Essential Electrical System

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mbrooke

mbrooke

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United States
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Technician
Why does code mandate essential electrical systems be divided into 3 branches? What practical safeguards are achieved? What year did code make this change? And does anyone know of the NFPA's reasoning?
 
My best guess is a desire to assign priorities, and to prevent issues in the lower priority branches from resulting in loss of power to the higher priority branches. I have code books dating back to 1996 at home. But I strongly suspect that this mandate started earlier than that.
 
charlie b said:
My best guess is a desire to assign priorities, and to prevent issues in the lower priority branches from resulting in loss of power to the higher priority branches. I have code books dating back to 1996 at home. But I strongly suspect that this mandate started earlier than that.
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Perhaps, but selective coordination would guarantee that far exceeding subdivision.
 
No it wouldn't, not in all scenarios. One of the requirements related to the Life Safety Branch is that no conductors in that branch can share a conduit with conductors from either other branch. The danger this attempts to preclude is a short circuit in an equipment branch wire causing arcing that results in damage to the LS wiring. Selective coordination would not prevent this event from happening.
 
charlie b said:
No it wouldn't, not in all scenarios. One of the requirements related to the Life Safety Branch is that no conductors in that branch can share a conduit with conductors from either other branch. The danger this attempts to preclude is a short circuit in an equipment branch wire causing arcing that results in damage to the LS wiring. Selective coordination would not prevent this event from happening.
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True, but neither would a separate ATS.
 
Off topic, but it caught my eye. In nursing homes the critical branch is allowed to have delayed transfer? :blink: And why would a sump pump need its own ATS? :?
 

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