buzz_ock Posted May 15, 2007 Share Posted May 15, 2007 about the previous post, opps, forgot to switch my timers to time!!!! works a treat, just in time as i got to leave for a few days Link to comment Share on other sites More sharing options...
scraglor Posted July 15, 2007 Share Posted July 15, 2007 i use those types of relays all the time at work, they are rated at 10amps, but this is for a resistive load, it's a misconception that it's the start-up current drawn from inductive loads that cause time/relay failure, this is not true, although the relay is rated at 10Amps,. and your start-up current draw maybe only say 5amps, this is not where the trouble lies. inductive loads store energy as a magnetic field, when you shut off power to an inductive load all this stored energy has to go somewhere, it goes into producing a high voltage at the terminals, this is how the high voltage pulse used to start HID lamps is created. this high voltage creates a spark across the gap between the relay contacts when the contacts are OPENED, not when they are closed on start up. this spark causes enough heat to melt the contacts and before they have a chance to open, they fuse together, this is why when timers fail, they usually fail in the on position. I haven't read the whole thread, but the relay used in the first page is used for motor control panels (and other control panels) it is used for various switchings to control CONTACTORS for heavy inductive loads, i.e. motors and HID lamps. these shouldn't be used to start your lamps if you are using any more than a 400watt lamp, i wouldn't even use one for this, it's not what they are designed for, and you can get a true lighting contactor for around £12, i.e. a 25Amp contactor from rs-online costs about £12, and each pole of the contactor is capable of switching 25Amps! that's 100Amps total for 12 quid! a proper contactor doesn't give off much heat, so can be mounted in a cheap plastic enclosure, about £3, plus the cost of a couple of a few plugs (one plug for each pole of the contactor, and one plug to go to the timer) you now have a contactor capable of switching 100Amps of light for under 20quid! (obviously you'd need a circuit and outlets capable of providing this, but i think for most people this is irrelevant) at the end of the day, a proper lighting contactor costs fuckall, so you may as well use something designed for purpose 1 Link to comment Share on other sites More sharing options...
dub_lover Posted July 21, 2007 Share Posted July 21, 2007 (edited) Hello all. I have been following this thread on and off for a while, and while there is the normal mix of good (primarily about the earthing issue - see Harry Botha!), strange and undeterminable advice being given, all ( as far as I can see) have missed a critical issue! YOU MUST ALSO REMEMBER THAT THE "NEUTRAL" LINE CAN SHOCK YOU!! The circuits given will indeed turn the light (and fans) on and off, but all do so by breaking the circuit on the live "side". Although this will turn the switched electical gear on and off with no risk of fire, the handling of this gear will still potentially present a serious hazzard to health!! It is completely possible to receive a "nasty" electric shock form the "neutral" side of an AC circuit: "Also, remember there can be a voltage potential between neutral wires and ground in the event of an improperly wired (disconnected) neutral, or if it is part of certain obsolete (and now illegal) switch circuits. The electrical appliance or lighting may provide some voltage drop, but not nearly enough to avoid a shock. "Live" neutral wires should be treated with the same respect as live wires. Also, the neutral wire must be insulated to the same degree as the live wire to avoid a short circuit" Source: http://en.wikipedia.org/wiki/Electric_shock The solution to this is to use both poles of the relay to switch the live AND the neutral lines - it will cost no more! I will post pictures of my own (which would fail the relevant BS btw - but not for the above reason!) contactor, showing the changes soon.... Edited July 21, 2007 by dub_lover Link to comment Share on other sites More sharing options...
Davey Jones Posted July 21, 2007 Share Posted July 21, 2007 (which would fail the relevant BS btw - but not for the above reason!) Why would it fail if it would then why bother posting it. I have thought about doing one cause this one is crap but I don't think there is a demand for it Link to comment Share on other sites More sharing options...
dub_lover Posted July 21, 2007 Share Posted July 21, 2007 Why would it fail if it would then why bother posting it.I have thought about doing one cause this one is crap but I don't think there is a demand for it I have fitted my contactor into a plastic (IP 65 I think box), but I used two M3 metal screws to mount the (insulated) relay socket - the heads of these are flush with the outside of the box. I do not feel these present any risk of shock, unless a live part of the circuit would breakk free and... I just feel that it was necessary to point out a potential danger in the design(s) presented before and I will openly admit that my own design has a flaw. I just think, on balance, that the shortcomings in mine are an acceptable risk to me. Ultimtely I will, however, accept your point! - I will adapt my device to be compliant by earthing the two screws before posting pictures! I am really trying to add to this forum! :-D Link to comment Share on other sites More sharing options...
Davey Jones Posted July 21, 2007 Share Posted July 21, 2007 The screws if isolated and not likely to present a potential won't need earthing but I would need to see it before commenting. Don't you have any DIN rail to mount it on then earth this thats the way. This is a contactor yeah not a relay. Link to comment Share on other sites More sharing options...
dub_lover Posted July 21, 2007 Share Posted July 21, 2007 The screws if isolated and not likely to present a potential won't need earthing but I would need to see it before commenting.Don't you have any DIN rail to mount it on then earth this thats the way. This is a contactor yeah not a relay. A contactor: http://en.wikipedia.org/wiki/Contactor ... Sorry if I got the terminology incorrect - I'm not an electrician, but I am a physicist for a profession -- so I may not be 100% au fait with the latest regs. but I do understand how 'leccy might or might not "move" around! .... hehe Link to comment Share on other sites More sharing options...
