Siemens 3RT2015-1BB42 — S00 Contactor Selection Guide

By Abdullah Zahid
11 min read
Siemens 3RT2015-1BB42 SIRIUS S00 3-pole power contactor 24VDC coil for AC-3 motor control

Siemens 3RT2015-1BB42 Power Contactor: Specs, Selection Guide & Alternatives

If you are sourcing a replacement or specifying a new 3-pole motor starter contactor for a 24 VDC control system, the Siemens 3RT2015-1BB42 is likely already on your shortlist. This SIRIUS family power contactor handles AC-3 motor switching duty at 7 A and 3 kW / 400 V, fits in a compact S00 frame at 45 mm wide, and operates from a 24 VDC coil — making it a direct fit for PLC-driven motor control circuits in packaging lines, pump stations, and light industrial OEM equipment. The single 1 NC auxiliary contact handles pilot signaling and basic interlocking without adding circuit complexity.

If you have already confirmed this is the right part, check current pricing and availability at LeadTime.ca — ships worldwide.

Who Should Buy the 3RT2015-1BB42 — and Who Shouldn't

This contactor is the right choice for engineers and technicians who need a compact, cost-effective 3-pole motor starter that runs from a 24 VDC control bus. It is the right fit when all of the following apply:

  • Your control system provides a 24 VDC command signal — this coil is DC only and will not operate from an AC supply
  • The motor being switched is rated at 2 HP at 230V, 3 HP at 460V, or 3 kW at 400V or below — this is the S00 frame ceiling
  • You need a 3-pole contactor for a standard three-phase induction motor on AC-3 switching duty
  • A single 1 NC auxiliary contact is sufficient for status indication or a single interlock signal
  • Screw terminal connections and 35 mm DIN rail mounting are compatible with your panel layout

If you need more auxiliary contacts for complex interlocking, the 3RT2015-1BB44 carries 2 NO + 2 NC. If your motor exceeds 3 HP at 460V, the 3RT2017-1BB42 at 12 A and S1 frame is the correct step up. For AC coil voltages such as 110V or 230V AC, select the appropriate voltage suffix variant within the 3RT2015 base model.

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What the 3RT2015-1BB42 Actually Does in a Motor Control Circuit

The Siemens 3RT2015-1BB42 is a power contactor from the SIRIUS product family, classified as a 3-pole electromechanical switching device for AC-3 motor control duty. In plain terms: it is the component in your control panel that physically opens and closes the three-phase power path to a motor when your PLC, safety relay, or start button sends a 24 VDC signal to the coil terminals A1 and A2.

When the coil is energized at 24 VDC, the three main contacts — identified as 1/L1 to 2/T1, 3/L2 to 4/T2, and 5/L3 to 6/T3 — close simultaneously, connecting three-phase supply voltage to the motor. When the 24 VDC signal is removed, the spring-return mechanism opens all three contacts and the motor coast-stops or transitions to a brake circuit. The single 1 NC auxiliary contact at terminals 21 and 22 opens when the contactor is energized, providing a status feedback signal or interlock to downstream circuits.

At 7 A AC-3 rating and 3 kW at 400V, this is positioned as the entry-level SIRIUS contactor for small motors. The S00 frame at 45 mm wide makes it the most space-efficient option in the SIRIUS range, and the 4 W coil power consumption at 24 VDC keeps the demand on your 24V power supply minimal. The coil resistance of 144 ohms and rated coil current of 166.7 mA are directly useful when sizing your control bus fusing or verifying PLC output card current budgets.

