Are you planning on renewing or adding circuit breakers to your current electrical installation? Is it possible to reduce the cost of purchasing these circuit breakers whilst still being adequately protected?
This NEW series introduces you to the technique of how circuit breakers are cascaded in a system.
In Part 1 we give an explanation of what cascading is, its advantages, and the conditions required to implement cascading. In Part 2, we touch on the topic of selectivity, by giving an overview on how it can be enhanced in your system by the implementation of cascading circuit breakers.
What is Cascading of Circuit Breakers?
The cascading of circuit breakers is a “back-up” protection system which is implemented to allow for the installation of circuit breakers that are not able to handle the full capacity of the prospective short-circuit current of a fault at the point of installation.
A requirement in cascading a system is to make sure that these circuit breakers are backed up a downstream/upstream fully rated circuit-breaker in a predetermined and tested coordination. It is vital to identify the fault level of a circuit breaker at a given point to allow for the installation of lower-rated circuit breakers downstream. This will ultimately allow for a reduction in costs.
What does Cascading of Circuit Breakers mean?
This is the term used when you have a panel with a high fault level (20kA) for example. The installation will consist of two circuit breakers in series. The main breaker located at the panel will be rated at fault level, whilst the breakers below can be of the lowest kA rating offered. You can save money without decreasing the safety level. The only problem with this system is when a fault occurs, then the upstream breaker, or both breakers, open to clear the fault.
What are the Advantages of Cascading Circuit Breakers?
When current limitation is implemented, it will benefit all downstream circuits that are controlled by the current-limiting circuit breaker concerned which, in most cases, is the main supply circuit breaker.
This principle is not restrictive, which means that current limiting circuit breakers can be installed at any point of the system where the downstream circuits could possibly be inadequately rated.
This results in:
- Simplified short-circuit calculations.
- Simplification which will result in a wider choice of downstream switchgear and appliances.
- The use of cascading circuit breakers will allow for the installation of lighter-duty switchgear and appliances which will ultimately reduce the cost.
- Light-duty equipment that is installed will need less space as opposed to heavy-duty equipment.
What are the Conditions Required for the Implementation of Cascading Circuit Breakers?
The implementation of the cascading technique should be allowed, provided that the amount of energy allowed through by the limiting circuit breaker is less than the withstand energy of all downstream circuit breakers.
How do you implement a cascading system?
When using a manufacturer cascading chart, you can only use a cascading system by using circuit breakers from the same manufacturer. When implementing the cascading of circuit breakers, it is important to follow the guidelines that are set in SANS 10142-1:2020. An example of a manufacturers’ cascading chart can be seen below.
In the second instalment of this series, we touch on the topic of selectivity by giving an overview on how it can be enhanced in your system by the implementation of cascading circuit breakers.
Resources:
1. SUBSCRIBE to our newsletters to receive this informative content straight to your inbox
2. DOWNLOAD a selectivity, cascading and co-ordination guide
3. CHAT to our experts for assistance with your circuit breakers
Sources:
https://www.electrical-installation.org/enwiki/Coordination_between_circuit-breakers
https://www.linkedin.com/pulse/everything-you-need-know-cascading-boris-fuchs/