...and you use a three-wire grounded plug (which admittedly approximately all computer equipment does). And because in some parts of Europe you find balanced mains, rather than hot-and-neutral mains. (That is, the two power wires are each hot to ground, 180? out of phase with respect to one another, very much like what in North America would be a 220V outlet.) /~\ The ASCII der Mouse \ / Ribbon Campaign X Against HTML mouse(a)rodents.montreal.qc.ca / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B

This depends on where in Europe. Most of Europe is, I understand, as you describe, but the part of Norway I was in (Troms?) certainly used balanced (or at least approximately balanced) mains, and I'm told it's usual in the rest of Norway too. There may be other such areas, though I don't know of any specific examples. /~\ The ASCII der Mouse \ / Ribbon Campaign X Against HTML mouse(a)rodents.montreal.qc.ca / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B

I can't be bothered to dig out the schemaitcs (I will do if necessary), but I am darn sure the DPST switch in my 'Bows just breaks the live and neutral wires of the mains supply to the PSU. It's a bit strange due to the fact that the mains switch is on the fan bracket, while the mains connectors are part of the PSU (so you have to trace wires through various connectors), but electrically it does the obvious thing. -tony

NO,NO,NO!!!!!!!!!!!!!! This can potentially leave a circuit floating, wich can be much more dangerous. Try to HI_POT test a device in this configuration, and you may very well let the "magic-smoke" out. If you are switching on the raw power side, the neutral should always remain connected. In fact this is code for many (most/all) CE/UL approval stamps!

Well, here you pretty much have to break both, even if one is neutral sometimes. Much better than having a "half hot" circuit. William Donzelli aw288(a)osfn.org

It can be important there too. I've been bitten a few times by shocks wire leak to a metal chassis and the plug happens to have been plugged in the wrong way around, so that the wire the device is designed to treat as neutral is actually the hot, and the power switch is in the lead that's actually neutral. Even since the advent of the polarized two-prong plug this is a real risk; "cheap things like lamps" are common targets for plug (and sometimes entire cord) replacement - and the sort of screw-terminal mains plug sold in small quantity to weekend bricoleurs is almost never polarized, and most of the amateurs doing such replacement I wouldn't trust to get it right if it were. (Heck, I wouldn't trust _me_ to get it right from memory - I can never remember whether the wide blade is hot or neutral; I have to test an outlet.) Things like that usually use grounded plugs anyway. At least here in North America (which is where you'd find 120V mains devices anyway). /~\ The ASCII der Mouse \ / Ribbon Campaign X Against HTML mouse(a)rodents.montreal.qc.ca / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B

I'm lost as to how a device with a switch that breaks both Live and Neutral can be *more* dangerous that a device with a switch that breaks only Live (or just breaks one line, for those of you who have to work with people who wire things up wrong ... "consumers" is the technical term, I believe). Antonio -- --------------- Antonio Carlini arcarlini(a)iee.org

Exactly why not? Are you saying that the main switch in your fuse box / consumer unit / breaker box / whatever you call the thing after the electricity meter in your house is a single pole device ? In the UK it is _required_ to be a double pole one, breaking live and neutral (and for 3 phase star installations it's required to break all 3 phases and neutral). The behaviour of a circuit with a double pole mains switch is known. And I have _never_ come across a problem that could only be explained by the fact that both mains wires were disconnected. The most common problem is that your neon tester will light on a disconnected wire due to capacitive coupling to a still live wire. This is a safe error, in that it says a wire is live when it's not. For the life of me I don't see how a totally isolated circuit can test dead on a neon tester but actually be live (in fact I don't see how it can be live at all if it's isolated on both live and neutral wires). Horrible things!. -tony

To all that have posted.... My original comment was made specifically in reference to 2-wire (therefore single phase) power sources WITHOUT an independent ground. Note: This is ALWAYS the case with a device that uses an external power supply wich just supplys a low voltage to the actual device (e.g. Wall Warts). The comment is totally in-applicable (IMHO) when there is a dedicated (non-switched) ground connection OR the power is multi-phase. With this as the configuration there are a number of issues that can (and undoubtably will) arise if both of the legs are disconnected in a power off condition. It is necessary to realize that this condition is EXACTLY equivilant to the device being unplugged! The first condition is discharge. This can be the result of either static or an external application of charge. [Oversimplifing things a wee bit] Charge will always seek to evenly distribute itself. It will do this through the path of least resistance. If the Ground of the circuit is available, this will typically be the most commong route, and is usuaslly designed to handle larger currents than paths between signals [which typically also have higher resistance]. Consider normal static protection. It is necessary (or at least good practice) to be VERY careful when dealing with loose chips (which have their power and ground paths disconnected). Also good to be careful with board level assemblies. Not so important when dealing with completely assembled units (while unplugged). The reason for the dramatic drop in static mortality in dealing with assembled units is the fact that the power supply is intact and can absorb/buffer most of the transients involved. If the power supply is external (closer to the actual source of power than the switch), it effectively does not exist. If the power supply can dump the charge via the external connection, so much the better. There is no chance of long term build-up (which would discharge when the connections are completed). Therefore, I (and most of the other design engineers I know) fully recommed ONLY switching the hot side of a 2 legged connection. David V. Corbin President Dynamic Concepts

