CSLB C-10 Electrical Contractor flashcards

Nonmetallic-sheathed cable approved for concealed dry-location wiring in dwellings, consisting of insulated conductors plus a bare equipment grounding conductor inside a plastic jacket.

• Governed by NEC Article 334
• Limited to dry locations unless rated NM-B for damp per listing
• Not permitted in commercial high-rise or exposed to physical damage without protection

Memory trick: 'N' for Normal dry homes = NM-B.

NEC Table 430.52 sets maximum percentages of motor FLC for sizing branch-circuit short-circuit and ground-fault protective devices, varying by device type.

• Inverse-time breaker: max 250% of FLC (typical motors)
• Non-time delay fuse: max 300% of FLC
• Instantaneous-trip breaker: max 800% (or higher with exceptions)
• Exception allows next standard size up if calculated value isn't standard

Memory trick: Inverse-time breakers get two-and-a-half times the current.

When multiple conductor sizes share a raceway, total their cross-sectional areas and compare to the 40% fill area from NEC Chapter 9 Table 4 to find the minimum trade size.

• Use Table 5 for individual conductor areas
• Use Table 4 for raceway 40% fill areas
• Round up to the next trade size that fits total area

Memory trick: Add up all the wire areas, then find a pipe big enough for 40% comfort

Branch-circuit conductors for a single continuous-duty motor must have an ampacity of at least 125% of the motor's full-load current rating.

• Formula: conductor ampacity ≥ 1.25 × FLC
• Use motor FLC from Table 430.250, not nameplate current, when applicable
• Select the smallest Table 310.16 conductor meeting the calculated ampacity

Memory trick: Motors need conductors sized a quarter bigger than FLC.

When SE cable feeds a subpanel, it must include a separate equipment grounding conductor because neutral-ground bonding is only allowed at the service.

• Neutral and ground must be separated at subpanels
• Feeders to separate structures need an EGC
• A grounding electrode system is still required at detached structures

Memory trick: Only the service gets to marry neutral and ground—subpanels must stay separated

Ferrous metal conduit installed in contact with corrosive soil or concrete requires supplementary corrosion protection beyond standard galvanizing.

• Applies to RMC and other ferrous raceways
• Concrete encasement alone may not be enough in corrosive soils
• Approved coatings like PVC jacketing satisfy this requirement

Memory trick: Corrosive soil needs a coat, not just concrete

Continuous loads (operating 3+ hours) require branch-circuit conductors and OCPDs rated at not less than 125% of the continuous load per NEC 210.19/210.20.

• Continuous = operates 3 hours or more
• Formula: OCPD/conductor ≥ 1.25 × continuous load
• Round up to next standard OCPD size if calculated value isn't standard

Memory trick: Continuous loads need a 25% safety cushion.

NEC 430.32 sets maximum overload relay/device settings based on motor service factor or temperature rise to protect against sustained overcurrent.

• SF ≥1.15 or temp rise ≤40°C: max 125% of FLC
• All other motors: max 115% of FLC
• Overload protects windings from long-term overheating, not short circuits

Memory trick: High service factor motors get a bigger 125% cushion.

A bonding grid using 8 AWG solid copper conductor connects pool structural and metal components to equalize voltage and reduce shock hazard, independent of the service grounding electrode system.

• Required per NEC 680.26 for permanently installed pools
• Bonds pool shell, deck reinforcing steel, and metal fittings within 3 feet of pool
• Not required to connect to the building's grounding electrode system

Memory trick: Bonding equalizes voltage; grounding sends fault current home — they're not the same job.

Multiwire branch circuits must have a means to disconnect all ungrounded conductors simultaneously to protect against overloading the shared neutral.

• Handle ties or two-pole breakers satisfy this requirement
• Protects against neutral overcurrent if one circuit is serviced while the other remains live
• Applies to circuits sharing a neutral across two ungrounded conductors

Memory trick: Tie the handles so the neutral never overloads alone.

Table 110.26(A)(1) sets minimum depth of clear working space in front of electrical equipment based on voltage and condition (1, 2, or 3).

• Condition 1: exposed live parts, grounded parts not on opposite side
• Condition 2: exposed live parts, grounded parts on opposite side
• Condition 3: exposed live parts on both sides
• 151-600V Condition 2 = 3.5 ft

Memory trick: More danger on both sides means more distance required.

NEC Table 300.5 reduces minimum burial depth to 12 inches for 120V, 20A-or-less circuits protected by GFCI.

