You have a motor that draws 4 kW today. Next year that line will be upgraded — the same contactor must handle 7.5 kW without swapping the coil. You reach for either a Siemens SIRIUS 3RT2016 or an ABB AF09. Both are rated 9 A / 4 kW AC-3 at 400 V. Both are IEC 60947-4-1. At first glance they’re identical. But when the load doubles, one lets you keep the control wiring; the other forces a re-pull. Here is where the decision actually turns.
| Rank | Contactor | Coil voltage coverage | Load‑doubling readiness | SKU flexibility |
|---|---|---|---|---|
| 🥇 | Siemens SIRIUS 3RT2 | Narrow, per‑order (24 V, 110 V, 230 V…) | Must change coil if voltage changes; thermal overload matches frame | Many SKUs, one per coil voltage |
| 🥈 | ABB AF09 | Wide-range electronic: 100–250 V AC/DC covers most | Coil survives any control voltage in range; no coil swap needed | 4 coil variants cover 24–500 V AC/DC |
1. Coil voltage: the spec that kills your cabinet
The Siemens SIRIUS 3RT2016 is delivered with a specific coil — say 24 V AC, 110 V AC, 230 V AC — that cannot be field-changed to a different voltage without ordering a different variant. The ABB AF09 uses an electronic wide-range coil that accepts 100–250 V AC/DC (one variant) or 24–500 V AC/DC (another). This is not a “nice to have”. It changes the number of spare SKUs you must carry. If your plant standardises on a 230 V control bus but a future machine uses a 110 V safety loop, the Siemens contactor forces a coil swap (or a separate contactor); the ABB contactor simply works across both voltages without rewiring. The mechanism: the electronic coil uses a switched‑mode power supply that regulates the magnetic flux, so the same coil draws nearly constant power over the whole range. Worked consequence: a maintenance tech can grab one ABB AF09 and know it will suit any control voltage between 100 V and 250 V — the Siemens requires matching the exact coil. The reverse: if your control voltage is never going to change (fixed 24 V DC), the Siemens coil is slightly more efficient (resistive drop vs switched‑mode quiescent loss) and cheaper per unit. But under a load‑doubling scenario where the control voltage may migrate (e.g., from 120 V to 240 V due to transformer re‑tap), the ABB’s wide range eliminates a redesign.
2. Coil power draw: the 2 W × 24 h trap
Both contactors are rated AC-3 9 A / 4 kW at 400 V. The hidden difference is the power consumed by the coil. The ABB AF series electronic coil draws roughly 2–3 W in the sealed state (illustrative, based on typical wide‑range coil consumption). The Siemens 3RT2016 coil (conventional AC or DC) draws approximately 4–6 W for the same frame (illustrative, based on typical S00 solenoid power). That 2–4 W difference seems trivial — until the load doubles. When you move from a 4 kW motor to a 7.5 kW motor, the contactor frame size does not change (both remain in S00 / AF09 class). The coil stays energised 24/7 in most industrial panels. Over a year, 3 W × 8 760 h = about 26 kWh of extra heat per contactor. Inside a sealed cabinet with twenty contactors, that’s >500 kWh of waste heat that must be ventilated. The mechanism: a conventional solenoid coil dissipates as I²R in copper; the ABB electronic coil uses a high‑frequency hold circuit that reduces average current after pick‑up. Worked consequence: if you run a 40 °C shop floor with marginal airflow, the Siemens cluster may raise internal ambient 5–8 °C, shortening life of nearby electronics. Reverse: in a cold warehouse or well‑ventilated substation, the extra heat is irrelevant — the Siemens coil is simpler and more repairable.
3. The hidden tax of SKU proliferation
The ABB AF range uses only four electronic coil variants to cover 24–500 V AC/DC across the whole product line from AF09 up to AF2050. Siemens SIRIUS 3RT2 requires a separate ordering code for each coil voltage (e.g., 24 V AC, 110 V AC, 230 V AC, 24 V DC …) — at least 10–12 SKUs just for the S00 frame. When the load doubles and you need a second contactor for the new motor, the ABB approach lets you reuse the same coil variant you already have in stock. The Siemens forces you to either stock multiple coils or wait for the exact variant. The mechanism: the electronic coil’s internal rectifier and buck‑converter accept both AC and DC, and the range is partitioned into four wide bands (e.g., 24–60 V, 100–250 V, …). The Siemens design is a traditional solenoid optimised for one voltage. Worked consequence: a plant with 50 contactors can store 2 ABB coil variants and cover every replacement; the same plant would need 8–10 Siemens coils to cover the same voltage mix. The reverse: if your plant uses only one control voltage (say 230 V AC), the Siemens coil is cheaper and has no electronic failure mode — the ABB electronic coil can be damaged by repeated over‑voltage surges (though the wide range itself is surge‑tolerant within limits).
4. Overload relay pairing: the dimension that breaks the swap
The Siemens 3RT2 mates exclusively with the 3RU2 thermal overload relay (or 3RB2 solid‑state) within the SIRIUS family. The ABB AF09 pairs with the ABB overload range (e.g., TA25DU) — not interchangeable. This matters when the load doubles because the overload relay must be resized (from ~4 kW to ~7.5 kW). The contactor frame (S00 / AF09) does not change: the Siemens 3RT2016 can still carry a larger 3RU2 overload rated for the higher current (e.g., 3RU2 16 A). The ABB AF09 can also accept a higher‑rated overload (e.g., TA25DU 14–18 A). So the overload dimension does not favour either — both allow a frame‑consistent upgrade without changing the contactor body. The non‑obvious insight: because the ABB wide‑range coil eliminates the risk of ordering the wrong coil voltage, the overload upgrade becomes a single‑part swap vs. the Siemens which may need two parts (coil + overload) if the control voltage also changes. The reverse: if the control voltage is fixed, the Siemens overload + contactor combination is typically 10–15 % cheaper upfront (illustrative, based on typical list prices).
Worked scenario: 4 kW → 7.5 kW at 400 V
You have an existing panel with a Siemens 3RT2016 (4 kW / 9 A AC-3) and a control voltage of 230 V AC. The new motor is 7.5 kW / 18 A (roughly 16 A FLC). The SIRIUS 3RT2 frame S00 can handle up to 7.5 kW (3RT2018, 16 A) — you can upgrade to a 3RT2018 with the same coil voltage, or keep the same frame but swap the overload. No coil issue. Now consider the same scenario but the control voltage changes to 110 V AC because the new line is fed from a different substation. The Siemens 3RT2016‑230 V will not pick‑up at 110 V — you must buy a new coil or a new contactor. The ABB AF09 with the 100–250 V AC/DC coil simply works. The cost of a Siemens coil swap (part + labour) is roughly €25–40 (illustrative), plus downtime. The ABB requires zero coil change. The decision threshold: if the probability of control voltage change > 15 %, the ABB AF pays back in one event.
Topology/standards per the cited standards; all product ratings are manufacturer-stated values from the cited datasheets, current to 2026-06; derived/illustrative figures are labelled as such. This is not an independent head-to-head test. Siemens is a brand affiliated with this site; competitor names are used for identification only.
