Journeyman Electrician Practice Test 1: Code Fundamentals & Wiring Methods

Per Article 100, SCCR stands for Short-Circuit Current Rating — the maximum fault current a component or assembly (panelboard, switchboard, motor control center) can be connected to and still withstand without damage beyond what its listing allows. SCCR is the equipment's ability to withstand a fault; AIC (interrupting rating) is the overcurrent device's ability to clear one.

SCCR is the shield! It tells you how massive of a fault the physical box can take before blowing apart. Don't confuse it with Interrupting Rating (AIC), which is the breaker's ability to actually turn that fault off.

Per 110.9, equipment intended to interrupt current at fault levels (circuit breakers, fuses) must have an interrupting rating at its nominal voltage that is sufficient for the available fault current at its line terminals. An undersized interrupting rating is a code violation regardless of normal load.

Look up 'Interrupting rating'. Remember that 110.9 is all about the breaker's ability to survive turning the fault off. It MUST be rated to handle whatever massive current is waiting at those line terminals!

This falls under NEC Table 110.26(A)(1), Condition 2 (Exposed live parts on one side, grounded parts on the other). For 151-600 Volts, the minimum depth is 3 feet 6 inches (3.5 feet).

Concrete walls count as 'Grounded'! If you have 480V and a concrete wall behind you, you need that extra 6 inches (3.5 ft total).

Per NEC 110.14(C)(1)(b), for circuits rated over 100 amperes or conductors larger than 1 AWG, equipment terminals are assumed to be rated for 75°C. Therefore, conductor ampacity must not exceed the 75°C column value, even if the wire insulation is rated for 90°C (like THHN).

Over 100 A = 75°C column. 100 A or less = 60°C column unless the equipment is marked for 75°C terminations (most modern gear is). THHN is 90°C wire, but its 90°C ampacity is only the starting point for ambient and bundling adjustments — the final ampacity can never exceed the termination column.

Article 100 defines the service point as the spot where the serving utility's equipment ends and the premises (customer-side) wiring begins — the demarcation line between the two. Where that point falls is decided by the utility.

Service point = where utility responsibility ends and yours begins!

The first row of the minimum-cover table ('All locations not specified below') calls for 24 inches of cover over direct-buried cables or conductors (Column 1) but only 18 inches over listed nonmetallic raceways such as PVC (Column 3).

Top row: cable = 24 inches, PVC = 18 inches (rigid metal conduit only needs 6).

Underground service conductors buried 18 inches or deeper without concrete encasement must have a warning ribbon run through the trench a minimum of 12 inches above the conductors or raceway, so anyone digging later hits the ribbon well before reaching the conductors.

The 12-inch warning rule! Backfill your trench with at least a foot of dirt over the pipe or wire before you roll out the red tape. If you put the tape right on top of the wire, the backhoe operator will rip them both up at the exact same time.

Raceways have to be installed as a complete system between outlet, junction, or splicing points before any conductors are pulled in. You may not sleeve a length of raceway over already-installed conductors.

Pipe first, pull second! Never try to sleeve a piece of EMT or PVC over wires that are already laid out. Build the entire raceway system, secure it, and then break out the fish tape.

Per 358.10, EMT is permitted in concrete, in direct contact with the earth, or in locations subject to severe corrosive influences, provided it is protected by approved supplementary corrosion protection. Bare EMT is not permitted in cinder fill or severely corrosive conditions.

EMT can go in the dirt or the slab, but it needs a raincoat! If you are burying thin-wall conduit or laying it in a concrete pour, it must have an approved corrosion-resistant coating or wrap applied so the chemicals in the earth or concrete don't rot it away.

Where 4 AWG or larger insulated conductors enter a box, cabinet, or enclosure from a raceway, they must be protected from abrasion by an identified fitting with a smooth, rounded insulating surface (such as a plastic bushing), unless the conductors are separated from the raceway edge by securely fastened insulating material. Conductors smaller than 4 AWG are outside this rule.

Remember the rhyme '4 and more, protect the core.' Once wire hits 4 AWG, it's heavy and stiff enough that dragging it across a raw metal edge during a pull will easily slice the insulation right off.

Conductors of different AC or DC circuits can share a raceway or enclosure as long as none of them is rated over 1000 volts. The only condition is that every conductor in the raceway be insulated for at least the highest voltage present on any conductor sharing it.

Since standard THHN/THWN-2 building wire is rated for 600V, pulling 120V and 277V together easily meets this insulation rule. The real QA/QC catch on these pulls is ensuring the different system conductors and their respective neutrals are properly identified and grouped at your termination points!

