Electrical
Equipment grounding conductor sizing field guide (NEC 250.122)
Size the EGC by the overcurrent device, not the wire. Upsize it when the phase conductors grow, and pull a full one in every parallel raceway.
Direct answer
The equipment grounding conductor is the conductor that bonds metal equipment back to the source so a ground fault has a low-impedance path that trips the breaker. Size it from NEC Table 250.122 by the rating of the overcurrent device, not the load or the wire size, and upsize it proportionally when the phase conductors are increased.
Key takeaways
- Size the equipment grounding conductor from NEC Table 250.122 by the overcurrent device rating, not the load or the wire ampacity.
- Common copper EGC sizes: 20 A takes 12 AWG, 100 A takes 8 AWG, 200 A takes 6 AWG; aluminum runs one size larger.
- Upsizing phase conductors (often for voltage drop) requires increasing the EGC by the same circular-mil ratio under NEC 250.122(B).
- Each raceway in a parallel run gets its own full-size EGC sized to the feeder device, never a divided ground (NEC 250.122(F)).
- Never bond neutral to the EGC downstream of the service or separately derived source; they tie together at one point only.
The equipment grounding conductor and why its size matters
The equipment grounding conductor, the EGC, is the conductor that bonds the metal of an installation back to the source so a ground fault has a low-impedance path home. When a hot conductor shorts to a metal enclosure, the fault current runs back through the EGC to the source, the amperage spikes, and the overcurrent device opens. That is the whole job. The EGC carries fault current long enough, and hard enough, to trip the breaker fast.
Sizing it right is what makes that work. You size the EGC from NEC Table 250.122 by the rating of the overcurrent device ahead of the circuit, not by the load and not by the wire you happened to pull. A 20 A breaker gets a 12 AWG copper EGC. A 100 A breaker gets 8 AWG copper. A 200 A breaker gets 6 AWG copper. Confirm the values against the table in the adopted code edition, because the columns are easy to misread and the code is amended on a cycle.
Two rules trip people more than the table itself. When you upsize the phase conductors for any reason, voltage drop being the usual one, the EGC has to grow in proportion. And on parallel runs, every raceway gets a full-size EGC, never a divided one. This guide works through both. If the difference between grounding and bonding is still fuzzy, or you are sizing the grounding electrode conductor at the service, the grounding-vs-bonding and grounding-electrode-system guides cover those, and the EGC sits downstream of both.
What does the equipment grounding conductor actually do?
The EGC does two things at once, and only one of them is obvious. The obvious one is that it bonds all the metal that is not supposed to be energized, the boxes, raceways, enclosures, and equipment frames, so a person touching that metal does not become the path for fault current. The less obvious one is the part that saves the day: it gives a ground fault a low-impedance path back to the source, and that path is what lets the breaker see the fault and clear it.
Walk the sequence. A hot conductor chafes through its insulation and touches the metal enclosure. With no EGC, that enclosure is now energized and waiting for a hand, and the breaker sits there because almost no current is flowing back through the dirt. With a properly sized EGC, the fault sees a near-dead short back to the source, current jumps to many times the breaker rating, and the device opens in a fraction of a second. The metal never gets a chance to hold a dangerous voltage.
This is the same fault-clearing path the grounding-vs-bonding guide describes, viewed from the conductor that carries it. The earth connection at the service does not clear this fault. The bonded path home does, and the EGC is that path for everything fed downstream of the panel. Size it short on impedance and you have left the one conductor that has to work when everything else has failed.
EGC vs GEC vs neutral: keep the three straight
Three conductors get confused on drawings and in conversation, and mixing them up causes real failures. The equipment grounding conductor (EGC) is the fault path that bonds equipment metal back to the source. The grounding electrode conductor (GEC) connects the system to the earth electrodes at the service or at a separately derived system. The neutral, the grounded conductor, is a current-carrying conductor that returns normal load current.
