| 摘要 |
The front cavity (2) has two entries above and two below, for standard conduits, each closed by a two-stage knock-out (5,6). Circuit components are contained within, using a retaining ring, twist fitting on the cavity mouth (22). Before pouring, the ring is replaced by a similarly fitted disk with embedded permanent magnets, firmly holding it against the metal formwork. Reinforcing bars are opt. passed through vertical tubes, integrally moulded (28,29), also used to facilitate side-by-side mounting. The box-like rear extension (3), open top and bottom, has corrugated sides, continuous in the upper half (34), slotted (40) in the lower (35). Two boxes, mutually inverted, can form an interlocked back-to-back pair of variable overall length.
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