System usually found on the continent. An execution signal and an end-of-section signal are used; these signals may either be colour lights or semaphores. The location of the execution signal can generally be spotted in the distance by a "shut off power" distant signal in black letters on a white background. Before reaching the "Shut off power" execution signal, the driver must have first cut all the power, and if necessary, interrupted the regenerative braking. The shut off power end-of-section signal allows the driver to resume normal traction unless otherwise indicated. With 25 000 V traction systems, the shut off power signals may be fixed or mobile. Shut off power signals are most often encountered at sectioning points between two areas with different 25 000 V substations. Units running with a single-phase current must shut off the power at a specific point, as the combined supply from two power sources out of phase with each other could damage the electrical equipment in the traction units. The advantage of a 1 500 V DC supply is that there is no such risk!