gkeithan
New member
- Location
- Middletown, CT
Per 690.8.B.2.a The circuit conductor shall be 125% of max current. So 156%, but do you use 90 deg C conductor or 75 degree conductor from Table 310.15(B)(16)?
PV Source Circuit Size
- Thread starter gkeithan
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
It depends on what wiring method you are using. You can use the 90C for derating but 75 C is the max for the ampacity as long as the wiring method is rated 75C. NM cable is only rated 60C
jaggedben
Senior Member
- Location
- Northern California
- Occupation
- Solar and Energy Storage Installer
To put it another way...The answer is that you do both, and use whichever wire size is greater.
If you are using equipment with 75C rated terminals (you almost always will be), then look up the conductor size in the table based on 75C.
Then do a temperature derating calculation using the wire you are using, which should be 90C. (Don't bother using anything not rated 90C for PV source circuits. Almost anything you buy nowadays will be rated 90C anyway.)
Whichever calc calls for the larger wire size, use that wire size. Since PV source circuits are often on roofs that get very hot, sometimes the temp calculation will call for a larger wire than the terminal rating does.
BTW, NM is not a valid wiring method for PV source circuits on the PV side of the disconnecting means.
If you are using equipment with 75C rated terminals (you almost always will be), then look up the conductor size in the table based on 75C.
Then do a temperature derating calculation using the wire you are using, which should be 90C. (Don't bother using anything not rated 90C for PV source circuits. Almost anything you buy nowadays will be rated 90C anyway.)
Whichever calc calls for the larger wire size, use that wire size. Since PV source circuits are often on roofs that get very hot, sometimes the temp calculation will call for a larger wire than the terminal rating does.
BTW, NM is not a valid wiring method for PV source circuits on the PV side of the disconnecting means.
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