On Friday, 9 November 2018 17:43:53 UTC, three_jeeps wrote:


I think the point in this thread is that one has to know what they are dealing with before employing an isolation transformer. I read the article. IMO, the article title is an attention getting and his point is that the isolation transformer presents a 'false sense of safety'. The assumption that most ppl will make is that one blindly needs to install an isolation xformer in all applications and it will keep you safe. There are limitations based on the circuits one is dealing with.

To remain safe when working on live equipment one needs to understand what one is dealing with whatever safety systems are in use. Isos have their limitations of course, so do all safety methods.

The assertion to be safe one must "use of an RCD, ELCB or other earth leakage detector" is a general statement but also a bit misleading. RCDs are NOT recommended and ELCBs are essential.

Woah. Voltage operated ELCBs are obsolete, a known hazard and offer no protection whatever against shock when working on a live chassis appliance. They only protect against the earth system becoming live as a result of a high current fault (not via a human) that would otherwise raise the earth system above 50v. That's all they do. They were obsolete in the 1980s. Current operated ELCBs _are_ RCDs.

This article explains things quite well..
https://www.linkedin.com/pulse/what-...lcab-engineers

It's yet another article with both correct points and some confusion.

The statement about live chassis 'only in TV of the 90's' is grossly incorrect.
My father owned/operated a TV/Radio sales and service shop from early 50 through 2000. I grew up in the shop and serviced TVs and other electronic gear from the 60, 70, and 80s. I can attest that the live chassis was not only in the 90's. I've seen it in the 70s and 80's TVs. I've also seen it in electronic gear in the 2010s - e.g. soldering stations/hot air rework stations from China, as well as three voltage power supplies from China.

Unless I'm mistaken I don't think anyone said live chassis kit only existed from the 90s. I have had live chassis stuff from post-2000, 90s, 80s, 70s, 60s, 50s, 40s, 30s, 20s and one item that might have been from the 10s or 20s. By the time you go that far back 'live chassis' becomes somewhat meaningless in that it was normal to have live bits all hanging out.

Point is, one needs to be aware of the realities of the circuitry they are working on and dont blindly apply 'safety measures'...that doesn't mean to ignore them. It means to apply them but know what areas of 'safety' they are meant to protect.

that of course is vital when working on live equipment. Anyone that does so without understanding what they're doing or gets careless is in trouble. In about of 99.2% of those cases a shock awakes them to the need to be sensible. Mortality is somewhere roughly in the region of 1 per 600 shocks.

There is NO safety system that can protect people against that. RCDs offer zero protection against shock from transformer derived B+, don't protect against L-N shocks and don't always work on L-E shocks. ELCBs offer no shock protection at all from live working hazards. Isos offer limited protection. Never touching the equipment with both hands offers limited protection. An earth-free workzone offers limited protection, etc etc. Sometimes you just need to know what you're doing or not do it.


NT