• Standard direct burial depth is 24 inches
• GFCI + 20A max reduces depth to 12 inches
• Depth measured from top of cable to finished grade

Memory trick: GFCI digs a shallower hole—only 12 inches deep

Voltage drop is calculated using VD = (2 × K × I × D) / CM for single-phase circuits, where K is the resistivity constant, I is current, D is one-way distance, and CM is circular mils.

• Copper K ≈ 12.9; Aluminum K ≈ 21.2
• NEC recommends max 3% for branch circuits, 5% total (feeder+branch)
• Formula uses one-way distance but factor of 2 accounts for round trip

Memory trick: Double the distance current travels, divide by wire's circular mils.

At any panel downstream of the service (or a separately derived system), the grounded conductor must be kept isolated from equipment grounding conductors and the enclosure.

• 4-wire feeder required to a subpanel with separate neutral and ground
• Bonding only occurs at the service or SDS transformer
• Isolated neutral bus prevents parallel current paths on the EGC

Memory trick: Bond once at the source, isolate everywhere downstream.

Locations with combustible dust in the air under normal conditions require threaded rigid metal conduit or IMC with dust-tight fittings per NEC 502.10.

• Applies to grain elevators, flour mills, and similar dust-producing facilities
• Threaded joints must be dust-tight, not just tight
• Flexible connections require dust-tight flexible fittings listed for the location

Memory trick: Dust demands threads — tight joints keep sparks in their beds.

Allows tap conductors up to 10 feet long, run in a raceway, to be sized smaller than the feeder they tap from, provided they meet minimum ampacity and termination requirements.

• Tap ampacity must be at least 1/10 of feeder OCPD rating
• Tap length limited to 10 feet, enclosed in a raceway
• Must terminate in a single OCPD not exceeding the tap conductor's ampacity

Memory trick: Ten feet, ten percent — the tap rule's simple scent.

Raceway nipples 24 inches or less in length may be filled to 60% of their cross-sectional area, and conductor bundling adjustment factors do not apply.

• Standard multi-conductor fill limit is 40%
• Nipples ≤24 inches allow 60% fill
• No ampacity adjustment factors apply to nipples

Memory trick: Short nipples get a bigger appetite—60% instead of 40%

Type AC cable includes an internal aluminum bonding strip in contact with its spiral metal armor, providing an effective grounding path per NEC 320.108.

• Distinguishes AC cable from MC cable construction
• Armor plus bonding strip together serve as the equipment ground
• MC cable usually has a separate grounding conductor instead

Memory trick: 'AC = Aluminum strip inside the Coil.'

The grounding electrode conductor size is based on the size of the largest ungrounded service-entrance conductor, per NEC Table 250.66.

• Table ranges increase GEC size as service conductor size increases
• 400 kcmil copper falls in the 350-600 kcmil range
• Corresponding GEC size is 1/0 AWG copper

Memory trick: Bigger service wires need a bigger ground wire—look it up in Table 250.66

Antioxidant compound is applied to aluminum conductor terminations to prevent oxide buildup that increases resistance and heat.

• Aluminum oxidizes quickly when exposed to air
• Antioxidant compound maintains low-resistance connections
• Only use devices listed AL-CU or CO/ALR for aluminum conductors

Memory trick: Grease the aluminum to stop the oxide from growing.

Electrical metallic tubing (EMT) must be securely fastened at regular intervals to prevent sagging and mechanical damage.

• Support required within 3 ft of each box or termination.
• Maximum support interval along the run is 10 ft.
• Applies to NEC Article 358 (EMT).

Memory trick: 'Three near the box, ten in a row' keeps EMT secure.

For single-conductor cables 1000 kcmil and larger, NEC 392.22(A)(1) requires the sum of cable diameters not exceed the cable tray width.

• Rule applies to conductors 1000 kcmil and larger
• Sum of diameters ≤ tray width (not area-based)
• Divide tray width by individual cable diameter to find max count

Memory trick: Big cables line up side by side, never wider than the tray.

Per NEC 314.16(B), each strap/yoke supporting a device counts as two conductor-volume allowances based on the largest conductor connected to it.

• Conductors: 1 volume allowance each based on size.
• All grounds together: 1 allowance based on largest ground.
• Device yoke: 2 allowances based on largest conductor connected.

Memory trick: 'Grounds unite, devices double' — grounds count once, yokes count twice.

Locations where flammable gases/vapors are present under normal operating conditions require explosion-proof wiring methods per NEC Article 501.

• Threaded RMC or IMC required per 501.10(A)
• Seals required per 501.15 to prevent flame/gas propagation
• Division 2 areas allow some additional wiring methods with restrictions

Memory trick: Explosive vapors demand threaded, sealed steel conduit.