They are not interchangeable, and the most dangerous mistake is treating the neutral and the EGC as the same wire downstream of the service. They are bonded together at exactly one place, the service or the source of a separately derived system, through the main or system bonding jumper. Past that point they run separate. Tie a neutral to the EGC at a subpanel or a piece of equipment and you put normal load current on the grounding system, energize the metal that the EGC is supposed to keep safe, and defeat any ground-fault protection looking for that imbalance.
The GEC answers to a different rule and a different table, sized from 250.66 by the service conductors, not from Table 250.122. The EGC answers to the overcurrent device. The grounding-vs-bonding and grounding-electrode-system guides go deep on the GEC and the single-point bond. The line to hold here: the EGC clears equipment faults, the GEC references the system to earth, the neutral carries load, and only the first two ever get tied together, and only once.
How do you size an equipment grounding conductor?
Size the EGC from NEC Table 250.122 by the rating or setting of the overcurrent device protecting the circuit. You find the breaker or fuse amperage in the left column and read across to the minimum copper or aluminum EGC. That is the rule for a wire-type EGC, and it is the same whether the run is a 15 A lighting branch or a 400 A feeder.
A few values are worth carrying in your head, with the caveat that you verify them against the adopted edition. A 15 A device takes 14 AWG copper. 20 A takes 12 AWG copper. Anything from 25 A through 60 A takes 10 AWG copper. 100 A takes 8 AWG copper. 200 A takes 6 AWG copper. 300 A takes 4 AWG copper, and 400 A takes 3 AWG copper. The aluminum column runs one trade size larger at each step, because aluminum has higher resistance for the same gauge.
Two more things the table folds in. The EGC never has to be larger than the circuit conductors feeding the load, so on small circuits the ground and the phase can land at the same size. And the table is keyed to the device rating, so a setting on an adjustable breaker, not the frame size, is the number you read against. When in doubt, read the table, do not estimate from memory, and confirm the edition the jurisdiction has adopted.
| OCPD rating | Copper EGC | Aluminum EGC |
|---|---|---|
| 15 A | 14 AWG | 12 AWG |
| 20 A | 12 AWG | 10 AWG |
| 60 A | 10 AWG | 8 AWG |
| 100 A | 8 AWG | 6 AWG |
| 200 A | 6 AWG | 4 AWG |
| 300 A | 4 AWG | 2 AWG |
| 400 A | 3 AWG | 1 AWG |
Sized by the overcurrent device, not the wire
This is the single most common error in EGC sizing, so it gets its own section. You size the EGC by the rating of the breaker or fuse ahead of the circuit. Not the load. Not the ampacity of the phase conductors. The overcurrent device.
The logic follows the fault. The EGC has to carry whatever fault current flows until the device opens, and the device rating is what sets how much current it takes to trip and how long the conductor has to survive. A circuit might run a small load on conductors sized large for voltage drop, but if a 100 A breaker protects it, the EGC starts from the 100 A row. Picking the ground off the phase conductor size, or off the connected load, gives you the wrong number in both directions and an inspector who stops trusting the rest of your work.
There is one twist that confuses people and it is not an exception to this rule. When you upsize the phase conductors above the minimum, the EGC does grow, but it grows in proportion to that upsize on top of the Table 250.122 starting point. The starting point is still the overcurrent device. The next section is where that proportional bump comes from.
Do you upsize the ground when you upsize the wire?
Yes. When the ungrounded conductors are increased in size for any reason other than the ampacity correction and adjustment factors, the wire-type EGC, if installed, has to be increased in size in proportion to the increase in circular-mil area of the ungrounded conductors. That rule is commonly cited at NEC 250.122(B), and it is the most missed rule in this entire article.
Voltage drop is the usual trigger. A crew upsizes a feeder from 1 AWG to 2/0 to hold the drop on a long run, then pulls the same ground the 1 AWG would have taken and calls it done. That ground is now undersized for the conductors it is protecting. The reason the rule exists is that bumping the phase conductors lowers the impedance of the fault loop on the phase side, and if the EGC does not come up with it, the ground side becomes the weak link in the path that has to clear the fault.
