LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
A 400a ATS is way more expensive to buy than even two 200a ATSs, as well as to wire and install.
My first 400 amp service. Need help!
- Thread starter jraymond
- Start date
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
That was why I installed two 200A ATS. The 400A was way more than two 200A.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
If you are supplying 2-200 amp feeders in the first place.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Which brings us back to it rarely being necessary to supply both panels when you have two, as the OP mentioned.If you are supplying 2-200 amp feeders in the first place.
And if you want to supply both panels, 702.4(A)(2) requires that the generator be able to supply the full load that is connected or big enough to feed an EMS set limit. The actual load versus the calculated connected load can greatly differ, but if this is a 400A service we can assume the calculated load is well over 200A. An ATS puts you on the path to oversizing the generator unless you have automatic load shedding equipment. Supplying only one 200A panel somewhat forces a homeowner decision as to what can be permanently shed. But even a 200A panel typically needs a large generator if it has no load shedding.
An ATS may have some simplistic load shedding capability (e.g. a few relays that cut out some specific circuits, like car chargers). Or you may be able to save and buy a smaller generator but then have to buy a pricey energy management system.
You can also go with two manual transfer switches in which case the homeowner can manually load shed if that becomes necessary.
An ATS may have some simplistic load shedding capability (e.g. a few relays that cut out some specific circuits, like car chargers). Or you may be able to save and buy a smaller generator but then have to buy a pricey energy management system.
You can also go with two manual transfer switches in which case the homeowner can manually load shed if that becomes necessary.
Excellent points, and its important to note common Generac load shed relay + ATS do not qualify as NEC article 750 Energy Management System (EMS), Generac and others now offer a more expensive product that they do say is a EMS.
when that section of code changed here a few cycles back it all but killed off the common method of a whole house 200A ATS and load shed relays, now I typically do a 100A 'critical loads' sub panel and no load shed relays. I did not really ever like those relays anyways they were problematic.