All 125V, 15/20A receptacles installed outdoors at dwelling units must have GFCI protection.

• Applies regardless of receptacle height or accessibility
• Covers patios, balconies, and yard receptacles
• Part of NEC 210.8(A) dwelling unit GFCI locations list

Memory trick: Outside, water lurks — GFCI must work.

Three-phase voltage drop uses the formula VD = (√3 × K × I × D) / CM, incorporating the square root of 3 factor unique to three-phase circuits.

• √3 (1.732) factor distinguishes 3-phase from single-phase VD formulas
• K = 12.9 for copper, 21.2 for aluminum (approximate constants)
• Recommended max voltage drop is typically 3% for branch circuits/feeders combined 5%

Memory trick: Three phases need the root-three factor before you find the drop.

Conductors run in parallel per NEC 310.10(H) must match in size, length, and material, with total ampacity equal to the sum of each conductor's individual ampacity.

• Applies to conductors 1/0 AWG and larger
• All parallel sets must be identical in every conduit
• Total ampacity = sum of each conductor's ampacity

Memory trick: Twins in parallel add their strength together

A pliable corrugated raceway used for concealed wiring in buildings of limited height, not for exposed or hazardous applications.

• Limited to buildings 3 floors or less unless concrete-encased
• Not permitted exposed to physical damage
• Prohibited in hazardous locations

Memory trick: ENT hides inside walls, never shows its face outside

At service equipment, certain connection methods (like reducing washers or oversized knockouts) are not considered reliable for bonding and require a supplemental bonding jumper.

• 250.92(B) lists acceptable bonding methods at service equipment
• Reducing washers alone are not an acceptable bonding method there
• A bonding jumper must bypass unreliable connections to maintain fault current path

Memory trick: Washers wobble, so wire a jumper to guarantee the ground path.

NEC 250.92(B) requires bonding jumpers at service equipment where concentric or eccentric knockouts may compromise the reliability of the grounding path.

• Concentric rings reduce metal thickness, risking poor continuity.
• Bonding jumpers or listed bonding bushings restore a reliable path.
• Applies specifically at service equipment enclosures.

Memory trick: 'Rings can break the ring of safety' — bond around weak knockouts.

NEC Chapter 9, Annex C provides pre-calculated maximum conductor fill counts for specific raceway types and conductor types, eliminating manual area calculations.

• Tables apply only when all conductors are the same size and type.
• Table C.1 is specific to EMT.
• Using Annex C tables directly is faster than manual 40%/31% fill calculations.

Memory trick: 'Same size, same table' — Annex C works only for uniform conductors.

The EGC size for a circuit is based on the rating of the circuit's overcurrent protective device, per NEC Table 250.122, independent of actual conductor ampacity.

• 60A OCPD → 10 AWG copper
• 100A OCPD → 8 AWG copper
• 200A OCPD → 6 AWG copper
• EGC must be increased proportionally if ungrounded conductors are upsized per 250.122(B)

Memory trick: 'Match the breaker, not the load' when sizing ground wires.

For transformers 600V or less with primary current 9A or greater, primary-only overcurrent protection may be sized up to 125% of primary FLC, rounded up to the next standard device size if needed.

• If primary current is less than 9A, up to 167% is permitted
• If primary current is less than 2A, up to 300% is permitted
• Rounding to next standard size is allowed per 240.6(A) when 125% doesn't match a standard rating

Memory trick: Above 9 amps, 125% is your cap — round up to fill the gap.

Type MC (Metal-Clad) cable uses an interlocked or smooth metal armor; standard versions are not moisture-sealed and require listing for wet or underground use.

• Interlocked armor does not prevent water intrusion by design.
• Special jacketed/listed MC cable is required for wet locations or direct burial.
• MC cable is common in commercial branch circuits and feeders.

Memory trick: 'Metal armor loves air, hates water' — needs a jacket to go underground.

Raceways such as EMT, IMC, and RMC are limited to 360 degrees of total bend between pull points to allow safe conductor installation.

• 360° = four 90° bends maximum
• Applies between pull points (boxes, conduit bodies)
• Exceeding this makes conductor pulling difficult and risks damage

Memory trick: Four quarter-turns and stop — 360 is the pull-point cap.

Type NM cable must be stapled/secured within 12 inches of boxes with clamps and at 4.5-foot intervals along the run.

• 12 inches from box with clamp
• 4.5 feet between staples in the run
• 8-inch exception applies only to single-gang nonmetallic boxes without clamps

Memory trick: A foot from the box keeps the cable in check.