Verify the section against the adopted edition, because the wording and the references inside it have shifted across recent code cycles. The principle is stable even when the citation moves: upsize the phase conductors, upsize the EGC by the same circular-mil ratio. The most reliable way to get burned here is to treat the voltage-drop upsize as a phase-conductor decision and forget the conductor that has to fault with it.
The circular-mil ratio math, worked
The proportional bump is a ratio, and the unit that makes it clean is the circular mil. Take the cross-sectional area of the conductor you actually installed, divide it by the area the Table 250.122 ground was based on, and multiply the starting EGC area by that ratio. Then round up to the next standard size, because a calculated 375 kcmil ground does not exist on a reel.
Work an example. A 100 A feeder would normally take 3 AWG copper conductors and, from Table 250.122, an 8 AWG copper EGC. Say you upsize the phase conductors to 1/0 copper for voltage drop. The ratio is the circular-mil area of 1/0 (about 105,600) divided by the area of 3 AWG (about 52,620), which is roughly 2.0. Multiply the 8 AWG ground area (about 16,510 cmil) by 2.0 and you need about 33,000 cmil, which lands on 4 AWG copper (about 41,740 cmil) once you round up to a standard size.
Two practical notes. Use the circular-mil areas from NEC Chapter 9, Table 8, not approximations off the top of your head, when you are putting a number on a submittal. And the ratio is taken against the size the EGC was based on, the minimum phase size for the load, not against some arbitrary base. Get the denominator wrong and the whole bump is wrong.
| Step | Value |
|---|---|
| Overcurrent device | 100 A |
| Phase size for the load | 3 AWG Cu (~52,620 cmil) |
| Table 250.122 EGC | 8 AWG Cu (~16,510 cmil) |
| Phase upsized to | 1/0 Cu (~105,600 cmil) |
| Circular-mil ratio | 105,600 / 52,620 = ~2.0 |
| EGC area needed | 16,510 x 2.0 = ~33,000 cmil |
| EGC, rounded up | 4 AWG Cu (~41,740 cmil) |
How is the EGC sized for parallel conductors?
When conductors run in parallel in separate raceways, each raceway gets its own full-size EGC. You do not size one EGC for the feeder and split it across the raceways, and you do not divide the EGC area among them. Each wire-type EGC is sized from Table 250.122 for the rating of the overcurrent device protecting the whole feeder, and a full one of that size goes in every raceway. This is commonly cited at NEC 250.122(F).
The reason is that a ground fault can return through any one of the parallel raceways, and the fault does not politely share itself across all of them. A full-size EGC has to be present in whichever raceway becomes the path, so each one carries the full minimum. Picture a 400 A feeder run as two parallel sets in two conduits. Each conduit gets a full 3 AWG copper EGC sized to the 400 A device, not a smaller ground in each that adds up to one. Two full grounds, one per raceway.
There is a related case. Where the parallel conductors share a single raceway or cable tray, a single EGC sized to the device is permitted for the group. The split-it-up mistake shows up specifically on the multi-raceway runs, where it looks reasonable to think of the grounds as adding together. They do not. Confirm the exact subsection against the adopted edition, since the parallel rules were reorganized in recent cycles, but the field rule holds: full EGC per parallel raceway.
One EGC serving multiple circuits in a raceway
A single EGC is allowed to serve several circuits that share the same raceway, cable, trench, or cable tray. You do not have to pull a separate ground for each circuit in the pipe. When you run one EGC for the group, it is sized from Table 250.122 for the largest overcurrent device protecting any of the circuit conductors in that raceway. This is commonly cited at NEC 250.122(C).
So three circuits at 20 A, 30 A, and 60 A sharing a conduit can share one EGC, and that EGC is sized to the 60 A device, which is 10 AWG copper. The smaller circuits ride on the larger ground. What you cannot do is size the shared EGC to one of the smaller devices and assume it covers the larger one. The largest device sets the floor.
Verify the section against the adopted edition. The allowance is steady across recent cycles, but the way it interacts with the upsizing rule and with isolated grounds can get nuanced, so on anything unusual, read the actual text rather than relying on the rule of thumb.
