Service Disconnect

newt

Senior Member
Look at a service disconnect (for a pv install that was a line side tap) that was rated for 200 amps and the fuses are 150 amp so they ran 2/0 copper for the service conductors i asked the insp. if they should be 3/0 copper to match max disconnect ampacity and not pv backfeed capability and he said no it would be find i disagree any thoughts
 

UMirza

Member
Location
Newyork
Your conductor should be sized to handle OCPD ratings. As 240.4 allows the conductor ampacity to be less at times when rounding off to next size OCPD. The enclosure or lug ratings and OCPD rating are two different variables. you are using 200A rated lugs & enclosure but only utilizing 150A. 2/0 @ 75C are rated 175A and should be acceptable. Check you voltage drops and other conditions of use.
 

jaggedben

Senior Member
2/0 copper is probably an accceptable size for 200A service conductors in any case. However, even if it wasn't, the service conductors only needed to be rated for 150A (assuming that is the correct number for the PV output according to 690.8).

Article 230 simply requires service conductors to be protected by OCPDs that are rated no higher than the conductor. The fuses are the OCPDs, not the disco. There is no prohibition on using a disconnect that is rated higher than the fuses. After all, that's pretty much how a fused disconnect works; the disco can be rated higher than the fuses but not lower.

The code is a little lacking in that Article 220 doesn't specify how PV is supposed to be accounted for as a 'load', but the reasonable interpretation is 125% of the inverters' rated output as set down in 690.8
 
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newt

Senior Member
Thanks I thought you had to size to it the disconnect in case a fuse was changed to the full rating of the disc.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Thanks I thought you had to size to it the disconnect in case a fuse was changed to the full rating of the disc.
Nope. If the fuse holder accepts a range of different values without adapters, it would be a good idea to mark the maximum fuse size inside the box. But other than that, it would be just like requiring that any branch wiring connected to a 200A main panel be rated for 200A in case somebody put in a larger breaker than the branch circuit was originally wired for. Not a code issue.
 
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