Engineers who need to pass power and signal wires through the walls of pressure and vacuum chambers usually reach for off-the-shelf sealed bulkhead connectors. Such connectors often seem like the best or only way to traverse chamber walls, but they can unnecessarily constrain designs, raise costs, and trigger electrical problems. Wire feedthroughs hermetically sealed with epoxy can be a better alternative.
Such feedthroughs pass all the conductors in a wire harness though the chamber wall with no loss of pressure or vacuum. Often, they permit design flexibility that’s not possible with off-the-shelf connectors. They also improve electrical performance by eliminating voltage drop and contact-resistance issues that affect connectors. And although they are custom products, hermetically sealed wire feedthroughs have a lower installed cost than comparable bulkhead connectors when specced into the right application.
It’s important to stress that point about the right application. The most obvious reason to select a connector instead of a continuous feedthrough is to let users disconnect wires from the chamber. Applications needing quick connections or disconnections on one or both sides of the chamber wall require bulkhead connectors. In these cases, though, it pays to pick high-quality connectors to avoid problems with electrical losses and substandard sealing. (See the related Machine Design article, Sealing off leaks.)
Most feedthrough applications, however, tend to be “sealed for life.” Here, the main design considerations are robust sealing and resistance to mechanical stresses with minimal electrical losses. Lots of applications fall in this category. Typical examples include high-voltage electrical switches, semiconductor wafer-processing equipment, medical-imaging systems, military ordinance-control applications, and space-simulation vacuum chambers.