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Discussion Starter · #1 ·
We have a project to install an 800kw 480-volt generator for an existing occupied building.
The building has an indoor electric room with 6 main varying in size from 800 amp to 200 maps plus a fire pump.

The outdoor transformer sits on a concrete sidewalk with a slot cut in the bottom for the primary and secondary conductors.

We opened the transformer in the presence of the utility construction planner and all agreed that the TX could be shifted to the left enough to allow us to have access to all of the secondary outside of the TX.

The question:
All of the indoor mains are grouped in one electric room.
The electric room isn't big enough to fit the new 2000 amp ATS in.
We need to take over the underground secondary outside and get it into the building through the ATS.
No way can the ATS can fit all of the individual, 10 per phase,
6- 350s,
1- 500s,
2- 600s,
1- 3/0
The utility 2000amp 6x 500s
the generator 1000 amp 3x 500s

I have resigned myself to the fact that we will need to splice all of the 40 individual conductors going underground to the electric room.

What to do with the secondary?
I planned on installing a new exterior 3 R panelboard on the concrete pad and terminating them on a breaker matching the interior main.
Or,
Plan B.
Assuming the secondary are considered outdoor taps, and outdoor taps are unlimited,
Can I terminate all of the various secondary conductors in a tap box, and feed that tap box from the output of the ATS instead of using a panelboard?

I know the description is a bit wordy.

TLDR:
Is it permissible to use a tap box in place of a panelboard with outdoor underground feeders?
 

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Can we look at it this way (assuming I'm understanding your situation)?

You have unfused secondaries going into an electric room landed at the main OCPD(s). They originate @ POCO transformer.

You want to interrupt them with an ATS. You'll be feeding unfused power into the electric room landed at the main OCPD(s).

Sounds like you don't even need to go into the electric room.

Drawing out a site plan would help. I think you're fine but I surely don't profess to be up on code changes. Draw it up and submit it to the plans examiner @ the bldg dept and see what they say. Not sure where it is but some places allow a quick 5-minute pre-application consultation at the counter. You'll still need fuel tank permit, maybe zoning, (add names of bureaucratic entities here), etc.
 

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Discussion Starter · #3 ·
Thank you Mike,
I want to add that the utility will be going into the ATS and the output of the ATS passing through either the tap box or a panelboard.
So, I think your comment captured what we intend to do.

I have another complication.
I will need to run the unfused TX secondary underneath and pass through the area under the tap box/panelboard.
It's very possible that I can dig in some conduits, or better yet, use direct bury rated cables from the TX secondary under the tap box and into the SE rated ATS.
I have a decent budget but my downtime is extremely limited to one weekend.
I need to pick up time where ever I can get it.
Direct bury secondary and the tap box would be a great time saver.
 

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How will you be handling neutral-ground bonds?

How will you handle no EGC's into the existing service disconnects?

Without seeing the job is there any way to drop a vault in outside next the building to intersect all the existing conduits? Install a utility trans type lid on it and set the ATS over it with a tap box beside it?

It'd give you an easy place to splice and extend wiring if need be. A person might be able to sawcut any existing concrete slab and excavate the hole in advance and just have the vault and lid sitting there waiting to drop in the hole as soon as you kill power.
 

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Can you do what @Cow said but custom make the vault in advance and break open conduits. Have everything else ready to go then at shutdown back pull cabling to tap box, and install new stubbing? Least amount of down time.
 

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Discussion Starter · #6 ·
Cow,
We typically remove the ground/ neutral jumperes in each switch.
Also, as you mentioned, we will need to pull a ground wire in each conduit.
The good part is the longest run underground is only about 25' and they are all decent size conduits.

JW,
We will for sure have to saw cut and have everything ready to go.
The work window is on February 28th weekend. It doesn't really get cold here but that is prime rainy season so we will for sure have to tent the Jobsite.
Someone here recently posted a source for a custom tap box, I'll have to find it.
 

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You might need to use thermal image scans to make sure the proper installation is done in the right place of the warehouse. Check my bio for more details.
 
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