A massive blaze that destroyed a lavish Upper East Side penthouse Saturday was sparked by a lamp cord, fire marshals said yesterday.

The luxury triplex on East End Avenue, near East 79th Street is owned by wealthy businessman Tuvia Feldman, a former Ness Technologies chief and victim of Bernie Madoff’s Ponzi scheme. It was unoccupied when the fire broke out at about 8 p.m.

The inferno caused extensive smoke and water damage. Officials gave no details about how the lamp cord caused the fire.

The residence, valued at $13.5 million before it was taken off the market six months ago, had been featured on NBC’s “LXTV Open House.”

The three-bedroom home included a grand steel-and-limestone staircase based on the legendary French ocean liner SS Normandie.

Seven firefighters suffered minor injuries in the blaze.