Re: Splicing in breakerpanel.
Bob, good to hear from you. To answer your question, not more than is eleborated by code, very frist sentence under the heading of 312.8 says enclosures for switches or overcurrent devices shall not be used as junction boxes, auxillary gutters, or raceways for conductors feeding thru or tapping off to other switches or overcurrent devices...ect...ect. Not a clear restriction however something to consider under the circumstances. I have installed the same manual transfer switches that you refer to on panels of vintage age with questionable gutter space.