Siemens Tiastar MCC: History, Specs, and Common Issues

The Siemens Tiastar is one of the most widely installed MCC platforms worldwide. With decades of production and continuous refinement, Tiastar MCCs are found in every type of industrial facility. This guide covers the history, specifications, and common issues you should know about.

History

The Tiastar MCC platform has its roots in the Siemens (formerly Allis-Chalmers and Furnas Electric) motor control product line. Siemens acquired Furnas Electric Company in 1987 and continued developing the MCC platform that eventually became the Tiastar.

The Tiastar name has been used since the early 1990s. Over the years, Siemens has released several generations:

• First generation: Basic Tiastar with conventional wiring
• Tiastar with CU (Communication Unit): Added network communication capability
• Tiastar with TM (Technology Module): Enhanced diagnostic and monitoring features
• Current Tiastar: Full IIoT capability with Siemens MindConnect integration

Despite these technology upgrades, the fundamental mechanical design has remained backward-compatible, meaning older Tiastar MCCs can accept current-production buckets with the correct stab configuration.

Specifications

Physical Dimensions

• Section width: 20 inches (standard)
• Section height: 90 inches (standard)
• Section depth: 20 inches or 24 inches
• Bucket heights: 6", 12", 18", 24", 36", 48"

Electrical Ratings

• Voltage: 600V AC maximum
• Horizontal bus: 600A to 4000A
• Vertical bus: 300A or 600A
• Short-circuit rating: Up to 100 kA symmetrical
• Listed per: UL 845, CSA C22.2 No. 254

Bucket Types

Siemens Tiastar supports a full range of bucket configurations:

• Feeder buckets (circuit breaker or fused disconnect)
• FVNR and reversing starters (NEMA sizes 0 through 6)
• Combination starters
• VFD buckets
• Soft starter buckets
• Lighting contactors
• Custom control units

Stab Connection Design

The Tiastar uses a proprietary spring-loaded stab design. Key characteristics:

• Three-phase stabs mounted on the rear of the bucket
• Spring tension maintains contact with the vertical bus bars
• Stab assemblies are available in different amperage ratings
• Stabs are NOT compatible with other MCC manufacturers

For detailed identification of Tiastar stab types, see our Siemens Tiastar guide.

Common Issues

1. Contactor Coil Failures

Siemens uses 3RT series contactors in Tiastar buckets. The most common failure is coil burnout, typically caused by:

• Excessive control circuit voltage (check transformer output)
• Mechanical binding preventing full closure (dirt, misalignment)
• Excessive operating frequency (cycling too rapidly)

Solution: Replace the contactor coil or the entire contactor. Siemens 3RT contactors are readily available.

2. Electronic Overload Relay Issues

Modern Tiastar buckets use Siemens 3RB or 3RU series electronic overloads. Common issues:

• Parameter settings lost after power interruption (older models without non-volatile memory)
• Communication faults when networked
• False trips due to electrical noise (especially near VFDs)

Solution: Verify overload settings against motor nameplate data. Ensure proper shielding of communication cables.

3. Stab Degradation

Like all MCCs, Tiastar stab connections can degrade over time:

• Oxidation of contact surfaces
• Spring fatigue reducing contact pressure
• Overheating from overloaded circuits

Solution: Regular thermographic inspection. Clean and re-tension stabs during scheduled outages. Replace stab assemblies that show signs of overheating.

4. Door Interlock Mechanism

The Tiastar door interlock prevents opening the bucket door when the disconnect is ON and prevents turning the disconnect ON when the door is open. Common issues:

• Interlock mechanism wear from frequent operation
• Misalignment after bucket removal and reinstallation
• Broken interlock springs or detents

Solution: Inspect interlock mechanism during preventive maintenance. Replace worn components before they fail completely.

5. Control Transformer Failures

Siemens uses machine tool transformers for control power in Tiastar buckets. Common failures include:

• Open primary or secondary winding from overcurrent
• Insulation breakdown from age and heat
• Incorrect fusing allowing sustained overloads

Solution: Replace failed transformers with the same VA rating and voltage ratio. Verify control fusing is correct.

Vintage Identification

Determining the vintage of your Tiastar MCC helps with parts sourcing:

• Pre-1995 Tiastar: Look for older-style door latches, mechanical overload relays
• 1995-2005 Tiastar: Transitional period, may have either mechanical or electronic overloads
• 2005-present Tiastar: Modern electronic overloads, may include communication modules

The MCC serial number on the main section nameplate usually includes the manufacturing date. Contact Siemens with the serial number if you cannot determine the vintage.

Replacement Bucket Options

MCC Depot manufactures Siemens Tiastar compatible buckets with new Siemens components. We match your existing stab configuration, bucket dimensions, and component layout.

What We Need to Build Your Bucket

1. MCC model and vintage (Tiastar nameplate data)
2. Bucket height and type (feeder or starter)
3. Motor HP, voltage, and FLA (for starter buckets)
4. Disconnect type preference (breaker or fused)
5. Control voltage and devices (pushbuttons, lights, switches)
6. Any special requirements (VFD, soft start, communication)
7. Photos of existing bucket (front, interior, stabs)

Call 307-442-0382 or email sales@mccdepot.com for a quote on Siemens Tiastar replacement buckets.