An electric ballast 1 is provided with an electric coil with windings having a width d which are wound on a synthetic resin coil base 10 comprising a box-like base part 11 of rectangular shape having four faces 111, 112, 113, 114. The base part is suited to accommodate an iron core of the coil. The base part is provided on either side with mutually parallel flanges 121, 122 which define the width d.
The ballast is provided with a separate, insulating synthetic resin cover which is in one piece and which, when positioned in engagement with the coil base, cooperates therewith to substantially completely enclose the coil windings.