ECN Forum Forums General Topics of the Trade General Discussion Area Anyone familiar with prefab addition wiring?

Prefab? You mean this addition came in on a truck? (modular premanufactured building)

Amp does sell an NM connector made for the purpose that can be concealed or even fished.

http://datasheet.octopart.com/208169-1-AMP-datasheet-14548063.pdf

You are right, splices normally need to be in a box and accessible.