When conductors of different sizes share a raceway, sum their individual cross-sectional areas from Table 5 and compare to the raceway's 40% fill area from Table 4.

• Sum all conductor areas including the EGC
• Use 40% fill allowance for 3 or more conductors
• Round up to the next standard trade size if the total area doesn't fit the smaller size

Memory trick: 'Add them all, then find the box that fits 40%.'

Conductor ampacity is limited by the lowest temperature rating among the conductor, termination, and equipment, per NEC 110.14(C).

• 90°C insulation doesn't guarantee 90°C ampacity use
• Terminals often rated 60°C or 75°C
• Always use the lowest rating in the circuit path

Memory trick: The weakest link (coolest terminal) sets the ampacity limit

The motor disconnecting means must be rated at least 115% of the motor's full-load current for motors rated 600V or less.

• Applies to the disconnect switch, not the branch-circuit protection
• Use Table 430.250 (3-phase) or 430.248 (1-phase) for FLC values
• Distinct from 250% short-circuit protection sizing under 430.52

Memory trick: 115% keeps the switch safely ahead of the motor's pull.

GFCI protection is required for all 125V, 15A/20A receptacles serving kitchen countertop surfaces.

• NEC 210.8(A)(6) governs dwelling kitchen receptacles
• GFCI trips on ground-fault current as low as 4-6mA
• Applies regardless of distance from sink

Memory trick: Kitchens and wet areas always get GFCI guards.

Box fill calculations count conductors, one allowance for all grounding conductors combined, and two volume units per device yoke.

• Each current-carrying conductor = 1 unit
• All grounds together = 1 unit (based on largest conductor)
• Each device yoke = 2 units
• 12 AWG = 2.25 in³ per unit

Memory trick: Conductors count once, grounds count once total, but devices count double

Conductors supplying continuous loads (3 hours or more) must be sized at 125% of the load current using the appropriate temperature column of Table 310.16.

• 125% factor applies to continuous loads per NEC 210.19(A).
• Use the ampacity column matching the equipment's terminal temperature rating.
• Round up to the next standard conductor size that meets or exceeds the requirement.

Memory trick: 'Continuous loads need a quarter more' — multiply by 1.25.

Feeder conductors must be sized at 125% of continuous loads plus 100% of non-continuous loads.

• Continuous load = operates 3+ hours
• 125% factor applies only to continuous portion
• Add non-continuous load at 100% to get total minimum ampacity

Memory trick: Continuous loads get a 25% cushion; non-continuous loads stay as-is.

Conductors in a metal wireway may not exceed 20% of the wireway's interior cross-sectional area.

• 20% max fill for general conductor fill
• Multiply total area by 0.20 to find max fill
• Additional derating applies if more than 30 current-carrying conductors are present

Memory trick: One-fifth full keeps the wireway cool.

NEC 250.53(A)(2) requires a single rod, pipe, or plate electrode exceeding 25 ohms resistance to be supplemented with an additional electrode.

• 25 ohms is the threshold for single-rod electrodes.
• If exceeded, one supplemental electrode is required (no further testing needed once added).
• Supplemental electrode must be bonded to the first.

Memory trick: 'Twenty-five or add a friend' — over 25 ohms needs a second rod.

LFMC combines a flexible metal core with a liquidtight nonmetallic outer jacket, making it suitable for wet locations and vibrating equipment connections.

• Common for motor and HVAC equipment connections.
• Listed for wet locations with liquidtight jacket.
• Fittings must also be listed for wet locations to maintain rating.

Memory trick: 'Liquidtight loves the rain' — LFMC handles wet, vibrating connections.

NEC 210.12(A) lists dwelling unit areas requiring AFCI protection on 120V, 15/20A branch circuits, covering most living spaces but excluding garages and unfinished basements/attics.

• Covers kitchens, family rooms, dining rooms, bedrooms, closets, hallways, laundry areas
• Garages and unfinished basements are generally exempt
• GFCI and AFCI are separate protections that can overlap in some areas

Memory trick: Living spaces get arc-fault guards; garages don't.

A conductor connecting the grounded system conductor or equipment to the grounding electrode system to stabilize voltage to earth.

• Sized per Table 250.66
• Connects to electrodes such as ground rods, water pipe, or ufer ground
• Does not normally carry current except during a surge or fault event

Memory trick: GEC = 'Grounds Earth Connection' for voltage stability.

NEC 230.71 allows the service disconnecting means to be composed of up to six switches or breakers grouped together, instead of a single main disconnect.

