UPDATE 1-Nexen's Buzzard oil field running under capacity

* Output down due to third-party pipeline constraint

* Expected to resume "any day now"

CALGARY, Alberta, Oct 20 (Reuters) - Nexen Inc's (NXY.TO) 200,000 barrel a day Buzzard oil field in the North Sea is operating below capacity, but the constraint is not major and should end soon, a company spokesman said on Tuesday.

The drop in output at the huge field is due to limitations on a third-party pipeline moving associated natural gas, Nexen's Michael Harris said.

Harris declined to give the specific volume that has been cut but said, "It's not enough to get too excited about."

Production should be back up to normal rates "any day now," he said.

Nexen is operator of Buzzard and its partner is Suncor Energy Inc (SU.TO).

Nexen shares were off 49 Canadian cents at C$25.89 on the Toronto Stock Exchange.

($1=$1.05 Canadian) (Reporting by Jeffrey Jones; editing by Rob Wilson)