Siemens 3rt2024-1bb40

By Abdullah Zahid
13 min read
Siemens 3RT2024-1BB40 SIRIUS Size S0 power contactor 24V DC coil for three-phase motor control

Siemens 3RT2024-1BB40 SIRIUS Power Contactor, AC-3e/AC-3, 12 A, 5.5 kW at 400 V, 3-Pole, 24 V DC, Auxiliary Contacts 1 NO + 1 NC, Screw Terminal, Size S0 — Specifications, Wiring, and Buying Guide

If you are sourcing a replacement or new 3-pole motor contactor for a 24 V DC control system and need a verified Size S0 unit rated at 12 A AC-3, the Siemens 3RT2024-1BB40 is the direct answer. This SIRIUS power contactor handles motors up to 5.5 kW at 400 V or 7.5 HP at 460 V, snaps onto a standard 35 mm DIN rail in 45 mm of panel width, and includes an integrated 1 NO + 1 NC auxiliary contact — all in a finger-safe IP20 housing rated from -25 to +60°C. For controls engineers retrofitting aging starters or OEM integrators building new motor starter packages, the 3RT2024-1BB40 lands squarely at the bottom of the purchase funnel: the specs are confirmed, the coil voltage matches, and the frame fits.

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

Who Should Buy the 3RT2024-1BB40 — and Who Shouldn't

The Siemens 3RT2024-1BB40 is the correct choice for engineers and technicians who can confirm all of the following:

  • Your control system delivers a regulated 24 V DC signal — not 24 V AC, 110 V AC, or any other class
  • The motor you are switching draws no more than 12 A under AC-3 duty cycle (motors up to 7.5 HP at 460 V or 5.5 kW at 400 V)
  • Your panel has at least 45 mm of DIN rail width available for a Size S0 footprint
  • Screw terminals are acceptable for your wire gauge — M4 screws accommodating 1.5–2.5 mm² main conductors and 0.5–1.5 mm² auxiliary conductors
  • The integrated 1 NO + 1 NC auxiliary contact configuration satisfies your feedback and interlocking requirements

If your motor exceeds 7.5 HP at 460 V, if you need a different coil voltage such as 110 V AC or 230 V AC, or if your interlock scheme requires 2 NO + 2 NC auxiliary contacts, step up to the 3RT2025-1BB40 (24 A, S0), the 3RT2026-1BB40 (32 A, S2), or specify the correct coil voltage suffix for your application.

On this page:

What the 3RT2024-1BB40 Actually Does in a Motor Control Circuit

The Siemens 3RT2024-1BB40 is an electromechanical switching device — its job is to connect and disconnect three-phase AC power to a motor on command from a low-voltage DC control signal. When 24 V DC is applied across coil terminals A1 and A2, the solenoid energizes, pulling in the armature and closing all three main contacts simultaneously. Those three normally open main contacts carry up to 12 A continuously under AC-3 duty — the standard cycle for squirrel-cage induction motors starting under full load. The integrated 1 NO + 1 NC auxiliary contact block closes and opens in sync, providing real-time feedback to a PLC input, pilot light, or thermal relay interlock without any additional add-on block required for standard single-motor applications.

The 3RT2024-1BB40 belongs to the Siemens SIRIUS modular contactor range, which is built to IEC 60947-4-1 standards. Size S0 is the smallest frame in the SIRIUS lineup and is dimensioned specifically for small to mid-range motor control: 85 mm high, 45 mm wide, 107 mm deep. At 5.9 W coil power consumption for both closing and holding, this contactor draws approximately 0.25 A from the 24 V DC supply — manageable on any standard 24 V industrial rail supply. The coil operates reliably across 0.8 to 1.1 times rated voltage, meaning the supply can range from 19.2 V to 26.4 V DC without compromising operation. The insulation voltage is rated at 690 V and the impulse voltage withstand is 6 kV, giving solid margin above typical 480 V industrial distribution systems.

Typical System Architecture for a SIRIUS S0 Motor Starter

The 3RT2024-1BB40 sits between the control logic layer and the motor load — it receives a digital switching command from above and passes three-phase power to the motor below. Understanding its position in the signal chain helps during commissioning and fault tracing.