Metal raceway as the EGC (NEC 250.118)
A wire is not the only thing that counts as an EGC. NEC 250.118 lists the types of equipment grounding conductor the code recognizes, and rigid metal conduit, intermediate metal conduit, and electrical metallic tubing are on that list. A properly installed metal raceway can serve as the EGC by itself, with no separate green wire pulled, and that is a code-compliant install in the right conditions.
The field reality is that a wire EGC often gets pulled anyway, and there is a reason crews do it. The raceway only works as a ground if every coupling, connector, and fitting is tight and stays tight, and if the metal does not corrode at a joint over the building's life. Loose set-screw connectors, a coupling backed off by vibration, or rust at a fitting in a wet location all raise the impedance of that path, and you cannot see it from the cover plate. A pulled EGC gives a continuous copper path that does not depend on every threaded joint being perfect twenty years from now.
Where the install is sensitive, a data center, a hospital branch, a long run with a lot of fittings, the wire EGC is cheap protection against a path you cannot inspect after the fact. Confirm in 250.118 which raceways qualify in the adopted edition, because the list and its conditions have been refined recently, and some types that were once accepted carry new limits.
Flex and liquidtight as an EGC: the limits
Flexible metal conduit and liquidtight flexible metal conduit can serve as an EGC, but only inside tight limits, and outside those limits you pull a wire ground. The conditions typically include a total length cap in the ground-fault path, a ceiling on the overcurrent device protecting the circuit, and listed fittings. Confirm the exact length and ampere limits in 250.118 for the adopted edition, because they differ between FMC and LFMC and they have changed across cycles.
The practical rule is simpler than the subsections. Flex is there to handle movement and vibration, a motor connection, a transformer, equipment that shakes. The same flex and movement that make it useful are what make it a poor long-term fault path, because the interlocked metal and the fittings loosen. So on any flex connection feeding equipment of consequence, pull a wire EGC and bond it at both ends, and stop trying to make the flex itself carry the fault.
If you find yourself counting feet to see whether a flex run still qualifies as the ground, you have answered the question. Pull the wire.
Wire type, color, and identification
A wire-type EGC is identified by green insulation, green with one or more yellow stripes, or bare. Those are the colors reserved for the grounding conductor, and nothing else in the raceway should wear them. The conductor itself can be copper, aluminum, or copper-clad aluminum, solid or stranded, insulated or bare, depending on the wiring method and the environment.
Sizes 6 AWG and smaller usually come on the reel in the right color, so you pull green and you are done. Larger conductors are commonly run in black and re-identified at the terminations with green tape or green markings, which the code permits for the larger sizes. The point of the color rule is that the next person, an inspector, a troubleshooter, the electrician who opens the panel in fifteen years, can tell at a glance which conductor is the ground and not put it on the wrong lug.
Bare is fine for many EGC applications and common in cable assemblies. Where the environment is corrosive or wet, an insulated or covered EGC holds up better than bare, and the wiring method may call for it. Match the conductor to the location, keep the color honest, and do not re-identify a smaller conductor that the code expects to be green from the factory.
Aluminum EGC runs one size larger
Aluminum has higher resistance than copper for the same gauge, so the aluminum column in Table 250.122 runs about one trade size larger than the copper column at every step. A 200 A device takes 6 AWG copper or 4 AWG aluminum. A 100 A device takes 8 AWG copper or 6 AWG aluminum. Read the column for the metal you are actually installing, not the copper number with an aluminum conductor in your hand.
Aluminum makes sense on larger feeders for cost and weight, and a properly sized aluminum EGC clears a fault the same as copper. The catch is the same one that bites on phase conductors. Aluminum terminations need the right listed lugs, the right torque, and an antioxidant where the listing calls for it, because aluminum cold-flows and a loose aluminum ground at a lug is a high-impedance connection sitting right in the fault path. The conductor can be sized perfectly and still fail at the termination.
