Building steel and multiple service enclosures sanity check

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electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
Consider a 400 amp service with two sets of 250 MCM AL from service point to a Ct cabinet, which feeds two sets of service entrance conductors and (2) 200 A service enclosures per 230.40 EX #2. Say this is a steel building built on a slab with a vapor retarder under the slab. Because of the vapor retarder, I dont see building steel qualifying as an electrode per 250.52(A)(2). However, 250.104(C) still requires building steel to be bonded (Lets assume it is likely to become energized). now 250.104(C) states that :
The bonding jumper(s) shall be sized in accordance with
Table 250.66 and installed in accordance with 250.64(A),
(B), and (E).
Click to expand...

So that conveniently skips over 250.64(D). So can I run a #2 CU from the building steel to ONE of the 200A service enclosures? I think so, but I just feel like I am not hitting the "entire" grounded conductor by only hitting one enclosure and "half" of the grounded conductor..... :unsure:
 
Me personally, would draw it out for a better perspective. words can be interpreted too many ways. Great question though.
 
electrofelon said:
So that conveniently skips over 250.64(D). So can I run a #2 CU from the building steel to ONE of the 200A service enclosures? I think so, but I just feel like I am not hitting the "entire" grounded conductor by only hitting one enclosure and "half" of the grounded conductor.....
Click to expand...
250.104(C) doesn't address multiple service disconnects so IMO hitting just one would be sufficient.
 
If I'm understanding correctly you sized the bonding conductor from 250.66 based on (2-250)Al service entrance conductors.
To get #2 cu for just one service disconnect.
Then no bond conductor from service disc #2 to steel.
When you one line it out it makes since.
The grounded (Netutal) conductor, most likely 250 AL to disc. Thus effectively bonding the 2-250 service entrance conductors at the tap or in ct cabinet.
Then the second service disconnect would not require a separate bonding jumper.

Not part of the original question.
If it was 250 AL to each disc.
You would run # 4 cu from each service disc to building steel. Based on 250.104 (C).
Never thought of doing it that single conductor way.
The key would be watch you service entrance conductors and how many sets and sizes of service disconnects.
Thanks
 
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