Checked against primary sources 2026-08-24

Equipment Grounding Conductor Sizing: Table 250.122, Not 250.66

The other grounding table, and the one people reach for by mistake. Sized from the overcurrent device ahead of it, not from the conductor beside it, and not from the service size. Then two separate rules cap the answer.

Test yourself: 25 free questions on this topic

What an equipment grounding conductor is

Article 100 describes it as a conductive path that is part of an effective ground-fault current path, connecting normally non-current-carrying metal parts of equipment together and to the system grounded conductor or to the grounding electrode conductor, or both. Put plainly, it is the metal path that carries fault current back toward the source so an overcurrent device can see the fault and open.

Three things follow from that description and each one turns up in items.

• It is a path rather than necessarily a wire. NEC 250.118 is the list of what the code accepts as one, and raceways and cable armor are on it, so a circuit with no green wire in it can still have an equipment grounding conductor.
• Its work is fault current, not load current. It carries nothing in normal service, which is why a grounding or bonding conductor is left out of the conductor count when adjustment factors are applied (NEC 310.15(F)).
• An informational note under the definition points out that the equipment grounding conductor also performs bonding, which is why the same conductor shows up in questions written from either vocabulary.

The definition is worth reading in your own book once, in place, because the phrase effective ground-fault current path is itself defined and 250.4 explains what it has to do.

Which conductor this is

It runs with the circuit conductors and bonds metal back toward the source. It is the fault-current path, and it is the only conductor on a branch circuit whose job is to be there when something has already gone wrong.

It is not the grounding electrode conductor, which ends on an electrode and takes its size from a different input entirely.

The quickest way to tell them apart in an item is the far end. Electrode, or a point on the electrode system, means the other conductor. Equipment means this one.

EGC versus GEC, the two tables and the two jobs

Two conductors, two tables, two jobs, and one letter between the abbreviations. Candidates lose points here by reaching for the wrong table rather than by misreading the one they opened.

The equipment grounding conductor is sized from Table 250.122, entered on the rating of the overcurrent protective device ahead of the circuit (NEC 250.122). Its job is to carry fault current from equipment back toward the source, and its far end lands on equipment.

The grounding electrode conductor is sized from Table 250.66 (NEC 250.66), and Article 100 describes it as a conductor used to connect the system grounded conductor or the equipment to a grounding electrode. Its job is to tie the system to earth, and its far end lands on an electrode or on a point on the grounding electrode system. Its input is a conductor size rather than a device rating, and 250.66(A) through 250.66(C) can cut the answer short depending on which electrode it lands on.

So the fastest test in an item is the far end. Electrode, or a point on the electrode system, means the grounding electrode conductor. Equipment means the other one. The subject of the rest of this page is the second of the two.

The input is the device rating

Wire-type equipment grounding conductors of copper, aluminum or copper-clad aluminum are sized from Table 250.122, entered on the rating of the overcurrent protective device ahead of the circuit (NEC 250.122).

Not from the circuit conductor size. Not from the load. Not from the service. From the device.

That is deliberate. The conductor has to hold together long enough for that specific device to open, so the device rating is the quantity that matters.

Look the value up in your own code book. The table is short and it is worth an individual tab, because it sits several pages away from the grounding electrode table that people confuse it with.

The cap that turns an absurd answer into the right one

An equipment grounding conductor is not required to be larger than the circuit conductors in the raceway or cable supplying the equipment (NEC 250.122).

That subdivision, titled Not Larger Than Circuit Conductors, sits first in the 2026 edition at 250.122(A), ahead of everything else, and it is there because the table alone can produce nonsense. A small circuit protected by a large device would otherwise take a grounding conductor bigger than the conductors it is protecting.

The parallel case has a cap of its own further down the section, and that one does look inside a single enclosure: the conductor in each raceway is not required to be larger than the largest ungrounded conductor in that raceway (NEC 250.122(H)). Keep the two comparisons apart rather than merging them.

An item that gives you a small conductor and a big device is testing this rule and nothing else. Read the answer choices for the one that equals the circuit conductor.

When it has to be upsized, and when it does not

Increase the ungrounded conductors for any reason other than as required in 310.15(B) or 310.15(C), and a wire-type equipment grounding conductor, if installed, is increased in proportion to the increase in circular mil area of the ungrounded conductors (NEC 250.122).

