LESS THAN STANDARD SEPARATION BETWEEN 2 ACR. OPERATIONAL ERROR.

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ACR X A BOS DEP CLRED VIA ARCER; SEY; HTO AND ACR Y; AN INTL FLT ARRIVING JFK. LOST STANDARD ATC SEP OF 5 MI WITH LESS THAN STANDARD VERT SEP. SAFETY WAS NOT COMPROMISED AND NO EVASIVE ACTION WAS NECESSARY AS THE CONFLICT WAS RESOLVED BY A VECTOR TO ACR X WHICH REGAINED STANDARD ATC SEP. MAJOR CAUSE OF THE INCIDENT WAS CTLR OVERSIGHT; HOWEVER MAJOR ACR ROUTES SHOULD NOT BE SO CLOSE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR CLARIFIED TYPES OF ACFT; ROUTES; ALT; ETC. ACR Y WAS ON J150 FROM HYA TO HTO VOR AND LEVEL AT FL230. C/A DID NOT ACTIVATE UNTIL AFTER LTSS HAD OCCURRED. NTAP SHOWED BTWN 4.0-4.7 MI LAT SEP WITH 300' VERT AS ACR X WAS CLBING THROUGH FL233 FOR HIGHER ALT. THIS IS A REALLY BUSY SECTOR (CAPE) AND A RUSH PERIOD HAD JUST ENDED AND RPTR SAYS HE THINKS HE RELAXED A BIT WHEN THIS INCIDENT TOOK PLACE. HE WAS IN PROCESS OF BEING RELIEVED AT SECTOR AND HAD EXPANDED SCOPE RANGE FROM NORMAL 75 MI RANGE TO ABOUT 125/150 RANGE TO TAKE A POINTOUT ON ANOTHER ACFT WHICH WOULD BE FACTOR LATER. LEFT SCOPE ON LONGER RANGE WHILE HE WAS BRIEFING RELIEF. THIS MADE IT HARDER FOR HIM TO JUDGE DISTANCE BTWN ACR X AND ACR Y.