The USPTO has reorganized Class 310: Electrical Generator or Motor Structure. Details are provided in Classification Order #1887. Class 310, which was created in 1953, is a bit atypical in that it is a residual class intended to cover technology related to electrical generator or motor structure not classified elsewhere. Which means that searchers may need to consult other related electrical and mechanical classes.
There are currently about 65,000 patents and 13,000 published applications classified in Class 310.