Panelboards, switchboards and motor control centres are the three kinds of equipment that divide and protect power inside a building. A switchboard is the large floor-standing line-up near the service that splits power into feeders. A panelboard is the wall-mounted box that divides a feeder into branch circuits. A motor control centre groups the starters and drives for motors in one place. Each has its own ratings, clearances and maintenance needs.
The names get used loosely on site, and many people call all three "the panel". The differences matter when you add load, plan maintenance or read a single-line diagram, because each type is built, rated and serviced differently.
Three types at a glance
The quickest way to tell them apart is by size and what is inside. A panelboard holds rows of small branch breakers behind a door. A switchboard is a set of tall steel sections with a main device and larger feeder breakers or fused switches. A motor control centre is built from sections stacked with removable units, often called buckets, each holding the starter or drive for one motor.
| Equipment | Where it sits | What it feeds |
|---|---|---|
| Switchboard or switchgear | Main electrical room, at or near the service | Feeders to panels, transformers, MCCs and large equipment |
| Panelboard | Electrical rooms and closets on each floor or area | Branch circuits to receptacles, lighting and small equipment |
| Motor control centre | Mechanical rooms and industrial plants | Motors for fans, pumps, compressors and process equipment |
Panelboards
A panelboard takes a feeder and divides it into branch circuits, each protected by a breaker sized to the wire it feeds. Panels are rated for voltage, bus ampacity, number of circuit positions and short-circuit current. Some have a main breaker; others, called main lug panels, rely on the breaker upstream. Many buildings have separate panels for lighting, receptacles, mechanical equipment and emergency loads, which makes maintenance and lockout clearer.
The panel schedule on the door lists what each breaker feeds. It is one of the most useful documents in the building and one of the first to go out of date. Breakers must be the type listed for that panel; mixing brands or types because they physically fit is a common and unsafe shortcut.
Switchboards and switchgear
A switchboard is a free-standing assembly of one or more steel sections, holding the service main device, metering and the feeder breakers or fused switches. People often use "switchgear" for the same thing, but in the trade switchgear usually means heavier equipment with each breaker in its own compartment, often drawout breakers that can be racked out for maintenance, and it includes medium-voltage equipment on large sites.
Because switchboards sit near the service, they see the highest available fault current in the building and often the highest arc flash hazard. Their ratings, protective device settings and maintenance records matter more than anywhere else in the system.
Motor control centres
A motor control centre, or MCC, gathers the controls for many motors in one place. Each bucket usually holds a disconnect or breaker, a starter or contactor, overload protection and control wiring, and may hold a variable frequency drive. Buckets plug onto vertical bus bars, which makes replacement quicker, but plugging buckets in and out while energized is hazardous work that must be done only by qualified workers following arc flash procedures.
MCCs are common in hospitals, universities, large commercial buildings and industrial plants. In smaller buildings, motors are often controlled by individual starters or drives mounted near the equipment instead. Either way, each motor needs a means of disconnect that can be locked off, so maintenance staff can isolate it safely before working on the fan or pump it drives.
Ratings that matter
All three types of equipment carry several ratings, usually on a nameplate inside the door or on the front of a section. They answer different questions, and confusing them is a common source of mistakes.
- Voltage and phase. The system the equipment is built for, such as 120/208 V or 347/600 V three-phase.
- Bus or continuous rating. How much current the bus bars can carry continuously. This is not the same as the sum of the breakers, which is often far larger.
- Short-circuit or interrupting rating. The fault current the equipment and its devices can safely withstand or interrupt, in kiloamperes. It must be at least the fault current available at that point.
- Series rating. Some panels rely on an upstream device to help interrupt high faults. The combination is tested and listed; replacing either device with a different type can void it.
What to check and record
- Clear working space in front of all equipment, with no storage, as required by the electrical code.
- Equipment names on the equipment that match the single-line diagram.
- Panel schedules that match the breakers, updated after every change.
- Spare breaker positions and spare capacity, recorded so the next project does not have to guess.
- Covers and dead fronts in place, with no missing knockouts or open spaces.
- Signs of heat, corrosion, moisture or dust inside electrical rooms.
- Arc flash labels where an arc flash study has been done.
- Maintenance history: thermography, cleaning, connection checks and breaker testing.
Visual checks from outside the equipment are something facility staff can do. Opening equipment, checking connections and testing breakers are work for qualified electrical workers following your electrical safety program.
A typical situation: the panel is full
A tenant wants six new circuits for a lab area. The panel on the floor has no spare positions. The common bad answer is to add tandem breakers that are not listed for that panel, or to tap another circuit. A better approach starts with the panel schedule and the feeder. If the feeder and transformer have spare capacity, a new sub-panel can be added, fed from the existing panel or from the distribution upstream. If they do not, the question moves upstream to the transformer and the switchboard. Each step is checked against the load calculation, and the new panel is added to the single-line diagram and given a name in the same pattern as the others.
How ehZee can help
We design and specify panelboards, switchboards and MCCs as part of our power distribution design service and assess existing equipment when loads change. For maintenance, read switchgear and panel maintenance; for motor control, read motors, starters and VFDs.
Common questions
How long does a panelboard last?
Often several decades, but replacement parts for older or discontinued panels can become hard to find. When a panel can no longer be maintained with listed breakers, replacement is usually the safer choice.
Can we store things in the electrical room?
Not in the working space in front of equipment, and ideally not at all. Storage blocks access in an emergency, can block transformer ventilation and adds fuel to any fire.
What is the difference between a breaker and a fused switch?
Both protect a circuit from overcurrent. A breaker can be reset after it trips; a fuse is replaced. Fuses can limit fault current very effectively, while breakers are more convenient and can have adjustable settings. Many switchboards use both.