Dear Treggers, We are involved in the development of an adjunct device that will be connected to a multitude of PABX proprietary feature phones from different manufacturers. The connections will be made through the narrow 4-pin socket connecting the handset to the base of the telephone. The add-on device will be connected to the handset itself.
The add-on device will be powered from a low-voltage mains adaptor with relevant CE-mark and UL listing. The device will also be equipped with a USB connection to allow connection of a personal computer. Can anyone specify (quoting the relevant safety standard paragraph) the degree of safety isolation required between the portions of the device that are connected to the externally connected PC (that are referenced to PC ground), and the portions of the device that are connected to the four terminals of the handset socket on the feature phones? This isolation will govern the cost/complexity of magnetic and optical isolation components, and the type of relay used for restoring original operation of the feature phone in the event of a local power outage. It is due to the difficulty of ensuring adequate isolation between normally-open and normally-closed contacts of reasonably economical relays that I am asking this question. I am hoping that the requirement may be sufficiently low that we will not require expensive relay types for this application. Thanks in advance for all answers received. David Drori Novarex Enterprises Ltd., PO Box 45178, Room 204, 2nd Floor, Park Center, Hamarpe 1, Har Hotsvim Industrial Area, Jerusalem 91450, Israel. Tel: +972 2 540 0168 Fax: +972 2 540 0169 GSM Cellular: +972 54 828011 E-mail: [email protected]
