**Assuming U.S. NEC rules: your cable sounds like SER, which cannot be installed underground—even inside conduit. With suitable replacement wiring, #2 aluminum normally supports a 90-amp feeder.**

1. **Direct burial or conduit?**  
   Check the lettering printed on the jacket. Gray jacket with three insulated conductors and one bare conductor strongly suggests **Type SE, Style SER**. If so, neither direct burial nor underground conduit is permitted. [Southwire’s installation guidance](https://www.southwire.com/medias/sys_master/root/h0e/h77/8902201409566/2310-AL-Flyer-HIGHRES.pdf) explicitly states this restriction.

   Use conductors listed for wet locations in conduit, such as **XHHW-2**, or a suitable four-conductor direct-burial product. If choosing USE-2, verify additional ratings permitting the portions inside buildings; USE-2 alone is insufficient for interior wiring. [Southwire’s feeder selection guide](https://www.southwire.com/medias/2405-LV-Cable-Selector-Technical-Reference-Document-Flyer-WEB.pdf?context=bWFzdGVyfHJvb3R8MzgzMDkzfGFwcGxpY2F0aW9uL3BkZnxoNGEvaGFhLzkwNjU1NzkyMTY5MjYvMjQwNS1MVi1DYWJsZS1TZWxlY3Rvci1UZWNobmljYWwtUmVmZXJlbmNlLURvY3VtZW50LUZseWVyLVdFQi5wZGZ8ODQzMWNkMWQ5ZjVkN2FiYTI5ZTkzYzA5MmViMGVkZDcxM2Q0OTBhZDdlNWVmMjhkNmEwMDgzNDI0NTAwYTJhYw) explains the distinctions.

2. **Maximum feeder breaker?**  
   **Normally a two-pole 90A breaker**, provided both ends have terminals rated for aluminum and 75°C, and no installation conditions require reducing ampacity. #2 aluminum is rated **75A at 60°C, 90A at 75°C, and 100A at 90°C**. The insulation’s 90°C rating does not authorize using 100A with 75°C terminals. [Southwire’s ampacity table](https://assets.southwire.com/ImConvServlet/imconv/7f1133975e3e4b8c5ab3ee2f1881b50f3d3d4ef8/origin?assetDescr=Aluminum+Service+Entrance+%28SE%29+Cable.spec)

   The special dwelling-service allowance sometimes permitting #2 aluminum at 100A generally does **not** apply to a garage-only feeder. A subpanel rated 100A or 125A can still be supplied through a 90A breaker.

3. **How many 15A and 20A breakers?**  
   There is no fixed number derived from the feeder amperage. You may install the number and types permitted by the panel’s labeling, provided the **calculated load** fits the feeder and the house service has sufficient capacity. Adding the branch-breaker ratings is not a load calculation.

   A two-pole 90A feeder supplies up to **90A on each 120V leg**; distribute loads between the legs. Continuous loads generally require sizing at 125%. [Schneider explains breaker ratings per pole](https://www.se.com/us/en/faqs/FA100453/).

If the garage is detached, also provide **two hots, an insulated neutral, and an equipment ground**, keep the neutral isolated from the enclosure and ground bar, and provide a garage disconnect and grounding-electrode system. Ground rods do not replace the feeder ground. [St. Paul’s garage wiring guide](https://www.stpaul.gov/sites/default/files/2023-06/DSI.Bldg_Electrical_Residential%20Garage%20Wiring.pdf)

Before installation, have the local inspector or electrician confirm the jacket markings, burial requirements, terminal ratings, and load calculation. **As described, the underground cable choice needs changing.**