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The Importance of Selecting the Correct, ACB, MCCB, MCB, and RCBOs in Electrical System Design and Adhering to Electrical Standards & Design

I have seen so many systems over the decades where changes have been made in the selection of a protective device or the incorrect cable size has had a detrimental effect on the system and can lead to a cascade failure and a lot of damage to those systems.

When designing electrical systems, it is crucial to select the appropriate Air Circuit Breaker (ACB), and Moulded Case Circuit Breaker (MCCB), Miniature Circuit Breaker (MCB), to ensure safety and efficiency. MCBs are available in various types, such as B, C, and D, and different breaking capacities, such as 6kA, 10kA, and 15kA. This article will discuss the differences between these MCBs and the importance of using the correct one.

You should always check your source readings and adjust for the worst-case scenario i.e., wet-dry environmental conditions, just because it works in the wet season, does not mean it will when the ground is baked dry and the resistivity of the soil increases, or the operational temperatures soar, your systems need to work at all times, this is something I see missed and not thought about on a regular basis.

Additionally, I will address the significance of adhering to electrical standards, such as BS 7671 and the Electrical Installation Design Guide by the IET, and the serious problems with electricians relying on the Max Zs of 1667 for an RCBO, as a magical get out of jail free card.

We will also discuss the dangers of not setting the parameters properly on Micrologic MCCBs and ACBs and the disastrous effects this can have, including arc faults and damage to electrical systems.

Differences Between B, C, and D Type MCBs

B, C and D-type MCBs differ in their tripping characteristics, which determine how quickly they will disconnect the circuit in response to an overload or short circuit.

  1. B Type MCBs: These MCBs are designed for general use in residential and light commercial applications. They trip between 3 to 5 times the rated current (In) and are sensitive to low-level short circuits.
  2. C Type MCBs: Suitable for commercial and industrial applications, C-type MCBs trip between 5 to 10 times the rated current (In). They are less sensitive to short circuits than B-type MCBs, making them ideal for circuits with inductive loads, such as motors and transformers.
  3. D Type MCBs: These MCBs are designed for circuits with high inrush currents, such as large motors, transformers, and X-ray machines. They trip between 10 to 20 times the rated current (In) and are the least sensitive to short circuits among the three types.

Differences Between 6kA, 10kA, and 15kA Breaking Capacities

Breaking capacity refers to the maximum current that an MCB can safely interrupt without causing damage. The higher the breaking capacity, the more robust the MCB.

  1. 6kA: Suitable for residential and light commercial applications with lower short-circuit currents.
  2. 10kA: Commonly used in commercial and industrial settings with higher short-circuit currents.
  3. 15kA: Designed for heavy-duty industrial applications with very high short-circuit currents, I have had many electricians that don’t even know these existed.
  4. This may not be the case always, you need to check your source reading, if you’re close to a transformer the fault levels can be very high and the Ka level of your device may no longer work, one size does not work for all!

ACB and MCCB Micrologic Devices.

Air Circuit Breakers (ACBs) and Moulded Case Circuit Breakers (MCCBs) are used in higher power applications and provide protection against overloads, short circuits, and earth faults.

Micrologic devices are electronic trip units used in ACBs and MCCBs to provide advanced protection and monitoring features. These devices can be customized to meet specific application requirements and ensure the safety and efficiency of electrical systems.

Importance of Using the Correct ACB, MCCB.

Safety: Using the correct devices ensures Selecting the appropriate MCB, ACB, and MCCB type and breaking capacity is crucial for the following reasons:

  1. That the circuit is protected against overloads, short circuits, and earth faults, preventing fires and equipment damage.
  2. Efficiency: Properly sized devices minimize nuisance tripping and ensure that the electrical system operates efficiently.
  3. Compliance: Adhering to the guidelines set forth in electrical standards, such as BS 7671 and the Electrical Installation Design Guide by the IET, ensures that the electrical installation meets the required safety standards.

Why you should never Rely on the Max Zs of 1667 for an RCBO.

Relying on the Max Zs of 1667 for an RCBO can lead to an unsafe electrical installation. It is essential to design the electrical system to work within the Max Zs of B, C, and D curve devices, as specified in electrical standards. This ensures that all of the equipment that makes up your Design which includes MCBs, ACBs, MCCBs, and RCBOs will trip within the required time, providing adequate protection against overloads, short circuits, and earth faults.

The Importance of Adhering to Electrical Standards

Adhering to electrical standards, such as BS 7671 and the Electrical Installation Design Guide by the IET, provides guidelines for the design, installation, and maintenance of electrical systems. Compliance with these standards ensures that the electrical installation is safe, efficient, and compliant with the required safety standards. Failure to comply with these standards can result in serious consequences, such as electrical fires, equipment damage, and even loss of life.

The Dangers of Not Setting Parameters Properly on Micrologic MCCBs and ACBs.

Not setting the parameters properly on Micrologic MCCBs and ACBs can have disastrous effects, including arc faults and damage to electrical systems. These devices are designed to protect electrical systems from overloads, short circuits, and earth faults, but improper settings can lead to catastrophic failures.

It is crucial to follow the manufacturer’s instructions and adhere to electrical standards when setting up these devices to ensure the safety and efficiency of the electrical system, and ensuring you follow the design calculations is vital for a safe system.

I would say that the misuse and total lack of understanding in the industry especially by the cowboy element of the reason for sound design, which has now infested everything from Domestic, Commercial, and now even Industrial systems in my opinion has led to thousands of badly designed systems that are potentially unsafe just waiting to have a problem it’s now only a case of when, not if!

Selecting the appropriate, ACB, MCCB, MCB or RCBO and adhering to electrical standards, such as BS 7671 and the Electrical Installation Design Guide by the IET, is crucial for designing safe and efficient electrical systems.

It is essential to select the appropriate devices based on the application and adhere to the guidelines set forth in electrical standards, you don’t get to pick and chose on a whim, this is a recipe for disaster.

Additionally, relying on the Max Zs of 1667 for an RCBO that I see so many electricians do, is not recommended as a get-out-of-jail-free card, as it can and does lead to an unsafe electrical installation.

Electricians must and need to be taught to understand the importance of proper design and adhere to the guidelines to ensure the safety and efficiency of electrical systems.

Finally, and I cannot stress this enough, it is crucial to set the parameters properly on Micrologic MCCBs and ACBs to prevent the potential for ARC faults and damage to electrical systems, setting them at Max settings is just a recipe for disaster.

More needs to be done in our industry to educate in a way that feels safe to electricians to accept that none of us knows everything and that it’s okay to ask.

Our education systems are not set up to do this, without charging huge fees to impart what I consider vital safety knowledge.

Many electricians I know are Dyslexic or have trouble grasping maths, yet there are no safe ways out there where they can learn without feeling like they are being put on the spot or the fear of ridicule, which means they continue making the same mistakes through lack of knowledge.

Our governing bodies and Leaders need to address this, in a way to reduce the anguish and mental stress caused by being put in the spotlight.

I have even mentioned that it would be a good thing to have a free refresher course to be available on the complicated area of mathematics that needs to be used properly almost every day in our industry, but at all levels, from apprentice up, if we don’t use it for years or decades we forget.

This coupled with practical examples of how to use the math such as resistors in parallel, an object lesson in Insulation resistance reading can and will make a difference in the advancement of this industry.

Author

Raphael Magnus IEng MIET, AQE, LCGI, NCRQ

If you would like to contact me to discuss your Design/ Compliance requirements, please call 01487-813-600 or contact us via our web page www.safe-electric.com.