A main switchboard carries the electrical backbone of a manufacturing plant. It supports production equipment, conveyors, motors, compressed air, HVAC, refrigeration, process equipment, control panels, safety systems, lighting, amenities, and future plant changes.
Switchboard sizing needs to start early. If a board is sized around current equipment alone, the site can run out of capacity as soon as a new system is added. The aim is to plan a board that can carry today’s demand, support realistic future growth, and be maintained safely once the plant is running.
What Main Switchboard Sizing Needs To Account For
Switchboard sizing should be based on the way the plant actually operates. A manufacturing site may have high-demand motors, variable speed drives, refrigeration, washdown systems, PLC panels, conveyors, lighting, general power, battery chargers, and equipment that cycles through the day.
The following table gives a quick view of the main inputs that need to be reviewed before the board design is locked in.
| Sizing Input | What To Confirm | Why It Matters |
| Connected load | Major equipment, downstream boards, and measured operating current | Sets the baseline demand the board needs to support |
| Starting load | Motors, compressors, pumps, conveyors, and high inrush equipment | Reduces nuisance trips and start-up problems |
| Maximum demand | Which loads can run together during normal and peak operation | Keeps the design matched to real plant behaviour |
| Future capacity | Spare ways, busbar capacity, cable entry space, and metering | Gives the site room to expand without another early upgrade |
| Site conditions | Incoming supply, cable routes, ventilation, access, and shutdown windows | Keeps the switchboard installation safe and practical |
Start With A Detailed Load Assessment
The first step is understanding what the plant needs to run. That means reviewing connected load across the full facility, then looking at how those loads behave during start-up, production, cleaning, changeovers, peak shifts, and maintenance periods.
Connected Equipment Across The Plant
A food manufacturing plant might run mixers, conveyors, refrigeration, compressed air, washdown pumps, metal detection, packaging equipment, pallet wrapping, lighting, amenities, and office services from the same electrical network. A packaging or warehousing site may have more conveyors, drives, scanners, dock equipment, and control panels.
Motor Starting Current & Running Current
Motor loads need close attention because starting current can be much higher than running current. Large pumps, fans, compressors, conveyors, and process machinery can place short, heavy demand on the electrical system during start-up.
Load Data To Capture Before Design
- Nameplate ratings for major equipment and downstream boards
- Measured operating current where the site has existing data
- Motor starting methods, drive arrangements, and duty cycles
- Known fault history, nuisance trips, and capacity limits
- Planned machinery, conveyors, refrigeration, control panels, or automation upgrades
Understand Maximum Demand & Diversity
Switchboard design needs to consider maximum demand, which is the likely highest demand placed on the electrical installation during normal use. It also needs to account for diversity, because some connected loads will run at different times or under different operating conditions.
In a real plant, three production lines may be installed with two running during a normal shift. Refrigeration may cycle with product temperature and ambient conditions. Cleaning systems may run after production has stopped. The aim is to design around the facility’s real electrical behaviour, so the board supports actual operation without creating capacity problems or unnecessary cost.
Build In Future Capacity Before The Board Is Ordered
Future capacity is one of the most important parts of main switchboard sizing. Manufacturing plants change quickly. A line that runs one product today may need extra upgrades within a few years.
What Future Capacity Can Include
Future planning usually needs to cover spare ways, space for extra switchgear, busbar capacity, cable entry space, metering, monitoring, ventilation, and safe access for maintenance. It may also include allowance for future distribution boards, machine feeds, or extra plant rooms.
Why Realistic Allowance Matters
This matters during a main switchboard upgrade tied to new machinery. If the switchboard installation is already being planned, it is the right time to ask what else the site may need. Planned spare capacity can make the next project easier, especially when the plant is adding equipment in stages.
Check The Incoming Supply, Cabling, & Site Conditions
A main switchboard can only perform properly if the upstream supply and surrounding infrastructure suit the site demand. During sizing, the incoming supply, service arrangement, transformer capacity, mains cabling, fault level, earthing, and available space all need to be reviewed.
This is where switchboard sizing connects with the broader site. A plant may need a larger main switchboard, new mains cabling, upgraded distribution boards, cable tray changes, new control cabinets, or revised cable routes to support the final design. Physical installation conditions also matter and should be considered.
Choose Protection Devices With Fault Isolation In Mind
Protection device selection is a major part of switchboard design. Circuit breakers, fuses, RCDs, surge protection, isolators, and motor protection devices all need to be selected to suit the load, cabling, fault level, equipment type, and installation environment.
