To pad that out slightly more - it's a train without continuous brake continuity. In terms of multiple units, this means you've isolated the brakes on the unit being hauled. It doesn't mean the unit is totally without brakes as the hauled unit may have a parking brake available. It's a situation I've found myself in more than once, as at a TOC we had a frequent issue of EMUs not being shut down correctly during an electrical isolation. This in turn drains the main batteries which means the control circuits can't be energised. In theory, another unit could rescue it, but in practice this rarely worked. The result was coupling the units with air (ie: main res pipe pressure gained so parking brakes held off), but without electrics. Another driver would be in the rear unit, ready to dump the main res and apply parking brakes should the units divide.
The downside to hauling a swinger is a speed limit of 5mph.
Still hoping someone could clarify if a 331/195 lash up would have brake continuity (just out of curiousity). I know an assisting loco can maintain brake continuity thanks to the sifa valve (also can't explain what that one is!).
