The energy method of Bernsteinet al.(1958) was used by Schindleret al.(1983) to derive a useful form of the linearised potential energy for coronal arcades. The basic state magnetic field and plasma are assumed to be in magnetohydrostatic equilibrium and independent of variations along the length of the arcade. A sufficient condition for stability is derived and is applied to two particular magnetic structures. When the axial field component vanishes, this condition becomes necessary and suficient.