Davey Jones Posted July 21, 2007 Share Posted July 21, 2007 Yeah maybe but only the regs course and installation courses will teach you how to do it safe, after all IMO some regs are stupid but they are there for safety and god damn them they work. Looking 4ward to the post Link to comment Share on other sites More sharing options...
Davey Jones Posted July 21, 2007 Share Posted July 21, 2007 Get some DIN rail for that contactor man its only cheap Link to comment Share on other sites More sharing options...
dub_lover Posted July 21, 2007 Share Posted July 21, 2007 Get some DIN rail for that contactor man its only cheap 'Electric man 2' - Still think we may be talking (somewhat) at cross purposes here! ... I do think we both have end-user safety in common though!... I need to hit the fluffy could of bedtime now... I'll try to find some batteries to fire up my (totally shitty) camera in the morning.... Night all... Link to comment Share on other sites More sharing options...
Themadhippy Posted July 21, 2007 Share Posted July 21, 2007 (edited) The circuits given will indeed turn the light (and fans) on and off, but all do so by breaking the circuit on the live "side". Although this will turn the switched electical gear on and off with no risk of fire, the handling of this gear will still potentially present a serious hazzard to health!! It is completely possible to receive a "nasty" electric shock form the "neutral" side of an AC circuit so if theres no live in the circuit how is it going to give you a shock? neutral is or should be at 0v with refrence to ground as the neutral is derived from the center of a star wound transformer,which is also connected to earth,Also in the most common method of supply (tnc-c-s ) the neutral and earth are conected at the point of entry to the consumer. edit to add in some allbe it rare circumstances any form of switching on the neutral is not permited Edited July 21, 2007 by Themadhippy Link to comment Share on other sites More sharing options...
Davey Jones Posted July 21, 2007 Share Posted July 21, 2007 Think he means switching the neutral and disconnecting it then it would be live but we just don't do it like that so there is no problem. Link to comment Share on other sites More sharing options...
dub_lover Posted July 22, 2007 Share Posted July 22, 2007 so if theres no live in the circuit how is it going to give you a shock? neutral is or should be at 0v with refrence to ground as the neutral is derived from the center of a star wound transformer,which is also connected to earth,Also in the most common method of supply (tnc-c-s ) the neutral and earth are conected at the point of entry to the consumer.edit to add in some allbe it rare circumstances any form of switching on the neutral is not permited I agree - there should be no voltage on the neutral side of a circuit - that's how AC power transmission works. But I for one, do not know where the local neutral is connected to earth. Any fault in this connection creates a resistance. Therefore any user connection from this "neutral point" to ground would introduce a parallel path to this faulty connection. Although the chances of the current through this path being significant are low, there is still a chance that it can happen, and that's not even allowing for botched diy jobs by the previous owner*. Like I said - I'll readily admit that I'm not an electrician - but I do not know any that would walk into someone's house, remove a socket cover and start touching the neutral connection! *I just moved out of a flat that had a socket with the earth and neutral wires swapped by the previous occupant - I only had a transistor radio plugged in. It worked great until I had a modern consumer unit with an RCD fitted so that I could install a shower (and other stuff :wink: ). Then, strangely enough, the RCD would trigger every time I turned on the radio!..... Just because something should be a certain way doesn't mean that it will be! Pictures of my unit... Link to comment Share on other sites More sharing options...
Davey Jones Posted July 22, 2007 Share Posted July 22, 2007 1. Thats a crappy relay no good for large loads at all 2. your wiring is messy you could of made a better job 3. Only the electric board are allowed to use the same conductor for neutral and earth like TMH said its TNC-S 4. there is nothing strange about a swapped neutral and earth tripping an RCD after all the current returns to the supply via the earth and not the RCD this creates an imbalance which trips it straight away. 5. I have disconnected many neutrals before when testing it has to be done as long as you go through the ritual your fine. 6. Does any one want to see a real contactor built by an electrician no offence mate but that one above is a complete pile of crap. Link to comment Share on other sites More sharing options...
dub_lover Posted July 22, 2007 Share Posted July 22, 2007 1. Thats a crappy relay no good for large loads at all2. your wiring is messy you could of made a better job 3. Only the electric board are allowed to use the same conductor for neutral and earth like TMH said its TNC-S 4. there is nothing strange about a swapped neutral and earth tripping an RCD after all the current returns to the supply via the earth and not the RCD this creates an imbalance which trips it straight away. 5. I have disconnected many neutrals before when testing it has to be done as long as you go through the ritual your fine. 6. Does any one want to see a real contactor built by an electrician no offence mate but that one above is a complete pile of crap. Morning! Electric man 2: 1. Who said I was running a heavy load? Not me - I only run one 400W HID and small cooling fan from it - the 4-way was what I had lying about; 2. I don't mind - it was put together for function, not form; 3. That was part of my original reasoning - I have absolutely no idea what the connection from my neutral to the electric board earth is like. I'm sure that all the Electricians follow the regulations, but then again so do the gas contractors and we all know what Transco has got wrong in the past!; 4. My bad - I was being sarcastic - of course this would trip an RCD; 5. Again - part of my point - you check the neutral before touching it; 6. None taken. My box cost considerably less than getting a professional to build it - That was the whole point! Maybe I am a little over-cautious. It's just better to be safe than sorry in my book! Link to comment Share on other sites More sharing options...
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