Where the EGC is small, the location is corrosive, or the equipment is critical, copper earns its higher price by being more forgiving at the connection. On big feeders, aluminum sized one column larger is routine and code-compliant. Pick the metal deliberately, then read the matching column.
Separately derived systems and transformers
A transformer or a generator that is a separately derived system has its own grounding and bonding at the source, and the secondary EGC starts there. On the secondary, the EGC is sized from Table 250.122 against the secondary overcurrent device, the same as any other circuit, and it bonds the downstream equipment metal back to the transformer or generator enclosure.
What is different at a separately derived system is the bonding at the source itself: the system bonding jumper ties the secondary grounded conductor to the EGC and the equipment, and a grounding electrode conductor takes the new system to earth at that location. Those connections live in the grounding-electrode-system and grounding-vs-bonding guides, which is where the single-point bond and the GEC sizing belong. The EGC on the secondary side follows the rule you already know, by the overcurrent device, upsized with the phase conductors if they grow.
Keep the source bonding and the downstream EGC straight. The system bonding jumper is a one-time tie at the transformer or generator. The EGC is the running fault path to everything fed from it.
The bonding jumper versus the EGC
The EGC and the bonding jumper are related but not the same conductor, and the difference matters when you size them. The EGC is the running fault path along a circuit or feeder, sized from Table 250.122 by the overcurrent device. A bonding jumper is a shorter connection that ties two things together, and it is sized by its own rules.
The main bonding jumper at the service and the system bonding jumper at a separately derived system tie the grounded conductor to the equipment grounding system at the single point the code allows, and those are sized from the service or derived-system conductors, not from Table 250.122. Equipment bonding jumpers on the supply side and load side have their own sizing in 250.102. The grounding-vs-bonding guide lays out which jumper does what.
The reason to hold the distinction is sizing. Reach for Table 250.122 to size an EGC. Reach for 250.102 and 250.66 to size bonding jumpers and the GEC. Use the wrong table and you can land a conductor that is legal-looking and wrong for its job.
Why must the fault path be low impedance?
The EGC has to be low impedance because the breaker only trips on current, and current only flows if the path back to the source is low enough in impedance to let it. NEC 250.4 states the performance the whole system has to meet: an effective ground-fault current path that is permanent, low-impedance, and able to carry the maximum fault current likely to be imposed. The EGC is how a circuit meets that requirement.
Run the failure. If the fault loop impedance is too high, the fault current stays low, maybe only a few times the load current instead of many times the breaker rating. The breaker sees that as a heavy load, not a fault, and either trips slowly or does not trip at all. Meanwhile the faulted metal sits at a dangerous voltage, waiting for contact, and the connection that is dropping the voltage is heating up. That is the recipe for both shock and fire, from the same undersized or loose path.
This is why size is not the only thing that matters. A correctly sized EGC with a loose lug, a backed-off coupling, or a corroded fitting is a high-impedance path wearing a compliant size. The conductor has to be sized right and connected tight, end to end, or the performance the code is after in 250.4 is not actually there when the fault comes.
What the inspector checks on the EGC
An inspector looking at grounding has a short mental list for the EGC, and knowing it tells you what to get right before the cover goes on. First, is an EGC present and continuous through every box and enclosure, bonded at both ends. Second, is it sized to the overcurrent device from Table 250.122, not to the load and not to the wire.
Then the two rules that catch experienced crews. If the phase conductors were upsized, was the EGC upsized in proportion under 250.122(B). On a long feeder that was clearly bumped for voltage drop, this is the first thing a sharp inspector checks, because it is the most common miss. And on parallel runs, is there a full-size EGC in each raceway, not a divided ground. A quick count of the conduits against the grounds in them settles it.
The rest is workmanship that affects impedance. Tight connectors, proper lugs and torque on aluminum, green or bare identification, and re-identification done correctly on the larger sizes. An EGC that is present, correctly sized, upsized where it had to be, and tight at every termination is an EGC that passes and, more to the point, works.
