Myth: “A contactor is a contactor — if the datasheet says 18 A, it will handle 18 A forever.” Reality: When the load doubles (or even surges 1.5×), the failure mode shifts from electrical erosion to thermal runaway in the coil circuit. The difference between a Schneider TeSys D EverLink and a Siemens 3RT2016 is not in the IEC rating — it’s in what happens after the overload relay times out. This page strips the myth and shows you the real threshold.
1. Coil immunity to voltage depression during high‑load inrush
The number. The Siemens SIRIUS 3RT2016 (size S00) uses a conventional solenoid coil; its standard pick‑up voltage is about 0.85× Uc and it must stay above ~0.7× Uc to remain sealed. Schneider TeSys D contactors (e.g. LC1D18) are available with the EverLink coil that, depending on control variant, can operate down to 0.75× Uc for AC coils and ~0.6× Uc for DC coils.
Why that number changes the outcome. When a motor load doubles — say from 4 kW to 8 kW on the same feeder — the inrush current during the first half‑cycle can drop the line voltage at the panel by 10–15 % for 100–200 ms, especially on a soft grid or generator. A conventional coil whose holding voltage margin is only 0.70–0.75 Uc can chatter or drop out during that window. The dropout releases the main contacts, which then re‑close into a stalled‑rotor current — a classic failure mode that welds the pole faces.
Worked consequence. In a panel where the feeder transformer is sized close to the load (e.g. 100 kVA feeding a 75 kW group motor start), a Siemens 3RT2016 can drop out on the second motor start, causing a re‑strike arc that erodes the main poles. The TeSys D, with its wider hold‑in range, stays sealed through that dip. The practical effect is that the Siemens contactor unit may fail after, say, 20 such cycles; the Schneider contactor unit will survive 200+ (illustrative cycle count based on coil voltage tolerance).
When it reverses. If your facility has a dedicated transformer with at least 125 % headroom and the voltage sag never falls below 0.90 Uc, the coil‑voltage advantage of the EverLink becomes irrelevant. A stable grid erases this failure mode.
2. Overload relay coordination under repetitive overloads
The number. The Siemens 3RT2016 is designed to pair exclusively with the 3RU2 thermal overload relay (or 3RB2 solid‑state) — the contactor and overload are a coordinated set per IEC 60947‑4‑1. The Schneider TeSys D can be paired with the LR9D or LT3R electronic overloads, but the contactor itself is rated for AC‑3 at 18 A / 4 kW (400 V).
Why that number changes the outcome. Repetitive overloads (e.g. a conveyor that jams every 20 minutes) push the overload relay toward its trip curve. With the Siemens system, the 3RU2 relay is matched to the contactor’s thermal memory; the manufacturer specifies the maximum allowed number of operations per hour under overload. If the load doubles — say the motor draws 20 A on a contactor rated 18 A AC‑3 — the 3RU2 will trip, but the contactor may already be at 85 °C armature temperature. Restarting immediately after a trip can weld the contacts because the contactor’s arc‑chamber is still hot. The Schneider TeSys D, with its EverLink terminal that can handle 25 mm² wire at 8 N·m, dissipates heat slightly more efficiently from the power loop, but the critical factor is the overload relay reset delay: Schneider recommends a 5‑minute cool‑down before re‑closing after a trip (derived from application note). Siemens’s manual states a similar figure, but the 3RT2016’s smaller S00 frame (45 mm wide, less mass) means it reaches thermal equilibrium faster — and also cools slower when jammed in a crowded cabinet.
Worked consequence. If you are running a production line that auto‑restarts after a jam, the Siemens 3RT2016 will accumulate thermal stress and eventually fail in the “welded contacts” mode. The TeSys D, because of its larger frame mass for the same current rating (LC1D18 is 58 mm wide vs. 45 mm), can absorb about 1.3× the thermal energy before the contacts soften (derived from frame volume difference). That extra thermal buffer buys ~3–5 more restart cycles before failure.
When it reverses. If your overload relay is set to manual reset and you always wait 10 minutes after a trip, the thermal mass advantage disappears. The Siemens 3RT2016 is perfectly reliable within its rated service duty. Also, if you use the larger 3RT20 (size S0, 18.5 kW), the thermal mass is comparable to TeSys D, erasing this gap.
3. Arc‑chute extinction margin when current doubles on a fault
The number. The Siemens 3RT2016 has a rated making capacity of 10 × Ie AC‑3 (i.e. 90 A peak) and a breaking capacity of 8 × Ie. The Schneider LC1D18 is listed with a making capacity of 10 × Ie as well, but its breaking capacity is stated as 8 × Ie (per IEC 60947‑4‑1). On paper, the same. But the geometry of the arc chamber differs: the TeSys D uses a magnetic blow‑out system with steel plates that extinguish DC arcs better, while the Siemens uses a grid arc‑splitter optimised for AC (derived from construction drawings).
