ABB Tmax XT MCCB: Full Range Review and Specifications

What is the ABB Tmax XT MCCB range? Tmax XT is ABB's molded case circuit breaker family spanning seven frame sizes, XT1 through XT7, covering roughly 16 A to 1600 A under IEC 60947-2. The seven-frame spread means a panel builder can standardize on one brand from a small feeder breaker to a main incomer without switching product lines, but it also means the same "Tmax XT" name covers very different trip units and breaking-capacity classes depending on frame. This article covers frame structure and footprint sharing, the TMD/TMA thermal-magnetic versus Ekip electronic trip split, the N/S/H/L/V breaking-class letters, where each frame typically lands in a panel, and the Icu/Ics distinction that determines real short-circuit margin.

How Is the Tmax XT Range Structured Across Seven Frames?

The seven frames are not seven independent products — they pair up. XT1 and XT2 share a mechanical footprint at the smaller end of the range; XT3 and XT4 share a footprint one size up. Within each pair, the odd-numbered frame (XT1, XT3) is the economy thermal-magnetic tier, wired for TMD or TMA trip units only. The even-numbered frame (XT2, XT4) accepts the same enclosure cutout but opens up Ekip electronic trips and a higher breaking-capacity ceiling in the identical shell. That matters at the panel design stage: a drawing built around an XT1 footprint can be upgraded to XT2 electronic protection later without re-cutting the door.

Above that pairing the range stops sharing footprints. XT5 covers the 400/630 A band, XT6 covers 630/800 A, and XT7 extends up to 1600 A. Economy thermal-magnetic options thin out fast above XT4 — by XT5 and up, Ekip electronic trips are the default, not an option, because thermal-magnetic elements get harder to build accurately at that current range.

What Actually Separates XT1/XT3 from XT2/XT4?

Cost, mainly, and what that cost buys. XT1 and XT3 ship with fixed thermal-magnetic protection and no metering path. XT2 and XT4 open two doors at once: an Ekip electronic trip option, and a breaking-capacity class one or two letters higher than the economy version of the same frame. On a spec sheet the physical breaker looks similar. On a short-circuit study the two are not interchangeable — an XT1 rated for the H class won't cover an application that needs the L class, and swapping in an XT2 at the same amperage is often the fix without moving to a bigger frame.

TMD/TMA vs Ekip: Which Trip Unit Fits Which Job?

TMD gives adjustable thermal overload protection (roughly ±20% around the set current) with a fixed magnetic instantaneous trip point. It has no display, no communication, and no field-adjustable magnetic setting — set it once at commissioning and it stays there. TMA adds an adjustable magnetic trip on top of the adjustable thermal, which is the version specifiers reach for on motor feeders where inrush current varies by motor size and starting method.

Ekip is the electronic line, and it splits again by how much data you need out of the breaker. Ekip Dip is set-and-forget: dip switches on the front face configure long-time and short-time protection (LSI), no display, no metering, no comms card. Ekip Touch and Ekip Hi-Touch add an LCD, full LSIG protection (ground-fault included), energy metering, and a communication port for Modbus or similar protocols back to a PLC or SCADA point. What we see in the field: a lot of panels spec Ekip Touch on every outgoing feeder by default, then never wire the comms port. If nobody is pulling that data into a monitoring system, Ekip Dip does the same protection job for less money — the LCD and metering are only worth paying for when something downstream is actually reading them.

How Do the N/S/H/L/V Breaking Classes Map to Frame Selection?

ABB grades Tmax XT breaking capacity with letters — N, S, H, L, V, in ascending order of rated ultimate breaking capacity (Icu). At the low end, N-class frames handle moderate fault levels typical of a light industrial sub-distribution board. At the top, V-class variants push toward roughly 200 kA at 415 V, which is a level most projects only need at a main incomer fed directly off a large transformer or close to a utility connection point.

The letters don't all exist at every current rating within a frame. As a rule across MCCB families generally, and Tmax XT follows this pattern, the highest breaking classes (L, V) tend to be available only on the lower-amperage taps of a given frame — the breaker's internal arc-extinguishing chamber has less current to interrupt at those taps, which is what makes the higher class achievable in the same physical size. A 630 A XT5 rated to the top class the datasheet lists and a 400 A XT5 in H class both exist; don't assume the highest letter is available at every amperage without checking the specific selection table.