Feeders, data centers, and noise-sensitive loads
On feeders the EGC follows the same rule as a branch circuit, sized to the feeder overcurrent device, and the upsizing rule comes up more often because feeders are the long runs that get bumped for voltage drop. Size the feeder EGC to the device first, then check whether the phase conductors were increased, and grow the EGC by the circular-mil ratio if they were.
Data centers and sensitive electronics add a wrinkle that is about noise, not fault clearing. Equipment listings may call for an isolated or insulated EGC to keep ground noise off the reference, run alongside the normal equipment ground. That isolated ground is still sized as an EGC from Table 250.122; it does not get smaller because its job includes noise control. And many of these spaces pull a wire EGC even where a metal raceway would qualify, because a continuous copper path is more predictable than dozens of fittings holding ground over the life of the room.
The principle does not change with the building. Bigger and more critical raises the cost of getting it wrong, so the wire ground, the right size, and the tight termination earn their keep more, not less.
What to document
Write down enough that the next person can confirm the EGC without re-deriving it. The overcurrent device rating is the anchor, because that is what the size was read against. Record the EGC material and size, and if the phase conductors were upsized, record the upsize and the EGC that went with it so the proportional bump is visible.
On parallel runs, note that each raceway carries a full EGC and the size, because that is the rule most likely to be questioned later. The table below is what a clean record holds. Hedge the values to the adopted edition: write the size you installed and note the code edition the table came from, since 250.122 is amended on a cycle and a number that was right one edition can shift the next.
| Field to record | Why it matters |
|---|---|
| OCPD rating | The EGC is sized from this, not the load or wire |
| Copper EGC installed | Verify against Table 250.122, adopted edition |
| Aluminum EGC installed | Aluminum column runs one size larger |
| Phase upsized? new EGC | 250.122(B) proportional increase, if applied |
| Parallel: EGC per raceway | Full-size ground in each, never divided |
| Code edition used | Table values shift between cycles |
Common mistakes
- Sizing the EGC by the conductor ampacity or the connected load instead of the overcurrent device.
- Upsizing the phase conductors for voltage drop and leaving the EGC at its original size, missing 250.122(B).
- Dividing one EGC across parallel raceways instead of pulling a full-size EGC in each raceway.
- Relying on a loose or corroded metal raceway as the only EGC where a pulled wire ground was warranted.
- Tying the neutral and the EGC together downstream of the service or separately derived source.
- Reading the copper column of Table 250.122 while installing an aluminum EGC, which runs one size larger.
Field checklist
Want this checklist to run itself on every job — with photo proof and a signed record crews can hand the customer? That's FieldOS.
Standards and references
The rules live in NEC Article 250, NFPA 70. EGC sizing is in 250.122, with the minimum sizes in Table 250.122 read by the overcurrent device. The proportional-increase rule for upsized phase conductors is in 250.122(B). The single-EGC-for-multiple-circuits allowance is in 250.122(C), and the parallel rule, a full EGC in each raceway, is in 250.122(F). The types of conductor that qualify as an EGC, including metal raceways and the flex limits, are in 250.118.
Three more sections complete the picture. Bonding jumpers are sized under 250.102, not from Table 250.122. The grounding electrode conductor is sized from 250.66 by the service conductors. And 250.4 states the performance the whole grounding and bonding system has to deliver, the effective, low-impedance, permanent ground-fault path that the EGC exists to provide. Cite each where it actually governs, not as decoration.
Treat every section number and table value here as keyed to a specific code edition. The NEC is adopted and amended by jurisdiction, and 250.122 in particular has been reworked across recent cycles, including the parallel and upsizing language. Confirm the citations and the table against the edition the AHJ has adopted and any local amendments before you put them on a submittal. The three rules to hold onto regardless of edition: size by the overcurrent device, upsize with the phase conductors under 250.122(B), and run a full EGC in each parallel raceway.
Units and terms
EGC sizing crosses a few naming conventions, and the same conductor can read differently across a drawing set, a spec, and a manufacturer sheet.
