Sub-Fed Panelboards

[tenee]

I am currently looking at feeding 4-480/277vac panelboards from an existing emergency panelboard. Currently they are all fed from their own MCC breaker. The emergency panelboard is powered by a generator when the power goes down through an ATS. Here's my delimma: The emergency PB is rated for 100 amps and the to-be sub-fed panelboards are 125 amps with main breakers. All of the panels grouped together are carrying about 40 amps total (including the E PB). Is there anything in the code that prohibits the redirection of the panelboards to the E panelboard? (This is customer driven to load up the generator more during testing - the building they are powering has allot of spare office space currently... ) Please advise.

Thanks in advance!

 

[charlie b]

Important question: Are you really dealing with an ?Emergency? system? Does Article 700 apply? Has some governmental agency declared that the types of loads that are intended to be powered by these panels are ?essential for safety to human life?? If so, then the rules for keeping ?Emergency? and ?Normal? circuits separated might get in your way. I can't say more without knowing more about the present configuration. If not, then the rules change significantly.

There is no rule against powering four panels, each rated 125 amps, from a single panel that is rated 100 amps. There is a rule that says you must size the panel to handle the load, but that will not be a problem.

 

[Mike01]

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The only problem would be if you tried to fit a 120A branch breaker into a 100A rated panel I do not think it will fit.

 

[hbendillo]

You will not be able to install 125-amp circuit breakers in a 100-amp rated panelboard. How was the load from the four panelboards measured? Have you considered what the starting current might be after connecting these panelboard to the emergency generator? Obviously the loads from the 4-480 volt panelboards are non-essential otherwise they would already be connected to the generator. I would advise connecting them with a separate feeder and distribution panel from the existing emergency panelboard so you can shed that load easily if necessary. I have not investigated code implications for what you are trying to do but as far good engineering practice, it is kind of sloppy.