Typical System Architecture for the 3RT2015-1BB42

The 3RT2015-1BB42 sits between the control logic layer and the motor load — it is the final switching element that translates a low-power 24 VDC command into a three-phase power switching event. Here is how it typically sits in the signal and power chain:

  • PLC digital output card or safety relay provides 24 VDC switching signal to coil terminals A1 (+) and A2 (−)
  • An upstream molded-case circuit breaker or fused disconnect protects the main contact circuit — this is mandatory, as the 3RT2015-1BB42 has no built-in short-circuit interruption capability
  • Three-phase supply enters the contactor at L1, L2, L3 main terminals; switched output exits at T1, T2, T3 to the motor terminals
  • The 1 NC auxiliary contact at terminals 21 and 22 feeds a pilot indicator lamp, PLC digital input card, or interlock relay in the control circuit
  • In direct-on-line (DOL) starters, a thermal overload relay is typically mounted downstream of the T terminals to provide motor overcurrent protection

Where Engineers Deploy the 3RT2015-1BB42

In manufacturing environments, this contactor is most commonly found switching small machine tool spindle motors, conveyor drive motors, and coolant pump circuits where the motor load is 2 to 3 HP and the control voltage is 24 VDC. The AC-3 duty rating makes it well-suited for across-the-line starts where the motor is fully loaded at start — the standard case for squirrel-cage induction motors running fans, blowers, and centrifugal pumps.

HVAC system integrators use it in air handling unit fan motor circuits and small chiller pump control panels. The S00 compact footprint allows dense panel layouts where multiple motor circuits must fit in limited enclosure space.

OEM machine builders standardize on the 3RT2015-1BB42 for new machine builds because it integrates directly into SIRIUS motor starter assemblies and pairs with SIRIUS overload relays and circuit breakers on the same DIN rail. Retrofit projects replacing aging contactors in legacy SIRIUS-based panels specify this model because dimensional and electrical interchangeability is guaranteed within the 3RT2015 base frame.

Pump station operators in water treatment and agricultural irrigation control also specify this model for small submersible or surface pump motor starters, particularly where PLC-controlled duty-standby schemes run two or more pump contactors from a single 24 VDC control bus.

Application Typical Deployment
Small machine tool motor control DOL starter with PLC output, 24 VDC coil command, thermal overload downstream
Conveyor system drive 3-pole switching for fractional to 3 HP conveyor motor, interlock via 1 NC auxiliary
Pump and fan control DOL start for centrifugal pump or axial fan motor up to 3 kW at 400V
HVAC air handling unit Compact panel integration, fan motor start/stop via BMS 24 VDC output
OEM machine builder panel Standardized SIRIUS starter assembly with overload relay on 35 mm DIN rail
Retrofit of legacy SIRIUS system Direct dimensional replacement of existing S00 contactor in service

Key Specifications: What You Need to Make a Purchase Decision

Parameter Specification
Frame Size S00
Main Contact Rating (AC-3) 7 A
Main Contact Rating (AC-1 @ 400V, 40°C) 18 A
Motor Power @ 400V (AC-3) 3 kW
Motor Power @ 460V / 230V (AC-3) 3 HP / 2 HP
Coil Voltage 24 VDC
Coil Current / Resistance / Power 166.7 mA / 144 Ohms / 4 W
Auxiliary Contact 1 NC (terminals 21–22)
Maximum Switching Voltage 690 VAC
Dimensions (W × H × D) 45 mm × 57.5 mm × 73 mm

Full technical specifications are available on the product page at LeadTime.ca.

3RT2015-1BB42 vs Related SIRIUS Models: Which One Do You Actually Need?

Model Frame Size AC-3 Current Motor Power @ 460V Auxiliary Contacts Coil Voltage Best For
3RT2015-1BB42 S00 7 A 3 HP 1 NC 24 VDC Basic single-interlock motor start/stop
3RT2015-1BB44 S00 7 A 3 HP 2 NO + 2 NC 24 VDC Complex interlocking or pilot signaling
3RT2017-1BB42 S1 12 A 7.5 HP 1 NC 24 VDC Motors exceeding 3 HP @ 460V
3RT2015-1AN20 S00 7 A 3 HP Varies 110V / 230V AC AC control systems without 24 VDC bus

If your panel uses 24 VDC control logic and the motor is within the 3 HP at 460V ceiling, the 3RT2015-1BB42 is the correct choice — check current availability at LeadTime.ca.

