Main switchboards and motor control centres do different jobs. They can look similar, they can share the same workshop, and they can even sit in the same room, but specifying one when you actually need the other is a common and costly mistake.
Quick answer
A main switchboard (MSB) distributes incoming supply to loads, sub-boards, and plant across a facility. It is the single point where the supply is received, metered, and split.
A motor control centre (MCC) is a specialised assembly that starts, protects, and controls multiple motor loads from one cabinet, usually with contactors, overloads, soft starters, or variable speed drives.
Most industrial sites need both: the MSB receives and distributes the supply, an outgoing feeder runs to the MCC, and the MCC then controls the motor loads. Commercial sites often need only an MSB.
| Attribute | Main Switchboard (MSB) | Motor Control Centre (MCC) |
|---|---|---|
| Primary function | Receive, meter, and distribute incoming LV supply to loads and sub-boards. | Start, protect, and control multiple motor loads from a single assembly. |
| Typical loads served | Lighting, general power, sub-boards, HVAC, submains, building services. | Pumps, fans, conveyors, agitators, compressors, process motors. |
| Key components | ACB or MCCB main, metering, MCCB outgoing feeders, distribution busbar, RCDs where required. | MCCB or fuse feeder, contactors, overload relays, soft starters, VSDs, control PLC, HMIs. |
| Typical form of separation | Form 2b or Form 3b (busbar separated from functional units). | Form 3b or Form 4a (full separation of each functional unit with its terminals). |
| Fault level range | Often higher, as it sits closer to the supply transformer (35-65 kA typical). | Typically lower due to cable impedance from the MSB (15-35 kA typical). |
| Control and automation | Usually limited to metering, basic monitoring, emergency power transfer. | Integrated PLC control, SCADA connection, process automation, drives. |
| Typical CWS platform | Schneider Prisma Plus G, Simotrol, Logstrup, or custom Quantum build. | Simotrol (fixed-pattern Form 4a), Schneider Prisma Plus G, or Logstrup. |
| Governing standard | AS/NZS 61439.1 and .2 for power switchgear and controlgear assemblies. | AS/NZS 61439.1 and .2, with motor-specific design verification. |
In this article
The MSB versus MCC question comes up in almost every industrial and commercial project brief. It matters because the two assemblies are engineered around different requirements, built to different forms of separation, and priced on different assumptions. Specifying one when the site actually needs the other leads to redesign, scope changes, or worse: a finished board that does not match how the plant actually runs.
New to either side of the comparison? Start with the dedicated explainers:
A main switchboard is the primary low-voltage assembly on a site. It receives the incoming supply (from the network transformer, from a generator, or from another upstream source), meters it, protects it, and distributes it out to the rest of the electrical installation.
Every building with a three-phase connection has something performing the MSB role, whether it is called that or not. On a small commercial site, the MSB might be a single wall-mounted enclosure. On a large industrial facility, it might be a multi-section floor-standing assembly rated for 4,000 A or more.
Typical MSB content includes:
MSBs sit close to the supply, so they typically carry the highest fault level on the site. That drives switchgear selection, busbar bracing, and internal arc considerations. For more on how fault level is determined, see our guide on what fault rating a switchboard needs.
A motor control centre is a specialised assembly that houses the starting, protection, and control equipment for a group of motor loads. Where an MSB hands power out to feeders and sub-boards, an MCC hands power into motor starters, typically one per motor circuit.
MCCs are typical on industrial sites: dairy plants, meat works, wastewater stations, pump stations, grain drying facilities, sawmills, food processing lines, and water treatment plants. Once a facility has more than five or six three-phase motors running under coordinated control, an MCC is usually the right architecture.
Typical MCC content includes:
MCCs are typically built to a higher form of separation than MSBs. Form 4a (also called “fixed pattern” construction) is the standard for larger MCCs, because it allows each motor starter to be isolated, maintained, or replaced without de-energising the rest of the assembly. That operational flexibility is worth the additional cost when you have fifteen or twenty motor circuits to maintain over the life of the plant.
At CWS, Simotrol is a long-standing in-house platform we build for both MSBs and MCCs. For MCC work it is configured as a fixed-pattern Form 4a assembly, built to the project’s specific starter schedule. For MSB work it is configured for distribution, metering, and outgoing feeder ways. For projects with specific consultant preferences or different form-of-separation requirements, we also build on Schneider Prisma Plus G or Logstrup.
The simplest way to tell them apart: if the assembly’s job is to distribute power to feeders and sub-boards, it is an MSB. If the job is to start, protect, and control a group of motors, it is an MCC.
An MSB is the right answer when the assembly’s job is distribution, not motor control. Indicators include:
Most commercial buildings (offices, schools, retail, warehousing, community facilities) need only an MSB with distribution boards downstream of it. The motors serving these buildings (HVAC, lifts, pumps) are either packaged with their own controls or small enough to start direct-on-line without any coordinated control system.
An MCC is the right answer when the site has a group of motors that need to be started, protected, controlled, and monitored as part of a process. Indicators include:
Think of an MCC as the “control room in a cabinet” for the motor side of the plant. It is where the process engineer sees each motor’s status, the maintenance team isolates individual starters for work, and the automation team integrates everything into SCADA or the plant PLC.
On most industrial sites, the question is not MSB or MCC. It is how do the MSB and MCC talk to each other.
