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a monster residence, parallel stand-by generators and a bus

Merry Christmas

Penfold17

New User
Location
Virginia
Occupation
Arch & MPE Engineering
Thank you to all ahead of time!
I usually find existing posts to point me to the correct code reference, but not this one... not after 2 days of reading and cursing myself

43k sf residence + poolhouse, New Jersey, 280kw service load per 220.82 b+c
circuits are dispersed among sub-panels, all fed from (4) main distribution panels
I am in mid-stride switching from 1ɸ 120/240v to 3ɸ 120/208 after months of utility runaround and hoops jumped through
owners want FULL stand-by backup generation, previously this was a pair of 1ɸ 150kw generacs, essentially halving the system as it split at the ATS's
NG for the fuel source, unless utility balks at my service size ask, with Diesel as fallback

I am now wishing to combine (2) 3ɸ 150kw's genny's at a Bus (trough, raceway, cabinet?), feeding 2 ATS's, and taking advantage of PSG
Assumed advantages... servicing, redundancy (expected normal load should be <75% of a single genny as house will have partial occupancy most of the time)

SETUP
planning fused service disconnect outside, adjacent the CT~meter
in basement E room will be (2) SER ATS's with factory utility disconnects, and likely (1) MDP
other (3) MDP's are remote... approx 75'
manual disconnect w lockout at each genny, and disconnect for each genny in building (bsmt E room) before Bus
there will be some load management, and staggering of the (2) elevators, 3 EV chargers, and the fleet of 20+/- 5T heat pumps on the roof

Generac Specifying Engineer informs me that this '2 genny's to 1 Bus to 2 ATS's' is typical.
My first rodeo regarding a genny install not 'off the shelf' as it were, hence me looking for guidance on particulars

Q1. Is the manual disconnect w lockout at each genny plus the Generac PSG sufficient to satisfy 445.18(e) ?
Q2. is there a conflict of the two ATS with this config, or does the 'paralleling reverse power protection' accommodate this
Q3. would I require a fused disconnect between the Bus and ATS ? (genny's have on-board OCP breakers)
Q4. does the main breaker of an MDP satisfy disconnect with ATS... IF it is immediately adjacent (in same room, within 4'ish)
Q5. a disconnect adjacent to the ATS is required for remote MCB MDP's, yes ? (though not fused, as MDP MCB acts as OCP ?)
Q6. am I undersizing the generators (158w/sf) by using the tabulated service load per 220.82 b+c
Q7. am I missing something, overcomplicating it ?

thank you again so much,
Shawn
 

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
It’s been a long time since I’ve done a Generac parallel, back then Generac didn’t make big generators, so they had to parallel two 150’s if I remember correctly. With that kind of money, they need to go with something better than Generac, because when it fails, they will be calling and chewing you out. If I remember correctly, the paralleling is done electronically between the generators. I know they had a lot of issues with it, but surely they have it figured out by now. That was about 20-25 years ago.
 
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