Guest anguscanplay Posted July 26, 2007 Share Posted July 26, 2007 My mates checked it out and is was more than happy to issue certificates for it and hes BSI 2391 certified. he needs to be certified imo - tell you what just leave it, then when you get an earth fault youll know because of the little tingle you get when your stood near the metal box ( im assuming its a metal box c/u ) and it`ll save on the heating too hmm I agree but alot of the advise on here isnt advice it's "get a pro to do it". Its just not a very friendly forum with alot of sarcasm and it kinda lets it down a bit. damm ther`s that sarcasm again lol, think you`ll find you started first this time lol , its a friendly forum considering the advise is coming from proffesionally trained and competant security engineers who quite frankly could be spending their time doing other things , you need to let us let off some steam every now and again to stop us posting the wrong advice malitiously(?), ok serious time now by earthing the screen on your cables youve connected them to a potential of 240vac when the cable isnt designed to carry that and created a fire risk im assuming you didnt connect the other end to the neg terminal otherwise your also exposing your devices to the same voltage and risk frying the lot - as Dave said your friend is wrong to certify other peoples work BUT i would be very interested to see which certs he has used to pass your alarm installation if any Non intended Angus ( bet your around for ages too ) Link to comment Share on other sites More sharing options...
Dandle Posted July 27, 2007 Share Posted July 27, 2007 ok serious timenow by earthing the screen on your cables youve connected them to a potential of 240vac when the cable isnt designed to carry that and created a fire risk im assuming you didnt connect the other end to the neg terminal otherwise your also exposing your devices to the same voltage and risk frying the lot - as Dave said your friend is wrong to certify other peoples work BUT i would be very interested to see which certs he has used to pass your alarm installation if any Non intended Angus ( bet your around for ages too ) Wheres the potential for 240vac to get to the earth screen? The whole point of a sheild on a cable is to take any induced voltages(interference) away and down to earth. The only way it would be live is if the whole control box and case become live(its only the control box end connected to earth BTW). Link to comment Share on other sites More sharing options...
Guest Dave the alarm man Posted July 27, 2007 Share Posted July 27, 2007 Wheres the potential for 240vac to get to the earth screen? if any part of the electric install though fault make the earth live, the screen of your cable is of the same potential, also if any of cable is taken outside (yes we can do this this with suitable mechanical protection) your screen connected to the equipotential bonding will be at a different potential to the ground (you are stood on), Link to comment Share on other sites More sharing options...
Alarm boy Posted July 27, 2007 Share Posted July 27, 2007 I think you've got your resistors round the wrong way Ryan, 4k7 across alarm pair, 2k2 in series with cable. Oh yeah, i think being away this long has made me lose it!!!!! plus having a few to many beers before technical talking dont help either! o well at least i had the right resistors! Ryan Williams - South coast service engineer for Banham Fire & Security Group* *Comments are my own and do not reflect those of Banham Fire & Security Group. Link to comment Share on other sites More sharing options...
Dandle Posted July 27, 2007 Share Posted July 27, 2007 if any part of the electric install though fault make the earth live, the screen of your cable is of the same potential, also if any of cable is taken outside (yes we can do this this with suitable mechanical protection) your screen connected to the equipotential bonding will be at a different potential to the ground (you are stood on), I would have alot more problems than the screen being live if that happened. As its not connected to anything there will be no current flow either through it so it hasnt really made it a fire risk either(worse case senario). No cable has run out side either. for the reply. Link to comment Share on other sites More sharing options...
Guest anguscanplay Posted July 27, 2007 Share Posted July 27, 2007 I would have alot more problems than the screen being live if that happened. As its not connected to anything there will be no current flow either through it so it hasnt really made it a fire risk either(worse case senario). No cable has run out side either. for the reply. dandle if it wasnt for the fact my broadband is duff and im on dial up i would explain in simple terms but i have neither the time nor the money to do so - do what you want , the fact you have made your house a danger zone is your perogative if you get an earth leakage on your mains 240vac you will now get a 240vac potential on the cables running to your alarm sensors - this is wrong - fact if you happen to touch the screen and neutral during an earth leakage your going to get a shock - this will hurt and could kill you - fact if you have a slight connection between the screen and the 12v dc connection your looking at a fire - this will burn your house down - fact if you have a slight connection between the screen and the 12v neg dc connection your alarm will do funny things and maybe catch fire - fact etc etc etc just disconnect the screen from earth or avoid touching the alarm and your radiators hmm if you find you have an induced AC problem buy a filter designed for the job Angus ( just do it right instead of arguing about it ) Link to comment Share on other sites More sharing options...
Dandle Posted July 27, 2007 Share Posted July 27, 2007 if you get an earth leakage on your mains 240vac you will now get a 240vac potential on the cables running to your alarm sensors - this is wrong - factif you happen to touch the screen and neutral during an earth leakage your going to get a shock - this will hurt and could kill you - fact No different to everything in the house thats earthed. Do you disconnect all the earths on your metal lamps, plumbing etc so you dont get a shock if theres an earth leakage? Everything in the house will now be live if theres an earth leakage, its metal and connected to the mains inc the control panel case. There will be much bigger problems if the house earth has 240v on it than the sheild of the alarm wiring. Even metal conduit carrying power cables should be earthed. if you have a slight connection between the screen and the 12v dc connection your looking at a fire - this will burn your house down - fact The screen is at the same potentail as the negative (0v) line which funny enough is also at the same potential as the earth. So theres 10.8watts of power there at the limit of the fuse, Is it the heat or the spark that will cause the fire before the fuse blows? Assuming my wiring is as bad as you think. if you have a slight connection between the screen and the 12v neg dc connection your alarm will do funny things and maybe catch fire - fact etc etc etc just disconnect the screen from earth or avoid touching the alarm and your radiators hmm Its actually 0v not negative dc, The screen is at the same potential as the sensor power 0v line(where did you get catch fire from). The rads in my house are also earthed or do they need disconnecting incase theres an earth leakage. Link to comment Share on other sites More sharing options...
whistle Posted July 27, 2007 Share Posted July 27, 2007 What about beldon and galaxy the screen is earthed on all sites and should be, although only at one end. Link to comment Share on other sites More sharing options...
antinode Posted July 27, 2007 Share Posted July 27, 2007 What about beldon and galaxy the screen is earthed on all sites and should be, although only at one end. Maybe we should be fitting MCB's on all our screen wires then, else the panel might catch fire lol. Trade Member Link to comment Share on other sites More sharing options...
Guest anguscanplay Posted July 27, 2007 Share Posted July 27, 2007 Hmm 240v ac down a .70 wire - like i said just do it makes no difference to me i will refer you back to my earlier comment " its called Seperated Extra Low Voltage for a reason " connect the screen to 0v not earth Link to comment Share on other sites More sharing options...
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