Siemens 3rt1056-6ap36

By Abdullah Zahid
13 min read
Siemens 3RT1056-6AP36 S6 power contactor 90kW AC-3 motor starter panel installation

Siemens 3RT1056-6AP36 Power Contactor, AC-3 90 kW / 400V, AC (50...60 Hz) / DC Operation 220...240V UC — Specs, Selection Guide and Alternatives

When a 75 HP pump motor fails at 2 AM or a controls engineer is spec'ing a mid-range motor starter for a new panel build, the search usually lands on one model: the Siemens 3RT1056-6AP36. This is a 3-pole electromechanical power contactor in the SIRIUS family, rated for AC-3 motor duty up to 90 kW at 400V — or 75 HP at 230V and 215 HP at 460V for North American installations. Its 220-240V AC/DC coil accepts both AC and DC control signals without modification, and the built-in 2NO+2NC auxiliary contact block handles most interlock and status signaling requirements out of the box. If you are confirming fit before placing a PO, this article covers the specs, selection logic, wiring overview, and honest comparison of alternatives.

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

Who Should Buy the 3RT1056-6AP36 — and Who Shouldn't

The Siemens 3RT1056-6AP36 is the right contactor when all of the following are true for your application:

  • Your motor's continuous power rating falls at or below 90 kW at 400V, 75 HP at 230V, or 215 HP at 460V in AC-3 general motor duty
  • Your control circuit delivers 220-240V AC (50/60 Hz) or 220-240V DC — no step-down transformer or coil substitution needed
  • Your panel or MCC bucket can accommodate the S6 frame footprint: 120 mm wide, 172 mm high, 180 mm deep
  • Your interlock and signaling design requires exactly 2 normally-open and 2 normally-closed auxiliary contacts
  • You are working in an ambient environment between -25°C and +60°C with a pollution degree 3 industrial rating acceptable
  • External short-circuit protection fuses — 355A for the main circuit and 10A for the auxiliary circuit — are already specified or can be added

If your motor exceeds 75 HP at 230V or requires more auxiliary contacts than 2NO+2NC, the 3RT1066-6AP36 (S7 size, 110 kW / 220A AC-3) is the correct next step up — and that distinction matters before you order.

On this page:

What the 3RT1056-6AP36 Actually Does in a Motor Control System

The Siemens 3RT1056-6AP36 is a 3-pole electromechanical power contactor from the SIRIUS product family, conforming to IEC 60947-4-1 for electromechanical AC contactors. Its job is straightforward: it sits between the motor power supply and the motor terminals, closing or opening three main contacts on command from a control circuit. When the 220-240V AC/DC coil is energized — by a PLC discrete output, a relay, a timer, or a pushbutton — the main contacts close and power flows to the motor. When the coil de-energizes, the spring-return mechanism opens all three main contacts and breaks the motor circuit.

The 2NO+2NC auxiliary contact block is integral to the unit and mirrors the coil state. The two normally-open contacts close when the coil energizes, providing a motor-run signal to a SCADA system, indicator lamp, or PLC input. The two normally-closed contacts open when the coil energizes, which is the standard configuration for hardwired emergency stop interlocks — the NC contact is wired in series with the coil circuit so that breaking it de-energizes the contactor immediately regardless of software state. Auxiliary contact reliability is rated at 1 faulty switch per 100 million operations at 17V and 1 mA, making them suitable for low-energy signaling circuits common in modern PLC architectures.

The S6 size frame uses conventional bar connection terminals throughout the main circuit, which means the terminal layout is compatible with standard MCC bucket designs and does not require ferrules or custom lugs for most industrial wire gauges. The contactor mounts via screw fixing to DIN rail or a panel mounting rail, and the mechanical life rating of 10,000,000 operating cycles gives it a credible service record in applications ranging from daily pump starts to intermittent compressor switching.

Where This Contactor Sits in a Typical Motor Starter Architecture

The 3RT1056-6AP36 occupies the switching position in the motor power path — downstream of protective fusing and upstream of the motor terminals. Understanding this position clarifies what it does and does not provide.

  • Three-phase supply (L1, L2, L3) enters the panel and feeds through an external 355A gL/gG short-circuit fuse before reaching the contactor main terminals
  • The 3RT1056-6AP36 main contacts (T1, T2, T3) interrupt or pass all three phase currents simultaneously on coil command
  • A separate overload relay (such as a SIRIUS 3RU or 3RB series unit) is typically mounted downstream of the contactor to protect against sustained overcurrent — the contactor itself has no built-in overload function
  • The 220-240V control coil is wired to a control transformer secondary, PLC relay output, or dedicated control circuit; a 10A gL/gG fuse protects the auxiliary circuit separately
  • The 2NO auxiliary contacts feed motor-run status signals to PLC inputs or indicator lamps; the 2NC auxiliary contacts provide hardwired interlock continuity in the safety circuit

Applications and Industries Where This Contactor Is the Standard Choice

Pump control in water and wastewater treatment is one of the most common deployments for this contactor. A 75 HP pump motor on a 230V three-phase supply is within the AC-3 rating, the PLC's discrete output drives a 24V DC relay whose contacts switch the 220V AC coil, and the 2NO contacts send a pump-run confirmation back to SCADA. This is a textbook installation that plant electricians have executed hundreds of times with this exact model.