Expert Verdict: Honest Assessment for Controls Engineers

The 3RT2015-1BB42 earns its place as the default choice for small motor control in SIRIUS-based panels. The 7 A AC-3 rating covers the overwhelming majority of auxiliary motor loads found in light manufacturing — coolant pumps, blowers, small conveyors, and HVAC fans — without the cost premium of larger frames. The 24 VDC coil is a natural fit for modern PLC-driven cabinets, and the coil power draw of just 4 W means you can run several of these from a standard 24 VDC SITOP or equivalent power supply without running into current budget problems. The B10 mechanical life of 1,000,000 cycles is competitive for this class of device, and the ambient operating range of -25°C to +60°C covers the vast majority of industrial enclosure environments.

Where this model falls short is straightforward: one auxiliary contact is genuinely limiting. If your circuit needs a run-indication signal and a downstream interlock simultaneously, you are already at the contact limit. In those cases, the 3RT2015-1BB44 is the correct specification — same frame, same coil, more contacts. Buyers sometimes discover this only after the panel is wired, which is an avoidable delay. The IP20 protection class is also a real constraint: this contactor must be enclosed in a rated panel, it is not suitable for open or washdown environments. And the AC-3 duty designation matters — if your application involves frequent plug switching under load (AC-4 duty), this model will wear contacts prematurely.

From a procurement standpoint, the 3RT2015-1BB42 is one of the more reliably stocked SIRIUS items globally. Standard lead times from distributor inventory typically run 1 to 3 weeks, with expedited options available in most major industrial supply markets. If you are building or maintaining a SIRIUS-standard panel, keeping 1 to 2 of these on the shelf is straightforward inventory management given the part's availability and cost tier. If this matches your system requirements, view current stock and pricing at LeadTime.ca.

For volume pricing or to confirm lead time before committing to a build, contact the LeadTime.ca team directly — we ship worldwide.

Wiring and Installation Overview

  • Connect three-phase supply to main terminals L1, L2, L3 and motor load to T1, T2, T3 — always install an upstream fused disconnect or molded-case circuit breaker before the L terminals, as this contactor provides no short-circuit interruption
  • Wire the 24 VDC coil with positive to terminal A1 and negative to terminal A2 — the DC coil is polarity-sensitive and will not energize with reversed connections; incorrect polarity does not damage the coil but the contactor will not activate
  • Connect the 1 NC auxiliary contact at terminals 21 and 22 to your PLC input card, pilot lamp, or interlock relay circuit — auxiliary contact current rating is 2.6 A at 400V AC-1
  • Mount on 35 mm DIN rail (EN 50022) in vertical orientation only; maintain a minimum 10 mm clearance above, below, and in front, with 6 mm side spacing to grounded metalwork
  • Screw terminal connections accept main conductors up to 2x 12 AWG and auxiliary conductors up to 2x 4 mm² — verify conductor sizing against motor full-load amps before final installation

What Engineers Get Wrong When Ordering This Part

Before placing your order, run through this checklist. These are the most common specification mismatches that result in return shipments and commissioning delays:

  1. Confirm coil voltage matches control system: This model is 24 VDC only; incorrect voltage will prevent coil from energizing
  2. Verify main contact pole count: This is 3-pole (3-phase motor control); single-phase motors require 1-pole or 2-pole variant
  3. Check auxiliary contact requirement: 1 NC contact only; if status feedback or interlock requires multiple contacts, select higher-variant model
  4. Confirm motor horsepower falls within rated range: 2 HP @ 230V, 3 HP @ 460V, 2 HP @ 220V, 3 HP @ 380-415V; oversizing motor beyond these ratings voids warranty and causes premature contact wear
  5. Verify AC-3 duty is appropriate: If motor is switched under load frequently (plug/unplug), AC-4 duty required; this model is AC-3 only
  6. Check mounting method compatibility: Screw terminal type; if snap-on terminals required, select alternative
  7. Confirm electrical standards compliance: IEC 60947-4-1 for IEC regions; UL-rated models available with different suffix (e.g., -0CC0 variant)

If any item on that checklist triggered a concern, contact the LeadTime.ca team before ordering — we can confirm the correct variant for your application or you can review the full product details at LeadTime.ca.

