Mike Dolt Enterprises
Mike Dolt Enterprises
User: Frederick Cox, Location: Massachusetts
Asked on: Wednesday, March 30, 2011 at 6:04 pm EDT
Answered on: Tuesday, May 14, 2024 at 3:31 am EDT
Question: A normal-power 480V switchboard originally direct-fed a 600 amp transformer load. An emergency power source was later introduced to feed this transformer, via a properly-installed 600/3 ATS. However, the original feeder cable was intercepted in the switchboard and extended to the ATS as the normal-source feed, and the load feeder out of the ATS (now = emergency power) re-entered the switchboard where it was spliced into the original transformer feeder. Thus, emergency power is running through the normal-power switchboard. Workmanship and materials appear good; just the decision to do it this way is in question.Is it sufficient to wrap the emergency cable with Scotch 77 fire tape and affix tags & labels describing the external emergency power source? Or must these emergency cables be completely removed from the switchboard? Thank you!
The emergency cables must be completely removed from the normal-power switchboard.
NEC Requirements
Article 700.12(B): Emergency systems shall be so designed and constructed that any single fault will not leave the system inoperable. Article 700.12(D): Emergency systems and normal systems shall be separated in such a way as to not create a hazard to one another.
Reasons for Prohibition
Mixing emergency and normal power sources creates a potential hazard if a fault occurs on either system. The presence of emergency cables in the normal-power switchboard could compromise the integrity of the emergency system in the event of a normal power outage. It is difficult to ensure the proper operation and maintenance of the emergency system if it is intermingled with the normal power system.
Acceptable Solution
The emergency power source should be completely isolated from the normal power switchboard. This can be achieved by: Installing a separate emergency switchboard. Installing a dedicated transfer switch cabinet. Running emergency cables in a separate raceway system.
Additional Considerations: The emergency cable wrap with fire tape is not sufficient to meet NEC requirements. Tags and labels alone will not provide adequate separation and protection between emergency and normal power systems. Flag for review