Main-tie-main interlock requirement

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kanaka360

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I am designing a project for an owner with some very specific electrical system requests. We intend to provide dual (redundant) utility services feeding a main switchboard in a main-tie-main configuration. The owner has requested that the transfer be manually operated, but that kirk-keys or similar interlocks not be utilized. This seems like an intrinsically terrible idea, but I'm having trouble locating anything that specifically prohibits this in the code. I've looked at article 702.5, but this seems to be more applicable to on-site generation. Does anyone have a different interpretation of 702, or another code section that I should look to?
 
I can't think of an NEC article that addresses this. I thought 705 might have something, but I don't see it there. But I am certain that no utility company will allow their system to be connected to a M-T-M setup that lacks interlocks to prevent their two utility services from being accidentally put into parallel with each other. If the two sources are not exactly in sync with each other, the result of such a parallel operation could be explosive and fatal to anyone standing anywhere close to the equipment.
 
Kicker here is that it's a primary metered campus distribution system, so the utility doesn't own anything downstream of their meter. The local Eaton rep tells me that they have this in place in various locations throughout the campus, and that Eaton has made them sign a liability waiver in order to provide the equipment.
 
490.21.B.7 reference

Otherwise, as Charlie noted, parallel xfrms possibility means twice fault current. Equipment must rated for this.

You should consider if you are comfortable stamping drawing like this. As discribed, I wouldn’t be.
 
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