Many industrial control panels feature a main breaker on the 24-volt side of the power supply, which then supplies power to smaller breakers. For example, a 40 amp power supply may have a 40 amp breaker on the +24 side that feeds 20 amp breakers connected to 24-volt branch circuits. Is it required by code to have the 40 amp breaker in place? It may be possible to simply connect a bus to the top of a row of breakers fed from +24 and directly supply branch circuit breakers. This setup raises questions about the necessity of the 40 amp breaker as mandated by electrical codes.
Is it necessary to have a breaker solely dedicated to powering other breakers? This may seem redundant, especially for low voltage systems.
I had the same thought - it seems redundant. If the intention was to have a single switch to power everything down, a simple switch or disconnect would suffice. After reviewing my coding notes, I couldn't find any indication one way or the other. I personally don't think it is necessary. The code specifies breaker/protection based on factors like power draw and distance, with no mention of one protection device preceding another. In my experience with industrial panels, I have never encountered this setup, so I recommend verifying that the 40 amp breaker doesn't feed the 20 amp breakers in another sub panel or device. It is more common for me to come across panels with no breakers or with bypassed ones due to frequent tripping. Those in the industry for a while can confirm this. So, consider yourself fortunate in this situation.
I appreciate both of your contributions immensely!
A great method to avoid overloading a power supply without using a 40A breaker is by distributing the load among multiple 20A individual breakers. By connecting 10 20A breakers to a 40A power supply, you can distribute a total potential of 200A safely. Just like in a house panel, where the main breaker safeguards the power supply while the branch breakers protect the individual feeder conductors and devices. This setup ensures that the transformer and feeders are protected while effectively distributing power to outlets and devices throughout the home.
Robertmee suggested a risky method of overloading a power supply by using multiple 20A breakers instead of a 40A breaker. By connecting 10 20A breakers to a 40A power supply, you could potentially draw up to 200A from it. However, it is important to remember that the branch breakers are there to protect the individual feeder conductors, while the main breaker is there to safeguard the power supply as a whole. While this may work in theory, it's worth noting that most DC power supplies are self-limiting and may not be able to handle such high loads.
While I see where you're coming from, it's actually quite important to adhere to the mandated electrical codes. This is primarily because the 40 amp breaker serves as a safety measure that prevents overloading and potential fires. Even though it may seem redundant, it ensures that the smaller, 20 amp breakers do not draw more than the 40 amps that the power supply can handle. The absence of the 40 amp breaker could lead to an overdraw of current and potentially catastrophic results. So, it indeed is more about safety than about the need. I would advise against bypassing any such precautionary measures stipulated by the codes.
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Answer: The need for a 40 amp main breaker on the 24-volt side of industrial control panels is a common question. While it may seem necessary for safety and code compliance, there may be situations where alternatives can be considered.
Answer: The discussion around bypassing the 40 amp main breaker and directly connecting a bus to branch circuit breakers raises questions about the compliance with electrical codes and the overall safety of the setup.
Answer: Understanding the implications of omitting the 40 amp main breaker, including potential safety risks, code violations, and impact on the functionality and reliability of the control panel, is crucial for proper installation and operation.
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