The two named sections are ambient temperature correction and adjustment for the number of current-carrying conductors. Upsize because a run is hot or crowded and the grounding conductor stays where the table put it. Upsize for voltage drop, or because somebody specified heavier wire, and it goes up with them.

The distinction has a physical reason behind it. Correction and adjustment are about the conductor getting rid of heat over the same distance. Voltage drop upsizing is about a run being long, and length is exactly what raises the impedance of the fault path.

This is a place where old study material is actively dangerous, because the previous wording turned on whether the conductor was larger than the minimum with sufficient ampacity, and it produced a different answer on a derating item.

Why the EGC is never required to be larger than the circuit conductors

NEC 250.122(A) puts it in one line: equipment grounding conductors are not required to be larger than the circuit conductors supplying the equipment. In the 2026 edition that subdivision sits first in the section, ahead of everything else, and the placement is itself a hint about how often it decides an answer.

The reason is in the job. The conductor has to hold together long enough for the device ahead of it to open, and the fault current reaching it can never be more than what the circuit conductors are able to deliver to the fault. A grounding conductor larger than the conductors feeding the fault buys nothing, and the table read at a large device rating will happily hand you one.

That is the whole of the trap. A small circuit protected by a large device produces a table answer bigger than the conductors it runs beside, and the cap holds the answer at the circuit conductor. An item built on this rule gives you exactly those two facts and nothing else.

Work it in order, because the cap lands last. Read the table at the device rating, apply the increase in 250.122(D) if the ungrounded conductors were upsized for something other than correction or adjustment, and then apply the cap. Skip the increase and you underanswer. Skip the cap and you overanswer, and both wrong answers are printed for you.

One more comparison sits further down the section and it is a different one. On conductors installed in multiple raceways and connected in parallel, the conductor in each raceway is not required to be larger than the largest ungrounded conductor in that raceway (NEC 250.122(H)). Keep the two apart: the general cap looks at the circuit conductors supplying the equipment, and the parallel cap looks inside one raceway.

Parallel runs, sorted by geometry first

The subdivision titled Conductors in Parallel, at 250.122(H) in the 2026 edition, splits before it does anything else, and the split is on where the conductors are, not how many there are.

• Conductors paralleled in the same raceway, auxiliary gutter or cable tray: a single wire-type conductor, sized on the overcurrent protective device for the feeder or branch circuit, shall be permitted as the equipment grounding conductor (NEC 250.122).
• Conductors paralleled in multiple raceways: a wire-type equipment grounding conductor, if used, goes in each raceway and is connected in parallel with the others, and each one is sized on that same single device rating (NEC 250.122).
• Multiconductor cables paralleled: the grounding conductor in each cable is sized on the device rating, and the grounding conductors in the cables are connected in parallel (NEC 250.122).

One conductor or several is decided by the enclosure count. The size is decided by the one device ahead of the whole run in every case, and it is never a share of that rating.

Then the second cap lands. The grounding conductor in each raceway is not required to be larger than the largest ungrounded conductor in that raceway (NEC 250.122). So on a paralleled feeder the per-raceway answer is bounded twice over, once by the table read at the device rating and once by the phase conductor lying next to it.

The wrong answers on a parallel item are almost always fractions. Divide by the raceway count and you will find your number on the sheet.

Working an item end to end

Four steps, in this order, and the order is what keeps you out of the traps.

1. Find the overcurrent protective device rating ahead of the circuit. Not the load, not the conductor.
2. Read Table 250.122 at that rating.
3. Check whether the ungrounded conductors were increased for something other than ambient correction or conductor-count adjustment. If they were, scale up in proportion to the circular mil increase.
4. Apply the cap. The answer never has to exceed the circuit conductors in that raceway or cable.

Run it on three cases. An ordinary 20 ampere lighting circuit: the table gives the answer and neither the upsizing rule nor the cap ever bites. A long feeder whose phase conductors were moved up two sizes for voltage drop: step three applies and the grounding conductor moves with them, in proportion to circular mils rather than by two table rows. A circuit whose conductors are small relative to the device ahead of them: the table hands you a number and step four holds the answer at the circuit conductor.

Skip step three and you underanswer. Skip step four and you overanswer. Both wrong answers will be printed for you.

