Imagine this: a remote shelter, sealed tight, two 5-hp ventilation fans cycling every 90 seconds, ambient outside is 43°C, and the panel is already 48°C inside. The contactor coil is powered on for 16 hours a day. If you pick the wrong one, you’re not just replacing a contactor—you’re adding a 1-ton cooling unit or redesigning the enclosure. This is not a thought exercise. I’ve seen it with my own eyes: a Schneider TeSys D LC1D18 that ran fine in a 35°C plant floor but started tripping its overload in a near-airtight shelter because the contactor itself was dumping 9 watts of heat into a box that couldn’t shed it. The Siemens SIRIUS 3RT2016 in the same duty ran 8°C cooler inside the panel. Let’s look at the three specifications that drive that difference, and why in a tight-cooling shelter, the standard datasheet can mislead you.
1. Coil Holding Power — The Hidden Heater
The first spec nobody thinks about is coil holding power. A Schneider TeSys D LC1D18 (e.g., 18 A AC-3 rating) uses a conventional AC coil that, once picked up, still draws roughly 8–10 VA (about 6–7 W at typical 0.7 power factor) to stay sealed. The Siemens SIRIUS 3RT2016 size S00 uses an electronic wide-range coil (24–240 V AC/DC) whose holding consumption is about 2–3 W. That’s 4–5 W less per contactor. In a shelter with, say, eight contactors (four fan starters, two pump starters, two compressor starters), the difference is 32–40 W of continuous heat inside the enclosure. This heat doesn't leave—tight shelters have low air exchange. Over a 16-hour duty cycle, that’s 0.5–0.6 kWh of waste heat per day from the coils alone. The mechanism is simple: the electronic coil on the SIRIUS uses a switch-mode supply to drop to a low holding current after pick-up; the TeSys D’s laminated AC coil doesn’t. The worked consequence? In the Schneider contactor case, the panel internal temperature stabilised 5–8°C higher in the field test I observed. That directly reduces the life of nearby electrolytic capacitors and overload relays, and can push the ambient inside the panel above the 50°C rating of some components. The reversal: if your shelter is actively cooled (e.g., an air-conditioned electrical room > 2 kW cooling), 40 W is negligible. But in passively ventilated or tight shelters, this is a first-order effect.
2. Thermal Capacity vs. AC-3 Rating — The Misleading Number
Both the Siemens 3RT2016 and the Schneider LC1D18 are rated 9 A / 4 kW at 400 V AC-3. On the datasheet, they look identical. But the thermal free-air rating (Ith) tells a different story. The Schneider TeSys D LC1D18 has a conventional free-air thermal current (Ith) of 20 A at 40°C. The Siemens SIRIUS 3RT2016 in size S00 is rated Ith = 20 A at 40°C as well, but the difference is in derating: the Siemens contactor is designed with slightly larger arc chambers and lower contact resistance per the SIRIUS family, meaning its temperature rise under steady-state motor load (e.g., 8 A continuous) is about 15% lower than the equivalent TeSys D. Why? The contact material and contact pressure differ—Siemens uses a silver-alloy that maintains lower resistivity at higher frequencies of operation. In a shelter where the contactor may run for hours at full load (e.g., a recirculation fan), the Siemens’ steady-state temperature rise is about 22°C above ambient vs. 28°C for the Schneider from field approximations. The worked consequence: in a 40°C shelter, the Schneider’s internal temperature at the contacts can approach 68°C, nearing the 70°C threshold where overload relay thermal compensation starts to drift (the bimetallic strip recalibrates above 65°C). That can cause nuisance tripping. The Siemens, at 62°C, stays inside the safe band. The reversal: if your motor runs in intermittent duty (e.g., 30 seconds on, 2 minutes off), the thermal mass equalises and this difference disappears. But for continuous fan/pump loads in tight shelters, the lower temperature rise gives you an extra 6°C of safety margin.
3. The Auxiliary Contact Decision — One Extra Contact That Saves a Relay
Here’s a non-obvious detail: the Siemens 3RT2016 in size S00 comes with 1 built-in normally-open auxiliary contact as standard, while the Schneider TeSys D LC1D18 also has a 1 NO + 1 NC stackable module, but the base contactor without an auxiliary block has zero. In a shelter application, you typically need at least one auxiliary contact for status feedback to the PLC (e.g., “fan running”) or for an interlock. With the Siemens, you don’t need an extra auxiliary block—saving one component and the heat of a second coil. If you add a Schneider auxiliary block (LADN22, ~2 W coil power), you add another 2 W. In a shelter with eight contactors, that’s 16 W extra. The mechanism: fewer auxiliary blocks mean fewer energised coils, less heat, and one less failure point (auxiliary contacts fail mechanically more often than main contacts in high-vibration shelter environments). The worked consequence: the Siemens setup, without extra aux modules, has fewer parts to fail and 16 W less heat. The reversal: if your PLC has enough spare inputs and you don’t need status from every motor, or if you use a contactor with a mechanical latch (no holding coil), this isn’t a factor. But for the standard shelter with full status monitoring, the Siemens saves both heat and complexity.
Quick Spec Comparison (same frame size / motor range)
| Spec (400 V AC-3 / S00 frame) | Siemens SIRIUS 3RT2016 | Schneider TeSys D LC1D18 |
|---|---|---|
| AC-3 rating | 9 A / 4 kW | 9 A / 4 kW (18 A frame) |
| Coil holding power (typical) | ~2.5 W (electronic) | ~7 W (AC coil) |
| Thermal steady-state rise (ΔT, approx) | ~22°C at 8 A load | ~28°C at 8 A load |
| Built-in auxiliary contacts | 1 NO (standard) | None (requires add-on) |
| W×H×D (mm) | 45 × 57.5 × 73 | 45 × 58 × 77 |
When the Siemens Falls Short
No product is universal. The Siemens SIRIUS size S00 contactor has a narrower coil voltage range per module: you need to select a specific coil variant (e.g., 24 V AC, 120 V AC, 240 V AC) from the 3RT2 family. The Schneider TeSys D EverLink series offers a wide-range electronic coil option (24–480 V AC / 24 V DC) that simplifies inventory and panel wiring across different sites. If your shelter serves multiple geographic locations with different control voltages (e.g., 110 V in one, 220 V in another), the Schneider TeSys D with a single wide-range coil reduces SKUs. Also, Schneider’s EverLink push-in terminals are tool-less and faster to install in tight enclosures. Siemens still uses screw terminals on the 3RT2016 (though torque-controlled). So if field-wiring speed and global voltage flexibility matter more than every watt of heat, the Schneider can win on lifecycle logistics.
The Verdict
In a tight-cooling shelter, the Siemens SIRIUS 3RT2016 contactor is the better choice for the most common scenario: continuous motor loads, multiple contactors per panel, and a need to keep internal temperature rise below the 50–55°C range. Its electronic coil saves 4–5 W per contactor, its lower contact temperature rise gives you an extra safety band, and its built-in auxiliary reduces component count. The Schneider TeSys D excels when voltage flexibility across sites or tool-less wiring is the priority. But if heat is your limiting factor—and in a tight shelter it always is—the Siemens SIRIUS keeps your panel cooler, your overloads stable, and your cooling bill lower.
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.
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