurrent protective device rating
- B The greater of the nameplate rated circuit current or the fuel cell system's overcurrent protective device rating
- C 125% of the nameplate rated circuit current, matching continuous-load sizing for other sources
- D The nameplate rated circuit current only, regardless of the overcurrent device rating
Show answer & explanation
Correct: B — The greater of the nameplate rated circuit current or the fuel cell system's overcurrent protective device rating
692.8(B) requires the feeder conductor ampacity to be not less than the greater of the nameplate rated circuit current or the fuel cell system's overcurrent protective device rating — it's a 'take the bigger one' comparison, not a sum and not a fixed multiplier like the 125% continuous-load rule used elsewhere.