Refeeding existing Switchboard

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shortckt70005

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Brief scope of work:
New location for existing Transformer
New 3500 amp switchboard in new Central Plant.
Breaker in switchboard of new Central Plant to feed existing 1600 switchboard in room 1C.
Contractor wants to pull new wires (4 -500 mcm 1-#2 Ground) from new switchboard to existing Transformer location to where a junction box will be installed. These 5 wires will be tapped at the existing transformer location to the existing wires feeding the existing switchboard in room 1C via junction box. Here is my concern, the existing wires from Transformer to existing switchboard in 1C have 3-500mcm and 1-2/0. Is this legal or is a Ground wire required?



Second question is : there is a 10,000 gallon diesel tank in the ground. The new secondary wires from new transformer location are less than 2' away from the tank? What is the minimum distance these 9 -3" secondary conduits should be away from the under ground diesel tank?



Thank You for Your Help

Shortckt

Help with two questions:
 
augie47 said:
Look at 250.30(A)(1) Exception 2 and (A)(2) Exception and see if they might apply.
Click to expand...
OK in my opinion, if the two buildings were tapped together at the transformer then I can see the separate derived grounds at each location. But in this application, the existing building is being fed from the new Central Plant, which the two are not really a separate buildings. Conduits, Chill Water piping, Duct work, all pass through each of the buildings. There is a fine line technicality of Code interpretation using these exceptions.
Being the original switchboard was the first point of bonding, I seem to think that with new Central Plant switchboard is now the first point of bonding now that a breaker from this switchboard is now feeding the original switchboard.
My interpretation might be wrong that is why I am asking for other opinions.
Thank You for responding
 
I had concentrated on the 2nd sketch and did not realize that 1C was being fed by the new switchboard (I thought it was transformer fed).
An equipment grounding conductor would be required IMO.

My references would apply were !C being fed directly off the new transformer. (Has this been considered ?)
 
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