Siemens 3VA1 vs 3VA2: Thermal-Magnetic vs Electronic MCCB
Siemens 3VA1 or 3VA2 — which one do you need? The Sentron 3VA molded case circuit breaker range splits at the trip unit: 3VA1 carries a fixed thermal-magnetic (TM) trip, 3VA2 carries an adjustable electronic trip unit (ETU), and that single difference decides frame ceiling, protection functions, and whether the breaker can report data back to a panel. A 3VA1 tops out around 630 A; a 3VA2 frame runs to roughly 1000 A, with LSIG protection and, on the higher ETU tiers, true RMS metering and communications. This article covers the frame and current split between 3VA1 and 3VA2, what each ETU tier from ETU320 to ETU850 actually adds, breaking-capacity classes on both lines, how trip settings differ, and why moving from thermal-magnetic to electronic protection means specifying a different breaker — not swapping a module.
The 3VA1/3VA2 Split: Trip Unit, Not Just Frame Size
3VA1 and 3VA2 are separate product lines within Sentron 3VA, not two settings on the same breaker. 3VA1 covers frame codes 3VA10 through 3VA16, all built around a fixed thermal-magnetic trip: a bimetal strip for overload sensing, a magnetic armature for short-circuit instantaneous trip. There's no electronic variant sold under a 3VA1 part number. 3VA2 covers a separate set of electronic frames, every one of them shipped with an ETU as standard, spanning ETU320 up to ETU850. Frame mechanics — pole spacing, terminal style, breaking-capacity tiers — carry across the family, but the trip technology does not cross the line.
Current and Frame Ceilings: 630 A vs 1000 A
3VA1 stops at roughly 630 A. Above that, Siemens doesn't offer a thermal-magnetic Sentron 3VA option — the next current step requires 3VA2. 3VA2 extends to around 1000 A on its largest electronic frame. This isn't a marketing tier distinction; a bimetal element that has to hold accurate calibration at 800-1000 A while staying compact enough for MCCB dimensions is a harder mechanical problem than Siemens chose to solve for 3VA1. Above 630 A, electronic sensing is simply the practical path.
ETU Tiers: What ETU320 Through ETU850 Actually Add
Not every 3VA2 breaker gives you the same protection. The ETU number tells you the tier, and the tiers stack functionality rather than just changing the price:
ETU320 — Base Tier
Long-time and short-time protection (LS), fixed or basic adjustable curves, no display beyond LED indicators. This is the entry point for 3VA2 — electronic sensing without the extras.
ETU350 / ETU550 — Mid Tier
Adds instantaneous protection settings and, moving into ETU550, the first metering functions — current readout, load monitoring. Still primarily a protection device with basic feedback.
ETU650 / ETU850 — Top Tier
ETU650 and ETU850 add ground-fault protection (the G in LSIG), giving full long-time/short-time/instantaneous/ground-fault coordination on one device. ETU850 tops the range with a graphic LCD display, communications (Modbus/Profibus depending on option module), and full power-quality metering — voltage, current, power factor, energy. If a specification calls for breaker-level data into a building management system, ETU850 is where that requirement gets satisfied, not a lower tier with an add-on.
Breaking Capacity: N and M Classes, Icu vs Ics
Sentron 3VA breaking capacity is marked by class letters, commonly N and M on the range, with the top 3VA2 frames reaching approximately 150 kA at 415 V on the highest class. Class selection is independent of trip-unit tier — you can pair a low breaking class with a full ETU850, or a high breaking class with a basic ETU320, depending on what the fault-current study at that panel location calls for.
Icu (ultimate breaking capacity) and Ics (service breaking capacity) are not the same number, and the gap matters for sizing. Siemens generally rates Ics at 100% of Icu on Sentron 3VA's higher classes, which is a real advantage over ranges where Ics sits at 50-75% of Icu — always confirm the specific class and frame rather than assuming parity. Icw (short-time withstand current) is mostly an ACB parameter; MCCBs including 3VA1 and 3VA2 generally have limited or no Icw rating, so short-time coordination studies that assume ACB-style withstand behavior don't transfer directly to this range. See our Icu vs Ics vs Icw ratings explainer for the full sizing logic.
Trip Settings: What Electronic Protection Enables
A TM trip's overload point is set at the factory and stays there for the life of the breaker. An ETU's long-time pickup is a dial-in setting, expressed as a multiplier of the trip unit's rated current.
Formula: Long-Time Pickup Setting (Electronic Trip) — Source: IEC 60947-2 Annex F
Ir = In × Ir(x)
| Symbol | Description | Unit |
|---|---|---|
| Ir | Long-time pickup (overload) setting — the current at which the breaker begins its overload trip curve | A |
| In | Trip unit rated current (frame/sensor rating of the ETU) | A |
| Ir(x) | Field-selectable multiplier, typically adjustable across roughly 0.4 to 1.0 on 3VA2 ETU tiers | — |
That adjustability is the practical reason to pick electronic over thermal-magnetic even at currents where 3VA1 would technically fit. A feeder sized for future load growth can be fitted with an oversized ETU frame and dialed down to today's actual load — try that with a bimetal element and you're stuck at whatever the factory calibrated. It also underpins how MCCB trip settings (Ir, Isd, Ii) get configured for selective coordination between upstream and downstream breakers, which a fixed TM curve can't be tuned into.
