Can we put an emergency power and a normal power in a common bus in a shaft to distribute in a high rise building in a Hospital.
This is from 1995::
With the exception of hospitals, where NEC Sec. 517-30(c)(3) requires metal race-ways to enclose the emergency circuits, the Code does not mandate specific wiring methods for the emergency systems. A building can be wired using whatever wiring method that is used generally within that structure. Some occupancies, however, do have wiring method restrictions, but they are generally based on the type of occupancy. For example, wiring in places of assembly usually must comply with NEC Sec. 518-4, which limits the wiring methods to metal raceways, nonmetallic race-ways encased in at least 2 in. of concrete, mineral insulated metal-sheathed (Type MI) cables, or metal-clad (Type MC) cables.
Even hospitals now allow rigid nonmetallic conduit in 2 in. of concrete, or non-metallic conduit of a certain wall thickness (Schedule 80) without encasement. Many design engineers, some local codes, and some related standards do impose additional restrictions on the allowable wiring methods for these circuits, and these must be followed as applicable.
Protecting life safety circuits in high rise buildings.
As a former hospital electrical engineer and current forensic engineer who investigates and analyzes fires and design defects, I would first note that the NEC is not a design specification, but rather a minimum recommendation for a usable system, where the designer is mandated to account for all conditions of use and failure, and then design accordingly. Perhaps this is one reason why hospital electrical designers are required to be licensed engineers (not that any extra wisdom is inferred by the license).
Hospitals are an occupancy/use that is expected to be fully available during any conceived emergency, including a fire within that hospital (as stressed by the JCAH, Joint Commission on Accreditation of Hospitals, during their bi-annual inspections). Even if normal and emergency feeds/circuits are in separate rigid metal conduits in a shaft, a fire within or venting through that shaft could easily melt the insulation with a short and trip-out ensuing in both circuits. So where possible, preferred design would have emergency and normal power circuits separated so as to eliminate a fire or other event from taking out both supplies.
Of course at the Patient Room, Operating Room, Clinical Lab, Emergency Room, Sterilization, etc, the normal and emergency power will converge near the user area. Yet, a fire in these areas will not normally take out the whole emergency power system, as it might in a shaft, chase or common bus.
Consider a common practice of digitizing all the control and safety functions of an appliance, machine or building. I have investigated several fires where there were no redundant overload, overtemp, etc sensors and circuits. Failures of a common cpu or modem have precluded the safety devices from shutting down the unit. There may not be a code or design standard requiring such redundancies but their absence represents design defects nonetheless that should not occur from seasoned designers.
Most law suits never go to trial and the results of any settlement are sealed. Unlike aircraft accidents, however, there is unfortunately little feedback from the forensic community to designers regarding issues as this one.
When designing, asking "What would Jesus do?" might not be helpful, but asking "How would an opposing expert view my design during an investigation" might bring some insight.
Retrieving data ...