Parallel questions are usually a division problem with a fraction planted in the options

How the exam asks about paralleling

Five of the 68 conductor sizing questions in our bank of 500 put a parallel run in front of you, and they cluster at the harder end of the difficulty scale. That is a small count with a large footprint, because paralleling is the topic that drags three other topics into one item: the derating a shared raceway triggers, the termination check on a single conductor, and the grounding conductor sizing rule in Article 250.

Watch the word itself. Our theory area carries a separate group of questions about resistors and circuits in parallel, and those are asking which quantity is shared between branches. A stem about paralleled conductors is asking about an installation permission and the conditions attached to it, so the first move on any item using the word is deciding which of the two subjects you are in.

The exam version of a parallel item is short. It gives you a total, a number of sets and one further fact, then offers four numbers of which three are arithmetic you could have done. The trap lines on our bank record the same three moves again and again: divided by the wrong thing, reported one conductor where the question asked for the set, or reported the set where the question asked for one conductor.

The floor, and what sits under it

Conductors of each phase, polarity, neutral or grounded circuit conductor may be connected in parallel only in sizes 1/0 AWG and larger (NEC 310.10(G)(1)). That floor sits higher than most candidates guess, and guessing low is the cheapest point to lose in the topic.

Underneath the floor the section names a short list of applications and nothing outside that list qualifies. Sizes smaller than 1/0 AWG are reached for control power to indicating instruments, contactors, relays, solenoids and similar control devices, and for frequencies of 360 Hz and higher, each subject to three stated conditions. A second exception permits 2 AWG and 1 AWG grounded neutral conductors in existing installations under engineering supervision. Read both in your own book before test day, because an item that parallels a small conductor is testing that boundary and nothing else.

The floor applies to the circuit conductors. Equipment grounding conductors and bonding jumpers in a parallel run are sized under Article 250, so a small grounding conductor in a parallel raceway is an ordinary sight. Notice which way the permission runs as well: paralleling is a restricted permission carrying a few extensions, and reading it as a general technique with exclusions bolted on produces confident wrong answers on the easiest items in the set.

What has to match, and why

Two conductors joined at both ends see the same voltage across them, so the current divides in inverse proportion to impedance. That is a fact about circuits, and good intentions leave it alone. Every matching condition in 310.10(G)(2) exists to stop one path taking more than its share.

Inside one group the conductors match on five things: the same length, the same conductor material, the same size in circular mil area, the same insulation type, and terminated in the same manner. Four of those five are about resistance, because resistance is what divides the current. The fifth is about the temperature the conductor may reach once the resistance has done its work.

The comparison runs inside one group and stops there. Each phase is compared against itself, and so is each polarity, the neutral, the grounded conductor, the equipment grounding conductors and the equipment bonding jumpers. 310.10(G)(3) says as much outright, so an item offering cross-phase matching as the answer is offering the inversion. A separate condition lands on the enclosures: where the sets run in separate cables or raceways, those cables or raceways carry the same number of conductors and have the same electrical characteristics, which is the clause that stops one set running in steel while its partner runs in PVC.

The division, and where it goes wrong

Because the code forces the conductors of one phase to be identical, the current divides evenly between the sets, and most parallel items are that division dressed up. A bank stem gives a feeder carrying 690 amperes run as three sets in three raceways and asks what each conductor of a set needs to carry. Three sets share 690 amperes, so each conductor carries 230 amperes, and that 230 is the figure that then goes through correction, adjustment and the termination check with each raceway worked as its own installation.

The three wrong options record three divisions. One divides by six, counting the conductors of a three phase set in place of the number of parallel sets. One divides by two, using a set count the stem never gave. One reports 690, which is the whole feeder and a figure no single conductor of the group carries.

The grounding conductor, and the fraction

Run a circuit in parallel through more than one raceway and each raceway takes its own wire-type equipment grounding conductor, where one is used, installed in parallel with the others and sized on the rating of the single overcurrent device ahead of the whole run (NEC 250.122(H)). The full device rating, in every raceway.

The reason follows from where a fault happens. A ground fault inside one raceway returns through that raceway's own grounding conductor, and it returns at the fault current the system can deliver. A grounding conductor sized by dividing the device rating among the raceways would be undersized for the only job it will ever have. Items here are usually one sentence long, and every wrong answer on offer is a fraction.

Two numbering points are worth your tab set. This is 250.122(H) in the 2026 edition and it was 250.122(F) in a 2023 book, because three rules ahead of it gained letters this cycle. Texas adopted the 2026 edition on 1 September 2026 under 16 TAC 73.100, and PSI referenced the examinations to the same edition from that day. The supply side of a service is handled elsewhere again: 250.102(C)(2) offers an individual jumper per raceway or a single jumper sized on the sum of the circular mil areas of the largest ungrounded conductor from each set, so a stem can hand you the geometry for one method and the answer for the other. The grounding and bonding area carries the rest of that material.

Each raceway carries a complete set

300.3(B) keeps the conductors of a circuit together in one raceway or cable, and it applies that separately to each portion of a paralleled installation. Each raceway of a parallel run therefore holds a complete set, one conductor of every phase plus the neutral.

Put every A phase conductor into one steel raceway and the magnetic fields stop canceling. The raceway becomes the core of an inductor wrapped around a current it cannot balance, and it heats. The same arrangement in a nonmetallic raceway still produces unequal impedance between the sets, which lands you back in the matching conditions. It makes a clean exam item because the wrong answer looks tidier than the right one, and sorting conductors by phase across raceways is exactly what the rule exists to stop.

