On medium to large projects it can be advantageous to provide emergency lighting using a static inverter connected to a number of the existing mains luminaires.

In these installations it is necessary for the normal supply and the static inverter supply to be selected by an automatic switching device within or external to the luminaire. Some suppliers offer a standard 230V AC change-over relay for this purpose but this ignores the fact that a free running static inverter is not tied to the grid frequency and will therefore be out of phase or in a worst case situation could be in anti-phase with the normal switched supply.

When a relay tries to switch between these supplies there is a tendency for the relay to suffer from arcing between the normally open and the normally closed contacts resulting in a temporary short circuit between the two out of phase supplies. This will cause external circuit protection to operate (fuses and/or circuit breakers) and will ultimately destroy the relay.

In extreme cases it can also damage the static inverter.

The SIM240 static inverter module is designed to eliminate these switching problems. The SIM240 utilises two interposing relays for the two supplies and introduces a time delay of approximately 500m sec between breaking the normal supply and connecting the static inverter supply. This sequence is reversed upon restoration of the monitored 230 volt supply when the SIM240 immediately breaks the static inverter supply and then after a similar time delay reconnects the normal lighting supply.

A dimming isolation facility is incorporated as standard for use with dimming ballasts to enable full light output to be achieved in the emergency condition.