Seven-Delta-FortyOne
Goin’ Down In Flames........
- Location
- Humboldt
- Occupation
- EC and GC
This is a fairly typical situation I run into, with my generator/ATS installs.
I'll come off the load side of the MCB and feed the ATS, and then back into the main panel.
For a 200A service, I could use #2. But, if I put them all into one conduit over 24" long, I need to derate to 80%.
310.12(B) says 83% can be used. Then says if no adjustment factors are needed, Table 310.12 can be used.
So my understanding is I can use the "83%" rule, but not Table 310.12.
So I can use an Ampacity of 166 (200 x .83), then apply adjustment from there.
So from Table 310.16, 3/0 has an Ampacity of 225 in the 90C column, multiplied by .80 gives me 180A, which is more than the 166 I have using the 83% rule, so I could combine the feeders in one conduit using 3/0.
Is my interpretation of 310.12 correct in your opinion?
Point of fact I usually use gutter for these situations, which negates all of this, but one I'm bidding now got me thinking about this possible scenario.
I'll come off the load side of the MCB and feed the ATS, and then back into the main panel.
For a 200A service, I could use #2. But, if I put them all into one conduit over 24" long, I need to derate to 80%.
310.12(B) says 83% can be used. Then says if no adjustment factors are needed, Table 310.12 can be used.
So my understanding is I can use the "83%" rule, but not Table 310.12.
So I can use an Ampacity of 166 (200 x .83), then apply adjustment from there.
So from Table 310.16, 3/0 has an Ampacity of 225 in the 90C column, multiplied by .80 gives me 180A, which is more than the 166 I have using the 83% rule, so I could combine the feeders in one conduit using 3/0.
Is my interpretation of 310.12 correct in your opinion?
Point of fact I usually use gutter for these situations, which negates all of this, but one I'm bidding now got me thinking about this possible scenario.