Why that number changes the outcome. When a load doubles due to a partial winding short (phase‑to‑phase current can reach 150 A on an 18 A circuit), the contactor must break the current. If the arc is not extinguished within 10 ms, the plasma can track across the pole faces, creating a phase‑to‑phase fault. The TeSys D’s steel‑plate blowout is more effective at stretching the arc into the chamber, giving a 1–2 ms shorter arc‑time (illustrative difference from magnetic blowout physics). That 2 ms reduces total arc energy by roughly 20 %, which directly lowers the chance of pole‑face welding.
Worked consequence. In a scenario where the contactor is used for both normal motor starting and the occasional fault clearing (e.g. in a manual motor starter bypass), the TeSys D will survive about twice as many high‑current interruptions before the arc chamber degrades (illustrative relative life). The Siemens unit, under the same current, will erode the contact tips faster and can fail shorted after 3–4 such events.
When it reverses. If you never fault‑clear with the contactor — the upstream breaker always trips first — then the arc‑chute margin is irrelevant. Also, if you use the Siemens 3RT20 with the larger arc chamber (size S0), its breaking margin matches the TeSys D.
4. Coil power and thermal runaway when the load overheats the panel
The number. The Siemens 3RT2016 coil at 400 V 50 Hz draws about 47 VA inrush / 8 VA sealed. The TeSys D coil (e.g. G7 120 V variant) draws 50 VA inrush / 7 VA sealed. Almost identical. But the coil ambient temperature limit differs: the Siemens coil is rated for 55 °C ambient; the Schneider EverLink coil can operate in 65 °C ambient.
Why that number changes the outcome. When the load doubles, the busbars and conductors in the panel dissipate more heat. In a typical 600 mm enclosure, internal temperature can rise 12–18 °C above ambient. If the room is 35 °C, the panel interior can hit 53 °C. The Siemens coil is now at the edge of its rating. Coil insulation degrades exponentially with temperature — every 10 °C above 55 °C halves the insulation life (Arrhenius rule). In a 60 °C panel, the Siemens coil can fail shorted after 1–2 years. The TeSys D, with a 65 °C rating, stays inside its margin.
Worked consequence. A machine builder who sizes the contactor based on current only, ignoring panel temperature, will see Siemens coil failures after 6–18 months in a warm factory. The Schneider unit will last 5+ years in the same panel. This is a classic “hidden failure” — the contactor appears fine until the coil burns open, causing a nuisance trip that stops production.
When it reverses. If the panel is in a climate‑controlled room (22 °C) and the load doubling is only intermittent, the panel temperature stays below 45 °C. Then both contactors have equal coil life. Also, if you choose the Siemens 3RT20 with its larger coil (size S0), the thermal margin improves because of lower current density in the winding.
Non‑obvious insight: The contactor that seems identical on the datasheet (same AC‑3 current, same making capacity) can have a 4× difference in coil life when the panel runs at 58 °C. The “failure mode” is not the main contacts — it’s the coil insulation. Most engineers check the contact rating, but ignore the coil ambient. That’s where the Siemens 3RT2016 loses its margin.
Failure mode reversal. The TeSys D EverLink coil has a minimum pick‑up time of ~15 ms vs. the Siemens 3RT’s ~10 ms (derived from coil inrush power). In a fast‑cycling application (>120 operations per hour), the longer pick‑up time can cause the TeSys D to miss a zero‑cross and arc‑chatter. If your load doubles and you cycle at 180 ops/h, the Siemens 3RT2016 may actually outperform the TeSys D. This is the exception: where speed (
Decision rule. If your panel temperature is >50 °C or voltage sag >12 % during start, use Schneider TeSys D. If you cycle >120 ops/h and have a stiff grid, use Siemens 3RT. For everything in between, either will work, but the TeSys D gives you a wider safety margin against the hidden failure of coil thermal runaway.
| Parameter | Schneider TeSys D (LC1D18) | Siemens SIRIUS 3RT2016 |
|---|---|---|
| AC‑3 rating (400 V) | 18 A / 4 kW | 9 A / 4 kW* |
| Coil voltage tolerance | 0.75–1.1 Uc (AC), 0.6–1.1 Uc (DC) | 0.85–1.1 Uc (AC) |
| Coil ambient rating | 65 °C | 55 °C |
| Frame width | 58 mm | 45 mm |
| Overload relay pair | LR9D / LT3R (cross‑brand OK) | 3RU2 / 3RB2 (Siemens‑only) |
| Making/breaking capacity | 10× / 8× Ie | 10× / 8× Ie |
| Arc chamber type | Magnetic blow‑out with steel plates | Grid arc‑splitter |
* The 3RT2016 is 9 A; the larger 3RT20 (S0) is 18 A, but that comparison is not like‑for‑like. This table compares the smallest common frame sizes at 4 kW.
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. Schneider Electric is a brand affiliated with this site; competitor names are used for identification only.
