Busbar question

[GerryB]

This older home has a 100 amp fused disconnect sw. The original panel or fuse box was replaced with a 200 amp mb panel. Still protected by the 100 amp fused disconnect so ok. The question is can you use the 200 amp Buspar rating for the backfed breaker even though it should actually be a 100 amp panel

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[Carultch]

This older home has a 100 amp fused disconnect sw. The original panel or fuse box was replaced with a 200 amp mb panel. Still protected by the 100 amp fused disconnect so ok. The question is can you use the 200 amp Buspar rating for the backfed breaker even though it should actually be a 100 amp panel

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This setup is functionally equivalent to a 200A busbar panelboard with a 100A main breaker.

To interconnect at a branch circuit, you are limited to 100A OCPD because of the 100A fused disconnect upstream. Assuming the loads are zero and the source is maximum at a particular instant, you don't want to nuisance trip the fuses, or exceed the ampacity of the probably #2 or #3 gauge wire that feeds the panelboard.

Regarding the 120% rule, your calculation would be based on 120% of 200A, which would allow up to 140A worth of PV, if connected at the opposite end. But because of the paragraph above, we are really limited to 100A

 

[jaggedben]

This older home has a 100 amp fused disconnect sw. The original panel or fuse box was replaced with a 200 amp mb panel. Still protected by the 100 amp fused disconnect so ok. The question is can you use the 200 amp Buspar rating for the backfed breaker even though it should actually be a 100 amp panel

Yes, you can. You could put 100A of solar on that. There's nothing that says the panel "should actually be a 100A panel."

 

[pv_n00b]

Ha, you are one lucky installer. Based on the busbar rating you could back feed 100A, or up to 140A if you put the PV breaker at the end. But the 100A OCPD will limit you to 80A, still probably more than you need.