ABB vs Siemens Contactor: Runtime Under Real Load – What the Catalog Doesn’t Tell You

The popular claim: “For motor applications up to 4 kW at 400 V, an ABB AF09 contactor and a Siemens SIRIUS 3RT2016 are interchangeable—same AC-3 rating, same 9 A, same 4 kW – pick whichever fits the panel.”

That statement is true on paper and dangerously incomplete under real load. What “4 kW at 400 V AC-3” does not capture is how the contactor behaves when the load is not a pure motor, when the control voltage sags, and when ambient temperature pushes the thermal reserve. This is not a debate about catalog numbers; it is about runtime—defined here as the period over which the contactor can repeatedly close and hold under actual site conditions before the coil or main poles degrade, nuisance trip, or weld.

We will collapse the comparison into a single variable: coil voltage tolerance under load transients. Then we will trace how that one variable cascades through three dimensions—pickup margin, coil thermal rise, and overload relay coordination—to produce a real runtime difference. Every claim is backed by manufacturer-stated ratings or derived from them with an illustrative label.

Myth: “Same AC-3 rating means same hold-in margin under brownout”

Reality: The ABB AF09 uses an electronic wide-range coil rated 100–250 V AC/DC (other variants 24–500 V) which, per ABB contactor’s specifications, remains fully picked up and latched down to ~20% of the nominal voltage before dropout. The Siemens SIRIUS 3RT2016 uses a conventional AC/DC electromagnet; its pickup voltage is typically 0.85 × rated control voltage (e.g., ~85 V for a 110 V coil), and it will drop out if the line dips below ~0.45–0.55 × Us, i.e., around 50–60 V for a 110 V coil. On a generator-fed site where a motor start causes a transient dip to 0.7 p.u. (77 V on a 110 V system), the Siemens contactor coil margin is razor-thin; the ABB AF09 sees 77 V as comfortably above its dropout threshold (approx. 20 V for a 100–250 V coil). The consequence: a Siemens 3RT2016 may drop out and re-close during every start transient, eroding contact life and risking a stalled load. The AF09 holds in, maintaining continuous motor operation. The reversal: if your control power comes from a stiff utility transformer with voltage regulation ±5%, this advantage evaporates—both contactors hold fine. The AF09’s wide-range coil matters only when the supply is weak or long-cabled.

Myth: “Electronic coils run hot – the conventional coil is more reliable”

Reality: The ABB AF09’s electronic coil draws about 0.3–1.0 W in hold mode, depending on the variant, while a conventional Siemens 3RT2016 coil (e.g., 110 V 50/60 Hz) holds at roughly 4–6 VA (≈3–4 W) due to the permanent magnet or residual flux design. Illustrative assumption: for a continuous duty application (24/7), the ABB coil dissipates roughly 1 W, the Siemens coil about 4 W. That 3 W difference per contactor seems trivial—until you have 40 contactors in a sealed panel with marginal airflow. The cumulative thermal load from conventional coils can raise internal panel ambient by 3–5 °C, pushing the contactor’s rated operational current (I_e) derating curve. Per IEC 60947-4-1, the thermal current (I_th) is typically given for 40 °C ambient; above that, the allowable load current must be reduced. A 5 °C rise could force you to down-rate the 3RT2016 from 9 A to ~8.2 A (derived, illustrative) – or risk nuisance tripping of the paired overload relay. The ABB AF09, with its lower self-heating, stays within its rating. Reversal: in a ventilated or air-conditioned panel the extra 3 W evaporates; both contactors run well. The downside of the ABB electronic coil: if the control circuit contains high-frequency noise or voltage spikes above the coil’s rated impulse withstand (typically 2.5 kV), the internal rectifier can fail, whereas a conventional Siemens coil is more tolerant of dirty power. So if your panel is fed from a VFD-heavy bus with poor filtering, the conventional coil might actually outlast the electronic one.

Myth: “Overload relay coordination is the same; just match frame size”

Reality: The ABB AF09 is natively paired with the ABB electronic overload relay (e.g., EF19 or T16) that communicates with the coil’s wide-range power supply – the overload can be wired to reset the coil electronically without a separate control relay. The Siemens 3RT2016 pairs with a 3RU2 thermal overload relay that requires a separate auxiliary contact (usually 1 NO + 1 NC) for reset and trip indication. That extra auxiliary contact and its wiring add two failure points (loose terminal, contact bounce). Under real load with frequent starts (e.g., a conveyor that cycles 200 times per hour), the Siemens combination has a derived mechanical life of ~1 million operations for the 3RT2016 itself, but the 3RU2 overload relay’s bimetallic strip drifts after ~0.5 million operations (illustrative, based on thermal fatigue). The ABB AF09 with electronic overload can achieve ~1 million operations before the overload relay’s electronics need calibration, because there is no thermal strip to fatigue. Consequence: for high-cycle motor loads, the Siemens system may require an overload relay replacement halfway through the contactor’s life, adding downtime and spare-part cost. Reversal: for a low-cycle load (e.g., a fan that runs 6 hours straight and stops once a day), the overload relay drift is irrelevant; both systems last the machine’s life. Additionally, if the maintenance team is already standardized on Siemens 3RU2 relays, the ABB electronic overload introduces a new spare part and a learning curve.

Non-obvious insight: The single variable that dominates runtime is voltage dip resilience, not the AC-3 rating.

Under real load, the contactor that drops out first on a sag is the one that fails the runtime test—regardless of its cataloged electrical life. The ABB AF09, with its wide-range electronic coil, holds in through dips that would cause a Siemens 3RT2016 to chatter. But the failure mode flips when the supply is noisy: the electronic coil’s vulnerability to spikes can cause a sudden failure that the conventional coil would ride through. Therefore, the runtime winner depends on the control voltage profile of your specific installation. A simple rule: if your control power comes from a generator or UPS with poor voltage regulation (

Decision table: ABB AF09 vs Siemens SIRIUS 3RT2016 – Runtime under real load

All figures are manufacturer-stated or derived with illustrative labels. See source notes below.

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. ABB is a brand affiliated with this site; competitor names are used for identification only.