in a steel trough as they are on the much 

 larger military submarines. Also, during con- 

 struction and maintenance periods tools or 

 other devices may be dropped on them. In 

 order to stabilize and support the cables of 

 STAR III the "Halo" device shown in Figure 

 7.34 was used; obviously this is merely sup- 

 port, not protection. 



Junction Boxes 



Junction boxes are used to interconnect 

 wires or cables. On submersibles they are 

 sometimes within the pressure hull, e.g., 

 SEA OTTER, though in many cases they are 

 external to the hull. In the VAST series of 

 submersibles there is no junction box what- 

 ever, because the only electric power lines 

 are from internal batteries to two electric 

 propulsion motors. 



When junction boxes are external to the 

 hull, they may be pressure resistant, solid or 

 compensated. Pressure-resistant boxes are 

 heavy and penetrations may be costly. In 

 some cases, however, it may be the only way 

 to protect components that cannot withstand 

 high pressure. Solid junction boxes (Fig. 

 7.35), wherein the electrical equipment is 

 potted in a block of elastomeric material, is 



Fig 7 35 A solid junction box consisting of 1547 amber urethane (Gen Dyn Corp) 



Fig 7 34 STAR Ills "Halo cable support. (Gen Dyn Corp.) 



inexpensive and, if transparent, allows easy 

 observation of the component parts. On the 

 debit side, access to the components is quite 

 difficult and water may intrude along pot- 

 ting-to-component interfaces. Equally frus- 

 trating is the fact that elastomeric materials 

 transmit significant shear stresses, and deli- 

 cate components, thus, may be ruptured or 

 fatigued by the motions accompanying 

 compression and decompression. As an ex- 

 ample, in tests at General Dynamics the 

 conductors soldered into the pin at the rear 

 of the receptacles in Figure 7.35 experienced 

 a number of breaks due to pressure cycling. 

 Postmortem revealed that the urethane was 

 compressing and pushing in, and when it 

 pushed it dragged the conductor along with 

 it and broke. Subsequent change to a higher 

 strength conductor and rerouting of the wir- 

 ing so that it received some support and 

 protection from the metal frame proved sat- 

 isfactory. 



Pressure-compensated junction boxes offer 

 advantages for components which can tolerate 



355 



