Frenchified
Member
Is the following installation legal per 240.4B
225A Breaker in a MDP feeding a 200A MLO panel (yes I know that isn't allowed per code, assume the panel is suppose to be 225A rated) using 3/0 copper THHN conductors (this is what I'm not sure of).
According to 240.4B(2) you are allowed to round up if the ampacity of the conductors does not correspond with the standard ampere rating of a fuse or a circuit breaker. In this situation 3/0 copper is rated for 200A which in my mind is a standard size so you can not round up. If it was fed with say 250 aluminum which is rated for 205A then you could round up to the next size.
Assuming the feeder does not feed a multi wire cord and plug receptacle circuit and we are under 800A does it meet requirement (2)?
An engineer for this installation is stating that you are allowed to round up to 225A because it is the next standard breaker size based on the ampacity of the copper conductors.
225A Breaker in a MDP feeding a 200A MLO panel (yes I know that isn't allowed per code, assume the panel is suppose to be 225A rated) using 3/0 copper THHN conductors (this is what I'm not sure of).
According to 240.4B(2) you are allowed to round up if the ampacity of the conductors does not correspond with the standard ampere rating of a fuse or a circuit breaker. In this situation 3/0 copper is rated for 200A which in my mind is a standard size so you can not round up. If it was fed with say 250 aluminum which is rated for 205A then you could round up to the next size.
Assuming the feeder does not feed a multi wire cord and plug receptacle circuit and we are under 800A does it meet requirement (2)?
An engineer for this installation is stating that you are allowed to round up to 225A because it is the next standard breaker size based on the ampacity of the copper conductors.
