How to test and maintain MCB switches for optimal performance?

Miniature Circuit Breakers are designed for durability and long-term use. An MCB might stay idle for years and still function as intended. But if a malfunction occurs, major errors can happen. Circuit breaker testing and maintenance can help in reducing that risk and ensure the smooth running of your electrical installation and connected equipment.

Why are MCBs important?

MCBs are used for connecting and disconnecting power to your home or place of business from the grid or an alternate source. Circuit breakers play a key role in protecting expensive appliances and equipment from damage caused by power fluctuations, as they can automatically disconnect power when a fault occurs. Thus, a circuit breaker can reduce the probability of equipment damage or downtime and save you from expensive repairs later on.

So, it becomes doubly important to test and maintain your MCB switches regularly and carefully.

Steps for checking and testing an MCB

Before we begin with the list of things to check when testing an MCB, please note that all such checks should be performed by a certified professional or an electrician with field knowledge. Handling electrical components without the proper tools and knowhow can be hazardous.

Now, let's have a look at the steps for testing an already installed circuit breaker for quality and performance.

Step 1: Visual Examination of the MCB Box and MCBs

1. The MCB box and plastic parts should be clean and without visible damage or defects. Since these components are often installed in exposed environments, there is always a possibility of damage, such as cracks or air bubbles or deformation on the surface.
2. The metal parts of the MCB box and MCB should not be corroded or showing signs of damage. Exposure to moisture or damp conditions can prematurely damage the external and internal metal parts in an MCB. And since metals are good conductors of heat and electricity, a damaged part can increase the risk of handling the device.
3. The content and color of the labels should be clearly visible. This is especially required if you plan to swap out components and install replacements. Undamaged MCB labels can help you identify the product specifications and easily find a like-for-like replacement.
4. Lastly, another thing to note is that the MCB should be aligned and fixed properly on the board without any protrusions or wires sticking out from the side.

Step 2: Testing the mechanical operation of an MCB switch

All miniature circuit breakers are factory tested for safe and smooth operation before shipping. For example, Lauritz Knudsen (Formerly L&T Switchgear) circuit breakers promise years of reliable use by going through a rigorous testing phase before they are packaged and made available to the end users.

Ideally, an MCB switch should be able to perform five on and off cycling operations without slipping or jamming. If your MCB switch passes this test, then it can be assumed that the MCB is mechanically sound.

Step 3: Checking the performance of your MCB switches

Testing MCB performance requires a slightly more technical approach than the visual and mechanical inspections recommended above.

1. Delay Testing: This is performed to verify the tripping time of an installed miniature circuit breaker under overload conditions. It helps in testing for thermal overload protection and magnetic short-circuit protection provided by the MCB.
2. Instantaneous Testing: There are different types of MCBs, separated by curve type (e.g., B, C, D) that defines the range of currents at which an MCB will trip (see table below). Instantaneous MCB testing allows the technician to determine if the unit is able to trip (open the circuit) within the pre-defined timeframe to ensure equipment and personnel safety.

1. Power Frequency withstand Voltage Test: This test is conducted to check the insulating strength of an installed MCB by applying high voltage at power line frequency (usually 50 Hz to 60 Hz) for specific durations. It tests the ability of the MCB to withstand voltage spikes that may occur in real-world electrical systems.

Also Read: 

• MCB (Miniature Circuit Breakers) Guide - Types, Sizes, And Uses
• What’s The Difference Between MCB And MCCB?

Things to remember when testing MCBs

Certain precautions to take before you begin testing an MCB box:

1. Have proper test equipment to carry out the maintenance. Normally, you will need a power source, a current transformer, a voltage transformer, a multimeter, jumper wires, and a test set.
2. Always isolate the circuit breaker from power supply. Also, lock out and tag the circuit breaker to prevent anyone else from accidentally activating it.
3. Know the technical specifications of the MCB you are testing. It's important to know the rated response time, trip current, and trip voltage to test an MCB. Testing a unit without knowing the specifications may lead to accidental damage or electrical hazards.
4. Remember to test the circuit breaker contacts. Contacts are the part that make or break the electrical connection to an MCB. Check their condition and alignment with a contact resistance tester.
5. Record and tag your test results after the checks. It will be helpful if and when you decide to test the electrical setup again.
6. Clean electrical products using a dry and non-abrasive cloth.
7. Disconnect and replace faulty MCBs, wiring, and other accessories immediately.

Which type of MCB is used in homes?

Now, you may be wondering, which type of MCB do you have at your home? Typically, Type C MCBs are used for domestic applications. These MCBs are capable of supporting medium current load and trip when the flow of current exceeds 5-10 times over normal.

Looking for High Quality MCB products online?

In case you recently had your electrical setup inspected and found some anomalies, and are now looking for high-quality replacement MCBs online, the Lauritz Knudsen (Formerly L&T Switchgear) is here to help you buy the best electrical components online. We are the official channel for selling Lauritz Knudsen (Formerly L&T Switchgear) products online in India. Sign-up today to browse and order MCBs and other electrical products at the best available prices.