Copper swell is isolated! (3,3)
I believe the answer is:
cut off
'is isolated' is the definition.
(thesaurus)
'copper swell' is the wordplay.
'copper' becomes 'cu' (chemical symbol).
'swell' becomes 'toff' (wealthy or high-class person).
'cu'+'toff'='CUT-OFF'
(Other definitions for cut off that I've seen before include "Device for interrupting a power supply" , "Leave nothing to in will - not a penny" , "Device for interrupting flow" , "Point after which something is no longer effective" , "disconnection?" .)