Abstract: Lengths of lay-in ducts, each in the form of an open top trough having exterior connecting flanges at its ends, are connected together in end to end relation in a run by bolts passed through the flanges. Each trough is provided with a cover which terminates a slight distance short of the trough ends. A joint sealing device common to the adjacent end portions of two connected troughs provides a seal between the device itself and the tops of the adjacent end portions of the trough, between the end portions of the covers and their associated troughs, and between the adjacent end portions of the covers themselves. The device extends across the troughs, and has one end hingedly connected to a supporting bracket which, in turn, is clamped fixedly in position on one of the connected trough flanges by one of the connecting bolts connecting the flanges together.