I've read some other post of people saying the 83% rule only applies to single family dwellings. But I see in 310.15 b7 it says or 2 family or multifamily of supplying entire load wether . So for instance if I had a 2 100 amp panels in each dwelling and a service rated 200 amps x 83% =166 A could i use 1/0 cu for the service according to 310.12?
Single phase dwellings and feeders.
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ramsy
Roger Ruhle dba NoFixNoPay
- Location
- LA basin, CA
- Occupation
- Service Electrician 2020 NEC
1) See Example D7 in Annex D.
2) Submit plans to AHJ, before inspection.
i) Some combination inspectors don't use that exception, without their planning department forcing them to allow it.
ii) In my state only building zone R3 qualifies for that exception, but some dwellings are not zoned as such, and inspectors may not recognize R3 in a mixed commercial district.
iii) If inspector challenges you, and you can't provide stamped plans, or recognized authority, like a deer in the headlights they will mow you down.
2) Submit plans to AHJ, before inspection.
i) Some combination inspectors don't use that exception, without their planning department forcing them to allow it.
ii) In my state only building zone R3 qualifies for that exception, but some dwellings are not zoned as such, and inspectors may not recognize R3 in a mixed commercial district.
iii) If inspector challenges you, and you can't provide stamped plans, or recognized authority, like a deer in the headlights they will mow you down.
curt swartz
Electrical Contractor - San Jose, CA
- Location
- San Jose, CA
- Occupation
- Electrical Contractor
The 83% only applies to the individual dwellings not the service conductors feeding multiple dwellings.
Also, 1/0 is only rated for 150 amps.
Also, 1/0 is only rated for 150 amps.
I think you are missing out on the word "individual" as in "the individual dwelling units" qualify.
So on a 6 unit dwelling, the conductors to each individual unit could employ the 83% but the overall service for the entire structure could not.
So on a 6 unit dwelling, the conductors to each individual unit could employ the 83% but the overall service for the entire structure could not.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
How does any inspector get to pick and choose what he allows if the code allows it?
jaggedben
Senior Member
- Location
- Northern California
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- Solar and Energy Storage Installer
By not having someone reasonable for a supervisor. Because suing AHJs isn't something most contractors are gonna do.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
As Augie stated you cannot use that table for the feeder or SEC's to multiple units so the ampacity is 150 amps. Something else to consider with 2-100 amp panels you do not necessarily need 200 amp conductors. They can be sized according to the aggregate of the load calculations for the two units so your #1/0's with an ampacity of 150 amps may be large enough.
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