Essential Electrical System

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mbrooke

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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?
 

charlie b

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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.
 

mbrooke

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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.

Perhaps, but selective coordination would guarantee that far exceeding subdivision.
 

charlie b

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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.
 

mbrooke

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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.

True, but neither would a separate ATS.
 

mbrooke

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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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