In compressed air systems, the 3RT1056-6AP36 handles the switching between across-the-line start and full-run modes, with the 2NC auxiliary contacts wired into the pressure transducer alarm circuit so that a high-pressure condition can drop the coil without PLC intervention. Food and beverage processing facilities favor the SIRIUS platform because the 10 million mechanical cycle rating supports the frequent motor starts common in conveyor and mixer applications without requiring annual contactor replacements.

The most commercially significant use case is direct replacement in legacy motor control centers. When a contactor fails in an existing MCC bucket, the 3RT1056-6AP36's S6 footprint and conventional bar terminal layout allow a maintenance technician to remove the failed unit and install the replacement within 1-2 hours, often without rewiring. This is the scenario that drives emergency stock purchases and justifies the premium over lower-cost alternatives.

Application Typical Deployment
Pump motor control (wastewater, water treatment) 75 HP at 230V, PLC discrete output via 220V AC relay, 2NO contacts to SCADA run confirmation
Compressed air compressor switching Across-the-line start, 2NC auxiliary contacts wired to pressure alarm interlock circuit
MCC bucket replacement (legacy retrofit) Drop-in for failed S6 contactor, same terminal layout, 1-2 hour swap without panel redesign
OEM machine builder (European 400V design) 90 kW at 400V AC-3 specified; derated to 150 HP at 460V for North American sites or upsized to 3RT1066-6AP36
Remote facility universal stock item Universal AC/DC coil covers most control voltage variants; single SKU serves multiple motor loads under 100 HP
Mining and petrochemical auxiliary motor loads Fan, conveyor, and agitator motors in pollution degree 3 environments; -25°C to +60°C ambient tolerance

Key Electrical and Physical Specifications

Specification Value
AC-3 rating (motor duty) 185A at 400V; 90 kW at 400V
AC-1 rating (resistive, 400V, 40°C) 215A
AC-4 rating (plugging/reversing) 160A at 400V
North American HP equivalents 75 HP at 230V / 215 HP at 460V (AC-3)
Control coil voltage 220-240V AC (50/60 Hz) or 220-240V DC; 0.8 to 1.1× rated voltage acceptable
Auxiliary contacts 2NO + 2NC, instantaneous; reliability 1 fault per 100 million operations at 17V / 1 mA
Frame size S6
Dimensions (W × H × D) 120 mm × 172 mm × 180 mm
Mechanical life 10,000,000 operating cycles
Ambient temperature range -25°C to +60°C operational

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

3RT1056-6AP36 vs. Larger and Smaller SIRIUS Variants: Which Size Do You Need?

Model Frame Size AC-3 Current Rating Power Rating Best Fit
3RT1044-6AP36 S3 32A AC-3 11 kW / 15 HP Small motor loads; cost and space savings
3RT1056-6AP36 S6 185A AC-3 90 kW / 75-215 HP Mid-range motors; universal AC/DC coil; MCC retrofits
3RT1066-6AP36 S7 220A AC-3 110 kW / 150 HP Motors above 75 HP at 230V; 460V loads above 215 HP
3RT1076-6AP36 S9 280A AC-3 160 kW / 215 HP Heavy industrial loads; large pump and compressor applications

If your motor falls cleanly within the 185A AC-3 envelope and your control circuit supplies 220-240V AC or DC, the 3RT1056-6AP36 is the correct choice — check current availability at LeadTime.ca.

Expert Verdict: Strengths, Real Limits, and Procurement Reality

The 3RT1056-6AP36 earns its position as a standard stocking item at industrial distributors worldwide because it solves three real problems simultaneously. The universal 220-240V AC/DC coil eliminates the SKU management headache that comes with maintaining separate AC and DC coil variants — one part number covers both control signal types. The 10,000,000 mechanical cycle rating is not marketing language; it reflects a product that has been installed in continuous pump and HVAC duty for decades with documented low failure rates. And the S6 frame with conventional bar connections drops into existing MCC bucket designs without mechanical adaptation, which is worth more than any specification when a motor is down and the clock is running.

