NEC Substation Clearances

[podobing]

Hello,
We are installing a customer-owned 25 kV to 4.16 kV substation. This is a skid mounted system, and the only exposed energized parts are the tips of the high side transformer bushings. The substation will be outdoors, and will be protected by a 7 foot high fence with a locked gate.
Table 110.31 of the NEC (Minimum Clearance from Fence to Live Parts) requires 15 feet of clearance. Table 110.34(A) (Minimum Depth of Clear Working Space) requires 6 feet under Condition 2 (exposed live parts on one side, and grounded parts on the other side).

My question is 'What am I missing?" The site is tight for space, so I would like to go as small as possible, yet have a safe installation.

Note: Regarding the 4.16 kV end, Table 110.31 requires 10 feet to the fence, and Table 110.34(A) requires 5 feet under Condition 2.

Regards,
Podo

 

[bacon4life]

NEC table 110.31 is aimed at providing protection from the general populace versus NEC table 110.34 provides adequate space for employees. NESC section 110.A.2 provides an exception to the distance requirements where the fence has "no openings through which sticks or other objects can be inserted..." Also, the NESC only requires a bit over 10 ft for 25 kV. Check to see how your AHJ applies the table 110.31 note that references the NESC.

 

[podobing]

Bacon4Life, Thanks for the response.
I have been told that NEC 90.5(C) (Explanatory Material) says "Explanatory material, such as references to other standards, references to related sections of this Code, or information related to a Code rule, is included in this Code in the form of informational notes. Such notes are informational only and are not enforceable as requirements of this Code."
I realize that the NESC allowed for a lesser clearance, and even though it is referenced in the NEC, it does not appear that I can use the NESC.

I do not know why the NEC would provide such an informational note under Table 110.31, when another statement in the NEC (90.5(C) does not allow it.

I think that the AHJ in this situation is the customer (Federal Government).

I am hoping that someone has run across this problem before.

Podo

 

[waross]

Have you investigated the possibility of insulating the high side conductors and the connections to the bushings?

Bill
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"Why not the best?"
Jimmy Carter