The first potential-free power module was introduced into the market by Semikron in 1975.

Some manufacturers offered panel-mounted jacks with potential-free auxiliary contacts that would open if a plug were inserted.

They contain the entire interface including the potential-free driver interface and require only a supply voltage of 5 Volt.

The limit switch assembly consists of 6 limit switches: 2 operating switches: 2 safety limit switches and 2 potential-free switches.