The honest limits are worth naming. This contactor is IP00 — it has no environmental sealing, so installations in washdown, outdoor, or heavily contaminated environments require an enclosure. If your facility ambient temperature exceeds +60°C, a sealed variant with special coatings is required and this unit is not the correct choice. For motor loads above 75 HP at 230V, specifying the 3RT1066-6AP36 (S7, 220A AC-3, 110 kW) gives appropriate electrical margin rather than running the 3RT1056-6AP36 at its upper boundary. Budget-sensitive new builds where a lower HP range is acceptable may find lower-cost alternatives sufficient, but in replacement and retrofit scenarios the availability and installation speed of the 3RT1056-6AP36 typically outweigh any per-unit price difference.

On the procurement side, this model is carried as standard stock by major industrial distributors with typical lead times of 1-3 business days from distributor warehouse. Volume purchases of 5 or more units typically attract meaningful discounts; 25 or more units can reduce cost by 25-30% compared to single-unit pricing. If you are sourcing for a facility upgrade or MCC rebuild involving multiple motor starters, bundling quantities at order time is the most reliable way to compress both unit cost and delivery timeline. 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

The following points summarize key installation requirements. For full wiring procedures, terminal torque specifications, and circuit diagrams, refer to the Siemens SIRIUS contactor installation manual.

  • Main circuit terminals use conventional bar connections; stranded copper conductors in the 2× 10-16 AWG or 2× 4-6 mm² range per phase are the supported configurations for the S6 frame
  • The 220-240V coil terminals are screw-type, separate from main contacts; 18-22 AWG coil wiring is standard; verify measured coil terminal voltage is within the 0.8-1.1× rated range (176V minimum, 264V maximum) before energization
  • Auxiliary contact terminals accept 20-16 AWG for the 2NO contacts and 18-14 AWG for the 2NC contacts; confirm continuity of NC contacts with a multimeter in de-energized state before connecting to the interlock circuit
  • External short-circuit protection is mandatory: 355A gL/gG fuse on the main circuit and 10A gL/gG fuse on the auxiliary circuit must be installed before commissioning — the contactor has no integrated protection
  • Maintain 10 mm minimum clearance to earthed structural parts on the sides of the contactor; installation altitude is suitable to 2,000 m above sea level without derating

Compatible Expansion and Protection Modules

The SIRIUS platform supports series installation of auxiliary blocks and protective devices alongside the 3RT1056-6AP36. The following compatible module types are referenced in the SIRIUS contactor system:

  • SIRIUS 3RU series thermal overload relays — mounts downstream of the contactor main terminals to provide sustained overcurrent protection; required for complete motor starter assembly as the 3RT1056-6AP36 has no built-in overload function
  • SIRIUS 3RB series solid-state overload relays — electronic alternative to thermal bimetal type; provides more precise trip class adjustment for sensitive motor loads
  • Auxiliary contact blocks (add-on type) — additional NO and NC contacts can be added to the contactor when the standard 2NO+2NC configuration is insufficient for complex interlock or signaling requirements
  • Suppressor modules — RC snubber or varistor suppressor modules for the coil circuit, recommended when coil switching creates noise on 24V DC PLC I/O circuits in the same panel

Wrong-Part Prevention Checklist Before You Order

Before submitting a quote request or purchase order for the Siemens 3RT1056-6AP36, verify every item on this checklist. These are the most common sources of ordering errors for this model:

  1. Confirm motor's continuous power rating (kW or HP) is within 90 kW / 75-215 HP range based on your supply voltage
  2. Verify supply voltage class (230V, 400V, 460V) — 3RT1056-6AP36 rated for 400V main circuit; verify conversion to 230V or 460V HP equivalents
  3. Check that 220-240V AC/DC control coil matches your control signal source (PLC output, relay, timer voltage)
  4. Confirm 2NO+2NC auxiliary contact count is sufficient for all interlocks, status signals, and feedback loops
  5. Measure physical space in panel/enclosure (120mm W × 172mm H × 180mm D) including terminal clearance for wiring
  6. Verify mechanical duty cycle (10 million cycles typical) is not exceeded if high-frequency switching expected
  7. Confirm external short-circuit protection fuses (355A main, 10A auxiliary) are already specified and available

If any item on this checklist cannot be confirmed, contact the LeadTime.ca team before ordering — our team can help verify fit and identify the correct variant if a substitution is needed.

Frequently Asked Questions

Can the 3RT1056-6AP36 coil be driven directly from a PLC 24V DC output?

No — the coil requires 220-240V AC or DC. A 24V DC PLC discrete output cannot drive this coil directly. The standard approach is to wire the PLC output to a 24V DC interposing relay, whose contacts then switch the 220V AC or DC supply to the contactor coil. This also provides galvanic isolation between the PLC I/O circuit and the higher-voltage control circuit.

