Hello PIC.ers, .. >Date: Sat, 21 Mar 1998 08:27:56 -0600 >From: Martin McCormick >Subject: Re: OT -16F84 near brush with death! >Nigel Goodwin writes: >Never touch any metal work without first testing it, just rub it gently >with the back of your finger, it will feel 'rough' if it's live. .. if it *is* alive, and wants to kick you, then your muscles will retract your fingers *away* from the juice. .. > I have noticed this effect on equipment that was >transformer-isolated, also. I think it may be either due to capacitive >coupling between the primary of the transformer and the chassis. It is a >on the housing of the motor and touching the body of the projector at the >same time. I have never since seen anything in public use as dangerously >designed as that projector. We basically condemned it and I cut the >pigtail. .. 12+ years ago I did development work for a Co. that mostly was in the machine shop turning-milling-welding-punch press production business. One of their welding folk *wired up* the 3 lines going to a 380 volt welding transformer. Of course, in this country's supply, that's 380 volt line-to-line, aye ....but the machine was a single phaser. What do you think he did with the remaining yellow/green conductor? Wired it into the 3rd phase, of course! This (mobile, rubber wheeled) machine worked every day for +/- 3 months until someone leant a piece of steel against both it...... and a building column. {earth-shatttering bang} The local fault protection pulled out the power, I'm happy to say. Ever since, I've wondered just how it was no-one was killed in all that three-month period. No amount of conventional RCD/ earth leakage at the industrial limit of 250 mA...(saves eqpt., not people) , o/current, fault level, or u/volt, shunt trip, phase loss protection etc. can save a body that becomes part of this circuit. .. Just to (only just) remain on-topic, can anyone venture a modern (PIC naturally) way to guard against this kind of incompetence? Best regards, John .. email from John Sanderson / JS Controls, Boksburg, RSA Manufacturer & purveyor of laboratory force testing apparatus and related products and services. Tel/fax: Johannesburg 893 4154 Cellphone 082 453 4815