Dale001289
Senior Member
- Location
- Georgia
'Backfeed' scenarios are not directly addressed in NEC:
Lets say an Electrical Superintendent needs480V temporary, construction power (approximately 300A) for Arc-welders,grinders, temporary lighting etcetera.
A nearby, existing substation contains a 480VMCC with three 100A circuit breakers and a 400A circuit breaker, not being used in thevertical sections. However the MCC’s main circuit breaker is locked out/taggedout because the upstream power transformer that feeds the MCC is undermaintenance.
You decide to back-feed the MCC from anotherlightly loaded transformer through the 400A circuit breaker and utilize thethree 100A branch circuit breakers for temporary power out to the unit. This is not a NEC violation but neither is it specifically addressed. Articles 408.36 and 590 indirectly touch upon it, but more is needed to highlight the need for safety for obvious reasons - could easily result in electrocution....precise language would have to be worked-out but here's the groundwork - For example:
· Apply signage on the 400A feeder circuit breakerstating “MCC is energized; back-fed from (name the source)”. Ref: ANSIZ535.4-1998
· Lock-out/tag-out ALL remaining MCC ‘buckets’other than three 100A breakers used for distribution to unit for constructionpower.
· Review for Arc-flash current.
· Ensurecompliance with Articles 110.9 and 110.10.
Lets say an Electrical Superintendent needs480V temporary, construction power (approximately 300A) for Arc-welders,grinders, temporary lighting etcetera.
A nearby, existing substation contains a 480VMCC with three 100A circuit breakers and a 400A circuit breaker, not being used in thevertical sections. However the MCC’s main circuit breaker is locked out/taggedout because the upstream power transformer that feeds the MCC is undermaintenance.
You decide to back-feed the MCC from anotherlightly loaded transformer through the 400A circuit breaker and utilize thethree 100A branch circuit breakers for temporary power out to the unit. This is not a NEC violation but neither is it specifically addressed. Articles 408.36 and 590 indirectly touch upon it, but more is needed to highlight the need for safety for obvious reasons - could easily result in electrocution....precise language would have to be worked-out but here's the groundwork - For example:
· Apply signage on the 400A feeder circuit breakerstating “MCC is energized; back-fed from (name the source)”. Ref: ANSIZ535.4-1998
· Lock-out/tag-out ALL remaining MCC ‘buckets’other than three 100A breakers used for distribution to unit for constructionpower.
· Review for Arc-flash current.
· Ensurecompliance with Articles 110.9 and 110.10.