Rulland Posted April 9, 2009 Share Posted April 9, 2009 Yet again a simple question turns into a full blown argument where members resort to 'I know more than you on that' and it results in tit for tat replies!. OK we all know that in a 'balanced' 3 phase supply the total current on the 3 phases SHOULD equal the star point or neutral-but some people don't work on 3 phase and balancing!-but they read and learn surely!. But this is just one example of the 'mindgames' that appear to go on within this group-for crying out loud we are all in the security industry, we are ALL still learning, no one knows ALL the answers-surely that is the reason for a 'Community Group'-or am I totally way off?. Hope everyone has a nice Bank Holiday weekend anyway-I know I mean well, and I hope to give all I can to this community and maybe sometimes I might be wrong with some of my answers-but some one will correct me-and thus I will learn !. Regards. Richard. Link to comment Share on other sites More sharing options...
esp-protocol Posted April 9, 2009 Share Posted April 9, 2009 So the reason your fuse blows on a live to earth fault in your house is because you get a path created between the live (in your house) through the general mass of earth (or could be continuous earthing conductor depending on system) giving negligible resistance... back to the earth electrode that is bonded to the starpoint of the transformer.... then through the phase conductor feeding all the way back to your house. The current can be 1000s of amps .... hence the reason your fuse/mcb blows pretty quick... The star point is always going to equal the mass of earth.... ie zero..... ish......!! Yet again a simple question turns into a full blown argument where members resort to 'I know more than you on that' and it results in tit for tat replies!.OK we all know that in a 'balanced' 3 phase supply the total current on the 3 phases SHOULD equal the star point or neutral-but some people don't work on 3 phase and balancing!-but they read and learn surely!. But this is just one example of the 'mindgames' that appear to go on within this group-for crying out loud we are all in the security industry, we are ALL still learning, no one knows ALL the answers-surely that is the reason for a 'Community Group'-or am I totally way off?. Hope everyone has a nice Bank Holiday weekend anyway-I know I mean well, and I hope to give all I can to this community and maybe sometimes I might be wrong with some of my answers-but some one will correct me-and thus I will learn !. Regards. Richard. I think you should reel it in. No ones arguing or going "tit for tat"... we are all discussing the point and trying to make it a bit clearer.... Link to comment Share on other sites More sharing options...
Rulland Posted April 9, 2009 Share Posted April 9, 2009 I think you should reel it in. Ehmm!-very constructive-as on numerous occasions!-LOL Link to comment Share on other sites More sharing options...
Chorlton Posted April 9, 2009 Share Posted April 9, 2009 Ehmm!-very constructive-as on numerous occasions!-LOL TBH mate I know topics can go argumentative but trust me this ain't one. It's a confusing issue and requires explaining, re-explaining and counter explaining but it's all good. nobodys making it personal until the 1st post on this page so lets continue from where the last page left off, agreed? the written words always sharper than the spoken! dudes C. Link to comment Share on other sites More sharing options...
esp-protocol Posted April 9, 2009 Share Posted April 9, 2009 Ehmm!-very constructive-as on numerous occasions!-LOL Well seeing as you have nothing constructive to add to this thread apart from some misguided drivel accusing members of arguing ... for which I can't see any evidence whatsoever .... I don't know why you chose to stick your negative oar in..... Link to comment Share on other sites More sharing options...
Rulland Posted April 9, 2009 Share Posted April 9, 2009 OK C-I meant no offence to anyone in particular with what I said and apologise if anyone took my remarks the wrong way. Lets get back on track then eh!. Richard. Link to comment Share on other sites More sharing options...
Chorlton Posted April 9, 2009 Share Posted April 9, 2009 no sweat ! back to triangles and the mystical world of points of something or other Link to comment Share on other sites More sharing options...
DirectFS Posted April 9, 2009 Share Posted April 9, 2009 So the reason your fuse blows on a live to earth fault in your house is because you get a path created between the live (in your house) through the general mass of earth (or could be continuous earthing conductor depending on system) giving negligible resistance... back to the earth electrode that is bonded to the starpoint of the transformer.... then through the phase conductor feeding all the way back to your house. No, esp - the reason a fuse blows is simple overcurrent. Nothing to do (necessarily) with any earth fault. It is going to get confusing here, as there are differences in the way fuses, MCBs, RCDs, and RCBOs operate. Most fuses are formed from low melting point aluminium or alu/zonc alloy, and are designed to melt at a load equivalent to x% over current (rated) in order to disconnect within the required time - a built in weak point, if you will. a fuse, per se, offers no direct protection against electrocution, or risk of an earth going "live". An MCB measures overcurrent, and is simply designed to trip much like a bi-metal strip when the current reaches x% over rated current. The advantage of an MCB is that it will detect the massive increase in current flow generated when live shorts to earth, and disconnect much more quickly than an equivalent BS88 fuse will disconnect. An RCD measures the difference in current on live and neutral conductors, and is simply designed to disconnect to prevent electrocution. The effect of this measurement is effectively the same as earth leakage, though this is not what is measures directly. Typically, an RCD in the UK will operate at around 30mA or 100mA - though 100mA is no longer acceptable in domestic installations. An RCD will NOT specifically protect against overcurrent - unless around 50-75% over rating at which point the contact in the RCD will likely melt anyway. An interesting point about RCDs - their trip current - the 30mA bit, is nominal at + or - 50%. Ergo, your 30mA RCD may well be tripping as low as 15mA residual earth current, or as much as 45mA. RCBOs are double pole devices which combine the functionality of an RCD (effective current imbalance across L-N (effective earth leakage), and an MCB - overcurrent protection. The star point is always going to equal the mass of earth.... ie zero..... ish......!! Yes, the star point is always at zero potential, irrespective of load on the star points - it isn't imbalance that causes problems though isolation might. In a TN-C system, earth leakage can only generally be caused on the installation side of the system, and not on the supplier side. TN-S and TT systems are wholly different matters. I think you should reel it in.No ones arguing or going "tit for tat"... we are all discussing the point and trying to make it a bit clearer.... How true. Hush your gums, indeed......lol. I'm quite sure tit and tat are both fully load balanced, harmonised, and at zero potential right now.... Bill. Bill Accord Fire & Security Services Ltd. www.accordfire.co.uk ~ TEL: 0845 474 5839 Link to comment Share on other sites More sharing options...
esp-protocol Posted April 9, 2009 Share Posted April 9, 2009 No, esp - the reason a fuse blows is simple overcurrent. Nothing to do (necessarily) with any earth fault. It is going to get confusing here, as there are differences in the way fuses, MCBs, RCDs, and RCBOs operate. So whatever happened to the earth fault loop impedance path... ? I'm not saying a fuse blows only because of earth faults... this was just the example.... Link to comment Share on other sites More sharing options...
Rulland Posted April 9, 2009 Share Posted April 9, 2009 A very concise and precise reply-to which I have read, digested and agree I recently changed a consumer unit from the old rewirable fuse type-to a 17th edition twin RCD type-A voltage between neutral and earth was apparent of around 12v-but all tests as required-external Ze etc gave the install a 'clean' bill of health. As previously suggested reasons could be various. Love you all guys- : Link to comment Share on other sites More sharing options...
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