By Blissom · Updated 2026-11-04
Feeder sets in 1-1/4"
Feeders are where 1-1/4" earns its place. Below, two copper THHN sets sized from the 75 °C column. At 100 A and under that requires equipment marked for 75 °C terminations (110.14(C)(1)(a)); most current panelboards are.
| Feeder | Conductors | Fill | Counted | Ampacity after adjustment |
|---|---|---|---|---|
| 100 A, 120/240 V single-phase | 3 × #3 + 1 × #8 | 22.0% | 2 | 100 A OK |
| 60 A, 208Y/120 V three-phase | 4 × #6 + 1 × #10 | 15.0% | 4 | 60 A OK |
The 100 A set has two current-carrying conductors; the single-phase neutral only carries the imbalance. Grounds follow Table 250.122: #8 for 100 A, #10 for 60 A.
For the three-phase set the neutral is counted, as it would be with mostly nonlinear load. That takes it to four, factor 80%. #6 THHN drops to 60 A, which still matches the 60 A breaker. One more counted conductor in the same pipe would not change the band, but a second feeder would.
Fill counts, every wire size
1-1/4" EMT: 1.496 in² internal area, 40% usable with three or more conductors.
| Wire | THHN / THWN-2 | XHHW-2 | THW |
|---|---|---|---|
| #14 | 61 | 43 | 28 |
| #12 | 45 | 33 | 23 |
| #10 | 28 | 24 | 18 |
| #8 | 16 | 13 | 10 |
| #6 | 12 | 10 | 8 |
| #4 | 7 | 7 | 6 |
| #3 | 6 | 6 | 5 |
| #2 | 5 | 5 | 4 |
| #1 | 4 | 4 | 3 |
| #1/0 | 3 | 3 | 2 |
| #2/0 | 2 | 2 | 1 |
| #3/0 | 1 | 1 | 1 |
| #4/0 | 1 | 1 | 1 |
| 250 kcmil | 1 | 1 | 1 |
| 300 kcmil | 1 | 1 | 1 |
| 350 kcmil | 1 | 1 | 1 |
| 400 kcmil | 1 | 1 | 1 |
| 500 kcmil | 1 | 1 | 1 |
| 600 kcmil | 1 | 1 | 1 |
Note 7 rounding applied. From 3/0 THHN up only one fits, under the 53% single-conductor limit. THW uses Annex C's larger dimensions.
Branch circuits: the same ceiling
A bigger pipe does not change how many branch conductors may share it. The bands for small wire are fixed by 310.15(C)(1):
| Wire and breaker | Fits by fill | Current-carrying limit | What stops you first |
|---|---|---|---|
| #14 on 15 A | 61 | 9 | Derating |
| #12 on 20 A | 45 | 9 | Derating |
| #10 on 20 A | 28 | 20 | Derating |
| #10 on 30 A | 28 | 6 | Derating |
The band-by-band derating table (80%, 70%, 50% and lower) is the same for every pipe size; it is on the 3/4" EMT page. The fill count includes one ground, which never counts toward the current-carrying limit.
So with #12 on 20 A you get 4 circuits with their own neutrals or 8 on 120/240 V shared neutrals. Most of the 45-wire fill goes unused. #10 on 20 A gets you 10 or 18 instead.
Grounds never count for derating (310.15(F)). Results may not exceed the 60 °C termination rating of 100 A and smaller equipment unless it is marked for 75 °C.
Example: four three-phase sets
Twelve 20 A, 120 V circuits on four 208Y/120 V multiwire sets: three phases and one neutral per set, plus a ground. With linear load the neutrals are not counted, leaving twelve.
| Conductors | Area each (in²) | Subtotal (in²) |
|---|---|---|
| 12 × #12 THHN (phase conductors) | 0.0133 | 0.1596 |
| 4 × #12 THHN (neutrals) | 0.0133 | 0.0532 |
| 1 × #12 THHN (ground) | 0.0133 | 0.0133 |
| Total, 17 conductors | 0.2261 | |
| Allowed: 40% of 1.496 in² | 0.5984 |
Fill is only 15.1%. Derating is the problem: twelve at 50% gives #12 15 A, below the 20 A breaker.
| Conductors | Area each (in²) | Subtotal (in²) |
|---|---|---|
| 12 × #10 THHN (phase conductors) | 0.0211 | 0.2532 |
| 4 × #10 THHN (neutrals) | 0.0211 | 0.0844 |
| 1 × #10 THHN (ground) | 0.0211 | 0.0211 |
| Total, 17 conductors | 0.3587 | |
| Allowed: 40% of 1.496 in² | 0.5984 |
In #10 the fill rises to 24.0% and each conductor holds 20 A. If the load is mostly nonlinear and the neutrals count, that makes 16, still in the 50% band and still 20 A. The other route is two raceways of two sets each.
Stepping up or splitting
- Feeder plus branch circuits in one pipe: every counted conductor of both shares the same factor. A 100 A feeder with four branch conductors alongside is six counted, and #3 at 80% is 92 A, under 100 A.
- A larger feeder: 125 A on three #1 copper and a #6 ground fills 1-1/4" to 34.7%. Legal, but a 1-1/2" EMT pulls far easier.
- Long runs with 360° of bends: large conductors take real force to pull. Add a pull point rather than counting on spare fill.
Check your own mix with the conduit fill calculator. NEC 2023 values; verify against the edition your inspector enforces. Hot rooftops add a 310.15(B) temperature correction.
Sources: NEC 2023: Chapter 9, Tables 1, 4 and 5 with Note 7 (fill); 310.15(C)(1) (adjustment for more than three current-carrying conductors), 310.15(E) and (F) (neutrals and grounds), Table 310.16, 240.4(D) and 110.14(C). Method.
Questions electricians ask
How many wires can go in 1-1/4 EMT?
45 #12 THHN, 61 #14, 28 #10, 6 #3 or 4 #1, all one size and including any insulated ground.
Will a 100 amp feeder fit in 1-1/4 EMT?
Yes. Three #3 THHN copper and a #8 ground use 22.0% of 1-1/4" EMT, well under 40%. Even 1" EMT passes at 38.0%, so 1-1/4" is about an easier pull.
How many 20 amp circuits fit in 1-1/4 conduit?
Derating, not the pipe, sets it. #12 THHN on 20 A tops out at 9 current-carrying conductors in any raceway. Pulling #10 for the same circuits raises that to 20 in 1-1/4".
Is the feeder neutral a current-carrying conductor?
On a 120/240 V single-phase feeder it normally is not counted. On a 208Y/120 V four-wire feeder whose load is mostly nonlinear, such as electronic equipment or LED drivers, it is counted (310.15(E)).
Feeder fill and bends, offline
- Conduit fill for feeder sets with any ground size
- Smallest trade size that passes, per raceway type
- Bending marks for 1-1/4" offsets and 90s
- Box fill for the junctions too
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