What is the difference between AC-1, AC-3, and AC-4 ratings, and which applies to my motor?

AC-3 is the relevant rating for standard squirrel-cage induction motors in normal start-stop duty — this is the 185A at 400V rating that defines the 90 kW / 75-215 HP capability of the 3RT1056-6AP36. AC-1 at 215A applies to resistive or slightly inductive loads. AC-4 at 160A applies to plugging, reversing, and jogging duty where the contactor interrupts a running motor repeatedly at high inrush. If your application involves frequent reversing or jogging, the AC-4 rating of 160A at 400V is the constraint to design against.

When should I choose the 3RT1066-6AP36 instead of the 3RT1056-6AP36?

Choose the 3RT1066-6AP36 (S7 size, 220A AC-3, 110 kW) when your motor nameplate exceeds 75 HP at 230V or exceeds 215 HP at 460V. The 3RT1066-6AP36 provides the next frame size up with a higher current rating and appropriate electrical margin for loads in the 75-150 HP at 230V range. Running the 3RT1056-6AP36 at or near its rated maximum in continuous duty shortens contact life and increases replacement frequency.

Is external short-circuit fusing actually required, or is it a recommended best practice?

External fusing is a hard requirement, not optional guidance. The 3RT1056-6AP36 has no integrated short-circuit protection. A 355A gL/gG fuse on the main circuit and a 10A gL/gG fuse on the auxiliary circuit must be installed to meet IEC 60947-4-1 compliance and applicable national safety codes. Under-fusing or omitting fuses entirely violates safety requirements and can result in equipment damage or personnel injury in a fault condition.

How do I confirm whether the 3RT1056-6AP36 is a direct drop-in replacement for the failed contactor in my MCC?

Verify three things: the frame size designation of the original unit (must be S6), the terminal layout and wire gauge compatibility (conventional bar connections), and the control coil voltage of the original (must be 220-240V AC or DC). If all three match, the 3RT1056-6AP36 is a direct replacement. If the original coil voltage differs — for example, 480V AC — a coil voltage mismatch exists and the wrong unit will be installed. Check the original contactor's nameplate before ordering.

What is the expected service life of this contactor in daily pump start-stop duty?

In normal industrial duty with fewer than 10 operations per day, a 5-7 year replacement cycle is the standard planning benchmark. In high-frequency applications exceeding 5 operations per minute on a continuous basis, quarterly monitoring of main contact voltage drop is recommended, with replacement planning triggered when contact voltage drop exceeds 0.5V under full load. The 10,000,000 mechanical cycle rating is a lifespan ceiling, not a replacement interval — actual service life depends on load current, switching frequency, and ambient conditions.

Why Order the 3RT1056-6AP36 From LeadTime.ca

  • LeadTime.ca ships worldwide — whether you are sourcing for a facility in North America, Europe, or anywhere else, the same stock and pricing apply
  • The 3RT1056-6AP36 is carried as a standard catalog item; standard lead times for in-stock orders are 1-3 business days from warehouse
  • Volume pricing is available for orders of 5 or more units — contact the team directly for a quote that reflects your full quantity requirement
  • The LeadTime.ca team can cross-reference coil voltage, frame size, and auxiliary contact configuration to confirm the correct part number before an order is placed

At-a-Glance Summary

  • The Siemens 3RT1056-6AP36 is an S6 frame, 3-pole electromechanical power contactor rated 185A AC-3 at 400V (90 kW), equivalent to 75 HP at 230V and 215 HP at 460V
  • Universal 220-240V AC/DC coil operates across both AC (50/60 Hz) and DC control signals with a voltage tolerance of 0.8-1.1× rated voltage
  • Standard auxiliary contact configuration is 2NO+2NC, instantaneous, with auxiliary contact reliability rated at 1 faulty switch per 100 million operations at 17V / 1 mA
  • Physical dimensions are 120 mm wide × 172 mm high × 180 mm deep; mounts via screw fixing to DIN rail or panel mounting rail
  • Mechanical life is rated at 10,000,000 operating cycles; ambient temperature range is -25°C to +60°C; pollution degree 3 industrial rating
  • External short-circuit protection is mandatory: 355A gL/gG main circuit fuse and 10A gL/gG auxiliary circuit fuse required
  • Conforms to IEC 60947-4-1; carries CE marking; UL 1077 applicable for North American installations
  • Standard distributor lead time is 1-3 business days; volume orders of 25+ units attract up to 25-30% discount versus single-unit pricing
  • For motors above 75 HP at 230V, step up to the 3RT1066-6AP36 (S7, 220A AC-3, 110 kW) — do not run this contactor at the upper boundary of its rating in continuous duty