Frequently Asked Questions

Can the 3RT2015-1BB42 coil operate from an AC supply?

No. The coil on the 3RT2015-1BB42 is rated for 24 VDC only. The main contacts can switch up to 690 VAC on the three-phase power circuit, but the coil control signal must be 24 VDC. If your control system provides only AC voltage, you will need either an external 24 VDC power supply or a different SIRIUS variant with an AC-rated coil such as the 3RT2015-1AN20.

What happens if I reverse the coil polarity?

The DC coil is polarity-sensitive with positive to A1 and negative to A2. Reversing the connections will prevent the coil from energizing — the contactor will not pull in. Reversed polarity does not permanently damage the coil, but the wiring must be corrected before the contactor will function. Color-coded wiring and clearly labeled terminals at A1 and A2 prevent this during installation.

How long will this contactor last in continuous factory duty?

The B10 mechanical life value is rated at 1,000,000 cycles at high demand rate. In a typical factory environment running 8-hour shifts at moderate switching frequency, that translates to approximately 2 to 3 years before contact inspection is warranted. For light-duty or intermittent applications, service life extends considerably beyond this estimate.

Does this contactor include short-circuit protection?

No. The 3RT2015-1BB42 is a switching device only and does not provide built-in short-circuit or overload protection. An external molded-case circuit breaker or fused disconnect must be installed upstream of the main L terminals, sized for motor full-load amps with a 125% multiplier. A separate thermal overload relay downstream of the T terminals is also standard practice for motor protection.

Is this contactor suitable for North American UL applications?

The 3RT2015-1BB42 is IEC 60947-4-1 compliant. For applications requiring UL 508 certification, Siemens offers UL-rated variants within the 3RT2015 family identified by a different suffix such as -0CC0. Verify the compliance requirement for your application before ordering, particularly for safety-critical or code-inspected motor control installations.

What is the difference between the 3RT2015-1BB42 and the 3RT2015-1BB44?

Both models share the same S00 frame, 7 A AC-3 main contact rating, 24 VDC coil, and screw terminal connections. The only difference is the auxiliary contact configuration: the 3RT2015-1BB42 has 1 NC contact, while the 3RT2015-1BB44 provides 2 NO and 2 NC auxiliary contacts. If your circuit requires more than one auxiliary contact for interlocking or multiple feedback signals, the 3RT2015-1BB44 is the correct choice — the two models are not pin-for-pin drop-in replacements at the auxiliary wiring level.

Why Order the 3RT2015-1BB42 From LeadTime.ca

  • LeadTime.ca ships the 3RT2015-1BB42 worldwide — no geographic restrictions on orders
  • Volume pricing available for multi-unit orders; contact the team directly to discuss bulk quotes before raising a purchase order
  • Sourcing support for hard-to-find SIRIUS variants and related accessories — if the standard suffix is out of stock, the team can identify equivalent alternatives
  • Fast response on lead time inquiries, useful before committing to a build schedule that depends on component availability

At-a-Glance Summary

  • Model: Siemens 3RT2015-1BB42 — SIRIUS family, S00 frame, 45 mm wide
  • Main contacts: 3-pole, 3 NO, rated 7 A at AC-3 and 18 A at AC-1 (400V, 40°C)
  • Motor power: 3 HP at 460V, 2 HP at 230V, 3 kW at 400V — AC-3 duty only
  • Coil: 24 VDC, 166.7 mA, 144 ohms, 4 W — polarity-sensitive (A1 positive, A2 negative)
  • Auxiliary contact: 1 NC at terminals 21–22; 2.6 A at 400V AC-1
  • Maximum switching voltage: 690 VAC on main contacts
  • Mechanical life: 1,000,000 cycles (B10, high demand rate)
  • Operating temperature: -25°C to +60°C; storage -55°C to +80°C
  • Protection class: IP20 (front and terminals) — requires enclosure in rated panel
  • Mounting: 35 mm DIN rail (EN 50022), vertical orientation, screw terminals
  • If you need more auxiliary contacts, specify 3RT2015-1BB44; for motors above 3 HP at 460V, specify 3RT2017-1BB42