The aim is to protect people, equipment, cabling, and the wider electrical installation. In a manufacturing plant, protection also needs to support practical fault isolation. If one section of a packaging line trips, the design should help limit the disruption and make fault finding easier for the maintenance team.
Protection Planning Should Consider
- The expected load on each outgoing circuit
- Fault levels and the breaking capacity of protective devices
- Motor protection, overload protection, and short-circuit protection
- Selectivity between upstream and downstream devices
- Safe isolation, clear labelling, and test documentation
Design Around AS/NZS 3000 & Site Compliance
Manufacturing switchboard work must be planned around the relevant electrical standards, regulations, and supply authority requirements. AS/NZS 3000, known as the Wiring Rules, provides core requirements for electrical installation design, construction, and verification in Australia and New Zealand.
Compliance affects protection, isolation, earthing, labelling, access, testing, verification, and documentation. Depending on the site, the project may also need to consider supply authority rules, WHS requirements, insurance expectations, internal site procedures, and relevant switchboard assembly standards such as AS/NZS 61439. Early design input makes the project easier to price, schedule, and verify at commissioning.
Plan The Switchboard Installation Around Production
Even the best switchboard design can create pressure if the installation is poorly staged. Manufacturing plants often have narrow shutdown windows, shift patterns, hygiene requirements, critical refrigeration loads, customer deadlines, and maintenance teams already managing active production issues.
What Can Be Prepared Before Shutdown?
A practical switchboard installation plan should confirm what can be pre-built, what can be staged, when shutdowns are required, and how critical services will be managed. Cable changes, temporary supplies, control interfaces, testing, and commissioning all need clear sequencing.
Who Needs To Be Involved?
Maintenance, production, safety, hygiene, engineering, and external suppliers all need clear outage timing, access zones, isolation responsibilities, test windows, restart procedures, and contingency plans. That coordination keeps a main switchboard upgrade moving without unnecessary site disruption.
When To Consult A Specialist
A specialist should be involved early when the plant is adding major equipment, upgrading production lines, experiencing recurring trips, reaching capacity, or reviewing an older board for reliability and compliance. Early advice can clarify whether the existing board can be retained, modified, or replaced as part of a broader electrical upgrade.
Specialist input is also important when the board feeds refrigeration, automated warehousing, process equipment, clean manufacturing zones, or high-demand motor loads. These areas can have higher uptime requirements and tighter commissioning windows, so the sizing and installation plan needs to be right before work starts.
A Specialist Review Can Help Confirm
- Whether the existing board has enough spare capacity for planned works
- Whether incoming supply or mains cabling needs review
- Which protection devices and isolation points suit the plant
- How to stage the upgrade around production or shutdown windows
Plan Your Main Switchboard Upgrade With Confidence
Sizing a main switchboard for a manufacturing plant starts with clear site information. Current load, future capacity, protection, compliance, installation conditions, and shutdown timing all need to be understood before the board is specified. If your site is planning a main switchboard upgrade, adding new machinery, expanding production, or dealing with repeated faults, now is the right time to review the electrical infrastructure properly.
Jarlam Electrics helps industrial sites plan and deliver main switchboard and distribution board installation and upgrades, mains cabling, control cabinet manufacturing, automation support, and wider site electrical works. The team can also coordinate broader plant changes where electrical infrastructure needs to align with equipment installation, production changes, or future expansion. To discuss your site, contact Jarlam online or call (03) 9059 2650.
Main Switchboard Sizing FAQ
What Is Involved In Switchboard Sizing?
Switchboard sizing involves reviewing connected loads, maximum demand, fault levels, protection requirements, spare capacity, cable routes, installation conditions, and future site plans. In a manufacturing plant, it should also consider motors, conveyors, refrigeration, compressed air, process equipment, automation, and shutdown timing.
How Do You Know If A Main Switchboard Is Too Small?
Common signs include limited spare capacity, frequent trips, overheating, overloaded circuits, difficult maintenance access, poor labelling, and delays when new equipment is added. A proper load review can confirm whether the board is still suitable.
Should A Main Switchboard Be Sized For Future Expansion?
Yes. Manufacturing sites should allow for realistic future growth where possible. Spare ways, cable entry space, busbar capacity, metering, and room for future switchgear can make later upgrades easier to manage.
Does AS/NZS 3000 Apply To Main Switchboard Work?
Yes. AS/NZS 3000, the Wiring Rules, is a key standard for electrical installation design, construction, and verification. Main switchboard work must also be planned around other applicable standards, regulations, supply authority requirements, and site procedures.