• Maximum of six switches or breakers total
• Must be grouped (same location) and each marked to indicate its purpose
• Applies to overall service, not each individual panel

Memory trick: Six switches can stand in for one big main.

Conductor size is chosen from NEC Table 310.16 using the temperature column matching the terminal rating, and the ampacity must equal or exceed the overcurrent device.

• Match conductor ampacity to breaker/terminal rating, not just load
• 75°C column is standard for most equipment terminals
• Always select the smallest size that meets or exceeds the required ampacity

Memory trick: Match the wire to the wattage, not less than the breaker's teeth.

NEC 220.43(B) requires track lighting loads to be calculated at 150 VA per 2 feet of track length for feeder/branch-circuit load calculations.

• Applies regardless of the number or wattage of fixtures actually installed
• Formula: (150VA/2ft) x track length = total VA
• Convert VA to amperes by dividing by circuit voltage

Memory trick: Every 2 feet of track adds 150 VA, no matter the bulbs.

NEC 250.118(6) allows flexible metal conduit to serve as an equipment grounding conductor only if the circuit is 20A or less and the FMC length does not exceed 6 feet.

• Both conditions (20A circuit AND 6 ft length) must be met.
• Exceeding either condition requires a separate EGC.
• Applies specifically to FMC, not LFMC (which has its own separate rule).

Memory trick: 'Six feet and twenty amps' — the FMC ground path double limit.

When more than two conductors occupy a raceway, NEC Chapter 9 Table 1 limits fill to 40% of the raceway's internal cross-sectional area.

• Use Table 5 for conductor area, Table 4 for raceway area
• 40% applies to 3+ conductors; 31% for 2, 53% for 1
• Always round up to next larger trade size if exact fit is close

Memory trick: '40 for more than two' — the fill rule for crowded raceways.

Box fill totals conductor volume, one allowance for internal clamps, and double allowance for each device yoke, all based on the largest conductor present.

• Conductors: 1 allowance each based on size
• Internal clamp: 1 single allowance total (largest conductor)
• Device yoke: 2 allowances per yoke (largest conductor)

Memory trick: Wires count once, clamps count once, devices count twice.

When more than two current-carrying conductors occupy a raceway, total conductor cross-sectional area cannot exceed 40% of the raceway's internal area per NEC Chapter 9, Table 1 and Table 4.

• Multiply individual conductor area by quantity for total fill
• Compare against 40% fill area for the raceway type/size in Table 4
• Round up to the next size if the calculated fill exceeds the allowance

Memory trick: Never pack more than 40% — wires need room to breathe.

NEC 352.44 requires expansion fittings in PVC raceways where thermal expansion/contraction is expected to exceed 1/4 inch based on temperature change and conduit length.

• PVC has a much higher coefficient of thermal expansion than metal raceways.
• Table 352.44 provides expected expansion per 100 ft based on temperature change.
• Failure to use fittings can cause conduit buckling or joint failure.

Memory trick: 'A quarter inch triggers the joint' for PVC expansion.

NEC 410.16 sets minimum clearances between luminaires and closet storage space based on fixture type to prevent contact with combustible stored items.

• Surface-mounted incandescent (enclosed lamp): 12 inches
• Recessed incandescent/fluorescent (enclosed lamp): 6 inches
• Surface-mounted fluorescent: 6 inches

Memory trick: 'Surface incandescent needs a foot of room.'

Overcurrent protective devices (OCPDs) for continuous loads (operating for 3 hours or more) must be sized at not less than 125% of the maximum continuous load current.

• Applies to feeders and branch circuits (CEC 210.20(A), 215.2(A)(1)).
• Ensures the OCPD does not trip prematurely due to heating effects.
• The calculated value is then matched to the next standard OCPD size (CEC 240.6(A)).

Memory trick: Long run, add a quarter, then pick the next fuse.

Equipment intended to interrupt fault current must have an interrupting rating not less than the available fault current at its line terminals.

• Applies to breakers, fuses, and switches
• Rating must be ≥ calculated available fault current
• Undersized AIC ratings risk explosive equipment failure

Memory trick: 'Never let the breaker's muscle be smaller than the fault's punch.'

Calculating the current (amperes) in a 3-phase circuit given the power (watts) and line-to-line voltage, using the formula I = P / (V * √3).

• Applies to balanced 3-phase loads.
• √3 (square root of 3) is approximately 1.732.
• Power (P) must be in watts (W) and voltage (V) in volts (V).

Memory trick: Power is Root-Three times Voltage, Current, and Power Factor.