(11-02-2015, 07:36 AM)ppppenguin Wrote: Al, your arrangment guarantees that the chassis of any "live chassis" set will be at 120V wrt earth. Connecting any earthed test gear to such kit will cause a direct short.
Just plain dangerous.
With that arrangement, yes, it is, agreed. But I am aware of that danger (no-one else uses that test bench) and on the very rare occasions when I do need to power an item which has a 'live chassis', I always use a separate, suitably-rated, isolation transformer. I should also add that upon review, I have discovered that I have not connected the incoming supply 'earth' to the 'earth' pin on the supply sockets. The transformer secondary centre-tap 0v. point is connected to those 'E' pins only. That gives me my '0v. reference'. So, "why use that isolating transformer in the first place?", you may well ask. Because with my arrangement, I have a maximum of 120-v. between earth and the supply rails: half of 240-v. Any electrical shock I receive will be less - so a safer work-space. Plus the supply is a balanced arrangement, with the advantages which that brings. That isol. transformer has a RCD fitted - as I mentioned in my earlier post.
Al.
