250.104(D) - "in the area served"

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dana1028

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San Francisco Bay area
250.104 - Bonding of Piping Systems & Exposed Structural Steel

Both (D)(1) & (D)(2) refer to "in the area served" .


I was wondering just how far this 'area' is from the transformer. How far away from the transformer does the piping system or steel have to be before it is no longer considered 'in the area served' by the transformer?


Do walls or fire assemblies effect the distance?
 
I think the idea is to prevent long paths for fault current, if we look at the fault current path for an SDS to a water pipe not bonded to the secondary side of the transformer it would have to flow all the way back to the bond from the primary supply through the panels then out the primary EGC that is run with the primary to the transformer across the jumper to the secondary side.

By providing a bond to these items in the area served by the SDS it will have a much shorter pathway back to the transformer secondary XO, so I think the intent is to bond the items in the area served by the transformer secondary circuit, lets say you have a maintenance shop located in an isolated part of the plant, and you have a 480/208/120 volt SDS that serves this maintenance shop only, then any exposed building steel, or waters lines that also run into this shop are required to be bonded to the XO or where ever the GEC is connected, I do not think it requires you to run out across the plant to connect to a water line that has no way of being energized by any circuits from the secondary of this SDS.

If you look at the exceptions you might only have to run an GEC to the building steel then just bond the water piping to it or visa versa.
 
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