The typical arrangement looks like this:
Larger sites commonly have multiple MCCs, each serving a discrete process area (a packing line, a utilities building, a water treatment plant, a boilerhouse). Very large sites may also have multiple MSBs.
The distinction matters at specification stage because the two assemblies are built to different assumptions. Squeezing an MCC-style scope into an MSB frame forces compromises on form of separation, maintainability, and automation. Scoping an MSB-style requirement into an MCC footprint produces an oversized assembly with capability the site will never use.
Three mistakes recur in project briefs:
The specification says “main switchboard” but the single-line diagram, BoQ, and functional description describe a motor control centre. Pricing the scope as an MSB misses the form of separation, starter architecture, and control system, all of which cost more to build than distribution switchgear. Resolve it before the tender goes out: if it has starters and a PLC, it is an MCC.
On small industrial sites, it is tempting to fit a handful of direct-on-line starters into the MSB rather than provide a separate MCC. That can work for two or three motors on a simple installation. Beyond that, the form of separation is wrong for motor control, the whole MSB has to be isolated to work on any single starter, and there is rarely spare space to add new motors later without a significant modification.
The opposite mistake: specifying Form 4a, a full PLC, and individual starter monitoring on a commercial building with four HVAC motors. The capability is real but the cost and complexity are not justified by the load profile. A well-specified MSB with appropriate outgoing feeders is often the better answer for commercial and light industrial work.
Clive Wilson Switchboards builds both MSBs and MCCs nationwide from our Invercargill workshop. Recent and current projects span from Auckland and Northland in the north, through Hamilton, Tauranga, Rotorua, New Plymouth, Napier-Hastings, Palmerston North, Wellington, Nelson, and Queenstown, to regional infrastructure across Southland and the West Coast.
MSB and MCC scope crosses every sector we serve: meat works in Auckland, dairy and food processing in Taranaki, Waikato, and Southland, water and wastewater in Wellington and New Plymouth, aluminium and metals processing in Southland, and commercial and light industrial work in Hamilton and Tauranga. On industrial sites we typically deliver both assemblies together as part of a coordinated package.
We build on four proven platforms: Schneider Prisma Plus G (accredited builder), Simotrol, Logstrup, and Quantum. MSB platform selection is driven by fault level, IP requirement, footprint, and whether integral metering or bypass gear is required. MCC selection is driven by starter count, form of separation, control system, and maintainability requirements. Manufactured under our ISO 9001-certified quality management system, with assemblies designed and verified to AS/NZS 61439. Avetta registered and SiteWise certified for procurement on major infrastructure projects. See our case studies for examples of recent MSB and MCC deliveries.
Getting the MSB / MCC choice right at specification stage saves re-work, re-design, and scope disputes later. If the assembly’s job is to receive, meter, and distribute, it is an MSB. If the job is to start, protect, and control motors, it is an MCC. If both jobs need doing on the same site, the answer is almost always one of each, connected by a well-sized submain feeder.
Where a project is genuinely on the boundary, share the load schedule and single line diagram at enquiry stage. The architecture usually becomes obvious once the motor side is on paper next to the distribution side.
On smaller sites, yes: an MSB can include a few motor starters as part of the outgoing feeder schedule. On larger sites this is usually a false economy, as the MSB form of separation is not ideal for motor control and maintainability becomes an issue. As a rule of thumb, once the motor schedule exceeds five or six circuits with coordinated control, a separate MCC is the right architecture.
At comparable main ratings, an MCC is usually more expensive than an MSB because it contains more functional units (starters, protection, drives, PLC), is typically built to a higher form of separation, and includes control and automation work. The cost difference is proportional to the starter count and the level of automation integration. A small MCC can be close in price to a similarly rated MSB; a large fully-integrated MCC can be several times the cost.
Form 4a (fixed pattern) is the industry standard for larger industrial MCCs because it allows each starter unit to be isolated, worked on, or replaced without de-energising the rest of the assembly. Form 3b is acceptable for smaller MCCs with fewer starters or where maintenance requirements are less demanding. The specifier should confirm the required form of separation at enquiry stage as it affects enclosure type, cost, and lead time.
Yes, and it is a common arrangement. The two assemblies are usually installed side by side with a submain feeder running between them. Switchroom sizing, ventilation, access clearances, and thermal considerations need to accommodate both assemblies. On larger sites, the MSB may be in one room and the MCC in a separate process area closer to the motor loads to reduce cable runs.
Not always, but often. A small MCC with a handful of direct-on-line starters and independent operation can be built without any PLC integration, using traditional hardwired control. More typically, an industrial MCC includes a PLC for sequencing, interlocking, and integration with the plant SCADA system. The control system scope should be defined alongside the starter schedule at enquiry stage, as it significantly affects design time and cost.
MCCs built to Form 4a are easier to modify without plant-wide shutdowns, because individual starter units can be isolated and replaced while the rest of the MCC remains live. MSBs are typically not built to the same level of separation, so adding new feeders or replacing switchgear often requires a planned shutdown of the whole assembly. This is one of the reasons MCCs are worth the additional cost on sites where operational uptime matters.
Both assembly types are built at our Invercargill workshop using the same quality management system and engineering team. On projects where both an MSB and an MCC are required, building them together lets us coordinate the cable interface, form of separation handover, metering scheme, and installation sequence as a single package, which typically shortens site commissioning time.
Reviewed by Chris Wilson, Co-Director, Clive Wilson Switchboards. Registered Electrician, 15+ years in LV switchboards. Updated April 2026.
