IMO Controls CT03C – Contact Block 2NC (B4TU02), 10A AC1 / 6A AC15, for IMO PB Series Pushbutton Enclosures

This is the IMO Controls CT03C – a Contact Block 2NC (B4TU02), 10A AC1 / 6A AC15, for IMO PB Series Pushbutton Enclosures available at SparksDirect for the best price. Purchase this item with confidence at Sparks today.

The IMO Controls CT03C is a contact block fitted with 2 Normally Closed (N/C) contacts, also known by its IMO part number B4TU02, designed for use within IMO's pushbutton and selector switch enclosures. It is rated for use with pushbutton enclosures and provides 2 Normally Closed contacts — meaning both contacts are closed (conducting) at rest and open simultaneously the moment the pushbutton actuator is pressed.

This makes the CT03C the natural choice for Stop buttons and Emergency Stop functions in motor control circuits, where interrupting the circuit on activation — rather than completing it — is the safe and functionally correct behaviour. It is not a DIN rail device, not a heating or lighting contactor, and has no coil; it is a passive contact block that clips into the rear of an IMO pushbutton enclosure body and derives its mechanical action from the pushbutton or selector switch actuator above it. 3M UK Plc

The CT03C uses the B4TU02 contact block format and is confirmed to carry IP65 protection from the front when assembled, with NC contacts that have positive opening action according to IEC/EN 60947-5-1. This positive opening (or "direct opening") action is a critical safety feature: it means the contacts are mechanically forced open by the actuator mechanism and cannot remain closed due to contact welding or spring failure — a mandatory requirement for Stop and Emergency Stop contacts under IEC/EN 60947-5-1 and ISO 13850. The B4TU02 is compatible with the full range of IMO BG pushbutton enclosures and suits actuators with 2 or 3 switch positions, making it suitable for use with momentary pushbuttons, maintained pushbuttons, rotary selectors, and key-operated switches within the IMO PB family. 

Technical Specifications

• Manufacturer Part Number: CT03C / B4TU02
• Contact Configuration: 2 × Normally Closed (N/C)
• Positive Opening Action: Yes — NC contacts per IEC/EN 60947-5-1
• AC1 (AC12) Current Rating: 10A at 220–690V AC
• AC15 Current Rating: 6A at 220–240V; 5A at 380–415V; 3A at 500V; 2A at 690V
• DC12 Current Rating: 10A at 24V; 6A at 60V; 2.5A at 110V; 0.8A at 220V
• Rated Insulation Voltage (Ui): 500V AC (B4T series)
• Making Capacity: 60A (cos φ = 0.7–1, 40–60Hz)
• Breaking Capacity: 50A
• Mechanical Life: 10 million operations
• Electrical Life (AC15): Up to 10 million operations at 100VA; 3 million at 300VA; 1 million at 800VA
• Maximum Frequency of Operation: 600 operations/hour
• Short Circuit Protection: 25A slow fuse
• Terminal Type: Screw terminals (M3.5, Pozidriv No. 2)
• Cable Cross-Section: 0.5–2.5mm² (solid or flexible); 0.5–1.5mm² (flexible with multicore cable end)
• Cables per Clamp: 2
• Ingress Protection (front, assembled): IP65
• Operating Temperature: −40°C to +60°C
• Housing Material: Plastic
• Compatibility: IMO BG pushbutton enclosures; IMO B3/B4 series pushbuttons and selector switches; actuators with 2 or 3 switch positions
• Standards: IEC/EN 60947-5-1, VDE 0660; UL, CSA (cULus) approved; CENELEC; LRS (Lloyd's Register of Shipping)
• RoHS Compliant: Yes

What Do People Want to Know?

Q: Why does the CT03C have 2 Normally Closed contacts rather than Normally Open, and why does this matter for a Stop button?

A Normally Closed contact is closed (conducting) at rest and opens when the button is pressed. For a Stop button, this is the only correct configuration: the NC contact is wired in series with the contactor coil's control circuit, so at rest (not pressed) the circuit is complete and the motor runs normally. When the Stop button is pressed, the NC contacts open, breaking the coil circuit and dropping the contactor — stopping the motor. If the wiring to the Stop button were to break or become disconnected, the circuit would also open, causing the motor to stop safely. This is called a "fail-safe" wiring arrangement and is a fundamental principle of industrial safety. The CT03C's NC contacts also incorporate positive opening action as required by IEC/EN 60947-5-1, meaning the contacts are mechanically forced apart and cannot be held closed by contact welding — an essential safety requirement, particularly for Emergency Stop applications. 

