100 amp Sub-panel Install

[BlameFNG71]

First time poster here, go easy on me. Anyway, individual has a reliance transfer switch going into main panel but wants to truly have a sub panel with portable generator feed (interlock or something again down the road, topic for another day). Main panel GE Powermark Gold 200a is maxed out, ton of 15 and 20 amp circuits here. SubPanel must be flush mount. See two options, first is to use #2 SER (75º and use 90 amp breaker in main) using top knockouts on main and sub and through the stud between panels for sub feeder (kinda of a tight radius as sub is in adjacent wall cavity) and use the current 1" hole in side of main panel where reliance TS switch connects to extend circuits (only hot and neutrals) to sub via a nipple between studs.

Second option is to just do a larger nipple between the panels to run both panel feeder (just do Copper THHN at this point) and branch circuit extensions. Seems easier but wanted to get input from this group.

 

[Little Bill]

First time poster here, go easy on me. Anyway, individual has a reliance transfer switch going into main panel but wants to truly have a sub panel with portable generator feed (interlock or something again down the road, topic for another day). Main panel GE Powermark Gold 200a is maxed out, ton of 15 and 20 amp circuits here. SubPanel must be flush mount. See two options, first is to use #2 SER (75º and use 90 amp breaker in main) using top knockouts on main and sub and through the stud between panels for sub feeder (kinda of a tight radius as sub is in adjacent wall cavity) and use the current 1" hole in side of main panel where reliance TS switch connects to extend circuits (only hot and neutrals) to sub via a nipple between studs.

Second option is to just do a larger nipple between the panels to run both panel feeder (just do Copper THHN at this point) and branch circuit extensions. Seems easier but wanted to get input from this group.

Is your journeyman working with you on this?

 

[BlameFNG71]

Is your journeyman working with you on this?

Yes, asked me to think/research about this. Pulled the reliance TS out of panel today, what a mess. The flex MC from TS to panel is 1" x 18" and has 20 wires in the thing, way exceeding nipple fill. It was a mess. Conclusion I have come to so far is we need two nipples one for feeder and one for extending branch circuits(10). Two 1" nipples should do it and not exceed 60%, but I now think SE cable between the two will be less time consuming keep labor in costs in check.