What Is an LT Panel? Full Form, Voltage Range, Components & Uses

An LT panel is a Low Tension switchboard, receiving power from a transformer and dividing the power to protected circuits. These LT panels are used at all factories, hospitals, malls, and housing societies, though few people might know about this.

What Is an LT Panel and the Full Form?

 

An LT panel is a metal enclosure receiving low voltage and distributing the power to different circuits with bus bars, breakers, meters, and protections. LT stands for Low Tension, which still prevails in the older literature and nomenclature in India and the Middle East.

 

The switchboard has protection, metering, and control equipment, including relays, current transformers, ammeters, and watt-hour meters. It is a control center from where the load is fed to the connected motors, lights, and sockets.

You can also find the term electrical lt panel while going through tenders and even drawings. It means the same electrical switchgear, but described from a different perspective. In other words, while the above-mentioned are the details of what an LT panel contains, the electrical lt panel defines the equipment as a whole.

What Is the LT Panel Voltage Rating?

An LT panel is generally a low-voltage switchgear rated for voltages up to 1,000 V AC and 1,500 V DC per IEC 61439-1.

 

However, in India, the available voltage is 415 V three-phase and 240 V single-phase.

 

A voltage higher than 1,000 V falls under HT (high tension), which requires a different kind of switchboard.

What Does the SLD Look Like: Transformer to LT Panel to MCC/DB?

The power from the transformer is fed into the low-tension panel, which further distributes the power to the motor control centers and distribution boards. All these are represented by a single line diagram.

 

       [ Transformer ]
         11 kV / 415 V
               |
               |
         [ LT Panel ]
               |
         +-----+-----+
         |           |
         |           |
      [ MCC ]      [ DB ]
      (Motors)   (Lights, Sockets)

 

The above drawing shows that the transformer steps down the voltage, while the board distributes the 415 V supply to various outgoing feeders. The MCCs (motor control centers) are the source of power for all the motors, pumps, and fans in the factory. The distribution boards (DBs) cater to the power required for the lights and sockets in the building. The isolation of a faulty DB from the LT panel ensures that the healthy boards continue to operate without any disturbance.

 

What Is an LT Room, and What Are the Design Guidelines?

An LT room is a room that accommodates the LT switchboard. Like the switchboard, the room should also be planned meticulously to avoid losses due to overheating.

 

 Some guidelines for room planning are:

• Adequate clearance in front of the board for working and maintenance
• Provision for air-cooling or air-conditioning as the breakers emit heat
• Fire-rated doors and dry, dust-proof floorings and cable trenches
• Provision for proper earthing and display of warning signs

What Are the Components of an LT Panel?

An LT panel has various components; it primarily contains incomers, busbars, feeders, protections, and metering.

 

What Does the Incomer of an LT Panel Do?

 

The incomer provides a connection between the transformer and the LT panel. It is generally an ACB (air circuit breaker) and serves as a master switch for the whole board.

What Are Busbars in an LT Panel, and What Do They Do?

 

Busbars are conductive copper or aluminum bars that carry current from the incomer to the various feeders. They are sized according to the current rating of the LT panel.

 

What Do Outgoing Feeders Contain?

 

The feeders contain MCCBs (motor control circuit breakers) or MCBs (miniature circuit breakers) or fuse switches, depending on the current rating.

 

What Protection and Metering Equipment Is Mounted on an LT Panel?

 

Relays, current transformers, ammeters, voltmeters, and energy meters are mounted on the protection and metering section.

What Is the Difference Between Main, Distribution, and Control Panels?

While the three may sound the same, they refer to three different types of switchboards.

 

What Is a Main LT Panel?

 

A main lt panel is the first power point after the transformer. It supplies the main incomer to the various sub-panels in the system. It is also often referred to as the PCC (power control center).

 

What Is an LT Distribution Panel?

 

An lt distribution panel is used to feed the load from the main panel to the sub-panels.

 

What Is an LT Control Panel?

 

An lt control panel houses the equipment to control other equipment like pumps, compressors, and fans. It also houses PLCs (programmable logic controllers), relays, and push-button starters.

What Is an LT ACB Panel?

An lt acb panel is a low tension panel that employs an ACB (air circuit breaker) as its incomer or bus coupler. An ACB has a rating of up to 6,300 A, depending upon the manufacturer.

