Hi Jim, You wrote: > The isolation aspect is limited to 60Hz > isolation. The prime power is > ungrounded. It will be fed through the > isolation transformer whose secondary > will be grounded to form a green wire > ground/neutral connection. For this I > don't think I need interwinding screens.
You still have the problem if there is a primary feed/secondary short, where full mains voltage can appear on the secondary. Low voltage secondaries my be sufficiently low impedance to take out your fuse, but high voltage secondaries(>120V) may simply get very hot while the external circuit suffers overvoltage. The Earthed interwinding screen effectively removes that possibility by providing a short circuit path to blow the supply fuse. > > However, I don't quite understand your > comment supporting switch on voltage > peaks. This seems to me to be counter > productive - or am I under a > misconception. I thought I would need a > switch on zero to minimize inrush > current. This is merely acknowledging that inductive circuits have 90 degrees lag on current. If your transformer is unloaded on switch on, the current will be at a minimum when the voltage is at a peak. These peak switching SSR's are produced just for that purpose, and are, in my experience, a God send. Conventional resistive or loaded transformer switching can use Zero Cross Over switching, as the I and V are in phase. Sorry about the confusion, Chris Dupres EMC Specialist. VG Microtech. [email protected] tel +44 (0) 1825 761077 fax +44 (0) 1825 768343 'Opinions expressed are personal, not necessarily Corporate'