  • PLC digital output or relay logic provides the 24 V DC signal that drives the 3RT2024-1BB40 coil at terminals A1 (+) and A2 (−)
  • A 24 V DC industrial power supply upstream of the coil circuit, protected by a 1–2 A fuse or miniature circuit breaker, feeds the control loop
  • A thermal overload relay (typically a SIRIUS 3RU series unit) is stacked adjacent on the same DIN rail, wired in series with the motor current and with its NC trip contact in the coil supply circuit
  • The 3RT2024-1BB40 main contacts (terminals 1/3/5 input, 2/4/6 output) switch three-phase supply voltage directly to the motor terminals
  • The integrated 1 NO auxiliary contact feeds back a motor-running status signal to the PLC input or remote indicator, while the 1 NC contact supports interlocking or alarm circuits

Where Engineers Deploy the 3RT2024-1BB40

HVAC systems are the most common field home for the 3RT2024-1BB40. Fan motors, circulation pumps, and chilled water pumps in commercial and industrial buildings routinely fall within the 5.5 kW at 400 V or 7.5 HP at 460 V AC-3 rating. In these applications the contactor cycles on a scheduled or thermostat-triggered basis, and the 10,000,000 mechanical operating cycle rating provides genuine service life.

Water treatment and wastewater facilities use the 3RT2024-1BB40 for circulation pump and aeration blower control where 24 V DC SCADA or PLC control systems are standard. The IP20 protection class is adequate for indoor control panel installations, and the -25 to +60°C operating temperature covers virtually all indoor mechanical room environments.

Compressed air systems — particularly reciprocating and rotary screw compressors under 7.5 HP — are another common deployment. The AC-3 rating of 12 A handles the full-voltage start current profile of these loads. Food processing and light manufacturing conveyor drives rounding out typical deployments where DIN rail panel space is limited and the 45 mm width of the S0 frame is a hard constraint.

OEM integrators building motor starter packages frequently specify the 3RT2024-1BB40 as the base switching element in bundled kits that include a thermal relay and surge suppressor, taking advantage of the SIRIUS modular stacking system.

Application Typical Deployment
HVAC fan and pump motor control 24 V DC PLC output drives contactor in scheduled on/off or thermostat-triggered cycle
Water treatment circulation pump SCADA-controlled start/stop with thermal relay overload protection stacked on DIN rail
Compressed air compressor motor Full-voltage direct-on-line start up to 7.5 HP at 460 V with AC-3 duty rating
Food processing conveyor drive Panel-mounted in space-constrained enclosure using 45 mm S0 width on 35 mm DIN rail
OEM motor starter package Bundled with 3RU thermal overload relay and surge suppressor for complete starter assembly
Retrofit of 110 V AC legacy starter Drop-in replacement in existing SIRIUS S0 footprint when upgrading to 24 V DC control architecture

Key Electrical and Mechanical Specifications for the 3RT2024-1BB40

Parameter Specification
Coil Voltage 24 V DC (operating range 19.2–26.4 V)
Coil Power (Closing and Holding) 5.9 W
Main Contact Current Rating AC-3 at 400 V 12 A
Main Contact Current Rating AC-1 at 400 V 40 A
Rated Power AC-3 at 400 V 5.5 kW
Number of Poles 3
Auxiliary Contacts 1 NO + 1 NC (integrated)
Insulation Voltage 690 V
Operating Temperature Range -25 to +60°C
Physical Dimensions (H x W x D) 85 mm x 45 mm x 107 mm

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

3RT2024-1BB40 vs. SIRIUS Family and Competitor Contactors — Which One Do You Actually Need?

The SIRIUS 3RT range is structured by frame size and AC-3 current rating. If your motor falls outside the 12 A AC-3 envelope, the correct answer is a different model number — not an oversized contactor running underloaded.

Model Frame AC-3 Current at 400 V Power at 400 V Main Contacts Coil Voltage Use Case
3RT2024-1BB40 S0 12 A 5.5 kW 3 NO 24 V DC Motors up to 7.5 HP at 460 V
3RT2025-1BB40 S0 24 A 11 kW 3 NO 24 V DC Motors up to 15 HP at 460 V
3RT2026-1BB40 S2 32 A 15 kW 3 NO 24 V DC Motors in 15–30 HP range
3RT2027-1BB40 S3 40 A 18.5 kW 3 NO 24 V DC Heavy-duty industrial motors

For engineers evaluating alternatives from other manufacturers, the table below shows the closest competitor equivalents by current class and coil voltage. The 3RT2024-1BB40 occupies the cost-effective small-frame tier; competitor models at 12 A AC-3 with 24 V DC coil are broadly available but may carry different footprint, auxiliary contact, or accessory ecosystem implications.

Brand Model Frame AC-3 Current Coil Voltage Price Tier Availability
Siemens 3RT2024-1BB40 S0 12 A 24 V DC Standard Good
ABB A9-22-30 A9 22 A 24 V DC Standard Excellent
Schneider TeSys F LC1F115F7 F / 5.5 kW 115 A 24 V DC Premium Good
Rockwell 100-C16 IEC C 16 A 24 V DC Premium Fair

If your system is built on the SIRIUS modular ecosystem — with existing thermal relay stacks, auxiliary blocks, and DIN rail layouts already specced to S0 — the 3RT2024-1BB40 is the correct choice and eliminates any accessory compatibility risk. Check current availability at LeadTime.ca before finalizing your BOM.