Paralleling also multiplies the conductor count wherever you put it. Two complete three phase sets plus their neutrals is eight conductors in one pipe, and six of those are current-carrying before anybody asks about the neutrals, so the adjustment in 310.15(C)(1) is already running. What the neutrals decide is which band you land in, and whether they count turns on the system and the kind of load.

Above 800 amperes the permission reverses

Parallel sets are how a feeder gets large, which is how parallel items end up carrying the one overcurrent rule that runs backward. 240.4(B) permits rounding the device up to the next standard rating above the conductor ampacity where its three conditions hold, and one of those conditions is that the rating selected stays at 800 amperes or below. Above that, 240.4(C) requires the conductor ampacity to meet or beat the device.

A bank stem gives a parallel set with a combined corrected and adjusted ampacity of 1150 amperes and asks which standard device may protect it. The standard ratings above 800 step 1000 and then 1200, and 1150 falls short of 1200, so the answer is the 1000 ampere device. The 1200 option is there for the candidate who carried the rounding permission across the threshold without checking where the threshold sits.

The same geometry helps on voltage drop, which is why paralleling turns up as an answer on long runs. A bank item takes a feeder dropping 8.4 volts, adds a second identical set, and the drop halves to 4.2 volts, because each set now carries half the current while its own resistance stays put. The drop calculation responds to the total cross-sectional area of the path, so a second set lands in the same place a much larger single conductor would.

What to do before you sit

• Memorize the floor as a number and the exceptions as a location. 1/0 AWG is the answer to a third of the items in this topic, and the applications underneath it are a page you locate in the book when a stem calls for them.
• Answer two questions on every parallel stem before you calculate: how many sets, and does the question want one conductor or the whole group. The bank's wrong options are built almost entirely out of answering the second one backward.
• Tab 310.10(G), 250.122 and 300.3(B) together, since a single parallel item routinely reaches all three. Publisher tabs only, because homemade ones are turned away at the door.
• Write the two sentences that carry the topic on the inside cover of your notes: current divides by impedance, so the code makes the paths identical, and fault current comes back through its own raceway, so every raceway gets a grounding conductor sized on the whole device.

Each portion of the Texas journeyman exam passes at 70 percent and the two portions are scored separately, so a handful of parallel items is a real share of the calculations half. The worked arithmetic for the division, the derating and the termination comparison sits in the question set.

Questions people ask

What is the smallest conductor allowed in parallel?

1/0 AWG. NEC 310.10(G)(1) permits aluminum, copper-clad aluminum or copper circuit conductors to be connected in parallel only in sizes 1/0 AWG and larger. Two exceptions sit under it. Sizes smaller than 1/0 AWG are permitted for control power to indicating instruments, contactors, relays, solenoids and similar control devices, and for frequencies of 360 Hz and higher, each subject to three stated conditions. Separately, 2 AWG and 1 AWG grounded neutral conductors are permitted in parallel for existing installations under engineering supervision. An item that parallels a small conductor is testing that boundary.

How is the equipment grounding conductor sized in parallel raceways?

On the rating of the single overcurrent device ahead of the whole run, in every raceway. NEC 310.10(G)(5) sends parallel equipment grounding conductors to 250.122 for sizing, and NEC 250.122(H) puts a wire-type conductor in each raceway, connected in parallel with the others and sized on that one device rating. A fault inside one raceway returns through that raceway's own conductor at whatever the system can deliver, so a conductor sized by dividing the rating among the raceways would be undersized for its only job. Every wrong answer on these items is a fraction.

Do paralleled conductors have to be the same length?

Yes, and four more conditions come with it. NEC 310.10(G)(2) requires the conductors making up each ungrounded conductor, grounded conductor, neutral, equipment grounding conductor, equipment bonding jumper or supply-side bonding jumper to be the same length, of the same conductor material, the same size in circular mil area, of the same insulation type, and terminated in the same manner. Length is resistance and resistance divides the current. An unequal set puts one conductor above its share indefinitely, under a device that sees only the total and will never operate.

Can two paralleled sets use different sizes?

The matching conditions run inside one group, so every conductor of one phase matches the others of that same phase on all five conditions. NEC 310.10(G)(3) says the conductors of one paralleled set may differ in physical characteristics from those of another set. Where the sets run in separate cables or raceways, though, those cables or raceways carry the same number of conductors and have the same electrical characteristics, which is the clause that stops one set running in steel while its partner runs in PVC. An option offering cross-phase matching is offering the inversion.

Does a parallel run trigger the conductor count adjustment?

It does whenever the sets share a raceway. Two complete three phase sets plus their neutrals is eight conductors in one pipe, and six of those are current-carrying before anyone asks about the neutrals, so 310.15(C)(1) is already running. What the neutrals decide is which band you land in, and the bands step down hard enough to move a conductor size. That is one reason parallel runs are normally pulled into separate raceways, and it is a useful check on any answer that appears to gain nothing for the trouble.

How does the termination check work on a paralleled feeder?

On the individual conductor, since that is what lands in the lug, and the sets add afterward. A bank item gives two sets where each conductor derates to 240 amperes and each conductor's termination column figure is 255 amperes. Each conductor is held to the lower of those, so 240, and two conductors per phase give a feeder of 480 amperes. The 510 ampere option uses the termination figure for both conductors and drops the derating, and a 495 option averages the two limits, which no rule in Article 310 or Article 110 permits.