Tap rule for 320 service for 400A ATS residential setup

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CustomElectricLLC

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Midlothian Texas
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Electrical Contractor
I’ve done my due diligence using the search functions but haven’t gotten a clear grip on this current setup I need to install.

ATS is SERVICE RATED. 320/400A meter/service w/ 2 existing MLO panels w/ 200A disconnects w/OCP. It has load side lug provisions for up to 250kcmil I believe to feed two separate runs to each panel/disco

To save time for everyone; 400A ATS is what I’m working with on this install.

Is there an issue with a tap rule being used in this setup where I would run feeder taps from the ATS to the disconnects which will then come out load side on discos and feed into panel. I’ve ready through 240.21 B 1 and don’t see anything that would be an issue. Taps will be less than 10’

Better yet I’m wondering if I can bypass 200A discos all together and install main breakers on the panels if possible to safe the extra stuff on the exterior

YES I am aware of the 83% rule of T310.12 A only limited to a feeder serving the entire load of the dwelling so I’ll be using 3/0cu on this install

TIA
6e8d1c56f9790a499fee93139f9d37dc.jpg



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Two 200a ATSs in a master/slave config would make this much easier.

You could either replace the discos with ATSs or add the ATSs to them.

If your load calcs are within 180a, you can stay with the same wire size.
 
Of course.
To use a single 400a ATS, you would have to:
Replace the load lugs in the meter.
Divide the outputs of the ATS.
Figure out how to route everything.
I'm sure we'll think of more.

Would the customer consider powering only one panel with some rearraging?
 
LarryFine said:
Of course.
To use a single 400a ATS, you would have to:
Replace the load lugs in the meter.
Divide the outputs of the ATS.
Figure out how to route everything.
I'm sure we'll think of more.

Would the customer consider powering only one panel with some rearraging?
Click to expand...

Load lugs are a great point. Didn’t think about that one. But I can just parallel (2) 3/0cu.


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I don't see an issue with the proposed install. As long as you comply with the tap rule. Remember no next size up rule on the tap conductors, but seems like you're covered using 3/0 copper.

One other comment however:. These two panel setups often work well having only one panel be on the generator, and the other can be for your shedded loads. Are you doing any load shedding or is the generator large enough to run everything?
 
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