Expert Verdict: Is This the Right Contactor for Your System?

The Siemens 3RT2024-1BB40 earns its place as the go-to Size S0 contactor for 24 V DC control architectures controlling motors up to 7.5 HP at 460 V. Its 10,000,000 mechanical cycle rating and 5,000,000 electrical cycle rating with the auxiliary block are proof-points that reflect real service life in HVAC and pump applications — not marketing numbers. The IEC 60947-4-1 rating means it integrates directly with SIRIUS thermal relays, motor protection blocks, and the broader modular SIRIUS accessory ecosystem without compatibility guesswork. The integrated 1 NO + 1 NC auxiliary contact covers the vast majority of single-motor start/stop-with-feedback applications without requiring an add-on block, keeping panel width at 45 mm.

Where the 3RT2024-1BB40 has real limits: it is not the right part if your motor exceeds the 12 A AC-3 rating at your system voltage. Undersized contactors in AC-3 service will fail prematurely through contact erosion and coil thermal stress. Similarly, if your facility standardizes on 110 V AC or 230 V AC control power rather than 24 V DC, the correct order is a different coil voltage suffix — this unit will not operate on AC voltage. Engineers who need 2 NO + 2 NC auxiliary contacts for multi-motor interlocks or safety relay loops should specify the 3RT2025-1BB40 or add an auxiliary contact block, not assume the integrated contacts are expandable without accessories.

From a procurement standpoint, the 3RT2024-1BB40 is a well-stocked SKU with predictable lead times compared to less common SIRIUS variants. Volume pricing and bundled motor starter kit pricing are available at LeadTime.ca for OEM integrators building multiple panels. 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 for the 3RT2024-1BB40

The following points cover the key requirements and verification steps before and during installation. Engineers needing full step-by-step wiring procedures should refer to the Siemens SIRIUS 3RT2 installation documentation.

  • Mount the contactor on a 35 mm standard DIN rail with a minimum 45 mm slot width; verify enclosure ambient temperature does not exceed +60°C at the mounting location
  • Terminate three-phase supply to main contact inputs (terminals 1, 3, 5) and motor leads to outputs (terminals 2, 4, 6) using 1.5–2.5 mm² copper conductors (14–12 AWG) tightened to M4 screw terminals
  • Wire the 24 V DC coil supply with polarity observed — A1 is positive, A2 is negative — and protect the coil circuit with a 1–2 A DC fuse or miniature circuit breaker upstream
  • Install a diode surge suppressor across the coil terminals (cathode toward A1 positive) to protect against inductive kickback during de-energization cycles
  • Connect the integrated 1 NO and 1 NC auxiliary contacts (wire gauge 0.5–1.5 mm² solid or 0.75–2.5 mm² stranded, 20–16 AWG equivalent) to PLC inputs, pilot lights, or thermal relay interlock circuits as required by the control scheme

Compatible Accessories and Motor Protection Modules

The 3RT2024-1BB40 is designed to work within the SIRIUS modular system. The following accessories are commonly specified alongside this contactor — confirm part numbers and compatibility with current SIRIUS documentation before ordering.

  • 3RU series thermal overload relays — stack directly adjacent on DIN rail in series with motor current for overload protection, with NC trip contact wired in series with the coil supply
  • Additional auxiliary contact blocks — extend the integrated 1 NO + 1 NC to support more complex interlocking or feedback requirements (maximum 2 total per contactor)
  • Surge suppressors — diode modules for DC coil circuits; varistors or RC snubbers for AC circuits in mixed-voltage panels
  • Mechanical interlocks — available for reversing starter configurations requiring two contactors with physical locking to prevent simultaneous energization
  • Contact aid modules (silver alloy overlay) — available for harsh duty applications where standard contact reliability is a concern

Wrong-Part Prevention Checklist Before You Order the 3RT2024-1BB40

Run through every item below before placing your order. This checklist is drawn from the most common field ordering errors for Size S0 SIRIUS contactors.

  1. Verify control system provides 24 V DC signal; do not confuse with 24 V AC or other voltage classes
  2. Confirm motor nameplate horsepower matches AC-3 current rating (12 A at 400 V = 3 HP at 230 V or 7.5 HP at 460 V)
  3. Check available mounting space is DIN rail compatible; S0 is compact but requires minimum 45 mm width
  4. Ensure existing auxiliary block stack supports 1 NO + 1 NC configuration (some applications need 2 NO + 2 NC)
  5. Verify screw terminal type is standard M4 and acceptable for field copper wire gauges (16-12 AWG main, 20-16 AWG auxiliary)
  6. Confirm operating temperature range (-25 to +60°C) matches installation location (not for outdoor unheated/heated cabinets exceeding limits)
  7. Check that magnet coil holding voltage tolerance (0.8–1.1 x rated) is met by DC supply regulation
  8. Inspect for RoHS/CSA/UL compliance requirements for your jurisdiction and end-use safety standards

If any item on this checklist flags a mismatch, contact the LeadTime.ca team to identify the correct SIRIUS variant before ordering — we ship the right part worldwide.