Q: What is the difference between the CT03C and the CT01C for stop button applications?

Both can provide NC contacts for Stop functions, but they differ in contact count and typical use. The CT03C provides two independent NC contacts, allowing the Stop button to simultaneously break two separate circuits — for example, both the direct wiring to the contactor coil and a separate "running" signal input to a PLC. The CT01C (B4TU11) provides one NO and one NC contact, which suits a general-purpose pushbutton that needs to both break one circuit and make another when pressed — common in interlocked or signalled stop arrangements. Where a pure double-NC stop or Emergency Stop contact is needed, the CT03C is the correct choice. 

Q: Can the CT03C be used with Emergency Stop (E-Stop) mushroom head buttons?

Yes — the B4TU02 contact block is confirmed compatible with IMO's BG-series pushbutton enclosures and suits actuators with 2 or 3 switch positions, including Emergency Stop actuators. When used with an E-Stop mushroom head such as the IMO BS3P44RED (pull-to-release) or BS3P44S3 (key-release), the CT03C provides the two NC contacts with positive opening required by EN ISO 13850 for Emergency Stop functions. The overall assembled unit should be verified against the full machine safety requirements of the relevant Machinery Directive and risk assessment before being relied upon as a safety-rated E-Stop. 

Who Can Install It?

The CT03C is an industrial control component for installation by qualified electricians or panel builders with experience in industrial motor control and machine safety wiring. While the contact block itself operates at low control voltages, it is almost always installed within a Stop or Emergency Stop pushbutton station forming part of a mains-voltage motor control circuit or safety-rated system. In the UK, wiring and commissioning such circuits falls under BS 7671 (IET Wiring Regulations) and, for machinery, the Machinery Directive / UKCA/CE marking requirements under the Provision and Use of Work Equipment Regulations (PUWER) and relevant harmonised standards including IEC/EN 60947-5-1 and ISO 13850. Where the CT03C is being used as part of a formally assessed safety function (e.g. a Category 1 or higher stop per ISO 13849), the design, installation and validation should be carried out or supervised by a competent electrical engineer with appropriate safety system expertise. Replacement of worn contact blocks in existing machinery by trained maintenance electricians working under proper isolation and safe-working procedures is common practice in industrial environments.

What Is It Used For?

The CT03C is a double-break Normally Closed contact block — both contacts open when the actuator is operated, and return to closed when released (or remain open for maintained actuators). Its principal applications are:

• Motor Stop buttons — the most common use: wired in series with the contactor coil control circuit so that pressing the red Stop button breaks both NC contacts simultaneously, interrupting the coil supply and de-energising the contactor to stop the motor. The double NC contact allows simultaneous breaking of the coil circuit and a PLC "running" feedback signal
• Emergency Stop pushbutton stations — used with IMO's range of Emergency Stop mushroom head actuators (Ø40mm, pull-to-release, key-release, or twist-release) in BG enclosures, providing the mandatory double NC, positive-opening contact arrangement required by EN ISO 13850 for Emergency Stop functions on machinery 
• Safety interlock circuits — installed in safety door switches, guard interlock pushbuttons, and light curtain reset stations where two independent NC contacts must open when a safety boundary is breached or reset is required
• Fail-safe control wiring — wherever a circuit must default to a safe (off) state if the pushbutton wiring is damaged or disconnected; NC contacts achieve this automatically because an open-circuit fault has the same effect as pressing the button
• Selector switch assemblies — used behind rotary or key-operated selector switches to break two circuits when switching from one operating mode to another, for example de-energising two separate outputs when moving a selector from "Run" to "Isolated"
• Building services and HVAC plant — fitted into pump set or air handling unit control panels as the Stop button contact block alongside a CT02C Start contact block, completing the classic two-button DOL motor starter station used across commercial and industrial installations

Note: Some images and pictures are for reference only. The item may differ from the image/picture due to manufacturer's change. Should you require the exact item in the picture, please call or email us to enquire.