Control panels

An electrical control panel is an enclosure that houses the switching, protection, control, monitoring and distribution equipment for part of an electrical system. Depending on what it is built to do, it may contain circuit breakers, contactors, relays, controllers, metering, busbars and protection devices. All of it is assembled, wired and tested as one unit so the system behaves predictably when something goes wrong.

An APFC panel (Automatic Power Factor Correction panel, also called a PFC panel) improves the power factor of an installation by switching capacitor steps in and out automatically as the load changes. A controller measures the power factor continuously and brings in only as much correction as the present load needs, rather than leaving a fixed bank connected regardless of demand.

Inductive loads such as motors, welding sets and transformers draw reactive current that does no useful work but still has to be carried by your cables, switchgear and transformer. Correcting the power factor reduces that circulating current, which frees up capacity in the existing installation and, on tariffs with a power factor penalty or incentive, changes what you pay each month.

An LT panel is a low-tension panel: it receives low-voltage supply from a transformer or generator and switches, protects, meters and distributes it to downstream circuits. It is the panel between the incoming supply and the rest of your plant, and it is where protection is coordinated so a fault in one feeder does not take out the whole installation.

They overlap, and in everyday use the terms are often swapped. Strictly, LT describes the voltage level (low tension) while distribution describes the job the panel does, which is dividing incoming power among outgoing circuits. A main LT panel usually both receives and distributes, and the smaller boards downstream of it are distribution boards. In tender language you will also see PCC, MCC, MDB and SMDB used for particular roles.

PCC is a Power Control Centre, the main incoming LT panel fed from the transformer or generator. MCC is a Motor Control Centre, an LT panel dedicated to starting and protecting motors. MDB is a Main Distribution Board fed from the PCC, and SMDB is a Sub Main Distribution Board fed from the MDB to serve a floor, zone or section. They describe roles within one distribution hierarchy rather than four unrelated products.

An HT panel is high-tension switchgear used to switch, isolate, protect and distribute power at medium voltage, typically where the utility supply arrives before it reaches a transformer. Because it operates above low voltage, interlocking, earthing arrangements and protection coordination are central to the design rather than optional extras.

VCB stands for Vacuum Circuit Breaker. A VCB panel is an HT panel that uses a vacuum circuit breaker as its switching and protection device. The contacts open inside a sealed vacuum interrupter, where the absence of any medium to ionise means the arc extinguishes very quickly at current zero, which is why vacuum breakers dominate medium-voltage switching and need little maintenance over a long service life.

The voltage level, and everything that follows from it. An HT panel handles medium-voltage supply upstream of the transformer, using vacuum circuit breakers, protection relays and strict interlocking. An LT panel works downstream at utilisation voltage, using moulded-case and air circuit breakers to feed the plant. On most industrial sites both are present, with a transformer between them.

An AMF panel (Automatic Mains Failure) watches the incoming mains supply, and when it fails, starts the generator, waits for healthy voltage and frequency, and transfers the load across. When mains returns and proves stable, it transfers back and shuts the generator down through its cooling cycle. No operator has to be present for any of it.

An ATS panel (Automatic Transfer Switch) transfers a load between two designated power sources according to its configured control scheme. The transfer switch itself is the mechanism that makes and breaks the connection, with mechanical interlocking so the two sources can never be paralleled accidentally.

They are related but not interchangeable. An ATS is the switching mechanism that moves load between two sources. AMF is the control function that detects mains failure and manages the generator: start, healthy-voltage check, transfer, return and stop. A complete generator changeover usually contains both, and on smaller systems they are built into one panel, which is why the terms get used loosely. What a given panel actually does depends on its controller and system architecture.

A synchronising panel brings two or more generators onto a common bus and keeps them running in step, matching voltage, frequency and phase angle before closing each breaker, then sharing load between the sets. It lets a site add capacity in stages, run only as many sets as the present load needs, and take one set off for maintenance without going dark.

Start from your single-line diagram and load list rather than a panel size. What voltage arrives, what has to be fed, what the maximum demand is, which loads are motors, how protection should be graded, what metering the utility or your energy team needs, and whether a generator is involved. Send us that and we will come back with the panel configuration, the switchgear selection and the price.

Effectively every panel is. Panels are designed against your single-line diagram and site constraints: enclosure dimensions and mounting, ingress protection, busbar sizing, cable entry direction, metering and communication requirements, and the switchgear brand your consultant has specified. Standard sizes exist as starting points, not as the finished article.