Where the letters moved

Three lettered subdivisions now stand at the front of NEC 250.122 where the 2023 edition had one, so every subdivision behind them shifted down two letters. The section runs from 250.122(A) through 250.122(I) where the previous edition stopped at (G). Increased in Size moved from (B) to (D), and Conductors in Parallel from (F) to (H).

The consequence for the exam is narrow but real. An item that quotes a subdivision letter is quoting the edition the exam is referenced to, and from September 1, 2026 in Texas that is the 2026 edition (16 TAC 73.100).

The safe habit is to find the subdivision by its title rather than by a letter you remember. Not Larger Than Circuit Conductors, Increased in Size, Conductors in Parallel, Feeder Taps. The titles have not moved.

Questions people ask

What is an equipment grounding conductor?

Article 100 describes it as a conductive path that is part of an effective ground-fault current path, connecting normally non-current-carrying metal parts of equipment together and to the system grounded conductor or to the grounding electrode conductor, or both. In plainer words, it is the metal path that carries fault current back toward the source so the overcurrent device can see the fault and open. It does not have to be a wire, because NEC 250.118 is the list of what the code accepts and raceways and cable armor are on it.

What is the difference between an equipment grounding conductor and a grounding electrode conductor?

The equipment grounding conductor carries fault current from equipment back toward the source, and it is sized from Table 250.122 on the rating of the overcurrent device ahead of the circuit. The grounding electrode conductor ties the system to earth, and it is sized from Table 250.66 on a different input entirely. The quickest way to tell which one an item wants is the far end of the conductor: an electrode, or a point on the grounding electrode system, means the grounding electrode conductor, and equipment means the other one.

Are equipment grounding conductors required to be larger than the circuit conductors?

No. NEC 250.122(A) says equipment grounding conductors are not required to be larger than the circuit conductors supplying the equipment, and in the 2026 edition that is the first subdivision in the section. The cap exists because the table entered at a large device rating can otherwise hand you a grounding conductor bigger than the conductors feeding the fault. A separate cap covers parallel runs, holding the conductor in each raceway to the largest ungrounded conductor in that raceway (NEC 250.122(H)).

What is an equipment grounding conductor sized from?

From the rating of the overcurrent protective device ahead of the circuit, read against Table 250.122. Not from the load, not from the conductor lying beside it, and not from the service size. The device rating is the input because the conductor has to hold together long enough for that particular device to open.

When does an equipment grounding conductor have to be increased in size?

Where the ungrounded conductors are increased in size for any reason other than the ambient correction in 310.15(B) or the conductor-count adjustment in 310.15(C). NEC 250.122(D) then increases a wire-type equipment grounding conductor in proportion to the increase in circular mil area of the ungrounded conductors. Upsize the phase conductors for voltage drop and the grounding conductor moves with them. Upsize them because the run is hot or crowded and it stays where the table put it.

How is the equipment grounding conductor sized in parallel raceways?

Where conductors are installed in multiple raceways and connected in parallel, a wire-type equipment grounding conductor, if used, goes in each raceway, is connected in parallel with the others, and is sized on the rating of the single overcurrent device ahead of the feeder or branch circuit (NEC 250.122(H)). It is not that rating divided by the number of raceways. The per-raceway cap then applies, holding each one to the largest ungrounded conductor in its own raceway. On a parallel item the wrong answers are almost always fractions.

What this page cites

• NEC 250.122 Size of equipment grounding conductors. Restructured for the 2026 edition into subdivisions (A) through (I) by NFPA code-making panel 5, second revision 8360, which states the restructure carries no technical change. source
• NEC Table 250.122 The sizing table itself, entered on the overcurrent device rating. Read it in your own code book. No value from it is printed here.
• NEC 310.15 310.15(B) ambient correction and 310.15(C) conductor-count adjustment, the two increases that do not drag the grounding conductor up with them.
• NEC 250.66 The other table, for the grounding electrode conductor, sized from a different input, with 250.66(A) through 250.66(C) cutting the answer short for particular electrodes.
• NEC Article 100 The definitions of equipment grounding conductor and grounding electrode conductor, paraphrased here rather than quoted. Read both in your own book.
• NEC 250.118 The types the code accepts as an equipment grounding conductor, which is why the answer is not always a wire.
• NEC 250.4 Why the fault-current path has to be low impedance and able to carry the fault.
• 16 TAC 73.100 Texas adoption of the 2026 NEC, effective September 1, 2026, which is the edition the examinations reference from that date. source