----- Original Message ----- From: "Peter L. Peres" To: Sent: Saturday, November 02, 2002 9:01 PM Subject: Re: [PIC]: Direct LED connection? > On Sat, 2 Nov 2002, Sean Alcorn - Avion Sydney wrote: > > *>But seriously though, if the US is running at 7mA and we use 30mA and > *>still see trips on refrigeration equipment, does it come down to our > *>dirty power that Roman already pointed out? Or is this simply due to > *>inherent operating characteristics of refrigeration equipment? I am > *>curious if they run refrigeration compressors through protected > *>circuits without nuisance trips in the US. > > Not from the US but really dirty power can trip GFIs. A common mode AC > filter before the panel (!) will cure this. Refrigeration equipment has > on/off cycles of compressors (with lots of turn-on current), contact > arcing and all the rest, like condensation bridging insulation > temporarily. If a particular piece of equipment on a circuit causes all > the faults then it could have bad insulation. GFI trip current is between > 15 and 30mA in most parts of the world. 30mA is not supposed to go > directly through someone's heart, it's the total fault current. I can > witness that up to 150mA will not start fibrillation, although it can be > very painful afterwards ;-) Maybe in the US the liability issues are > larger (i.e. someone once injured his spine by tripping on a marmalade jar > while being electrocuted with 7.2 mA of mains from a partly dismantled > electric knife with which he was trying to cut off his left ear, and sued > successfully - so the authorities decided GFI current will be 7.0mA). > > Incidentally the resistance required to pass 7mA peak at 120V is about > 24k, 30mA peak at 240V is under 11k. The 'hand to hand' resistance of a > normal man is usually over 50k when not wet etc. So you can't fib from > touching with both hands (at least in theory). Right now I measured 200k > between left and right hand. > > Otoh there are noGFI interrupters on high voltage power supplies and > inside valved equipment ;-) > sort of related A guy I was working with, made contact with 415v 400Hz while voltage checking in a distribution panel. Went across the chest. Straight after had a ecg and other tests, while rather shaken up tests found no damage. Three months had a medium heart attack. The doctors couldn't explain why. They said there was nothing they could find which could have caused a heart attack. Had a few zaps myself, but nothing across the chest, I always do the old keep one hand in the pocket or only hold one lead and use a clip on the other. Most painfull I've ever had was from rf equipment, 200w HF amp, one of the joints on the test rig hadn't been done up properly. This was the only zap I've had that left a burn mark and it took a few weeks to heal up. Even though 8000VDC can be reasonably painful. First electronics kit I was ever given was a negative ion generator. Rather dodgy Dick smith electronics one. It had no isolation and plugged straight into 240v. A certain smart arse 14 year old changed the current limiting resistors, used high rating caps and diodes. If you took the end cap off a hobby dc motor you could get the rotor to shoot about 15 feet or if attached it to a cooper coil fire ball bearings or small lumps of iron up to 30 feet. A real safe kit for parents to give as a first electronics kit :-) Talking about dirty power, my old mans business partner lives outside Perth (WA) has had horrendous problems with both brownouts and overvoltage. Measured volatages range between 140VAC and 400VAC on a single phase 240V system. -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu