I am working on a project that will result in the removal of a panelboard which has all molded case breakers for branch circuit protection, typically 20A, 1-pole breakers. In place of the "breaker" panel a fused panelboard will be used. All fuses are 150V, fast-acting, current limiting type. Question - Can current limiting fuses be used in lieu of the breakers? Does this satisfy the intent of Article 240? Comparing a 20A MCCB time-current curve with a 20A current limiting fuse curve indicates that the current limit fuse would likely never open under an overload condition say 150% or so but will respond faster than the MCCB for short circuit conditions.
The reason for the replacement from MCCB to fuse is that the panels are fed from UPS systems which is an energy limited electrical source. Fast clearing of a branch circuit fault results in less disturbance of the UPS electrical system. Also - this system is in a chemical plant. All branch circuit loads are instrumentation and the loss of power to the instruments could put the plant in an "upset" condition.
The reason for the replacement from MCCB to fuse is that the panels are fed from UPS systems which is an energy limited electrical source. Fast clearing of a branch circuit fault results in less disturbance of the UPS electrical system. Also - this system is in a chemical plant. All branch circuit loads are instrumentation and the loss of power to the instruments could put the plant in an "upset" condition.
