22-06-2015, 08:21 PM
(22-06-2015, 07:48 PM)pwdrive Wrote: "In fairness, the sets on soak probably wouldn't have had earthed test gear connected to them"
Maybe not at the BBC
The death lead...no prizes for guessing (no googling)
Those that were/are in the radio/tv servicing trade will probably know.
An isolating transformer if used correctly isolates the operator from the mains as well.
Lawrence.
Well, if the sets did have earthed test gear connected, and everything was working with no fireworks, then no problem! An isolation transformer is only needed for a small number of scenarios - such as when connecting to a live chassis or the "hot" side of a switched-mode PSU. In most cases the isolation afforded by the DUT itself is perfectly fine - and an RCD offers protection for when it isn't. Did you at least use RCDs back then?
Yes, I have worked for the Beeb for a long time, but I have worked elsewhere too, and have probably done more hours at service benches outside of the BBC. I've seen a lot of very bad practice first-hand. Against that, within the BBC, engineers are much better educated about the risks, and are all the safer for it. The funny thing is that it doesn't cost the business any more to be safe - you just need to get engineers to think about things properly. I'll never understand why this subject causes so much apparent confusion, given that we're talking about incredibly simple stuff here - I mean, how can someone successfully fault-find line output stages or PAL decoders yet not understand the basics of voltage sources?
Perhaps an extension lead with the earth lifted? Usually for the 'scope - seen that done countless times! For the benefit of anyone reading (and the Forum Owner!), this is a Bad Idea. Keep all test gear firmly earthed!
Perhaps not quite as dangerous as the lead a friend uses to connect his generator to his house (a BS1363 mains plug on each end!)
(also, a Bad Idea!)So how does an isolation transformer isolate the operator, given that said operator must be assumed to be earthed because he or she will be reaching out to touch test gear, etc, or perhaps standing on the floor? Or am I confusing semantics?
