Breaker Interrupting Ratings (AIC) for MCC Bucket Breaker Frames

Every fault-current study, arc-flash label, and bucket replacement runs into the same question: what can the breaker in that unit actually interrupt? The frames in legacy MCC buckets span decades of catalogs, several corporate acquisitions, and a naming system where one letter changes the interrupting rating by a factor of three. The ratings below are UL interrupting capacities in kA RMS symmetrical, compiled from the manufacturer documents cited under each table.

How to read the families: each manufacturer tiers the same physical frame by interrupting capacity. Square D encodes the tier in the second letter (FAL standard, FHL high, FCL extra-high, FIL current-limiting). Eaton/Cutler-Hammer prefixes the F-frame (FD standard, HFD high, FDC extra-high). GE uses TED to THED, TFJ/TFK to THFK, TJK to THJK. Siemens steps ED4/ED6 to HED4 to CED6. Two breakers that look identical in the bucket can differ by 80 kA of interrupting capacity, which is why the study needs the exact catalog number, not the frame name.

Square D: F-frame (100 A) and K-frame (250 A)

Source: Schneider Electric Digest, Circuit Breakers section DE3, CSA/UL Certified Interrupting Rating selection tables. Note that FCL and KCL carry no 600 V rating: an FCL in a 600 V class lineup is a misapplication regardless of its 65 kA rating at 480 V.
Type	Amps	Max voltage	AIC @ 240 V	AIC @ 480 V	AIC @ 600 V
FAL (240 V cat.)	15-100 A	240 V	10 kA	not rated	not rated
FAL (FAL34xxx)	15-100 A	480 V	25 kA	18 kA	not rated
FAL (FAL36xxx)	15-100 A	600 V	25 kA	18 kA	14 kA
FHL	15-100 A	600 V	65 kA	25 kA	18 kA
FCL	15-100 A	480 V	100 kA	65 kA	not rated
FIL (current-limiting)	20-100 A	600 V	200 kA	200 kA	100 kA
KAL	70-250 A	600 V	42 kA	25 kA	22 kA
KHL	70-250 A	600 V	65 kA	35 kA	25 kA
KCL	110-250 A	480 V	100 kA	65 kA	not rated
KIL (current-limiting)	110-250 A	600 V	200 kA	200 kA	100 kA

The catalog number matters more than the family name. A 240 V class FAL interrupts 10 kA; the 600 V class FAL of the same amp rating interrupts 18 kA at 480 V. On a study, the difference between reading the frame label and reading the full catalog number is the difference between a pass and a mislabeled bucket.

Square D: modern PowerPact replacements

Source: Schneider catalog 0611CT1001, PowerPact H-, J-, and L-Frame Circuit Breakers, and se.com datasheets (HDL36100, HGL36100, HJL36100, HLL36100). H-frame covers 15-150 A, J-frame 150-250 A. † 240 V values are standard catalog figures pending direct confirmation against 0611CT1001; the 480 V and 600 V columns are datasheet-verified.
AIC class	Example types	AIC @ 240 V	AIC @ 480 V	AIC @ 600 V
D	HDL, JDL	25 kA †	18 kA	14 kA
G	HGL, JGL	65 kA	35 kA	18 kA
J	HJL, JJL	100 kA †	65 kA	25 kA
L	HLL, JLL	125 kA †	100 kA	50 kA
R	HRL, JRL	200 kA †	200 kA	see catalog

Eaton / Cutler-Hammer: Series C F-frame

Sources: Eaton technical data TD01203013E (Series C F-Frame) and eaton.com product data for FD3100, HFD3110, FDC3100, EHD1100; HMCP data per Eaton Vol. 4, CA08100005E. † 600 V values sourced from Eaton spec data as republished by authorized distributors. HMCP interrupting ratings other than the 480 V figure are published as combination ratings with the starter they protect, which is how UL lists them.
Frame	Amps	Max voltage	AIC @ 240 V	AIC @ 480 V	AIC @ 600 V
EHD	15-100 A	480 V	18 kA	14 kA	not rated
FD	10-225 A	600 V	65 kA	35 kA	18 kA †
HFD	15-225 A	600 V	100 kA	65 kA	25 kA †
FDC	15-225 A	600 V	200 kA	100 kA	35 kA †
HMCP (motor circuit protector)	3-150 A	600 V	combination-rated	65 kA	combination-rated

The HMCP row deserves a note because it is the one engineers misread most. A motor circuit protector is a magnetic-only device UL-recognized as a component of a combination starter, not a stand-alone listed breaker. Its usable interrupting rating is the tested combination rating with the specific starter in the bucket, which is why Eaton publishes most HMCP ratings in the starter tables rather than the breaker tables.

GE: E150, F225, and J600 lines

Source: GE BuyLog Catalog, Section 6, Molded Case Circuit Breakers Quick Reference Guide (UL File E-11592). In the J600 line the trailing 4 or 6 is the frame ampacity (400 vs 600 A), not the voltage class; both are 600 V rated. THED 110-150 A units carry 42 kA at 240 V.
Frame	Amps	Max voltage	AIC @ 240 V	AIC @ 480 V	AIC @ 600 V
TED4	10-150 A	480 V	18 kA	18 kA	not rated
TED6	15-150 A	600 V	18 kA	18 kA	14 kA
THED	15-150 A	600 V	65 kA	25 kA	18 kA
TFJ / TFK	70-225 A	600 V (3P)	25 kA	22 kA	18 kA
THFK	70-225 A	600 V	65 kA	25 kA	18 kA
TFL	70-225 A	600 V	100 kA	65 kA	25 kA
TJK4 / TJJ	125-400 A	600 V	42 kA	30 kA	22 kA
TJK6	250-600 A	600 V	42 kA	30 kA	22 kA
THJK4 / THJK6	125-600 A	600 V	65 kA	35 kA	25 kA

Siemens: Sentron ED frame

Source: Siemens Molded Case Circuit Breakers, ED-Frame Sentron Series datasheet, order no. CPDS-ED123-0520, UL 489 AIR interrupting ratings table.
Type	Amps	Max voltage	AIC @ 240 V	AIC @ 480 V	AIC @ 600 V
ED2	15-125 A	240 V	10 kA	not rated	not rated
ED4	15-125 A	480 V	65 kA	18 kA	not rated
ED6	15-125 A	600 V	65 kA	25 kA	18 kA
HED4	15-125 A	480 V	100 kA	42 kA	not rated
HHED6	15-125 A	600 V	100 kA	65 kA	18 kA
CED6	15-125 A	600 V	200 kA	200 kA	100 kA

Why this matters at replacement

Available fault current at the bucket stab is a property of the system, not the breaker, and it has generally risen over the life of a facility as utility services and transformers were upgraded. A breaker adequately rated when the lineup shipped in 1985 can be under-rated in the same slot today. The fastest failure mode on a study is the quiet one: a standard-tier FAL or TED in a bucket on a bus that now sees 30 kA available.

Every feeder bucket we build ships with a 65 kAIC breaker as standard, at or above the interrupting rating of nearly every legacy frame in these tables, so the replacement unit is never the weak point of the study. Buckets are built in our UL 508A panel shop and configured by lineup, height, and rating: configure a replacement. For replacement breakers themselves, including THED, FDC, and HMCP units for legacy buckets, see repair parts.

Ratings above are compiled from the manufacturer documents cited under each table. Values marked † came from manufacturer spec data republished by authorized distributors rather than a catalog PDF we opened directly, and are flagged for that reason. Always verify against the breaker label and current manufacturer data before relying on a rating in a study.