Four fire engines and 21 firefighters and officers were called to two electrical substation boxes alight in Mays Lane, Barnet.
Two electrical substation boxes and a garden shed were damaged by fire.
The Brigade was called at 1957 and the fire was under control at 2123. Fire crews from Finchley, Barnet, Southgate and Mill Hill fire stations attended the scene.
The cause of the fire was accidental and is believed to have been caused by an electrical fault within the substation.