THE EE REPORTED WAS REPAIRING A BROKEN ALUMINUM CONDUIT LOCATED ON THE 1.5 FLOOR IN B.426. AS HE ATTEMPTED TO PULL BOTH RUBBER-TYPE INSULATED CABLES (APPROXIMATELY .25 INCH DIAMETER EACH), BOT H CABLES HUNG IN THE .75 INCH DIAMETER ALUMINUM CONDUIT AT AN LB CONDULET. AT THIS MOMENT THE EE EXPERIENCED PAIN IN HIS LOWER BACK. THE EE WAS TREATED AT THE LOCAL MEDICAL CLINIC & RETURNED