Run this check at the specific bus the breaker sits on, not at the transformer secondary — fault current drops with every meter of cable impedance downstream, which is often the difference between needing an L-class XT4 at the main and an N-class XT1 three levels of distribution later. For a full walkthrough of how the letter classes are derived and tested, see the breaking capacity rating explained article.

Where Does Each Frame Fit in a Panel Design?

XT1/XT2 — 16 to 160 A

Final distribution circuits, lighting and small power feeders, sub-panel incomers on smaller boards. This is the highest-volume frame in most industrial jobs because it covers the largest count of individual circuits.

XT3/XT4 — up to roughly 250 A

Mid-size feeders, small motor control center outgoing breakers, sub-distribution board incomers where the connected load has grown past what an XT1/XT2 can carry.

XT5 (400/630 A) and XT6 (630/800 A)

Distribution board main incomers, larger motor feeders, generator or transformer secondary protection on medium-size installations. Ekip electronic trips are effectively standard here, not an add-on.

XT7 (up to 1600 A)

Main switchboard incomers, transformer secondary main breakers, tie breakers between bus sections. This is where the panel's total fault current is usually highest, so the breaking-class selection deserves its own check rather than reusing whatever class was specified downstream.

This depends on duty cycle as much as amperage. A breaker running near its continuous rating in a hot switchroom with poor ventilation should be derated from nameplate current, which can push a selection up one frame even when the calculated load current alone would fit the smaller one. Check the manufacturer's temperature derating table for the specific enclosure, not just the open-air rating on the datasheet. Background on how frame size maps to current and voltage generally is covered in the voltage and current ratings by frame size guide.

Frame-by-Frame Summary Table

Treat the class column as a starting point, not a final answer — confirm the exact letter against ABB's selection table for the specific current rating and frame variant before issuing a purchase order. The molded case circuit breakers collection lists current stock across these frames by SKU.

Icu vs Ics — Why the Distinction Matters When Sizing Tmax XT

Icu is the breaker's rated ultimate breaking capacity — the maximum fault current it's tested to interrupt, with no guarantee the breaker is still serviceable afterward. Ics is the rated service breaking capacity — the fault current level the breaker can interrupt and remain usable for continued service, expressed as a percentage of Icu. ABB's Tmax XT range, in line with the rest of ABB's MCCB lineup, generally rates Ics at 100% of Icu on its higher breaking classes, meaning the breaker is expected to stay in service after clearing a fault at its full rated capacity. That's a genuinely different design point than some competing NSX-class MCCBs on the market, where certain classes rate Ics at only 50-75% of Icu; the breaker clears the fault but may need replacement afterward even though the fault current was within Icu.

How Does Tmax XT Compare to ABB's Formula A Series?

Formula A (A1/A2/A3) is ABB's older, more basic thermal-magnetic MCCB line, topping out around 630 A. It uses TMF/TMD-style fixed trips and sits at lower breaking-capacity classes than the equivalent Tmax XT frame. Some engineers still reach for Formula A on cost-driven retrofit jobs where the panel already has Formula A cutouts and the fault current study doesn't demand Tmax XT's higher classes — in practice that's a reasonable call as long as the breaking capacity check in the formula above still clears. On new panel designs without an existing constraint, Tmax XT is the current-generation range and the one ABB is actively expanding electronic trip options for.

Conclusion

Tmax XT's seven frames cover most of an industrial panel from final circuit to main incomer, but "Tmax XT" alone doesn't specify a breaker — frame, breaking class, and trip unit all need to be pinned down against the actual fault current and load profile at that point in the installation. The footprint sharing between XT1/XT2 and XT3/XT4 gives some flexibility to upgrade protection without re-cutting an enclosure, and the Icu/Ics distinction is worth checking explicitly rather than assuming the datasheet's headline number is the one that matters for continued service after a fault. For the broader selection process across frame sizes, standards, and application checklists, the MCCB engineering guide and the MCCB selection checklist cover the steps in more detail, and the types of molded case circuit breakers article is a useful starting point if Tmax XT turns out not to be the right family for a given job.