3VA1 vs 3VA2 at a Glance
| Criteria | 3VA1 (Thermal-Magnetic) | 3VA2 (Electronic/ETU) |
|---|---|---|
| Frame codes | 3VA10 – 3VA16 | 3VA2x electronic frames |
| Rated current range | Up to ~630 A | Up to ~1000 A |
| Trip unit | Fixed TM (bimetal + magnetic) | ETU320 – ETU850 |
| Protection functions | Long-time + instantaneous only | L, S, I, and on G-capable ETUs, ground-fault |
| Setting adjustability | Factory-fixed, not field-adjustable | Field-adjustable pickup and time delay |
| Metering / comms | None | From ETU550: basic metering; ETU850: LCD + comms + full metering |
| Breaking capacity class | Up to N class | Up to M class, ~150 kA at 415 V on top frames |
| Typical use case | Simple feeder/distribution circuits, cost-sensitive | Selective coordination, motor feeders, monitored circuits |
Upgrading TM to Electronic Protection: A Breaker Swap, Not a Module Change
Some MCCB ranges let you pull a thermal-magnetic trip block and drop in an electronic one on the same breaker body — Schneider's ComPact NSX does this with its field-swappable TM-D/TM-G and Micrologic modules. Sentron 3VA doesn't work that way. 3VA1 and 3VA2 are different breaker families with different housings and internals; there's no module that converts one into the other. If a panel spec changes mid-project from "basic overload protection" to "needs ground-fault protection and Modbus," the fix is replacing the breaker, not reconfiguring it.
What we see in the field: this catches people who assume all MCCB trip units work like the field-swappable ranges they've used before. It's worth confirming trip-unit architecture per brand before a panel design locks in current-carrying components, because the cost of getting it wrong on Sentron 3VA is a full breaker change late in the build, not a parts-bin swap. Our thermal-magnetic vs electronic trip unit guide covers this distinction across brands, and the broader frame and current considerations are in our MCCB voltage, current, and frame size guide.
When to Specify 3VA1 vs 3VA2
3VA1 fits circuits under roughly 630 A where the protection scheme is simple — long-time overload plus instantaneous short-circuit, no ground-fault requirement, no data pull-off, and no expectation the setting will need adjustment later. It's the lower-cost path when the fault-current study and load profile are both settled and unlikely to change.
3VA2 is the default once any of the following apply: current above 630 A, a need for field-adjustable settings, ground-fault protection, selective coordination against other electronic breakers, or metering/communications back to a PLC or BMS. This depends on duty cycle and how firm the load profile actually is — a feeder that might see load growth is cheaper to over-spec with an adjustable ETU now than to replace with a bigger breaker later. For the general engineering background behind both lines, see our MCCB engineering guide, and browse current stock across brands in our molded case circuit breakers collection.
Frequently Asked Questions
Can a 3VA1 be converted to a 3VA2 by changing the trip unit?
No. 3VA1 and 3VA2 are different breaker families with different housings, not a shared body with swappable trip modules. Converting from thermal-magnetic to electronic protection means specifying and installing a different breaker.
What is the practical current ceiling for 3VA1?
Around 630 A. Sentron 3VA doesn't offer a thermal-magnetic option above that; higher currents on this range require 3VA2's electronic frames.
Does every 3VA2 breaker include ground-fault protection?
No. Ground-fault protection (the G in LSIG) is available on the higher ETU tiers such as ETU650 and ETU850. Lower tiers like ETU320 give long-time and short-time protection without a dedicated ground-fault function.
Is ETU850 always the right choice for a new panel?
Only if the project needs its specific capabilities — ground-fault protection, communications, or detailed metering. If those aren't required, a lower ETU tier or a 3VA1 covers simple overload/short-circuit protection at lower cost.
Does Icw matter when comparing 3VA1 and 3VA2?
Rarely. Icw (short-time withstand current) is primarily an air circuit breaker parameter. MCCBs including both 3VA1 and 3VA2 generally carry limited or no Icw rating, so short-time withstand coordination studies built around ACB behavior don't apply directly here.
Can I set the same trip curve on a 3VA1 as on a 3VA2?
Not exactly. A 3VA1's thermal-magnetic curve is fixed at the factory. A 3VA2's ETU gives a field-adjustable pickup and time-delay band, so the two can be brought close for a given application but the 3VA1 curve can't be dialed to match a specific 3VA2 setting after installation.
Conclusion
3VA1 and 3VA2 answer different questions. 3VA1 covers straightforward overload and short-circuit protection up to about 630 A with a fixed, lower-cost trip. 3VA2 covers everything from 630 A up to roughly 1000 A, plus any circuit needing adjustable settings, ground-fault protection, or metering and communications — regardless of current. Because the two lines don't share a trip-unit architecture, the choice has to be made at the specification stage; there's no field upgrade path from one to the other once the breaker is installed.
