How to determine panel bus rating when there is no label?

[photonboy]

I see this a lot in plan sets, they specify a bus rating when there is no label anywhere on the panel. Since I'm working in PV the bus rating is part of a calculation that determines what size backfeed breaker can be installed.

I often wonder if in the absence of a label the bus rating becomes whatever is most convenient for the person determining what breaker they can install.

I've always felt that bus ratings should be indelibly stamped on the bus in an easy to see location, especially since there are safety concerns with knowing what amperage it can handle.

How do y'all figure out what the rating is with no labels?

 

[jaggedben]

Generally assume it's the rating of the breaker protecting it.

 

[photonboy]

Generally assume it's the rating of the breaker protecting it.

I kinda do that but was hoping for a more definitive method, especially with panels that have no main breaker. I review solar PV systems and in order to determine if the installation is code compliant I need to know if the backfeed breaker is adhering to the 120% rule. We see a lot of old panels who's labels have long peeled off, panels that have had main breakers up or downsized, no breakers, etc. I get uncomfortable making assumptions about things that can have safety ramifications.

 

[jaggedben]

Nothing more definitive I'm afraid.

In some subdivisions where the homes were all built at the same time, a neighbor may have the same panel with the label still intact.