Per Table 310.4(A), the '-2' suffix indicates the insulation is rated 90°C in both dry and wet locations. THWN-2 is the conductor that allows you to size from the 90°C column even when the conduit is wet (e.g., underground PVC). Standard THHN and THW do not have the wet-90°C dual rating.

The '-2' is your ticket to the 90-degree column in wet environments! Without it, your ampacity drops to the 75-degree column the moment that pipe goes underground.

Per Table 310.4(A), the 'W' in conductor markings (e.g., THW, THWN, XHHW) indicates the insulation is approved for use in wet locations. Conductors without the 'W' are limited to dry or damp locations.

W = Wet! If your pipe goes underground or outside, that 'W' is non-negotiable. Without it, your wire is strictly limited to dry or damp locations.

NEC 300.14 (300.16 in the 2026 NEC) requires a minimum of 6 inches for free conductors. NEC 314.16(B)(1) says that when an unbroken conductor forms a loop or coil at least twice that minimum (12 inches or more), it counts as two conductors. Because the unbroken loop is 14 inches, it meets this threshold and must be counted as two conductors.

Measure those loops! A standard straight pull-through only counts as 1 wire. But if you leave a long service loop (12 inches or more) inside the box, the Code penalizes you and makes you count it as 2 wires.

Per NEC 314.16(C)(2), a conduit body may hold splices, taps, or devices only when the manufacturer has permanently stamped its volume on the fitting. You must then calculate the box fill to ensure the splices don't exceed that stamped volume.

Not all condulets are created equal! If you buy a cheap conduit body that doesn't have a volume stamp on the inside, it is legally just a pull-point. If you bury a wire nut in there, the inspector will make you rip it out!

Step 1: Six 12 AWG conductors count as 1 each (6 allowances). Step 2: Up to four ground wires count as a single volume allowance (1 allowance). Step 3: Splice connectors (wire nuts) are considered small fittings and are exempt (0 allowances). Step 4: Pigtails originate and terminate in the box, making them exempt (0 allowances). Step 5: Lock rings are small fittings and are exempt (0 allowances). Step 6: One receptacle counts as a double volume allowance (2 allowances). Total: 6 + 1 + 0 + 0 + 0 + 2 = 9 equivalent conductor volume allowances.

Ignore the noise! Exams love to throw pigtails, splices (wire nuts), and lock rings at you to see if you'll bite. Only count the incoming/outgoing wires, the device (x2), and the grounds (first 4 = 1 allowance).

Step 1: Calculate 10 AWG volume (4 conductors x 2.50 cu in = 10.0 cu in). Step 2: Calculate 12 AWG current-carrying volume (6 conductors x 2.25 cu in = 13.5 cu in). Step 3: Calculate the ground wire allowance. Per 314.16(B)(5), the first four EGCs count as 1 allowance, and the 5th counts as 1/4 (0.25) allowance. Total ground allowances = 1.25. Multiply by the volume of a 12 AWG wire (1.25 x 2.25 cu in = 2.8125 cu in). Step 4: Add the totals together (10.0 + 13.5 + 2.8125 = 26.3125 cu in).

When you have mixed wire sizes, you can no longer just count 'wires' — you must convert everything to cubic inches! Notice how 25.75 is the trap answer for anyone who forgets the extra 1/4 allowance for the fifth ground wire.

Step 1: Look up the standard volume for a 4 x 2-1/8 inch square box in Table 314.16(A), which is 30.3 cu in. Step 2: Under 314.16(A), you count the box itself plus any volume-marked extension ring, plaster ring, or domed cover attached to it. Step 3: Add the box volume to the extension ring volume (30.3 + 21.0 = 51.3 cu in).

Mud rings and extension rings give you free space! Always look up your base box in Table 314.16(A) first, then add the stamped volume of whatever ring or domed cover you bolt onto it.

NEC 314.16(B)(5) dictates that up to four EGCs entering a box count as a single (1) volume allowance. For every EGC beyond the first four, you must add a 1/4 (0.25) volume allowance. For six EGCs: The first four = 1 allowance. The 5th and 6th = 0.5 allowance (0.25 x 2). Total = 1.5 volume allowances.

Grounds get a group discount, but the free ride ends at four! The first 4 grounds cost you 1 full allowance. Every ground wire after that adds an extra 1/4 allowance. And remember, it is always based on the largest ground wire in the box!

Count the allowances: 6 conductors [314.16(B)(1)] + the grounds (three, so one allowance) [314.16(B)(5)] + one internal clamp (one) [314.16(B)(2)] + one device yoke (two) [314.16(B)(4)] = 10 equivalents. Volume = 10 × 2.25 cu in (Table 314.16(B), 12 AWG) = 22.5 cu in.

Up to four grounds count as one allowance (each extra ground adds 1/4); an internal clamp counts as one; a device yoke counts as two.