And everybody else has been talking about machines with a built-in PSU with a separate safety earth (ground) wire. The Rainbow tht started this discussion is certainly like that. Nobody is suggesting that the switch should open the safety earth -- in fact I think that is prohibited by every set of regulations I've seen. I have worked on devices that have wall-wart type PSUs (that is to say an oversized plug containing a transformer) or with external mains transformers and with a safety earth in the low-voltage cable that's tied to the eart hpin of the mains plug. This earth was not connected to any of the low-voltage current-carrying wires in the cable. Ah... Well the 'dedicated ground connection' is common in properly-designed equipment IMHO. If you'ew going to allow a relatively low resistance path (low enough to disipate static charges) between one of the current-carrying mains conductors and the low voltage side then all bets are off!. Maybe then it would be safer for the device if both wires are not switched (although this is not certain!), but the device is possibly lethal to the user anyway! I'd rather have an unswitched ground connection (also used to disipate static) and double pole swtiching of the current-carrying conductors. -tony

Assuming the switch functions correctly (and is wired correctly), the behaviour of a device with such a switch in the off position is pretty certain: it's identical to a device that has the mains lead pulled out. So such a device should worry you no more or less than one on a shelf waiting to be put to use. I assume that I'm missing something fundamental and that we are talking about different things here somehow ... Antonio -- --------------- Antonio Carlini arcarlini(a)iee.org

On Wednesday 24 March 2004 23:45, William Donzelli wrote: How is this different from a circuit that doesn't chop both conductors? alex/melt

I don't believe it. You have to have DPST switches in Germany/Holland because Schuko plugs are not polarized. And pretty much every power supply these days is universal -- 90 to 265 volts -- with a baker's dozen approval stickers on it. CE and UL, KEMA, TUeV, etc. So DPST is fine for UL. paul

Not around here. Probably nowhere at this point. At some point it was probably OK. Certainly we all have seen some horrible electrical jobs done by professional electricians. However, for the most part they do a decent job, and they know lots of things about code that most people do not know (or think they do, but are mistaken. Trust me, there are zillions of little rules that most people ignore). The number of horrible jobs done by amateurs, even the "good" ones, far outnumbers the number of horrible jobs done by professionals. This is the reason I do very little plumbing work in my house. I just don't know the rules, and I do not want to screw up. William Donzelli aw288(a)osfn.org

Yes. That wasn't it. There was a little plastic part broken inside that looked un-glue-able. It still clicked, but no electrical contact was made any more. YMMV, of course, but that's what happened to mine. Thanks for the correction about what the switch actually does. The wires looked like they went different places, so I just assumed they were different circuits, No reason for that, of course. -- - Mark 210-522-6025, page 888-733-0967

That's pretty much what happened to my switch. The rocker rocks but won't "stick" in either on or off and no contact is made. I did find what looks like a nearly correct part at JameCo (http://www.jameco.com/cgi-bin/ncommerce3/ProductDisplay?prmenbr=91&prrf nbr=3295&cgrfnbr=501&ctgys=) I'm still holding out hope for an "original" though. I still haven't found what I need for the fuse holder on the Heathkit. Erik Klein www.vintage-computer.com www.vintage-computer.com/vcforum The Vintage Computer Forum -----Original Message----- From: cctalk-bounces(a)classiccmp.org [mailto:cctalk-bounces@classiccmp.org] On Behalf Of Tony Duell Sent: Tuesday, March 23, 2004 3:38 PM To: cctalk(a)classiccmp.org Subject: Re: Electronic components sources other Oh, right... The 'HP' switch I am looking for is a replacement for one that failed in much the same way -- the plastic became brittle with age, and cracked. It couldn't be repaired (at least not without making a complete new part, something I didn't really want to try to do). -tony