Frequently Asked Questions

Can the 3RT2024-1BB40 be used with a 24 V AC control supply instead of 24 V DC?

No. The 3RT2024-1BB40 has a 24 V DC coil and will not operate correctly on 24 V AC. Applying AC voltage to a DC coil causes the contactor to chatter, fail to hold, or overheat within minutes. If your control system supplies 24 V AC, you need a variant with an AC-rated coil — verify the coil voltage suffix when ordering.

What is the maximum motor size this contactor can handle?

The 3RT2024-1BB40 is rated at 12 A AC-3 at 400 V, corresponding to 5.5 kW at 400 V and 7.5 HP at 460 V three-phase. For motors exceeding this rating, the 3RT2025-1BB40 (24 A, S0 frame) or larger SIRIUS variants are required. Sizing the contactor to the motor's actual nameplate current under AC-3 duty is critical — do not assume any margin covers a larger motor.

Does the integrated auxiliary contact eliminate the need for an add-on auxiliary block?

For most single-motor start/stop-with-feedback applications, yes — the integrated 1 NO + 1 NC auxiliary contact handles PLC feedback, pilot light, and basic thermal relay interlock wiring. If your application requires more than one NO and one NC contact simultaneously, you will need to add an auxiliary contact block. The 3RT2024-1BB40 supports up to 2 total auxiliary contacts per contactor with the appropriate add-on.

How do I verify whether an existing installed contactor is a direct 3RT2024-1BB40 replacement?

Confirm the frame is Size S0 (85 mm x 45 mm x 107 mm), the coil voltage is 24 V DC, the AC-3 current rating is 12 A at 400 V, and the auxiliary contact configuration is 1 NO + 1 NC. These four parameters define a direct replacement. Also check terminal type — the 3RT2024-1BB40 uses screw terminals; if the existing unit has spring terminals, the replacement part number will differ.

What surge suppression is required for the DC coil circuit?

A diode suppressor wired across the coil terminals — cathode toward A1 (positive), anode toward A2 (negative) — is the standard protection for DC coil circuits. At 5.9 W coil power and 24 V supply, nominal coil current is approximately 0.25 A; a 1 A rated diode provides adequate margin. Omitting coil suppression on DC circuits is a leading cause of premature coil failure and contact welding in high-cycle applications.

Is the 3RT2024-1BB40 suitable for outdoor panel installation?

The 3RT2024-1BB40 carries an IP20 protection class, which is appropriate for indoor control cabinets only. For outdoor installations, the contactor must be housed in an enclosure rated for the environmental exposure — the contactor itself does not provide ingress protection against moisture, dust, or spray. Also verify that the outdoor ambient temperature at the cabinet interior remains within the -25 to +60°C operating range.

Why Order the 3RT2024-1BB40 from LeadTime.ca

  • Global shipping — the 3RT2024-1BB40 ships worldwide from LeadTime.ca regardless of your facility's location
  • Sourcing hard-to-find SIRIUS variants — if you need a specific coil voltage, frame size, or accessory bundle, the LeadTime.ca team can source across the SIRIUS range
  • Volume pricing available for OEM integrators and facilities building multiple motor starter panels
  • Direct contact with technical staff for coil voltage confirmation, lead time verification, and BOM cross-referencing before order placement

At-a-Glance Summary

  • Model: Siemens 3RT2024-1BB40 — SIRIUS Size S0 power contactor
  • Coil: 24 V DC, operating range 19.2–26.4 V, 5.9 W consumption
  • Main contacts: 3-pole, 3 NO, rated 12 A AC-3 at 400 V (40 A AC-1 at 400 V)
  • Rated power: 5.5 kW at 400 V (AC-3); equivalent to 7.5 HP at 460 V
  • Auxiliary contacts: 1 NO + 1 NC integrated, no add-on block required for standard applications
  • Dimensions: 85 mm H x 45 mm W x 107 mm D — mounts on 35 mm DIN rail
  • Terminal type: Screw M4 — 1.5–2.5 mm² main, 0.5–1.5 mm² auxiliary
  • Operating temperature: -25 to +60°C; protection class IP20
  • Mechanical life: 10,000,000 cycles; electrical life with auxiliary block: 5,000,000 cycles
  • Insulation voltage: 690 V; impulse voltage withstand: 6 kV; pollution degree 3
  • Standard: IEC 60947-4-1; integrates with SIRIUS 3RU thermal relay and modular accessories