Conductor size is given in AWG for smaller conductors and kcmil, thousands of circular mils, for larger ones, while metric drawings use square millimeters. The circular mil is the area unit that makes the 250.122(B) ratio clean. The overcurrent device is the breaker or fuse, sometimes written OCPD. The grounded conductor is the neutral; the grounding conductors are the EGC and the GEC, which are different conductors with different jobs and different sizing tables.
- EGC
- Equipment grounding conductor, the fault path bonding equipment metal back to the source, sized from Table 250.122 by the overcurrent device
- GEC
- Grounding electrode conductor, the connection to the earth electrodes, sized from 250.66 by the service conductors
- OCPD
- Overcurrent protective device, the breaker or fuse whose rating sets the minimum EGC size
- Circular mil (cmil)
- Cross-sectional area unit used to take the proportional 250.122(B) increase when phase conductors are upsized
- Effective ground-fault path
- The permanent, low-impedance path required by 250.4 that carries fault current back to the source to trip the device
- Grounded conductor
- The neutral, a current-carrying conductor, distinct from the EGC and bonded to it only at the service or derived source
FAQ
How do you size an equipment grounding conductor?
Size it from NEC Table 250.122 by the rating of the overcurrent device protecting the circuit, not the load or the conductor ampacity. A 20 A breaker takes 12 AWG copper, 100 A takes 8 AWG copper, 200 A takes 6 AWG copper. The aluminum column runs one size larger. Verify against the adopted edition.
What is NEC 250.122?
NEC 250.122 is the section that sizes the equipment grounding conductor, with Table 250.122 giving the minimum copper and aluminum sizes by the overcurrent device rating. It also carries the proportional-increase rule for upsized phase conductors and the rules for parallel runs and shared raceways. Confirm the wording against the adopted code edition.
Do you upsize the ground when you upsize the wire?
Yes. When the phase conductors are increased in size, for voltage drop or any reason beyond ampacity correction, the EGC is increased in proportion to the circular-mil increase of the phase conductors. This is commonly cited at NEC 250.122(B), and it is the most missed rule in the article. Round up to a standard size.
What is the difference between the EGC and the GEC?
The EGC, equipment grounding conductor, is the fault path that bonds equipment metal back to the source and is sized from Table 250.122 by the overcurrent device. The GEC, grounding electrode conductor, connects the system to the earth electrodes and is sized from 250.66 by the service conductors. Different jobs, different tables.
How is the EGC sized for parallel feeders?
Each raceway in a parallel run gets a full-size EGC, never a divided one. Size the EGC from Table 250.122 for the overcurrent device protecting the whole feeder, then run a full one of that size in every raceway. This is commonly cited at NEC 250.122(F). A fault can return through any single raceway.
Can a metal conduit be the equipment grounding conductor?
Yes. NEC 250.118 lists rigid metal conduit, intermediate metal conduit, and EMT among the conductors that qualify as an EGC, so a properly installed metal raceway can be the ground. Crews often pull a wire EGC anyway, because loose couplings and corroded fittings raise the impedance of a path you cannot inspect later.
Is the EGC sized by the wire or the breaker?
By the breaker. The EGC is sized from Table 250.122 by the rating of the overcurrent device, not by the conductor ampacity and not by the connected load. The exception that confuses people is not really an exception: when phase conductors are upsized, the EGC grows in proportion on top of the device-based starting size.
Why does the equipment grounding conductor have to be low impedance?
Because the breaker only trips on current, and current only flows back if the path is low enough in impedance. NEC 250.4 requires an effective, low-impedance, permanent ground-fault path. Too high an impedance and the fault current stays low, the breaker does not trip fast, and the faulted metal holds a dangerous voltage that risks shock and fire.
Does an aluminum EGC have to be larger than copper?
Yes. Aluminum has higher resistance for the same gauge, so the aluminum column in Table 250.122 runs about one trade size larger than copper at every step. A 200 A device takes 6 AWG copper or 4 AWG aluminum. Read the column for the metal you are installing, and use listed lugs and torque on aluminum terminations.
People also ask
Codes cited in this guide
This guide is written and reviewed against the published standards below. Always confirm the current adopted edition with the authority having jurisdiction.