 

IEC 60947-2 specifies the requirements for ACBs, which have the ability to break extremely high fault currents. They are generally used for larger loads, such as those in factories and commercial buildings, where a simple MCCB fails to suffice.

 

ACBs also have the provision of adjustable trip settings, which helps in achieving selectivity. This is vital since it prevents unnecessary tripping of circuit breakers, thus saving downtime as well as equipment damage.

Where Are LT Panels Used?

LT panels are used in almost all electrical installations requiring a transformer for power distribution. 

 

The various applications of low-tension switchboards are in:

• Factories and warehouses
• Hospitals, data centres and airports
• Malls, offices and residential towers
• Water treatment plants and pump stations
• Solar plants, where inverter output joins the grid

Every site chooses its configuration. A hospital requires backup changeover while a factory requires motor feeders.

How Is Low Tension Different from High Tension?

The main difference between LT and HT is the voltage rating. HT panels are generally rated higher than 1,000 V, such as 11 kV, 33 kV, etc., while the low-tension board works under 1,000 V.

 

HT switchboards are used to step down the voltage, while the low-tension panel is used to step up the voltage. In other words, HT switchboards are at the receiving end of the power, and the LT boards are at the feeding end.

 

If you have a 11 kV breaker panel, it is not the same as an LT panel. Confusion between HT and LT is one of the most common mistakes while purchasing switchboards. Vendors often receive purchase orders for the wrong kind of panel, resulting in huge losses.

How Do You Maintain Your Switchboard?

It is essential to carry out regular maintenance to avoid failures.

 

Plan a complete shut down of the switchboard in an annual service, and carry out a thermal scan of the running board with a thermal imager.

• A typical maintenance schedule is given below:
• Tightening of loose busbar joints and terminal lugs
• Cleaning of bus bars and breakers
• Testing of relays and trip settings
• Testing of earthing and insulation

Tightening of lugs is a crucial activity, as it avoids local heating at these points. It often proves to be cheaper than the lost production due to a faulty connection.

What Standards Should an LT Panel Follow?

A good LT panel should be compliant with IEC 61439 or IS/IEC 61439, the international standard concerning low-voltage switchgear and control gear assemblies.

 

Some of the important aspects of the standard applicable to the LT panel are:

• Type tested designs with proven performance
• IP ratings as per IEC 60529 corresponding to the location and accessibility
• Form of separation (Form 1 to 4) based on the isolation requirements
• Fault levels corresponding to the transformer rating

It is crucial to ensure that the fault rating of the board is sufficient for the given system.

What Mistakes Should You Avoid?

The majority of the problems with switchboards stem from poor planning. The following are some of the most common planning errors:

• Going for undersized busbars to cut costs, resulting in losses due to heating.
• Selecting breakers without considering the fault level of the transformer may result in nuisance tripping.
• Not providing spares for the number of feeders required in the future will only cause rewiring and extra work.
• Not maintaining updated wiring diagrams will create many headaches while identifying faulty circuits.

How Do You Choose the Right LT Panel?

While selecting the right switchboard, ensure that the rating of the board, form, and enclosure are compatible with the connected load, fault level, and future expansions.

 

Some of the important questions to ask before selecting a panel are:

1. What is the rating of the transformer?
2. Which loads are connected to the board? Do you have continuous or intermittent loads?
3. Do you have expansion plans in the next five years?
4. Do you require an automatic changeover with a genset?

 

Provide 20 to 25 percent spare feeders if the growth plans are on the higher side. It is also essential to buy the panel from a reliable manufacturer who provides test certificates and after-sales service. A switchboard is a long-term asset that needs to be taken care of for a decade or more.

 

Planning an electrical installation for a factory, hospital, or commercial building? Contact Burak Electric to discuss your LT panel requirements and explore suitable panel solutions for your project.

Summary

An LT panel, short for low-tension panel, receives 415 V power from a transformer and feeds protected circuits through MCCs and DBs. It works up to 1,000 V AC under IEC 61439-1.

Main, distribution, control, and ACB versions serve different jobs in the same chain. Choose by load, fault level, standards, and future growth. A well-planned LT room keeps it safe.

Contractors, consultants, and plant managers can request a quote and compare LT panel options for their project.