Mike Dolt Enterprises
Mike Dolt Enterprises
User: creyc, Location: New Jersey
Asked on: Thursday, April 28, 2011 at 8:25 pm EDT
Answered on: Tuesday, May 14, 2024 at 4:46 am EDT
Question: Is it commonplace to find in an electric room of a commercial building, an MCB type 400A distribution panel feeding 3-4 225A MLO-type panels out of breakers?The distribution panel is fed from a transformer within the same room, which is itself protected by an enclosed circuit breaker.Is this common practice? I assume the MCB distribution panel is because the panel is located on the secondary of a transformer?This might all be kosher, I'm just trying to learn a bit more about the things I'm asked to draw.
Yes, it is relatively common to find the following electrical distribution configuration in a commercial building
A 400 Amp main circuit breaker (MCB) distribution panel, fed from a transformer within the same room. Multiple (3-4) 225 Amp molded case circuit breakers (MCCBs) connected to the MCB distribution panel.
Reasons for this Configuration
Transformer Secondary Protection
The MCB distribution panel provides protection for the transformer secondary winding, which is typically rated at the same amperage as the transformer's output (e.g., 400 Amps). The MCB trips if the transformer secondary experiences an overload or fault, protecting the transformer from damage.
Sub-Distribution
The 225 Amp MCCBs connected to the MCB distribution panel serve as sub-distribution panels, providing power to various circuits and equipment in the building. The sub-panels have a lower amperage rating than the main distribution panel, allowing for more granular protection and isolation of individual circuits.
Fault Isolation
In the event of a fault on one of the sub-panels, the corresponding MCCB will trip, isolating the faulty circuit and preventing it from affecting other circuits.
Additional Notes: The enclosed circuit breaker protecting the transformer provides primary overcurrent protection. The use of MCBs on the transformer secondary is common practice because they offer high interrupting capacity and fault protection. The specific amperage ratings of the panels and circuit breakers may vary depending on the load requirements of the building.* It is essential to ensure that the distribution system is properly designed, installed, and maintained to meet safety and code requirements. Flag for review