Determining Bus rating on older panel

[titan1021]

I am doing a residential remodel on a home that is about 25 years old. The house has an existing sub-panel in the garage. This sub-panel is fed by a 90a breaker at the main service. I would like to increase the sub-feed and breaker to 125a. The main panel however is missing all of its labels, so I'm not sure what the main bus rating is. The panel is a sylvania/zinsco brand. I've checked other houses in the same track for any original labels and they to are missing. The service is underground fed and upgrading the panel would be more than this customer wants to get into. Any input on how to determine the bus rating on a panel like this would really be appreciated.
Thanks

 

[BryanMD]

I am doing a residential remodel on a home that is about 25 years old. The house has an existing sub-panel in the garage. This sub-panel is fed by a 90a breaker at the main service. I would like to increase the sub-feed and breaker to 125a. The main panel however is missing all of its labels, so I'm not sure what the main bus rating is. The panel is a sylvania/zinsco brand. I've checked other houses in the same track for any original labels and they to are missing. The service is underground fed and upgrading the panel would be more than this customer wants to get into. Any input on how to determine the bus rating on a panel like this would really be appreciated.Thanks

The size of the conductors (among other factors) are what will determine the size of the new main breaker and should have determined the existing 90A breaker.

As to re-using the existing 25yo zinsco... DON"T!
Pony up for a new panel.

 

[brian john]

The best way to accomplish this is to REPLACE THAT Zinsco JUNK. It is hardly worth the electrons it has already carried at 90 amps why give it the benefit of additional electrons for it's resume.